P0300 & P219A codes

ktuck · May 9

Two new issues I discovered this morning. The first possibly pertains to the P0097 code. I found that I had not tightened one of the two screws holding the new MAF sensor. The sensor was not completed flat against the intake tube and could be "rocked" a little. This no doubt was causing unmetered air to escape. I had not tightened the screw enough because I remember it felt like it was about to strip out and that was the last thing I needed. Anyway, this morning, I tightened the screw, it did not strip, and the sensor sits fully against the mounting as it should. The second thing points to some kind of issue with a rich mixture on bank 2. Bank 2 upstream sensor is reading high (around .78 to .85) and is not oscillating at all. Since the denso sensor I just removed had evidence of a black, sooty mixture, perhaps this issue has origin outside of the O2 sensor itself, like a bad ground or something? It is still staying in open loop. It went into closed loop shortly after start up, but soon went back to open. The IAT sensor 2 was already higher than sensor 1 shortly after start up (78 compared to 91). So perhaps that is the reason for open loop?

asilverblazer · May 9

15 hours ago, ktuck said:

P0097, P0300, P219A, P050D, P0171, P0174

At this point, I can't help but wonder if I could have a faulty ECM/PCM? However, it appears ECM failures are not as common.

Probably wouldn't hurt to take a step back and look everything over, is all the wiring good, sensors plugged in completely, no corrosion, etc. There has been a lot of work performed on the intake of the engine, something may have gotten damaged. Inspect for vacuum leaks, intake leaks, oil cap on and tight, dip stick fully seated.

The IAT is a pretty simple sensor, and the code is very specific.

Quote

P0097

Note: The scan tool display range is between −40 to +150°C (−40 to +302°F).

The ECM detects that the IAT sensor 2 signal is less than 13 Hz, colder than −60°C (−76°F), for greater than 5 s.

Circuit/System Verification

Engine idling.

Verify the scan tool IAT Sensor 2 parameter is between −38 to +149°C (−36 to +300°F).

If not between −38 to +149°C (−36 to +300°F)
Refer to Circuit System Testing.

If between −38 to +149°C (−36 to +300°F)

Operate the vehicle within the conditions for running the DTC. You may also operate the vehicle within the conditions that you observed from the freeze frame/failure records data.

Verify the DTC does not set.

If the DTC does set
Refer to Circuit/System Testing.

If the DTC does not set

All OK

I bet this code doesn't repeat.

The presence of P0300 and P0219A is odd because P0219A should not set in the presence of P0300. P0219A is sensitive to O2 sensor and intake conditions.

P050D is another fueling specific problem.

Quote

Conditions for Setting the DTC

This DTC sets if the engine control module detects variations in crankshaft rotation speed caused by the lack of adequate fuel delivery during dual-pulse mode.

P0171 and 174 should not be present with the P0300 either but indicate lean conditions.

Short version... the PCM is having trouble correcting the air fuel ratio either it isn't getting an accurate idea of the amount of air or it isn't able to deliver the correct amount of fuel.

asilverblazer · May 9

19 minutes ago, ktuck said:

Two new issues I discovered this morning. The first possibly pertains to the P0097 code. I found that I had not tightened one of the two screws holding the new MAF sensor. The sensor was not completed flat against the intake tube and could be "rocked" a little. This no doubt was causing unmetered air to escape. I had not tightened the screw enough because I remember it felt like it was about to strip out and that was the last thing I needed. Anyway, this morning, I tightened the screw, it did not strip, and the sensor sits fully against the mounting as it should.

Good!

19 minutes ago, ktuck said:

The second thing points to some kind of issue with a rich mixture on bank 2. Bank 2 upstream sensor is reading high (around .78 to .85) and is not oscillating at all. Since the denso sensor I just removed had evidence of a black, sooty mixture, perhaps this issue has origin outside of the O2 sensor itself, like a bad ground or something? It is still staying in open loop. It went into closed loop shortly after start up, but soon went back to open. The IAT sensor 2 was already higher than sensor 1 shortly after start up (78 compared to 91). So perhaps that is the reason for open loop?

My memory is fuzzy but the upstream sensor should fluctuate as each pulse of cylinder gas passes over it. A steady reading could indicate a sensor fault, or it could be so sooted it up that it can't read. Either case will cause the PCM to not be able to correct the air fuel ratio. If the sensor isn't reading and it doesn't detect anything then it could be assuming incorrectly and leaning out the bank unnecessarily. I would not rule out a thorough diagnosis of the O2 sensor circuit.

Can you re-summarize what parts you have replaced when? I might be going in circles not understanding what you have done already, somethings may already be corrected.

Have you cleared codes prior to new tests?

Edited May 9 by asilverblazer

ktuck · May 9

7 hours ago, asilverblazer said:

Good!

My memory is fuzzy but the upstream sensor should fluctuate as each pulse of cylinder gas passes over it. A steady reading could indicate a sensor fault, or it could be so sooted it up that it can't read. Either case will cause the PCM to not be able to correct the air fuel ratio. If the sensor isn't reading and it doesn't detect anything then it could be assuming incorrectly and leaning out the bank unnecessarily. I would not rule out a thorough diagnosis of the O2 sensor circuit.

Can you re-summarize what parts you have replaced when? I might be going in circles not understanding what you have done already, somethings may already be corrected.

Have you cleared codes prior to new tests?

I bought the truck exactly two years ago from the original owner who took very good care of it. It had 87K and ran perfect. Around 89K, I put a fresh set of AC plugs in it (12622441- same ones it had in it originally). It continued to run very well, and my mpg picked up a little. I have made many trips to WV. About 12,000 miles later, it developed a miss (no CEL). I replaced the drivers' side with yet another set of AC plugs. I took it for a test drive and the miss was gone so I did not bother with changing the passenger side plugs. This was early 2023.

It ran well throughout the summer and in September, while driving back from WV, it developed a pretty strong miss and CEL came on and eventually started flashing. I stopped at an Autozone to have it scanned it had a P0301. I bought a standard brand ignition coil and replaced it in their parking lot, and it corrected the problem.

Two or three months went by, and it started missing again and the engine light came on intermittently. It set a P0306. Once again, I replaced the coil, in fact I replaced all of them except #1 which had already been replaced. This is early 2024, the misfiring continued but was off and on. Sometimes I would drive for 2 or 3 hours, and it would run like a top.

Gradually the missing got worse and more frequent. I tested my plug wires and there was some resistance inconsistency between them, so I put a new set on, this was Jan 2024 and around 110K miles. The truck ran good for a few days and the engine light started popping back on. This time it was the dreaded P0300 and also P0306 with it. I switched plugs, wires and coils around to cylinder 6 from cylinder 8 which is probably the most consistently firing cylinder of any of them. The problem stayed on #6. In February, the misfiring was getting so bad, I was hesitant to drive it very far, trips to WV were out.

Another code started popping up was the P219A. Also, a code pertaining to the O2 sensor on bank 2. I don't remember the code number, but I ended up replacing the bank 2 upstream sensor with a Denso sensor. At that time, it took care of that code but the P0300 and P219A remained. I started noticing extremely high negative fuel trim numbers for bank 2 and a lesser extent, bank 1. For the most part, bank 1 at the time seemed to be doing a little better. The truck started missing on #2 and to a lesser extent #5. I had the truck at a specialty shop and later had a GM tech look at it. The specialty shop said I had collapsed lifters and a noise in the bottom end (a noise I still haven't heard). They gave me a $9000 quote for a Jasper replacement engine. The GM tech said he suspected injectors. I went that route and replaced all 8 with a set of GM 12668390 injectors. That was in the middle of March. The problem remained and I seemed to think the truck ran worse after the injectors were replaced. I thought I may have boogered something up so eventually I went back in and put another set of injectors in. Both times I did everything slowly and methodically. Nothing was messed up, the intake gaskets were exactly in the grooves, nothing leaking, nothing left loose, and I tested for vacuum leaks thoroughly-none found.

That brings me to this week. as I have described, just yesterday, I installed new GM upstream O2 sensors on each bank and a new MAF sensor. I replaced the S & B CAI system and put everything back stock for the air induction system. Another part I replaced that I had forgot about is the fuel tank pressure sensor. Diagnostics led me to that, so I replaced it. It did not affect the misfiring issue, however. Now the truck has gone from an occasional misfire to steadily misfiring and basically being undrivable (flashing CEL).

I have cleared the codes several times, generally when I have need to disconnect any sensor and then obviously when I had to intake and fuel rails off to replace the injectors. I ran the truck for about 20 minutes earlier today with the scan tool connected, and so far, you are correct, the P0097 has not reset. But something is going on with bank 2. Even though it is pretty much staying in open loop, bank 1 O2 sensors are fluctuating to some extent, but bank 2 is basically doing nothing and staying very high, only ranging from about .81 to .86 roughly. On the other hand, bank 1 sensors are reading super low in the area of .002 or .003. Occasionally, they'll jump up to .7 or higher and I cannot read any fuel trim numbers because I guess open loop status locks that out.

Pretty much all the live data was within spec, at least all that I could see when in open loop and I've already mentioned about the O2 sensors. But just to give you an idea of the current misfire situation the following is a list of the historical misfires recorded this afternoon after running it about 20 minutes

#1 185

#2 63

#3 27

#4 274

#5 7557

#6 162

#7 384

#8 2

Strikes me odd, that for all the apparent issues presumably with bank 2, it's total of misfires was 501 while bank 1 had 8153.

ktuck · May 10

13 hours ago, asilverblazer said:

Probably wouldn't hurt to take a step back and look everything over, is all the wiring good, sensors plugged in completely, no corrosion, etc. There has been a lot of work performed on the intake of the engine, something may have gotten damaged. Inspect for vacuum leaks, intake leaks, oil cap on and tight, dip stick fully seated.

The IAT is a pretty simple sensor, and the code is very specific.

I bet this code doesn't repeat.

The presence of P0300 and P0219A is odd because P0219A should not set in the presence of P0300. P0219A is sensitive to O2 sensor and intake conditions.

P050D is another fueling specific problem.

P0171 and 174 should not be present with the P0300 either but indicate lean conditions.

Short version... the PCM is having trouble correcting the air fuel ratio either it isn't getting an accurate idea of the amount of air or it isn't able to deliver the correct amount of fuel.

I fiddled with it some more this evening. It seems to me that the next order of business is to determine why it is staying in open loop long after it has warmed up. It's kinda weird but I'm seeing a pattern of the two loops in reverse. When I first start it cold, it is in closed loop. After just a couple minutes it goes into open loop and stays there, just the opposite of how it should be. Is my PCM drunk or something?! Are there any other variables that control switching into closed loop than coolant temp and O2 sensors?

This evening, for some unknown reason, it felt smoother than it's been. I went to misfires and #5 is the only one misfiring now. I think I saw one misfire on #7 and all the rest had zero over about a 15-minute period. The counter resets about every 10 seconds but during that short time, #5 registers around 180 misfires. I'm considering pulling the valve covers again, or at least bank 1 and taking a real close look at #5 and make sure there is no valvetrain issue there. I guess there could be two separate problems at the same time. Bank 2 has some weird fueling issue going on but now the misfire is solely on bank 1, strange indeed.

Also, I remembered two other parts I've changed recently, the pvc valve and the evap purge valve. These two items were mentioned as a possible but unlikely reason for high negative fuel trim, so I thought with the miles the truck has, might be good to replace each of them at this point anyway. Obviously, neither had any positive effect on the trims. I'm considering switching the two new upstream O2 sensors from the bank they are on to the other one and see what happens. But mainly, I think I need to get this thing back in closed loop again.

asilverblazer · May 10

You must be exhausted... sigh.

Current codes are still P0300, P219A, P050D, P0171 and P0174?

It looks like that up until January 2024 at around 110k miles all engine misses were ignition related. All 03xxx codes call for a thorough ignition diagnosis prior to moving to a fueling problem.

If the ignition problem remains unchecked the fuel injectors are still working as intended and by virtue of the poor ignition sending unburnt fuel into the exhaust. likely fouling O2 sensors and also indicating rich condition that the PCM would try to correct by leaning that bank out. This would be seen in fuel trims. Now the P219A code starts appearing, a fuel trim code. This led to O2 sensor replacement that corrected it, likely because of the sooty/rich unburnt fuel from poor ignition fouling the sensor. Notably the P0300 and P219A codes remain. Meaning the original problem has not been corrected.

In mid march the injectors are replaced based on a recommendation from a GM tech. The problem remained and has up to today.

It seems to me that after reviewing all this, a complete diagnostic of the ignition system has not been done. The truck has new(ish) plugs in it that might be fouled from poor combustion, I would pull and clean them. The wires are new, I would caution that like sensors 'house' brand are not recommended (I personally have had a brand new set with a bad wire in it). Lastly, the coils are also new but one could still be bad (#5).

15 hours ago, ktuck said:

But something is going on with bank 2. Even though it is pretty much staying in open loop, bank 1 O2 sensors are fluctuating to some extent, but bank 2 is basically doing nothing and staying very high, only ranging from about .81 to .86 roughly. On the other hand, bank 1 sensors are reading super low in the area of .002 or .003. Occasionally, they'll jump up to .7 or higher and I cannot read any fuel trim numbers because I guess open loop status locks that out.

#1 185

#2 63

#3 27

#4 274

#5 7557

#6 162

#7 384

#8 2

I'm inclined to think that an ignition (still possibly fuel) problem exists on cylinder 5, the spikes in O2 readings from that bank correspond to those miss fires. Swap 3 and 5 coil, then wire, then plug to see if the miss fires from 5 move to cylinder 3.

I think first get the obvious miss fire corrected, then figure out bank 2.

ktuck · May 10

15 minutes ago, asilverblazer said:

You must be exhausted... sigh.

Current codes are still P0300, P219A, P050D, P0171 and P0174?

It looks like that up until January 2024 at around 110k miles all engine misses were ignition related. All 03xxx codes call for a thorough ignition diagnosis prior to moving to a fueling problem.

If the ignition problem remains unchecked the fuel injectors are still working as intended and by virtue of the poor ignition sending unburnt fuel into the exhaust. likely fouling O2 sensors and also indicating rich condition that the PCM would try to correct by leaning that bank out. This would be seen in fuel trims. Now the P219A code starts appearing, a fuel trim code. This led to O2 sensor replacement that corrected it, likely because of the sooty/rich unburnt fuel from poor ignition fouling the sensor. Notably the P0300 and P219A codes remain. Meaning the original problem has not been corrected.

In mid march the injectors are replaced based on a recommendation from a GM tech. The problem remained and has up to today.

It seems to me that after reviewing all this, a complete diagnostic of the ignition system has not been done. The truck has new(ish) plugs in it that might be fouled from poor combustion, I would pull and clean them. The wires are new, I would caution that like sensors 'house' brand are not recommended (I personally have had a brand new set with a bad wire in it). Lastly, the coils are also new but one could still be bad (#5).

I'm inclined to think that an ignition (still possibly fuel) problem exists on cylinder 5, the spikes in O2 readings from that bank correspond to those miss fires. Swap 3 and 5 coil, then wire, then plug to see if the miss fires from 5 move to cylinder 3.

I think first get the obvious miss fire corrected, then figure out bank 2.

Thanks for the ideas, blazer. Makes sense to go back to the ignition side of #5. Neither the wires nor coils are OEM. I think this may be a case of not leaving a stone unturned. Strikes me odd that the black, sooty O2 sensor was on bank 2 but it set a P219A, not P219B. I've been thinking about why its running smoother now, but in open loop, as I understand things, the computer sends a pre-determined richer mixture and ignores the O2 sensors altogether. This fixed richer mixture may be why its running smoother, all except #5 which may well have its own problem otherwise. I wonder if it is configured in a way that if things get too screwed up fuel-wise, the computer can literally dictate open loop until correction is made?

This afternoon, my wife and I are heading back down to our little cabin in WV for a week. I'll be back on the 18th to resume the battle! Meanwhile, I'll be studying up some more about this problem and likely I will go ahead and order new wires (OEM) and maybe another MAF sensor. The one that is in there is not OEM. This open loop deal didn't start until after I replaced the two upstream O2 sensors and the MAF.

asilverblazer · May 10

2 hours ago, ktuck said:

...is configured in a way that if things get too screwed up fuel-wise, the computer can literally dictate open loop until correction is made?

Short answer yes.

I wouldn't worry too much about being 'stuck' in open loop. That should correct itself when the problem is corrected. In open loop it is ignoring the O2 sensors, the only problem immune to that would be an ignition problem, cylinder 5.

Once that is resolved (cylinder 5 miss fire), you have on hand an assortment of O2 sensors to try on bank 2 to see what is happening.

ktuck · May 20

I got to the Silverado today. Here are the changes I made and the results which include some reversals. I installed a fresh set of GM spark plugs on all eight cylinders. Also replaced all plug wires with a set of GM wires. I replaced the non-GM MAF sensor with a GM sensor. Finally, I switched the two new GM upstream O2 sensors. What I noticed was bank 2 O2 sensor was black and sooty, as were all the plugs on bank 2 except #2 (attached photo). The O2 sensor on bank 1 looked normal but # 3 was black and sooty, #5 looked a tad wet fouled but not really black, 1 and 7 looked normal, light tan electrodes.

As a result, the truck now goes onto closed loop within just a few minutes of cold start up. It appears to remain in closed loop during idle periods and the duration of reviewing scanner data. Both O2 sensors are sending normal and similar readings to the ECM. The engine seems to be running smoother, however after about 10 minutes it throws the P0300 code again. Then something I cannot figure out. there has been a reversal of the misfiring cylinder. Last week the misfire had gone away on #2 and just #5 was misfiring. After these changes I made today, #5 is now firing normally and #2 is misfiring again. I cannot see where the new parts I installed could cause this reversal. LTFT remains negative and quite high. Within five minutes after cold start up, bank 2 went to -34% and bank 1 to -22%. STFT trims were mostly holding close to zero but always on the negative side. Throughout all of this, the spark plug color has gone from light, almost white (as I mention in my OP) to now most cylinders black and sooty. The cause for that reversal remains a mystery to me as well. One final test before I knocked off for the night, I repeated the injector balance test. Once again, 5 of the 8 failed. Oddly enough, among the three cylinders to pass, was the new misfiring culprit #2, along with #3 and #8. Any ideas about this situation are welcomed, thanks.

asilverblazer · May 20

10 hours ago, ktuck said:

...the truck now goes onto closed loop within just a few minutes of cold start up. It appears to remain in closed loop during idle periods and the duration of reviewing scanner data. Both O2 sensors are sending normal and similar readings to the ECM. The engine seems to be running smoother, however after about 10 minutes it throws the P0300 code again... Last week the misfire had gone away on #2 and just #5 was misfiring. After these changes I made today, #5 is now firing normally and #2 is misfiring again... LTFT remains negative and quite high. Within five minutes after cold start up, bank 2 went to -34% and bank 1 to -22%. STFT trims were mostly holding close to zero but always on the negative side... I repeated the injector balance test. Once again, 5 of the 8 failed. Oddly enough, among the three cylinders to pass, was the new misfiring culprit #2, along with #3 and #8. Any ideas about this situation are welcomed, thanks.

Now the only code is P0300?

Is the MIL flashing?

What do the miss fire counts look like? (Cylinder 2 looks lean, fuel trims must be leaning that bank out so much that it is miss firing the leanest of the injectors - this is probably happening on both banks to an extent)

5 Injectors fail the balance test... was it the same 5 injectors as before?

Quote

The scan tool fuel injector balance test is performed while the engine is running at idle. The scan tool pressurizes the fuel rail to a predetermined pressure before each fuel injector is pulsed for a precise amount of time allowing a measured amount of the fuel to be injected. This causes a drop in the system fuel pressure that is recorded and used to compare each fuel injector.

Despite what has been done, and no other obvious faults, to me it keeps looking like the injectors are still a problem - which seems unlikely that you would get this many that are bad. If the injectors on one bank are not equal or balanced, then the fuel trims will cause one cylinder to be richer/leaner than the others on that bank. Maybe try swapping injectors 3 and 4 so that bank 1 (cylinders 1, 3, 5 and 7) are all failed or 'bad' injectors and bank 2 has mostly passed 'good' injectors (cylinders 2, 4 and 8 except for cylinder 6). Then I would expect the miss fire to move to cylinder 6, since it is the out of balance injector on that bank.

Quote

Diagnostic Instructions

Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

Review Strategy Based Diagnosis for an overview of the diagnostic approach.

Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC Descriptors

DTC P0300

Engine Misfire Detected

Circuit/System Description

The engine control module (ECM) uses information from the crankshaft position sensor and the camshaft position sensor to determine when a engine cylinder misfire is occurring. By monitoring variations in the crankshaft rotation speed for each cylinder, the ECM can detect individual cylinder misfire events.

Extreme cylinder misfire events can cause catalytic converter damage. The malfunction indicator lamp (MIL) will flash when the conditions for catalytic converter damage are present. When the ECM detects that one or more specific cylinders are misfiring, the DTC for the respective misfiring cylinder will set and up to 2 of the corresponding fuel injectors are disabled for a minimum of 30 s. The ECM will then re-enable the fuel injector and, after approximately 200 engine revolutions, will determine if the misfire is still present. If the misfire is still present, the ECM will disable the fuel injector again repeating the process. If the misfire is not present, the fuel injector will remain enabled by the ECM. In Spark Ignition Direct Injection (SIDI) system applications, if a fuel injector fault DTC is set during a misfire event, the ECM will not re-enable the injector.

Conditions for Running the DTC

The engine speed is less than 1,000 RPM and DTC P0315 is set.

The engine speed is greater than 1,500 RPM.

The crankshaft position and camshaft position sensors are synchronized.

The engine coolant temperature (ECT) is between −7 and 130°C (19–266°F).

If the ECT is colder than −7°C (19°F) at start-up, this diagnostic will not run until the ECT is between 21–130°C (70–266°F).

The battery voltage is between 9–32 V.

The vehicle is not in a acceleration or deceleration condition.

The ECM is not detecting a rough road signal.

The fuel level is at least 11%.

The ECM is not in fuel cut-off or deceleration fuel cut-off mode.

The DTCs run continuously when the above conditions are met.

Conditions for Setting the DTC

P0300

The ECM detects a crankshaft rotation speed variation indicating a misfire rate sufficient to cause emissions levels to exceed a predetermined value or a misfire rate high enough to cause catalyst damage.

Action Taken When the DTC Sets

DTCs P0300–P0308 are Type B DTCs.

When a catalyst damaging level of misfire is present, the ECM may disable the fuel injectors for up to 2 misfiring cylinders and will flash the malfunction indicator lamp (MIL).

Diagnostic Aids

A misfire DTC could be caused by an excessive vibration from sources other than the engine. Inspect for the conditions listed below:

A tire or wheel that is out of round or out of balance

Variable thickness brake rotors

An unbalanced drive shaft

Certain rough road conditions

Transmission operation

A damaged or defective accessory drive component or belt

High resistance in the circuits of the injectors may set a misfire DTC without setting an injector DTC. Test the injector circuits of the affected cylinder(s) for a high resistance if you suspect a condition.

If the condition is intermittent, observing the scan tool IC Circuit Test and Fuel Injector Circuit Test Status parameters may help isolate the condition. The circuit test status parameters will change from OK or Not Run to Fault/Malfunction if a condition exists.

A condition in the heated O2 sensor (HO2S) heater control circuits may set a DTC P0300.

Circuit/System Verification

Note: Before starting the engine, review the freeze frame failure records data to determine if the misfire sets during a cold start or at operating temperature. If there is a cold start condition and the engine is started, the engine will need to be cooled down before the next attempt to start the engine within the fail conditions.

Engine Running at normal operating temperature.

Verify there is no abnormal engine noise.

If abnormal engine noise is present
Refer to Symptoms - Engine Mechanical.

If abnormal engine noise is not present

Perform the scan tool Crankshaft Position Variation Learn procedure.

Verify no DTCs are set.

If any DTCs other than P0300–P0308 are set
Refer to Diagnostic Trouble Code (DTC) List - Vehicle.

If DTC P0300–P0308 is set
Refer to Circuit/System Testing.

If no DTCs are set

Verify the scan tool Cylinder 1–8 Current Misfire Counter parameters do not increment.

If increments
Refer to Circuit/System Testing.

If does not increment

Engine Running, perform the Cylinder Power Balance Test with a scan tool.

Verify the engine speed changes when each injector is disabled and then enabled.

If engine speed does not change
Refer to Circuit/System Testing.

If engine speed does change

Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.

Verify the DTC does not set.

If the DTC sets
Refer to Circuit/System Testing.

If the DTC does not set

All OK.

Circuit/System Testing

Note: An erratic or weak spark is considered a no spark condition.

Verify none of the following conditions listed below exist:

Damage, carbon tracking, or fluid intrusion of the spark plug boots and/or spark plugs

Vacuum hose splits, kinks, and incorrect connections

Engine vacuum leaks

Crankcase ventilation system for vacuum leaks

Fuel pressure that is too low or too high. Refer to Fuel System Diagnosis.

Contaminated fuel. Refer to Alcohol/Contaminants-in-Fuel Diagnosis.

Exhaust system restrictions

If a condition exists
Repair or replace as necessary.

If no conditions exist

Ignition OFF, connect the EL 26792 - HEI Spark Tester to the appropriate spark plug wire, engine Cranking.

Verify the spark output.

If no output or the output is weak
Refer to Electronic Ignition System Diagnosis.

If the output is good

Ignition OFF.

Verify the conditions listed below. Refer to Ignition System Specifications.

The correct spark plug type

The correct spark plug gap

The correct spark plug torque

If a condition exists
Repair or replace as necessary.

If no conditions exist

Exchange the suspect spark plug with another cylinder that is operating correctly.

Engine Running.

Verify the scan tool Cylinder 1–8 Current Misfire Counter does not increment for the cylinder where the suspect spark plug was installed.

If increments
Replace the spark plug.

If does not increment

Test or inspect for the conditions listed below:

A lean or rich Q17 Fuel Injector—Refer to Fuel Injector Balance Test.

An engine mechanical condition—Refer to Symptoms - Engine Mechanical.

Repair Instructions

Gas Engine Ignition Spark Plug Replacement

Repair Verification

Install any components or connectors that have been removed or replaced during diagnosis.

Perform any adjustment, programming or setup procedures that are required when a component or module is removed or replaced.

Clear the DTCs.

Turn OFF the ignition for 60 s.

If the repair was related to a DTC, duplicate the Conditions for Running the DTC and use the Freeze Frame/Failure Records, if applicable, in order to verify the DTC does not reset. If the DTC resets or another DTC is present, refer to the Diagnostic Trouble Code (DTC) List - Vehicle and perform the appropriate diagnostic procedure.

Engine Running, verify the scan tool Cylinder 1–8 Current Misfire Counter parameters do not increment.

If the misfire counter parameters increment, a misfire condition still exists.

To verify that the performance of the catalytic converter has not been affected by the condition that set this DTC, perform the Repair Verification for DTC P0420 or DTC P0430. Refer to DTC P0420 or P0430.

ktuck · May 20

5 hours ago, asilverblazer said:

Now the only code is P0300?

Is the MIL flashing?

What do the miss fire counts look like? (Cylinder 2 looks lean, fuel trims must be leaning that bank out so much that it is miss firing the leanest of the injectors - this is probably happening on both banks to an extent)

5 Injectors fail the balance test... was it the same 5 injectors as before?

Despite what has been done, and no other obvious faults, to me it keeps looking like the injectors are still a problem - which seems unlikely that you would get this many that are bad. If the injectors on one bank are not equal or balanced, then the fuel trims will cause one cylinder to be richer/leaner than the others on that bank. Maybe try swapping injectors 3 and 4 so that bank 1 (cylinders 1, 3, 5 and 7) are all failed or 'bad' injectors and bank 2 has mostly passed 'good' injectors (cylinders 2, 4 and 8 except for cylinder 6). Then I would expect the miss fire to move to cylinder 6, since it is the out of balance injector on that bank.

I also have a P050D code. The MIL has not been flashing. Three of the five cylinders failed both tests (4,5, and 6). The misfire counts show only #2 misfiring. A few misfires on #1, but usually no more than 1 or 20 for each 20 second cycle. None of the other cylinders show any misfires at all, including #5 which is strange. The plugs I pictured are what they looked like before changed out for a new set of GM plugs and wires and a new GM MAF sensor. So far, I have only run it for about 20 minutes or so. I plan to run it a little longer and pull the plugs again to do a comparison.

Personally, I'm at the point I feel it has to either be an injector problem still or PCM going crazy on me. One thing I do recall, and I wish I had taken better notes of what all I've done to this truck, but the last time I had the intake off, I had steady misfires on #2 and #5. Suspicious of the second set of injectors (that were bought off ebay even though they were advertised as GM factory), I replaced the injectors on 2 and 5 with two of the original injectors that came from the truck when it was new. It is now interesting that neither of the plugs from those two cylinders show the black, sooty coating. Could that mean the original injectors, despite over a hundred thousand miles, perform better than the ones I bought on ebay?

asilverblazer · May 21

Did the original injectors ever get tested?

Presumably somewhere among the 16(?) injectors you have on hand you could compile 8 that pass testing.

I would prefer to test parts than buying (more) new ones, but that is your prerogative.

ktuck · May 22

8 hours ago, asilverblazer said:

Did the original injectors ever get tested?

Presumably somewhere among the 16(?) injectors you have on hand you could compile 8 that pass testing.

I would prefer to test parts than buying (more) new ones, but that is your prerogative.

No, they haven't been tested. That is something I had asked about awhile back. Turns out there is no injector testing facility near me so I figure on finding a place I can mail them to for testing. Yes, that is absolutely my next step. Many folks have told me "GM" injectors that are sold on ebay or amazon can be counterfeit. That could be my whole problem in a nutshell. I am tired of spending the little bit of money I have on Silverado parts. I agree, surely out of 16 injectors, there can be 8 that are good. I'm thinking the original ones that had just over 100K miles may be better than any of them if the others are counterfeit.

I have now run the truck over an hour since new factory plugs, wires and MAF sensor. I have provided a picture of all 8 and the black sootiness is gone except for cylinder 3 and partially cylinder 6. The picture of plug number 6 shows black on one side of the electrode and clean on the other. I don't know if that is indicative of some kind of particular problem or not, but without any doubt, the changes made have greatly reduced the black sooty plugs on most cylinders. O2 sensor data looks perfectly normal on both banks. However, the LTFT has not been reduced at all, -34% bank 2 and -21% bank 1. So much of what I have read about high negative long-term trims, points mostly to injectors so I am going to have to see that thru until I can confidently rule it in or out. I ran another injector balance test and this time just 3 cylinders failed (1, 2, and 7).

The P0300 and P050D codes remain with a steady MIL. Cylinder 2 still the primary misfiring cylinder, but other cylinders (#1, #3, #6) are doing likewise. It seems the misfiring cylinders are kinda playing musical chairs. Depending on the day, it seems different cylinders are the culprits. Below is the latest historical count of misfires by cylinder:

1 574

2 1823

3 530

4 16

5 86

6 339

7 143

8 20

ktuck · May 22

Do any of you all know of a reputable, or have experience with a facility that tests fuel injectors that I can send mine off to? thanks

newdude · May 22

11 hours ago, ktuck said:

Many folks have told me "GM" injectors that are sold on ebay or amazon can be counterfeit. That could be my whole problem in a nutshell. I am tired of spending the little bit of money I have on Silverado parts. I agree, surely out of 16 injectors, there can be 8 that are good. I'm thinking the original ones that had just over 100K miles may be better than any of them if the others are counterfeit.

Are you buying these? 8pcs Genuine 12668390 GM Fuel Injectors For 14-19 Chevrolet GMC 1500 5.3L FJ1217 | eBay

I hope not...Those are NOT "Genuine GM", especially not for $140 for all 8 of them. Those are counterfeits/aftermarkets made to look GM. The packaging alone isn't even correct.

12710481 is the current OE number. There are many legitimate places they can be purchased from at a discount, but are about $80-110 each from legit sources.

Here's the labeling on the OE injectors: