Code P0300 Random/Multiple Misfire and loss of power under load

[RKCRLR]

A cheap chinese brand (Topoint).  But my research indicated that the cheap sensors usually work OK initially but but don't last as the OEM sensors.  Since I was doing this by trial and error I didn't want to spend a bunch of money on something that may not be the problem (I've already done that a lot).  It is unlikely that I would get 4 new sensors that have the exact same problems as the 4 sensors that that I'm replacing.  

I still have the original sensors that I could test and reinstall if it would help for troubleshooting.  

[CamGTP]

Anything other than AC Delco or Denso sensors are complete garbage for these specific trucks. Cheap sensors read incorrectly straight out of the box and give error code all the time.

 

Denso sensors aren't even a lot of money of these trucks anyway. Like $36 each for them online.

 

There really isn't much left to try here. From the parts cannon you listed, the motor has been changed, new spark plugs and the rest of the ignition system has been done as well.

 

With the fuel side, you said pressure is good and there is minimal to no exhaust back pressure. All that left is either dirty injectors or a wiring issue from a harness that is 24 years old by now. Would be pretty unlikely to see a computer driver failure that is very sporadic like this.

[RKCRLR]

9 hours ago, CamGTP said:

Anything other than AC Delco or Denso sensors are complete garbage for these specific trucks. Cheap sensors read incorrectly straight out of the box and give error code all the time.

 

Denso sensors aren't even a lot of money of these trucks anyway. Like $36 each for them online.

 

There really isn't much left to try here. From the parts cannon you listed, the motor has been changed, new spark plugs and the rest of the ignition system has been done as well.

 

With the fuel side, you said pressure is good and there is minimal to no exhaust back pressure. All that left is either dirty injectors or a wiring issue from a harness that is 24 years old by now. Would be pretty unlikely to see a computer driver failure that is very sporadic like this.

I'd be willing to try the Denso sensors if it can be determined there is a high probability the non-OEM replacement sensors as well as the original sensors are causing the problem.  It seems there would be a way to test sensors if they are bad.  

If the sensors are bad and telling the computer the truck it is running lean shouldn't I see fuel trim trying to compensate for it?  The same with dirty injectors.  My (limited) experience with dirty injectors is they cause problems during low load conditions but smooth out at full throttle.  I thought about running some injector cleaner through it but wouldn't dirty injectors show up in some other data?  

Edited September 30, 2024 by RKCRLR

[RKCRLR]

I cleared the faults and took another drive while logging the data (attached).  I didn't get a check engine light but I could feel the power being lost.  When I stopped and turned around initially the power came back, I was just starting out at part throttle and it was like a switch was thrown.  The power remained until I let off the throttle because of my speed.  When I applied full throttle again the power was gone.  When I got home p0300, P0131, P0137, P0151, and P0157 were pending.  All but one cylinder had multiple misfires in history.  

 

I noticed that once the problem started there were a lot of zeros for short term fuel trim, especially at 100% throttle.  

trackLog-2024-Sep-30_12-23-55.csv

Edited September 30, 2024 by RKCRLR

[CamGTP]

Fuel trims don't operate in open loop while at wide open throttle. Long term fuel trims may carry over into power enrichment but the short term fuel trims will always go to zero.

 

If those low voltage codes keep coming up for bank 1 sensor 1/2 and bank 2 sensor 1/2, then it's either the sensors that are the problem or the wiring to the sensors. If it was my truck, I'd be replacing them with Denso sensors before doing anything else.

 

I tuned a truck a few weeks back that ran really good everywhere but full throttle. it was down on power and the o2 voltages would basically flat line when you put the pedal to the floor. The fuel pressure was good and the fuel trims where good too. Pressure never dropped and it always followed the commanded fuel pressure that the computer was asking. His o2 sensors had over 200k on them and we thought it could be the age that was causing them to read wonky. He ended up getting a ton of lean codes and other o2 sensors codes because the MAF sensor ended up being faulty. It was not reading the correct amount of air coming into the engine, thus the computer was never giving it enough fuel and causing the o2's to show lean.

 

So I wouldn't rule out the MAF being a cause for all of this too.

[RKCRLR]

1 hour ago, CamGTP said:

Fuel trims don't operate in open loop while at wide open throttle. Long term fuel trims may carry over into power enrichment but the short term fuel trims will always go to zero.

 

If those low voltage codes keep coming up for bank 1 sensor 1/2 and bank 2 sensor 1/2, then it's either the sensors that are the problem or the wiring to the sensors. If it was my truck, I'd be replacing them with Denso sensors before doing anything else.

 

I tuned a truck a few weeks back that ran really good everywhere but full throttle. it was down on power and the o2 voltages would basically flat line when you put the pedal to the floor. The fuel pressure was good and the fuel trims where good too. Pressure never dropped and it always followed the commanded fuel pressure that the computer was asking. His o2 sensors had over 200k on them and we thought it could be the age that was causing them to read wonky. He ended up getting a ton of lean codes and other o2 sensors codes because the MAF sensor ended up being faulty. It was not reading the correct amount of air coming into the engine, thus the computer was never giving it enough fuel and causing the o2's to show lean.

 

So I wouldn't rule out the MAF being a cause for all of this too.

I'm not dead set against getting some Denso sensors but I'd want to understand what is going on before I throw more parts at it.  I've already got a new truck on order and this truck will be going up for sale (too many cancelled/interrupted camping trips).  If I were to replace the Chinese sensors with Denso sensors I'd probably only replace the upstream sensors to start with to verify they correct the low voltage condition there, if that makes sense.  

 

So does the computer ignore the O2 sensors during WOT?  One thing I've noticed is the CFM seems high (i.e., 1200 CFM at 4K RPM).  Using the formula (cubic inches)*(RPM)/3456 I get 525 CFM at 100% volumetric efficiency.  However that should cause a rich condition, correct?  

 

I've attached a reformatted file for easier reading.  

trackLog-2024-Sep-30_12-23-55.ods

[asilverblazer]

I haven't read up the latest here (or looked at the latest logs) but it WAS lean according to O2 sensors at WOT, when it should be rich - power enrichment.  I'd check out the MAF sensor too.

 

Has it ever used an oiled air filter?

Edited October 1, 2024 by asilverblazer

[RKCRLR]

3 hours ago, asilverblazer said:

I haven't read up the latest here (or looked at the latest logs) but it WAS lean according to O2 sensors at WOT, when it should be rich - power enrichment.  I'd check out the MAF sensor too.

 

Has it ever used an oiled air filter?

I only have used paper filters.  I removed the MAF and inspected it.  I didn't see anything wrong and it wasn't oily but I didn't try to clean it.  I didn't want to damage it and it appeared to be working correctly.  When RPMs were doubled the reading approximately doubled.  I recorded mass flow rate rate during my last logging session but I could record output voltage directly if it would help.  

 

I agree the O2 sensors indicate a lean (low voltage) condition.  What seems strange is the long term fuel trim doesn't seem to attempt to correct for it.  Going by Commanded AFR the power enrichment is inconsistent.  Sometimes it reduces down to 11.5 AFR at 100% throttle and sometimes it doesn't but the O2 sensors are showing lean either way.  

 

It's not clear to me if the power enrichment should be happening all the time at WOT.  The service manual states:

 

Acceleration Mode
When the control module senses rapid changes in the throttle position and the manifold pressure, the
system enters the acceleration mode. The system provides the extra fuel needed for smooth acceleration.  

 

Another thing that seems strange to me is how long the 02 sensors are below 100 mv.  My experience with fuel delivery problems under high load conditions (admittedly on carbureted systems) is that they recover quickly under part or no load conditions.  This doesn't seem to be happening here.  

Edited October 1, 2024 by RKCRLR

[RKCRLR]

Does anyone know what "[GM]H2OS Sensor (mV)" is in Torque Pro?  It is a single PID I can log.  Is it the supply voltage for the O2 sensors?  Or O2 sensor heaters?  

I noticed that it varies a lot and there is a rough correlation between low voltage there and low voltage at the O2 sensors.  

 

 

Edited October 1, 2024 by RKCRLR

[asilverblazer]

That log shows some weird stuff happening.

 

At line 296, short term fuel trims go to 0 and stay there for the remainder of the log.

 

At line 344-425, the upstream O2 sensor readings stop fluctuating, throttle is showing 100% but commanded AFR stays at 14.9 instead of going to 11.5.

 

Line 696-733 O2 sensors stop reading.

 

Focusing on lines 250-300 show what I would expect: Throttle goes wide open to 100% commanded AFR goes rich. The problem as I see it is that the upstream O2 sensors show lean when they should be reading richer. I looked at the timing advance to see if the advance is correlating to the O2 readings but not seeing a pattern there. 

 

I do see a correlation between the timing advance and long term fuel trims.

 

Fuel flow and air flow are tracking together consistently.

 

When the O2 sensors are reading, the difference between the upstream and downstream is negligible, The catalytic converters could be bad. The voltages are fluctuating together, but the fluctuations look abnormal to me.

 

My conclusions are leaning towards the O2 sensors are reading poorly cutting of short term fuel trims.

 

[RKCRLR]

I studied the logged data and made a summary.  I've attached a refined copy.  Hopefully someone can make better sense of this than I can.  Just looking at the data I'd suspect a fuel delivery problem but that isn't supported by my fuel pressure gauge readings.  Power enrichment is hit and miss and it is like the computer gave up on adjusting the fuel trims. 

First part throttle acceleration around 12:27:06.  O2 sensors reading as expected, combination of long term and short term fuel trim around 25%. 

Part throttle acceleration around 12:27:54.  O2 sensors reading as expected, combination of long term and short term fuel trim around 25%-30%.  Long term fuel trim transitions to ~25% and short term fuel trim transitions to close to zero by end of run. 

Part throttle acceleration at 12:28:58 transitioning to full throttle acceleration at 12:29:04.  Part throttle acceleration similar to previous.  At full throttle computer enters enrichment mode, LTFT decrease to less than a few percent, STFT at zero, O2 sensors go below 100mV. 

Part throttle acceleration at 12:29:20 transitioning to full throttle acceleration at 12:29:25 and then back to part throttle at 12:29:34.  During part throttle acceleration LTFT ~25% and STFT at zero.  At full throttle computer does not enter enrichment mode, LTFT decreases to ~2%-5%, STFT increases to 30%-35%.  LTFT stays  around 5% and STFT is 25%-35% during subsequent part throttle operation ending at 12:29:39.  O2 sensor readings generally as expected during part and full throttle operation. 

Full throttle acceleration around 12:29:44.  Computer enters enrichment mode, LTFT around 5%-6%, STFT at zero, O2 sensors sometimes go below 100 mV.  After this LTFT is around 5% and STFT is at zero for all part and full throttle conditions.  It's like the computer gave up on adjusting the fuel trim. 

Between 12:30:32 and 12:32:13 I did a short part throttle acceleration, a long full throttle acceleration, a short part throttle condition, and another full throttle acceleration.  Computer never entered power enrichment mode and O2 sensors never got above 100 mV. 

At 12:32:50 I did a partial throttle acceleration that transitioned to full throttle at 12:32:55.  The computer didn't enter power enrichment mode until 12:32:58 and the O2 sensors were below 100 mV prior to that.  There are a few points that O2 sensors were above 100 mV during enrichment mode but they were generally below 100 mV. 

Full throttle acceleration between 12:34:39 and 12:34:48.  Never entered power enrichment mode and O2 sensors always below 100 mV. 

Part and full throttle acceleration between 12:34:55 and 12:35:03.  Computer entered power enrichment mode at full throttle.  Sometimes the O2 readings looked good and sometimes not. bank 1 did better than bank 2. 

Part throttle acceleration between 12:37:11 and 12:37:23.  O2 sensors below 100 mV. 

Full throttle acceleration between 12:37:34 and 12:37:41.  Computer entered power enrichment mode and O2 sensors as expected.  Looked like a good run. 

Full throttle acceleration between 12:38:44 and 12:38:52.  Computer entered power enrichment but most O2 readings below 100 mV. 

Low throttle operation between 12:39:19 and 12:39.42.  O2 sensors looked good for first couple of seconds then went below 100 mV. 

Low throttle operation between 12:39:52 and 12:40:11.  O2 sensors looked good for first couple of seconds then went below 100 mV. 

Low and part throttle operation between 12:40:34 and 12:41:34.  O2 sensors looked good for first second then went below 100 mV. 

trackLog-2024-Sep-30_12-23-55.ods

[RKCRLR]

3 hours ago, asilverblazer said:

That log shows some weird stuff happening.

 

At line 296, short term fuel trims go to 0 and stay there for the remainder of the log.

 

At line 344-425, the upstream O2 sensor readings stop fluctuating, throttle is showing 100% but commanded AFR stays at 14.9 instead of going to 11.5.

 

Line 696-733 O2 sensors stop reading.

 

Focusing on lines 250-300 show what I would expect: Throttle goes wide open to 100% commanded AFR goes rich. The problem as I see it is that the upstream O2 sensors show lean when they should be reading richer. I looked at the timing advance to see if the advance is correlating to the O2 readings but not seeing a pattern there. 

 

I do see a correlation between the timing advance and long term fuel trims.

 

Fuel flow and air flow are tracking together consistently.

 

When the O2 sensors are reading, the difference between the upstream and downstream is negligible, The catalytic converters could be bad. The voltages are fluctuating together, but the fluctuations look abnormal to me.

 

My conclusions are leaning towards the O2 sensors are reading poorly cutting of short term fuel trims.

 

I made a post of my observations in parallel to your post.  By your statement are you saying that you think the O2 sensors are faulty and my next step should be to replace them with Denso sensors?  Their readings seem to make sense sometimes, especially at an idle.  When I watch real time data at an idle with the truck warmed up I can see the upstream sensors varying between 100 mV and 900 mV while the downstream sensors stay low.  And why would the LTFT be around 5% and the STFT be at 0% if the O2 sensors are giving erroneously low readings?  Wouldn't the computer try to compensate for that by increasing the fuel trim?  

 

Edit:  I see what you mean about the upstream and downstream O2 sensors fluctuating together under load.  But cats wouldn't cause operational problems unless they were plugged, correct?  

Edited October 2, 2024 by RKCRLR

[RKCRLR]

So, what should my next step be?  

[asilverblazer]

13 minutes ago, RKCRLR said:

I made a post of my observations in parallel to your post.  By your statement are you saying that you think the O2 sensors are faulty and my next step should be to replace them with Denso sensors?  Their readings seem to make sense sometimes, especially at an idle.  When I watch real time data at an idle with the truck warmed up I can see the upstream sensors varying between 100 mV and 900 mV while the downstream sensors stay low.  And why would the LTFT be around 5% and the STFT be at 0% if the O2 sensors are giving erroneously low readings?  Wouldn't the computer try to compensate for that by increasing the fuel trim?  

All the log data seems to be what is expected except the O2 sensors. It might be a sensor quality or signal integrity issue. Once that occurs I'm not sure how the computer compensates.

 

The sensors should work better hot, yours appear to be doing the opposite. 

 

The apparent intermittent O2 signal performance could be wiring.

 

However, seems like you indicated the part quality might be suspect of the O2 sensors - based on that and if no questionable wiring conditions exist I would strongly consider new/better sensors.

 

 

[RKCRLR]

Alright, parts cannon reloaded.  I've got two genuine Denso 234-4103 O2 sensors on order.  

 

Downstream O2 sensors being faulty won't cause these operational problems, correct?  My understanding is they will just throw a code that would prevent me from passing emissions testing.  I figure if the upstream sensors fix the problem I'll deal with potentially faulty downstream sensors then.  If they don't fix the problem then I'll move on to other things.  Is there a flaw in my logic?