2000 Suburban Misfire - trying to see $06 data

trey3 · July 3, 2020

I see this is a pretty common issue, and I am trying to narrow it down. Thanks to a previous post, I know it is not my Catalytic converter. It idles fine and cruises down the highway fine, but even a slight hill, it is a pretty obvious miss. No MIL or stored code.

My question is regarding the $06 data. I have purchased TOAD and OBD Auto Doctor but can't figure out how to display the cylinder misfire data count. Other $06 data displays fine.

Is it safe to assume a 2000 is capable of outputting such data? I want to make sure I am not trying to get data that isn't there. It should be since it is OBDII, or is GM hiding it?

I know it is a long shot, but if anyone is familiar with either program and how (if?) it works with a 2000 pcm, I would be very thankful to hear from you.

Edited July 3, 2020 by trey3

chem_man · July 4, 2020

I am not familiar with those apps, but I know using Torque Pro I can monitor misfire counts on my 1999 Silverado with the 5.3 L V8, so I would assume it's possible on a 2000 5.3 L V8 as well.

trey3 · July 5, 2020

That is great to know. Now I just need to round up an Android device. Thanks for the info.

trey3 · July 6, 2020

Thanks again chem_man for the info. I finally found a combination of Android and scan tool that would work with Torque Pro.

It tells me:

TID: $0c CID:$20

Max 172 Current 53,727

TID: $0c CID:$30

Max 381 Current 53,675

So obviously a misfire. I added in each cylinder and 0 was displayed for all of them. I would assume it has to track that somehow to throw a specific cylinder code. Do those numbers above correspond to a cylinder?

Edited July 6, 2020 by trey3

CamGTP · July 6, 2020

No, not really.

P0300 would be a random cylinder misfire.

Then P0301 through P0308 would be cylinders 1 to 8, those would lead you to the specific cylinder.

trey3 · July 6, 2020

Ahh, so basically this vintage isn't able to tell the exact location of a random misfire. If it is bad enough it will be detected on a specific cylinder, thus a P0301 through P0308 code.

Correct?

chem_man · July 7, 2020

Actually, you should be able to create a display for each cylinder and have it show either the current misfire count or the history misfire count. I have 16 different displays for my 1999 Silverado - a Current Count display and a History Count Display for each cylinder. They are labeled MF CX Cur and MF CX Hst (where the X in CX stands for the Cylinder Number.

You might have to go into vehicle settings in Torque Pro and enter your vehicle information in order for the parameters to be enabled.

What I did was to add a new display by pressing down on a blank page in Torque Pro so "Add display" would pop up. I then selected "Add display", I chose "Digital Display" from the list of images, then scrolled through the listing of parameters to be monitored until I came across "[GM}MIsfire Cyl.1 Current" and then I pressed that selection, and then I picked small for the size. Then I repeated choosing [GM}Misfire Cyl.1 History". Then I repeated for Cylinders 2 through 8.

As CamGTP stated, P0300 is a random/nonspecific misfire code. It sets whenever there are enough misfire counts caused by something (fuel, spark, vacuum leak) somewhere, but not enough misfire counts to specify which cylinder is misfiring. Now, understand, this is sort of an initial flag that something is going on, but it is not happening enough for the PCM to figure out which cylinder is misfiring. This is where monitoring misfire counts comes in handy because the cylinder or cylinders causing the P0300 code will show the "raw data" so to speak and assist in narrowing down which cylinder is "problematic".

For instance let's say that you are monitoring all 8 cylinders for current and historical misfire counts. After the engine has been running for a minute or two you see that Cylinder 3 has a current misfire count of 25 and a historical misfire count of 100, AND all the other cylinder misfire counters are showing a Current misfire count of either 0 or 1, and a historical misfire count of either 0 or 4, then you can see where something is going on with Cylinder 3.

What is going on is for you to diagnose. It could be something simple like a spark plug being somewhat dirty, or a spark plug wire going bad. Or, it could be a fuel delivery problem (caused by a dirty fuel injector or an improperly seated fuel injector plug). Or it could be something more complex/serious like an exhaust valve not closing all the way because it's spring has lost tension.

This is where the detective work comes in beginning with looking at the simplest and most frequent causes of the misfire, and then working your way down the diagnostic tree to the more complicated, "harder" to find causes. Note - most of the time it will be something like a dirty spark plug, a bad spark plug, a spark plug wire not seated properly at one end or the other, a spark plug wire degraded by heat or oil contamination, a bad ignition coil that shows up when it gets hot, the electrical connector to the ignition coil is not seated properly, etc.

Now, if whatever is causing the P0300 to set get worse (and the PCM sees more misfire data) the PCM will set a P030X code where X is the Cylinder number.

I hope this helps you understand what is (and is not) going on,

Good luck trey3.

trey3 · July 8, 2020

I forgot to mention it is about to hit 340,000 miles. So it very well could be something valve related or other internal issue. The past few months I have noticed the valve tap, or whatever it is, that has been happening for the past 200,000 miles at startup isn't as loud as it once was. I guess it could be stuck.

I replaced the plugs and wires. I also learned about the 2008 TSB about the AC Delco spark plug gap change from .060 to .040. Still had the misfire.

Since they are all original and I plan to keep the truck, I have ordered new OEM colis, knock sensors, camshaft position sensor, and fuel pressure regulator.

I am going to clean and test all of the injectors off the vehicle and clean the intake. It is soaking now. I did notice today while doing some pressure washing the little hose to the fuel pressure regulator was split at the boot on the intake. It might have been that. Ordered a new one of those too. Since I am in so deep, I am going to replace the valve cover gasket, mainly to take a look inside.

If that doesn't cure it, it might be time for a long block. Then I will be making post to discuss a 6.0 swap.

Thanks again Chem_man.

chem_man · July 9, 2020

Thanks for the update. WOW! 340K on the engine. Yes, some parts just might be a little tired.

While waiting for the parts to show up, do a compression test if you are able to. It might answer a few questions regarding the P0300.

Good luck and been happy to be helpful!

trey3 · July 11, 2020

I installed everything last night and there is a big improvement in engine idle and power. The computer isn't reporting any misfires. I am still hearing a bit of what sounds like a light backfire or knock under load. That may be because the cats are currently removed for testing and it is louder and put together with cheap clamps. I am going to have the cats welded back on. That should quite things down.

Like I said before, the mystery tapping at startup is now no longer. I suspect that rod or lifter is stuck. I did a compression test and it was bouncing around 130psi on most cylinders. It would bleed off to about 90 pretty quick. I have since learned a fluctuating needle is an indication of misfire or a sticking valve.

It is likely gummed up with something. I forgot to mention I replaced the head gasket about 15 years ago due to coolant leaking into the oil. A few years after, I had to pull the oil pan and clean out the sludge and change the pickup. I also forgot to mention I had a minor mystery coolant leak start up again last summer and I suspect it was doing the same thing. I added some Bars Leak liquid aluminum and that stopped the consumption. But I bet that coolant contamination didn't help.

I also found the camshaft position sensor was seriously baked. I am sure any moisture was shorting out the wires.

My new plan is to run a bottle of Techron before I have the cats welded back on. The next oil change I may run a bottle of motor flush. I know that could very well make things worse. At this point it might be worth the gamble. I am not too worried since I could likely pay for a new engine with about 8 months of payments on a new Suburban. Don't get me started on what happened to the truck part of the new ones...

This project wasn't without other drama (not just the heat index of 110).

First, I am pretty sure I got fake AC Delco coils from an Amazon seller. I should have known at half the price. The box looked better than any AC Delco box I had ever seen or I would have likely fallen for it. It was a nice gloss. What is odd is the Amazon coils themselves look more legit than the actual one I got form O'reilly. The coil on the right is the real one. Does everyone agree, or am I being paranoid? It wasn't worth the extra $250 for the doubt, especially since they will likely take up residence on a new engine at some point.

chem_man · July 12, 2020

trey3, glad to hear you got it running smoothly!!! YIKES on that camshaft position sensor - the picture of the plug looks horrible!

Regarding the ACDelco coils, how does the price you paid on Amazon compare to the price Rockauto charges? If they are close, then the Amazon ACDelco coils could be legit. What strikes me the most is it looks like you have 2 completely different coils in the picture - the one on the left from the big box looks smaller than the one on the right. Is it an illusion or are they different sizes?

OK on all the other work you did in the previous years. As far as your plan goes, it sounds good to me. The only thing I would do differently is I would run a few shorter than usual oil & filter changes using an HD oil like Chevron Delo Conventional 10w30 or 15W40 and then go back to your usual routine. The Delo HD oils have more detergents than conventional passenger car motor oils from what I have read on a couple of other forums. That way you won't "shock treat" the engine with some motor flush. Just my preference.

Good luck and thanks for the update!