Does it have to learn to idle?

[Sqrly]

I'm looking at it differently. We've eliminated most things except maybe a bad fuel injector, which can only be verified with an injector balance test. We saw that it goes into negative fuel trims once the O2 sensor lights off and goes into closed loop. This might be inducing an actual lean condition and misfires from it because of possible erroneous sensor data for a false rich condition.

How about this for a test. Reconnect and return everything back to normal, reset codes and then disconnect the upstream O2 sensor. See if the stalling and misfires go away.

You realize I live in Ca right? A CARB compliant catalytic convertor is like $1500.

The only things I've eliminated are the TB and the spark plugs. Everything else is still suspect.

A set of injector O-Rings is cheap, I can swap injectors and see if the miss on #2 moves. Gaskets are pretty cheap too, I may dig in and physically inspect the lifters.

 

[Mike534x]

You realize I live in Ca right? A CARB compliant catalytic convertor is like $1500.

The only things I've eliminated are the TB and the spark plugs. Everything else is still suspect.

A set of injector O-Rings is cheap, I can swap injectors and see if the miss on #2 moves. Gaskets are pretty cheap too, I may dig in and physically inspect the lifters.

I believe Mooseman is just suggesting that you temporarily unplug the upstream O2 sensor and see how the truck behaves. The cat will be fine for that short duration of time, while checking to see if the problem still persists. A few hours won't hurt it.

On the off chance, did you check to see if the intake manifold bolts were maybe loose? I've seen old posts dealing with misfires, vacuum leaks, running too rich and the fix for some of them was retightening the intake manifold. Wouldn't hurt to give them a once over and see if you find anything.

 

[Mooseman]

On the off chance, did you check to see if the intake manifold bolts were maybe loose? I've seen old posts dealing with misfires, vacuum leaks, running too rich and the fix for some of them was retightening the intake manifold. Wouldn't hurt to give them a once over and see if you find anything.

I would have suggested this too however the problem is the opposite. It's running rich to the point that the fuel trims are running negative (removing fuel). Not known yet if this an actual rich condition or erroneous readings by the O2 sensor.

What if we're looking at it the wrong way? What if instead of too much fuel, it's not getting enough air? How's the air filter? Searched this thread and didn't find it mentioned. It doesn't have a MAF so that's not it. The TB you say is good and it's not throwing a code for it. Valvetrain could do that if the valves aren't opening enough.

Before you start ripping out the intake manifold, you should do a compression test. Didn't find that mentioned neither.

 

[Mike534x]

I would have suggested this too however the problem is the opposite. It's running rich to the point that the fuel trims are running negative (removing fuel). Not known yet if this an actual rich condition or erroneous readings by the O2 sensor.

Ahhh I missed that part, my mistake! I don't think it hurts to take a rachet and just give the bolts a once over still just to see if they feel snug. If he can unplug the upstream sensor, at least that helps narrow down the list of suspects. If the O2 sensor is ruled out, then the issue could very well be fuel injector related (maybe one is weaker then the others?)

I may have missed it, but was the fuel pressure regulator inspected?

 

[Sqrly]

The cat will be fine for that short duration of time, while checking to see if the problem still persists. A few hours won't hurt it.

I do believe it is actually running rich and resetting it and running without the upstream O2 would force it to use a rich fuel trim on top of the already rich condition the ECM is compensating for. I'm not willing to risk damage to the CAT by making the mix go even richer. The temps I took indicate it's working very hard to compensate for the current rich condition the other sensors are reporting. In other states one can use the $135 EPA CAT but here I would have to pay $1500 just for the part.

The pressure regulator - I don't really have a way to test it. I hooked a pressure gauge up at the filter, it stays steady @50psi but that doesn't tell me what the pressure is at the injectors so, I'm throwing that part at it just to eliminate it from the troubleshooting. It won't be here for another week.

What if we're looking at it the wrong way? What if instead of too much fuel, it's not getting enough air? How's the air filter? Searched this thread and didn't find it mentioned. It doesn't have a MAF so that's not it. The TB you say is good and it's not throwing a code for it.

Air Filter - that info is way back there somewhere. When I got it it had a K&N filter that had not been cleaned in years. I'm surprised the vehicle even ran. I replaced it with a stock air filter. I would have kept the K&N if it had been salvageable.

TB - I pulled it and ran it through all the tests. It checked out ok.

Intake bolts - I've read that too and though probably not related, it is on the to-do list. Just because it's a known issue.

I haven't done a compression test yet. I have a tester somewhere. I believe I made it by welding an air hose fitting to the metal part of a spark plug.

I haven't checked the oil pressure either. I'm hoping it because it's not throwing a warning that's it's high enough. I do see an oil warning when it stalls because the ECM starved it for fuel when it switched to trim cell 21 with that -44. The warning comes up just before the RPM reaches 0. So I believe the switch is working.

It had conventional oil in it when I got it. It actually wasn't too bad. I'm using Valvoline 5W-30 high mileage synthetic blend for now. The plan is to run the blend for 2 more oil changes then go full synthetic.

Valvetrain could do that if the valves aren't opening enough.

This is my current prime suspect. Remember the noise that's worse at idle? I haven't completely "ruled out" any of the sensors but at this point I tend to believe they are all working and doing exactly what they are meant to do by trying to correct for a rich condition caused by a mechanical issue.

Popping the valve cover off and inspecting under it should give me a good idea of how clean/dirty the engine is on the inside and I can poke at the lifters.

Lifters - Has anyone put in the cheap ones from Rockauto? $120 is way better then $310

It's quite possible that by performing much needed maintenance on the vehicle that the previous owner neglected, I have caused hidden issues to surface.

Clean the sludge out of the engine and the lifters might be getting less pressure or it loosened something that plugged them. Clean the injectors and they may be spraying more fuel. It's definitely getting more air then it used to. And who knows how all the different goo that was used when someone replaced the rollover valve with a hose barb interacts with gasoline. Does (pick a goo) dissolve in gas and go through the filter only to end up deposited on the injectors and pistons?

The only thing I'm totally sure of is I came to the right place to ask for help. Everything I've learned from you guys about this vehicle is invaluable.

 

[TJBaker57]

Jumping back a bit, you found you have some misfires going on. I decided to have a look at my own under similar operational conditions.

I drove a few miles to Dollar General, grabbed a couple items and drove back. similar mileage.

Here is a screenshot of total current misfires against engine coolant temperature.

 

[Sqrly]

Jumping back a bit, you found you have some misfires going on. I decided to have a look at my own under similar operational conditions.

I drove a few miles to Dollar General, grabbed a couple items and drove back. similar mileage.

Here is a screenshot of total current misfires against engine coolant temperature.

View attachment 115362

Look at my #2 cylinder, it's pretty bad at idle. The scale auto adjusted to 0-100.

I don't like how the sensors record a misfire though. I bet if I hit the block with a hammer while it was running the ECM would record missing and knocking LOL

But, it's just a piece of a bigger picture.

 

[Mooseman]

Lifters - Has anyone put in the cheap ones from Rockauto? $120 is way better then $310

I've seen others use Enginetech timing components without any issues. Not sure about lifters though. I've seen one person here replace his lifters but can't find that thread. I did find this one:

yet another lovely 4.2l valve tick

I know there are like 100 of these on here but I figured mine is a little different and I love troubleshooting so here is my issue. the description of my problem: The past few weeks my 4.2 has been making the typical complaint of sounding like a diesel engine when at idle all the way up to...

gmtnation.com

 

[Mooseman]

I don't like how the sensors record a misfire though. I bet if I hit the block with a hammer while it was running the ECM would record missing and knocking LOL

It's with the crank sensor. It sees the cylinder not contributing as much as the others when it slows down on that cylinder. The knock sensor would retard timing if it detects knock.

 

[Sqrly]

I've seen others use Enginetech timing components without any issues. Not sure about lifters though. I've seen one person here replace his lifters but can't find that thread. I did find this one:

yet another lovely 4.2l valve tick

I know there are like 100 of these on here but I figured mine is a little different and I love troubleshooting so here is my issue. the description of my problem: The past few weeks my 4.2 has been making the typical complaint of sounding like a diesel engine when at idle all the way up to...

gmtnation.com

I've already read that thread, that's how I learned about the tool needed get the lifters in and out.

I found a used one on Ebay, there's half a dozen more on there at the moment for around $30-$40.

 

[TJBaker57]

Look at my #2 cylinder, it's pretty bad at idle. The scale auto adjusted to 0-100.

Agreed. You have a concern there, but I noticed it did not misfire again after the initial event when not yet warmed up.

Now when I have had enough to cause a flashing check engine light there was more like 12000 or more misfires registered.

ps/edit: There is also a PID/sensor for ALL current misfires. This will sum up all the cylinder misfires over a short period.

 

[Sqrly]

Agreed. You have a concern there, but I noticed it did not misfire again after the initial event when not yet warmed up.

Look at the very end of cylinder 2 and you can see it started to miss again when I parked.

It actually misses less when it's cold.

 

[Sqrly]

I thought of another 'test'.

The vehicle spends very little time being driven when it is fully warmed up so it spends an unusually large amount of time in an open loop.

Once a week we make a 60 mile round trip of mostly freeway speeds. We always take the Honda simply because it averages 43 mpg.

Next time, we'll take the GMC but, I'll reset it by shorting the battery cables then do a 5 minutes 'learn to idle' right before leaving.

After the drive I'll get the trims and see what it 'learned'.

Hmm, my phone will be bt'd to the audio system, we do have spares lying about, I think I'll install the scanner app on one of those so I can log misfires too.

 

[TJBaker57]

The vehicle spends very little time being driven when it is fully warmed up so it spends an unusually large amount of time in an open loop.

Have you witnessed this in your data logs??

Mine gets into closed loop surprisingly fast and I don't even have the SAIS which should in theory make acquiring closed loop even faster.

Here I startup at 40°F and get into closed loop in under a minute while idling.

 

[Sqrly]

Have you witnessed this in your data logs??

Mine gets into closed loop surprisingly fast and I don't even have the SAIS which should in theory make acquiring closed loop even faster.

Here I startup at 40°F and get into closed loop in under a minute while idling.

View attachment 115377

Um, no. I haven't actually looked at the open/closed state but a few times so my sentence was incorrect.

I was reffering to the situation shown in the log in post #194 where it took over 3 minutes for the downstream O2 sensor to start sending real time data.

Almost every time the vehicle is driven, it's for less then 5 miles. The vehicle is not warmed up at all for 2/3 of those trips. For the remaining 1/3 it's warmed up idling for comfort and/or to defog the windows only to an avg. coolant temp of about 160° before being shut off for 15 minutes before the actual trip.

You've stated that after being reset, the vehicle takes more time then that to 'learn' fuel trims.

Maybe it's learning during the wrong conditions? So my plan is to change those conditions and observe the results to see if they are different.