Will PayPal Someone $25 If They Can Figure Out What's Wrong

[edwardzracing]

Alright... this is not exactly a Gen III problem, but there isn't a lot of activity in the Vortec forum, so I wanted to make the post here. I cannot for the life of me figure out what's wrong with my truck.

Truck is a 2000 S-10 with the 4.3L Vortec V6 and A4.

I've had an issue with the truck getting warm and running like royal ass. It misses HORRIBLY like it's running out of gas. I just put a new fuel pump in it, fuel pressure seems fine. When cold, the truck runs excellent... like nothing is wrong. Heats up, runs like shit. I replaced the o2 sensors and it seemed to fix it, but nope, problem is still there. I tried disabling the EGR to eliminate that, and that was no fix. Unplugged the MAF, still no fix. Unplugged IAT, still no fix.

Should I try unplugging the EGR rather than disabling it via the computer? I recorded some data... hopefully I recorded the right PIDs to help you guys. I didn't get a reading on injector duty cycle. Could one of those be somewhat plugged? I'd think it'd run like crap ALL THE TIME if that were the case... not just when it's hot. I'm going to post 2 logs. I started recording AFTER it began acting up... this was the worse it's ever ran. I parked the truck and worked on a friend's computer for a few hours... came back out and recorded a bit of data on my way back home after it cooled down.

Maybe someone can look these logs over and get an idea as to what might be going on. I'm running out of ideas. Should I try unplugging the o2's and see what happens? They're brand new so I don't know how they could be the problem. Anyways, like the title states... if someone can give me an idea that works and resolves the issue... I'll send 'em a quick $25.00 for their efforts in helping. No PayPal? Hell, I'll send you a money order. I know it's not much, but I'm desperate for some kind of help. The tune on the PCM was STOCK prior to my temporary effort at disabling the egr. I have not changed anything else.

Thanks for reading.

Brad

[GAMEOVER]

Post up the current tune

[mr.prick]

Post up the current tune

And the stock tune as well.

[waterbug1999]

To me, it sounds like a bad temp sensor, but its readion ECT. Not familiar with the vortecs, but my Trans Am did the exact same thing.

[edwardzracing]

Alright... posting up the current and stock tunes. I smoothed VE tables on the current tune, and I did a little tweaking to the transmission tables as well on my current tune; just to firm up the shifts a little, but it's definitely not transmission-related as I can put it in neutral after it's heated up, try to hit the throttle and rev it and it still misses like crazy. Here they are though. Remember, even after reloading the stock tune it still runs like ass after heating up. Willing to try just about anything at this point.

Thanks to everyone for their input. Glad to see there's some interest.

[Big Mike]

Does it idle smooth even when hot?

Any DTC codes? Does the CEL blink when it's running poorly?

Last time I had a Vortec 4.3 do what you're describing it was the ignition coil weakening when it got hot causing misfiring. Turns out this is NOT AT ALL UNCOMMON. Seem's there well know for it.

[edwardzracing]

Does it idle smooth even when hot?

Any DTC codes? Does the CEL blink when it's running poorly?

Last time I had a Vortec 4.3 do what you're describing it was the ignition coil weakening when it got hot causing misfiring. Turns out this is NOT AT ALL UNCOMMON. Seem's there well know for it.

Yeah, I'm wondering if I have a coil going bad myself. No DTC's or check engine light... check engine light never flashes or anything. It seems to idle just fine, even while hot, but once I get into the throttle... even really slowly... it bogs, and misses... doesn't backfire... just acts like it's out of gas. Even in park. GRRRR!! Thanks for responding Think it over.

[Lextech]

The distributor/cam sensor gears go bad also. They will get sharp edges on the teeth. Just a thought.

Jeff

[joecar]

Warm Log:
HO2Sx1 voltages:
- go to zero immediately when TP is opened and trims shoot up very high;
- show average cycle time 0.5s (seems too short);
MAF:
- stays low like RPM, but does not really mirror RPM;

There may be an air leak in the exhaust;
There may be a problem with the MAF sensor;
There may be some bad ground connections;


Cold Log:
HO2Sx1 voltages:
- go to zero some time after TP is opened;
- show average cycle time 1.5s (seems about right);
MAF:
- follows/mirrors RPM;



BTW (unrelated): HO2S22 is flatlined zero... bad connection...?

[edwardzracing]

Warm Log:
HO2Sx1 voltages:
- go to zero immediately when TP is opened and trims shoot up very high;
- show average cycle time 0.5s (seems too short);
MAF:
- stays low like RPM, but does not really mirror RPM;

There may be an air leak in the exhaust;
There may be a problem with the MAF sensor;
There may be some bad ground connections;

Would an air leak in the exhaust be something I could hear (exhaust leak)?? Wouldn't it have to be a pretty big exhaust leak to make it run that bad? I can take a video from inside the truck and let you both hear and see what's going on.

I tried running it without the maf, and the problem still exists. Could it still play a role in this problem even while unplugged?

No idea where to start with ground connections. Would it be a ground that has something to do with something that requires more voltage after the truck heats up? Wouldn't a bad/loose ground cause a poor condition regardless of temperature?

Cold Log:
HO2Sx1 voltages:
- go to zero some time after TP is opened;
- show average cycle time 1.5s (seems about right);
MAF:
- follows/mirrors RPM;

BTW (unrelated): HO2S22 is flatlined zero... bad connection...?

Is that the o2 behind the cat? I don't know if it's even working... I didn't think much of that sensor as I wasn't sure it had any effect on this problem. I tried disabling cat protection and that didn't change anything either. Would engine coolant temperature have anything to do with this issue?