good point.........they can get loose or tighter and mess things up...........my buddies lt4 hotcam car had problems stuttering/breaking up at high rpm WOT and it was from the rockers.

 

I have put a brand new map sensor on it, and then went back to the old one. I also swapped in the MAP sensor from my other T/A too, and there was the same problem.

I'm pretty convinved that it's a temperature related problem too as the car is fine when first started and then progressively gets worse until it's at it's worst at about 3-4 minutes of running time. It's not completely isolated to the right bank, because once it steps in to closed loop the left side LTerms take a dive too.

I'm going to pull the valve covers tomorrow, and take a look. I don't really want to play with anything that I'm not certain about. I figured that if there is indeed a collapsed lifter that I'd have some pushrod play in there.

 

I was looking at the datalog that you sent me last week.
To be honest, I'm not very impressed with the O2's at all. Very lazy. How old are these?
The injector pulsewidth on the side that the short term fuel trims are pegged at 1 are noticably lower than the other side...so that bank is really rich. It's completely out of adjustment and the computer want's to pull more fuel. If this is the program with the 26 injector constant, I still questions whether or not that is correct.
Some other things that might not have anything to do with your stumbling problem but still need to be addressed are the high idle map, low closed TPS spark advance, low idle rpm for that cam, and misadjusted IAC. All my personal opinion of course.
If it were my car I'd be fixing these things first and see what happens. Might not do a damn thing, but there obviously not helping either.

 

Well Since it has turned winter and very cold I can tell you that my problem is definately temperture related. Before I installed my 160 deg. stat. after the temperture got above or around 180 that you could feel it start to run like crap, it would hesitate and bog down real bad, exhaust note would be real raspy and just run like crap the higher the temp got the worse it would get. After the 160 deg stat. install now it runs great for as long as I am driving at normal pace but if I stop at a store or get stuck in traffic for a long period of time and the temp goes up to 180 to 185 range it will start to run like crap again. What I have noticed is that after the temp goes up and it starts to run bad is I can get on the highway and drive till the temp goes back down after a few minutes it will start to run great again until I shut the car off to go in a store or get stuck in traffic again. I have done everything I know to do and changed almost every sensor I know to change I have been living with this problem for almost three years now. I have scanned it and checked for codes which turned up nothing. Maybe my temperture related story will help.

 

Have you replaced your Coolant Temp sensor yet? they are cheap... Just a thought.


Marvin

 

Well, the O2's just got replaced with brand new AC Delco, so there's no worry there.

I really have ruled out a tuning issue at this point on the car because I ran the original tune that I got, the one that pulled the 375/363 on the dyno. The stumble and richness was still there. So it's not that.

It's something mechanical/temperature related, but I'm leaning towards the mechanical actually. The temp of the car isn't even 125* when the problem start to appear.

I have not replaced the coolant temp sending unit as I have seen no need to replace it. I have gotten no erroneous readings at all from it.

Looks like I may have to throw in the towel on this one and eat into my paintjob money by taking it to Jay Fisher Pontiac if I can't find the problem under the valve covers.

 

Ok, I bumped the closed tps spark advance to 26*, which helped my vacuum out. I hooked the vacuum gauge up to it, and was pulling between 14-15 in hg of vacuum. This also help with the stumble problem, but only put it off. It still showed up, just took a lot longer. However, once it got into closed loop, I watched my Integrator Values on the left side peg at about 122 and the right side just took a nose dive down to about 72, so it's still loading up on fuel on that side.

On another note, when I made the Closed TPS Spark Advance adjustment, now the car won't idle below 1000 rpm. It won't come down, even in closed loop.

 

Just put a 28* advance chip in, and pulled a solid 15 in hg of vacuum. I've got a new datamaster log if anyone would like to take a look. Once into closed loop, you can totally see how it loads up on fuel. the Right LTerm pegs at 108 and the left Creeps down to the 11x range.

Car still didn't idle down to 900 like it should though? Is this a result of the new Closed TPS Spark Advance, and how do I correct it.

 

I'm going through almost the same problem. Some times it just falls on its face, And usaully at the worst times. Like today I stopped at a light next to a ws6. Talk to the guy he said it was stock. Well the light turns green and I step on it. It just falls on its face. Slow take off and then it picks up. By then its to late he's already pulled on me. I'm so sick of this. I would like to find an answer to this.

 

I've been dealing with this problem for quite a while now myself. One bank always goes full rich and the car will not idle. I have changed absolutely everything I can. Every sensor, opti, coil, IAC, IAT, ICM, PCM, 3 Alvin chips, O2's, MAP, coolant sensors, wiring harness, readjusted the valves 4 times, with nothing to show from it... I think the problem lies somewhere in the tuning of the car. The first chip I had from Alvin made the car run great after the rebuild, but the idle was way to low so I sent it back to him, and ever since I have had nothing but problems. I am so sick of this, it is time to finally get some answers. I hope someone can finally answer this problem.

 

Programing .

 

Not in my case. We've tried a variety of things, to no avail. It's most likely something mechanical because I've ruled out everything else.

 

Just changed my rocker arms to the Comp cam Pro magnums. It seems to have done the trick. The car is running 100% better.

 

Glad you got it figured out.

 

Well had a rocker break on me. So they had to be changed. They made a big differance. I'd say it's worth the try and go to full rolers. If you don't already have them. I beleive shoebox has a rocker adjustment page. It's a pain but if it can solve your problem it will be worth it.