Well, thought I should throw an update.

I've managed to completely isolate the problem to Fast Throttle Movement only. Any light throttle driving and the car reacts fine. Fast throttle movement and I get a stumble at idle and if moving under load I get a complete fall-on-your-face hesitation, with a quick recovery. Above about 2500-3000 though, It doesn't want to do the hesitation.

I can't find anything wrong with the car. I am replacing the O2's, EGR, and going to bring my TPS volts down from .92 at idle, and putting in a new fuel filter. But I still can't find anything wrong. I made a post asking about a possible sticky fuel injector once it warms up, as it's the last thing I can think of.

I just wish I could find the problem. I've been battling this since August now, and it's killing me that I can't get it fixed.

 

that's the problem I described; only modifying the CPU code fixes it.

 

Ok, new EGR, O2's, Changed the oil, new Fuel Filter, adjusted the TPS to a .74 idle reading, and another tune from Alvin, the original tune that made the 375/363 pull.

Nada. Although on the scanner I noticed before the car got into closed loop (didn't let it run that long, the problem was obivously still there), the right side was loading up on fuel. The O2 millivolts were in the upper 500 to mid 600 range and slowly creeping higher. The left side was staying right at about 450 + or - about 50 max each way. But the right side was constantly at 550 or more, the number I saw most was about 610. Obviously, the right side is loading up on fuel for some reason. When I shut the car off it was at about 635 average.

Before the right O2 mV started to climb up, the car was fine, but once it started climbing, the fast throttle movement stumble was there again. Real quick, just a little putter, but the same thing as always. So,

Does anyone have anything I can check to see why the right side would be loading up on fuel like that?

The only thing I can think of at this point would be a valve not compeltely opening. But could that only present itself as a problem at fast throttle movement?? It's not a sticking injector, as I don't have a hard start problem. I'm just really stumped now.

 

How are your fuel rails? only thing i can think of... My friend has the exact same problem... Maybe he will post.... RObbyrob where r u?

 

have you checked the cat on that side ??? also do you have any friends with o2 sims ?? maybe you should see if it runs better when its being fed ideal readings ??? youve tried everything else just about it seems.

 

You might want to try and upgrade the guage on the wire going to the fuel pump... Its worth a shot for only like 20 bucks.. When you stomp it the wire might not be able to carry enough power all of a sudden but turn out ok as the rpms move up...

 

failing lifter?

 

Ok, 93 Trans Am. Single cat, only two O2's, so that rules out the cat.

It doesn't seem to be a fuel pump thing. The right bank is loading up on fuel, not a shortage of fuel like a failing pump would cause. There's no hard starting issue, and I've pulled the rails, so fuel injectors are out of the question.

Possible failing lifter, but shouldn't be as they're brand new Comp "R" lifters as of last August. I'm also thinking a possibly overtightened valve rocker, but why would one just go tight all of a sudden after being run???

 

I have heard nothing but bad stuff about those R lifters.. Do a search on them..

 

But if it was a collapsed lifter, wouldn't the problem be aparrent at all stages, not just a fast throttle movement?? Also, wouldn't said lifter cause the cylinder that it's on not to fire consistently, thus not causing the header to heat up for that cylinder??

On another note, can I tell if I've got a collapsed lifter just by pulling the valve cover???? Please tell me I can as I just really don't have time to pull the intake manifold right now.

 

oops , sorry didnt see that. Im at work and the day is almost through , fallen asleep at the wheel here.

 

If i were you i would try to adjust the rockers again.. It wouldnt cost anything and would take you about 20-30 min... I had to readjust mine and the car is 100X better! Much smoother too... Before when i hit the gas the engine would shake and then smooth out at high rpms and i kept getting lines on my back bumper from running rich. It also robs the torque from you and pretty harsh at that!. Its amazing what those little POS's can do to ya..

 

You cnt tell a collapsed lifter from taking the valve cover off either.. only way to tell i would think is a stethascope....

 

what I can see after reading all this posts is that its temperature related. I see that the longer you keep the car running the worse it gets and its only on one side. Another thing you said you tested your MAP sensor I believe? did you removed the MAP sensor from the Intake manifold and used a vacum pump with a vacum gage while checking on the scanner the reading? I believe its done with the Key ON engine OFF.

You keep the MAP sensor wires connected... with the MAP sensor removed from the manifold you test it using a vacum pump connected to the MAP sensor itself, the pump has to have a vacum gage attached to it. you apply some vacum and write the reading from the scanner and vacum pump... you try at different amounts of vacum like one reading per Inch of vacum... My scanner reads in volts so I have to translate to inches of vacum applied....

I am probably not making sense but you test the MAP sensor removed from the Manifold, keep the connector plugged to the sensor and scanner runing... they Key ON but keep engine OFF... Also you can do some quick pumps on the vacum pump and see if the MAP sensor follows with a quick response (sticky maybe?).


Anyway I hope I made sense.

Marvin

 

well probably ok since its new..........i just heard a few guys installing a cam and re-using stock lifters that go bad and cause probs.


also, lifters pump up with oil pressure or whatever, so that might explain why it happens at idle and when you punch it (before the pressure builds).


im no expert, i was just throwing the idea out, mainly cause i thought you might be reusing the stockers.