99 GT bad miss at 2000 rpm

[StuartGT]

Hey everyone i recently finished doing a tranny swap in my 99 gt i have a procharger D1sc on the car and a predator tuner. i put the procharger on the car approximately 4 years ago had fun with it and decided i wanted to change the way i put it to the pavement. so i ordered all the **** to swap from an automatic to a t56 i also put 3.90 gears in the rear. when i finished i realized i couldnt just swap ecu's because i have to get the manual ecu tuned for the procharger. so i drove the car around for a few weeks had alot of fun and it ran great it just threw codes for all the automatic trans **** not being there. then one morning i get in the car and get going down the road and the thing just starts intermitently spitting and sputtering at 2000 rpm on the dot. When this happens my air fuel ratio guage pins all the way down to rich. so i turned around went home and started checking everything 02 sensors, coilpacks, spark plugs and checked for exhaust leaks but none were an issue.
I spent a good 4 hours last night on this site seeing if anyone had any insight and found that there are hundreds of posts with people having the same problem but not one of the posts ever posted a solution to the problem and in all of the posts people say check your plugs coils etc. but it didnt fix the problem in any of them.

so i guess im wondering if my ecu quite possibly is going up due to the fact i am running an auto ecu in a now 6 speed car. i had planned on getting the car dyno tuned by jpc performance in MD but im not taking the trip accross the bridge till i find out what is causing this problem.

one thing that every post had in common was they all had a predator tuner is it possible that there are a bad batch of tuners out there. i reinstalled the tune to adjust the gear ratio on

so if anyone has any insight into what it may be please let me know

 

[trinity_gt]

Sounds like a misfire. If the car is misfiring (did you see an MIL or check for error codes?) the AFR will appear to go fat since the cylinder(s) not firing are pouring raw fuel into the exhaust. Which bank is the AFR sensor on? -- knowing this might allow you to narrow the problem to that bank since it showed rich.

How did you go about checking the COPs? What did the plugs show?

 

[StuartGT]

it is a misfire but only at 2000 rpms. my diagnotic tool was only showing the failure codes for the auto trans shift solenoids no misfire codes. the boots on the COPs were all intact and it idles fine and does not do it until 2000 rpms. if i give it enough throtle it will jump past 2000 and the rpms will rise normally with no miss

 

[StuartGT]

So for i was working on the car today and i took it for a spin and it was still missing and bucking driving. i had less than a quarter tank of gas so i gassed the car up and when i left the gas station with a full tank the car was no longer bucking it was smooth all the way when i accelerated. does anyone know why that made it stop bucking?

 

[slonlow2000]

All i've found so far its a hit and miss problem, mine has done it ever sicne I bought it about a year ago. I dont have any kinda after market tune, so thats not the cause. The only performance mod I have is a CAI that was on there when I bought it. Theres lots of people out there that have 100% stock cars with the problem, and even a guy running twin turbos full custom tune the whole works with the same low RPM stumble.

I know its not the answer your lookin for, just what I've found after a little diggin.

 

[StuartGT]

thanks man i guess ill keep tinkerin with it

 

[Pearl02]

I was gonna suggest that maybe you had some "trash" around the filter of your fuel pump. When you filled the gas tank, the gas dispursed away from the fuel pump filter. However, you said your a/f gauge was reading rich when the "miss" started. This throws my theory out. If this was the case, I would suspect that the car would run "lean" due to lack of fuel. It's amazing the amount of "trash" that can get in a tank. I guess I really don't have a answer for you. Keep plugging at it. Pearl02.

 

[StuartGT]

I know its been a while but i just dropped my fuel tank and figured out that one of the fuel delivery lines in the tank on the fuel pump assembly had a hole in it so for anyone that has a similar problem in the future checking the lines on the pump would be a good place to look first. i was using my predators real time data feature and saw that my fuel pressure was dropping off to 4 psi. so that hole was causing it to happen when my fuel tank level got below the hole. im guessing the car would go into limp mode when the ecu realized it lost pressure i guess thats why my airfuel read rich.

 

[wmburns]

Check your MAF. Remember reading recent post about car holding back at 2k RPM. Turned out to be wire chaffing to the MAF. Apparently the MAF extender wiring harness chaffed against the body.

Start by cleaning the MAF.

Next double check no moisture in the spark plug wells.

Next data log the MAF, open/close loop, fuel pressure, RPM, timing, coolant temperature, IAT, TPS position, LTFT, STFT and anything else that may be usesful.

This could be a weak/noisy TPS (long shot). If it is, it will show up in the data log.

It doesn't make sense that the auto PCM would work for a while and then quit. My $$ is on something changing. Like outside temperature. Vacuum leak or the like.