acceleration problems under boost

[JeffreyS]

I have a problem bothering my 91 Talon AWD 5spd and was hoping that other people may have seen this and may have some idea of where to turn next (I'm tired of taking it to a shop and having them probe around with no clue of what to do)

My car's problem ONLY happens when the temperature is up to normal (so it doesn't happen when the car first starts).

When I start the car, I can accelerate at full, mid, or low boost (let's say 15, 10, 5 PSI) with no problems. However, when the car is warm, and I try to accelerate at non-max boost (10 or 5 PSI), the car will jerk or buck UNTIL I let off the accelerator. If I keep the car under boost (0 PSI), NEVER does this happen.

Possible coincidence or contributing cause, the check engine light may come on before or after this happens, but is intermittant, and doesn't necessarily stay on.

A local shop attached a computer to the car and read the code to be "low voltage", at which point the alternator was replaced - that was the last time I've had the car in to the shop.

I've done an ECU reset (to my knowledge - disconnected the battery for ~15 minutes, turned the iginition key a few times to dump the capacitor charge, and reconnected the battery), but the light still comes on (this was before the alternator was replaced).

Parts replaced: sparc plugs wires (replaced with new Taylors), MAS, alternator

The boost controller is fine, the blow off valve is fine (or else they wouldn't operate normally and hold boost, right?)

To throw one last wrench in the works, if the check engine light does go on, and I get the bucking bronco effect, I've found that if I let off the acceleration, and then floor it, there's no hesitation or delay in response!!!

Any help would be greatly appreciated!

 

[larryd]

have u checked your plugs themselves?

 

[crankbender]

Hacking your aircan has probably done a few things to the running of the car that you are not aware of. First off you are now bringing in HOT engine bay air that is very thin and the turbo is having problems getting a bite. This causes the air comming out of the turbo to be VERY hot. You get detonation and pull timing. If you have the aircan and the honeycombs for the mas put em back in. Also if you have put a breather on the valve cover make sure the port on the intake piping is covered! The voltage that the ECU reads affects how long it takes the ecu to open the injectors. having the ECU throw a code for low voltage can delay your injector fire by as much as 2.5 ms! Reset the ecu again!

What kind of voltages are you running off your O2 sensor? Do your windows (power) work with the key on and the engine not running (tests the 80 amp fusable link)?

 

[JeffreyS]

I have not check the plugs themselves yet, but will do so tonight...

With respect to the MAS, I have not removed any of the internal honeycombs, and the aircan, though hacked is still probably 1/2 there (only front portion is open). The power windows do work with the key turned, but the car not yet running.

I'll do some homework tonight and post more info then.

Thanks for the replies!!