Hi folks..

So heres my problem

The car runs fine at idle and revs fine with no load, but under load above about 3000 rpm the motor backfires through the intake, misses and is generally having a bad time. Crusing the car around town is fine with no problems. I notice this problem most when getting on the freeway or accelerating from a stop sign at WOT. When this happens I just get off the throttle and increase speed more slowly.

So heres what Ive checked so far:

1. Fuel pressure is good at 45psi
2. Base timing is good at 6 deg
3. IAC and TPS good voltage according to shop manual
4. Replaced cap, rotor and plugs
5. No trouble codes

Um what else did I check.. Thats about it.. Ive been having this problem for quite some time now, but fortunatly its not my daily driver.

Anyone have any suggestions? This is my first exp with a cpu controlled car so Im a little lost. My 2 guesses thus far are that 1. theres something going on with the cpu when the car is at WOT and its not compensating properly, or 2. theres some sort of timing issue.

The engine is totally stock except for an adjustable fuel pressure regulator I installed after having some fuel pressure probs.

Any help/suggestions would be VERY much appreciated!

Thanks again!

 

Sounds like a weak spark. Try replacing the coil, maybe the distributor module. If you know how to check the spark or have a tester (yellow or blue spark, that kinda thing) then you could try that first before buying anything. Thats where i'd be looking.

 

also check with a voltmeter that the voltage of the tpsvoltage goes up smoothly to about .54 volts with no throttle to around 4.2 volts at wide open throttle. if the number starts jumping around or doesnt count up as you open the throttle that will be a big problem for the computer.

 

How many miles on the car? Timing chain stretch can cause the timing to drift under a load while remaining "ok" at idle.

 

now correct me if i am wrong but isnt there no such thing as a 1986 L98 except the alleged one that was made for testing and what not?

 

from what i understand, 50 made it out the door.., but in 87...., not in 86

 

Supposedly 50 were produced IN '86 but were not EPA certified.
'87 began the production year for them.

However, the supposed 50 were in Camaros, not Birds.