Hesitation & Check Engine Light
 

Good Afternoon!

Driving my 1991 Vert on my way back to town I heard a slight pop (possibly a back fire) and then the check engine light went on. I down shifted to see if there was an issue and I have almost no power from 3000RPM to 5500. It won't rev any higher unless the load is removed. The engine light doesn't flash, the oil/water/volt all seems to be perfectly normal. No other lights are blinking. What I did notice however was that there seems to be a very noticeable "Whirrrrrr" noise when I let it run and I check under the hood. It increases with throttle and it seems to be from the passenger side of the engine bay. I'd like to check the engine light but I can't remember how to do it on a vehicle that old.

Any suggestions?

89-91 CPU Trouble Codes

Banzai Racing Compression Test

Does sound like an issue with vdi or 5/6th ports. Try those above first. Always good to do those simple tests first to get a baseline before chasing your ass.

Can you describe the 'whirrr' a bit more? Could be a number of things. And also i would pull those codes and i can almost bet it will show a TPS code. The S5 ones seem to be very tempermental.

the S5 is old enough that the light won't flash. its either on or off.

I ran the codes and it seems to be trailing coil pack which sorta makes sense because after a few runs the problem happens after I've driven for two minutes or so. It'll pull easily through 1st and 2nd. When I come to a stop and try again it revs fine to 3000ish and then jerks, shakes, and rattles and barely advances any farther in revs. The best way I can describe the whirr is almost like a rotor is tagging along for the ride and not producing it's own power. If I have a chance tonight, I'll record it.

Ah this makes much more sense. Thank you!

Thanks for the helpful sites. Looks like I have a Tuesday night project.