I have had this problem since I inheireted the the car from my mom. It is a 1990 Pontiac Formula with TBI 305 and manual transmission. The problem is when driving, it has intermitent power loss. been doing it for the past couple years. Finally took it to the dyno shop and had them run some pulls on the dyno. Told them that it feels like the timing was dropping off. sure enough, they hooked a timing light to it while putting it under load and the timing went to zero. I have replaced everything that has to do with timing and no change. One of their techs suggested a knock sensor, but I had already replaced it. so I did it again. Same thing. I even replaced the esc and est modules. Again, no change. I am starting to think that maybe it is the computer or the wiring harness. Was wondering if anyone else has had or has heard of the same issue. One of the guys at my work said it may be a loose solder joint in the computer. But I dont want to keep throwing parts at it. On a side note, it did put a little over 180 hp to the wheels, not bad for a car with 235k on the odometer. Only mods I have are 3 in exhaust, custom y pipe of my own design, k&n filter, and 46 mm tbi. Let me know what you guys think could be the problem. Fairly new to the F-bodies. Sorry, have always been a ford guy.

 

Too hot of plug?

Check the sensor wiring all the way back to the controller.

Anything that's loose and transmits noise/vibration to the engine- especially on the exhaust- can trigger KR. Is your exhaust hung securely and doesn't touch anything?

I'm more familiar with late model PCM's, but some of the factory tunes have extremely sensitive KR parameters, and aggressive KR attack and decay settings. Others are notorious for false KR (355 platform for instance).

 

Do an ohm check of your knock sensor. Knock sensor wire and then ground the other probe from the meter to the body of the car. See what you get back.

 

Is your timing advancing like it should?

 

it advances to an extent. I did notice, however, when i put a new coil on it stopped, rather, was less noticeable. plugs are stock. exhaust is secure. I've been a mechanic and exhaust bulder for the past 10 yrs. Engine diagnostics are not my specialty. in depth engine performance i am still learning. timing is at stock specs. the under hood sticker says 0 degrees. I have even run it with the knock sensor unplugged comepletely for a few miles and it does the same thing. It will pick up, fall on its face, pick up again, but it does it sporatically. every now and then I can get 1-3 gears just fine. the other day I was adjusting my fuel pressure and decided to play with the wires now it is doing it all the time. You can actually hear it. No one I know seems to have run across this before.

 

What wires? You can pick up an ecm from a junkyard for $25

 

finally put a different ecm in the car. swapped the prom with my prom as the other ecm came from an automatic. no change. Now I am convinced it is in the wiring harness. I did forget to mention that the whole front end was creamed when my mom owned the car, and I was told just recently it started acting up when she got it back. I am at wits end. I just did a complete tune and hped the new ecm would fix the problem. looks like I get to tear into the wiring harness. Can the prom cause any of these problems?