: Power inconsistancy, acceleration, normal? More than one car..

08-13-10, 11:23 AM
Ive noticed this in every northstar car ive driven now.. most noteably 97, 98, and 99 STS.

97 with relpaced donor engine
98 with brand new engine from GM
99 with HG gone, leaking into #2
98 concours, unknown engine but car had 400,000km

At first we noticed it just as a day to day thing, we could tell some times the cars wouldnt accelerate as hard some times. I decided to pay more attention to it. Even from one light to the next, the inconsistancy's are there. Red light, green, it accelerates hard, shifts hard and breaks traction on shift. Next red light, not nearly as much pull, doesnt break traction. Next light, more pull than the first light, slight up hill grade, tires spin all the way to 70k. Its like this every day for both cars im driving now. And i noticed it on all my other cars.

I just assume that the PCM is doing it, reading conditions and telling the engine to run accordingly.


08-13-10, 12:15 PM
Rather strange observation - doesn't happen in my STS or F-150......or in any other car I/we have owned. IF the PCM were fooling with the engine controls as a matter of habit then accurate, repeatable track runs would be impossible.

:sneaky: Now, it's a known fact that engines run better at night or just after a car wash, and a Lunati Cams sticker is good for 5 hp at idle, but engine controls changes from light to light......that's curious.

09-04-10, 04:06 PM
I've noticed the same thing with all my Caddys. Sometimes they really storm off the line, and other times, they seem to bog - as if the timing gets seriously retarded. No codes ever seemed connected with these inconsistencies, but they did seem more evident in really hot weather. The difference was what I would call very evident, as if you were used to running with just the driver, and then suddenly added 5 more healthy adults to the load.

I always wrote them off as the engine retarding the timing for some unknown reason. :confused:

09-04-10, 06:37 PM
Maybe you need to look into an accelerometer or "G-meter" of some sort so you know that it's not just placebo. How can you just "feel" that it's not pulling as hard with repeated runs? Tire spin could just be different traction coefficients in different areas/pavement.

09-04-10, 07:11 PM
Tire spin could just be different traction coefficients in different areas/pavement.

Remember that a fair percentage of these cars have a torque limiter in addition to an engine speed limiter: Too much variation in front wheel speed (side to side), wheel speed vs. vehicle speed, and engine power level vs. wheelspin WILL cause radical torque limiting, in some cases even applying the front brakes to stop wheelspin and/or dropping 4 fuel injectors to limit engine power delivery.

The workarounds and circuit diagrams of how to defeat these power limiters have been posted here, in PCM Tuning, and Seville/Deville a year or two back; be ready to learn a course in electrical engineering.