This is in regards to the '89 IROC in my signature.

I've actually noticed this ever since I've been driving the car, but I recently took my first trip in it and it really started to bug me. Basically, the car seems to have the most power up until about 10-15 minutes after I start it (assuming it's cold when I start it). After that period of time--and/or when the temp gague starts to approach 220 (i.e. if I'm doing stop/go city driving)--I can tell that the car just doesn't have the same power as when I started it. Even if I'm on the highway and temp gague is less than 220, it still doesn't have the power it should.

Of course, as I'm only using the SOTP gague to determine this, so I can't really give any numbers or anything. I'm just mostly curious as to what could cause power loss after the car has been running long enough to reach operating temperature.

I should also note that I've been dealing with a "long-term" overheating issue with this car for quite some time now where the car only maintains a reasonable coolant temperature when it is moving at highway speed--if I let it idle or drive at a slow speed for even a couple of minutes, the temperature gague climbs rapidly. Might be a separate issue (I hope it is), but I just thought I'd throw that in...

Thanks

 

Well Sancho, I have this same problem in my RS. I believe what it is, as you increase heat power will decrease. I believe the hotter engine raises the temperature of the incoming air which in turn lowers horsepower. However, this should only be maybe 5 hp at the most. If anyone else can explain why you lose power as temperature increases, please feel free to fill us in.

 

how lonag since u have replaced the O2 on the car? i'd start there. if the car runs good cold, then gets hot and has a noticeably large power loss that follows, that is because the ecm is now in closed loop (it starts using the 02 for mixture purposes).
start there if you haven't already replaced it. i've gotten a bad new 02 w/o the ses light. i noticed a power loss and the car didn't idle as smotthly. don't rule it out.

man sancho that 89' is giving hell huh? just some encouraging words here. hang in there it'll be worth it when it's done. hell mine had all sorts of problems now it has 2 problems. the brakes do not work right and the car isn't pretty(she we'll be). she sure runs good and quick though . best of luck.

 

Yeah, I meant to add something about that... I realize that a hotter engine will inherently loose power (although by a negligible degree, AFAIK). Also, I know that hot air is less dense, and that hurts power as well.

A thought that I had was that mabye the increased temperature of the engine at operating temperature (and above) could be causing pre-detonation (or detonation or ping--not sure which), which the knock sensor is picking up. The ECM might then be modifying the timing which, in turn, hurts performance.

If that's the case, I wouldn't know where to begin troubleshooting. I do always put in the highest octane fuel that is available (92/93 octane).

 

Another major consideration is that the stock PROM will lean the fuel mixture slightly, reduce the targer idle RPM, and allow less timing advance as the coolant temperature increases.

You can safely install a 180°F thermostat to counteract some of this. To maximize the effect, you can install a fan control or redundant fan switch that turns the cooling fan on at no more than 200°F. Of course, you can reprogram the PROM to accomplish the same things. Check it out:
Cooling.pdf