1993 850 N/A 5speed 220k miles. New cap rotor, plugs, filters, flame trap, timing belt, ect....
Once the system has reached closed loop, while accelerating, around 2800 to 3000 rpm, I feel a loss of engine power. The power loss is not huge, and it doesn't seem to miss or run particularly rough. If you have ever driven a really slow and weak 4 cyl vehicle when the a/c compressor came on, and it kills the power - this is about the same feeling. The power really comes back on around 3800 - 4000 RPM. I am assuming, that whatever robs power at 2800, is corrected around 3800 - at least it feels that way.
This power loss is pretty consistent. It does not happen during warm up, in fact, the engine has to reach the normal operating temperature completely, before this happens.
Any clues what to look for? Any tests that I may be able to perform, to give me some clue as to whats changing? I'm running 93 octane fuel, so if the timing is being retarded, it shouldn't be because of detonation.
I have not made any performance modifications..... - yet.
Thanks,
Cranky

 

Maybe blocked exhaust/cat or bad O2 sensor? Have you pulled any codes?

 

Have you cleaned the throttle body?

 

I've not cleaned the throttle body. I plan to though.
If the cat was stopped up, it wouldn't regain power at higher RPMs would it?
I haven't replaced the O2 sensor. If the O2 sensor is bad, will it not set a check engine light?
Thanks, Cranky

 

Most of the time the O2 will set a code.
See what happens after the throttle is cleaned.

 

Yes, a bad O2 will set a code. That being said, if there's more than 100K on the sensor, you may want to consider replacing it. It's a judgement call...