Low power when warm/MAP shows no load

[comanche]

02 SL1 SOHC M/T 297k miles

When cold the car has "reasonable" power (taking into consideration age, miles, etc). Computer display showing engine load will range from 45% up to 100 when pedal is 3/4 down under heavy load.


After 15-20 minutes of driving, the car has a noticeable reduction in power. Still usable, but exacerbated when under heavy load or pulling a trailer. Worthy of note is that when warm the computer display showing engine load will go up to only 80%. Today I was pulling a trailer and going up a steep hill, pedal mashed to the floor and in 4th gear, the car was slowing down... yet the engine load display showed only 81%.

Does this sound like a MAP sensor issue?

[OldNuc]

See if you can look at the raw MAP live data. With your foot on the floor and loosing speed in 4th the MAP should show close to atmospheric pressure and and show a 18-21" Hg vacuum at idle. This could be a failing fuel pump also.

[comanche]

Initial live data shows 100% load when cold, 29 in. Hg

80% load when hot, 29 in Hg.

This doesn't make sense to me but maybe I'm missing something...

[OldNuc]

You can not have 100% engine load at 29" vacuum. So, based on that verify that you have power to the map, no fail code. It is possible the scanner is producing bad data so check that out by reading the MAP key on Engine off and then at idle, it should change values if it is working. My advice at his point is to pull the MAP and verify it has a clear path into the intake and if it does than go to the pick and pull and harvest another MAP off of a DOHC or SOHC with the al;aluminum intake manifold. Look for a 103 stamped into the top visible side of the MAP. If it looks the same it fits and the 103 is the correct curve for either engine.

[billr]

I'm guessing that scanner is showing actual MAP, in inches of Hg; not manifold vacuum in inches of Hg. A MAP of about 29" Hg = 100% load is correct. I think that MAP sensor circuit, including wiring, sensor, connectors, and PCM is suspect. It could even be something else connected to the 5V supply for the MAP sensor, like the TPS.

Also, how about the IAT/MAT, what does it read when the engine is hot and 29" Hg MAP = 80% load? If the IAT is quite hot, then I think the perceived "load" is reduced due to reduced inlet-air density.

[OldNuc]

A reading of 29" at WOT is also invalid except at the instant of a full throttle opening.

Any 5V bus high or low voltage sets a code. Any seriously out of range TPS signal also sets a code.

[comanche]

TPS was replaced about 6 months ago to fix a different issue.
Air filter is a K&N and I do clean it occasionally.

Scanner is a CRP123.

Hopefully Saturday I'll have time to pull the MAP and check things out, do some more data checking.