Losing power after 20% throttle

[JCorbo25]

Updated
Things to check (in order of probable causes):
ECU - leaky caps
Power transistor - maybe coil pack, spark plugs, or spark plug cables
clogged exhaust/cat - creating backpressure
TPS - not going past % throttle open
TB grounding cable - playing hell with sensors
BCS - failed(?) - maybe less likely unless the digital boost gauge was reading full boost

I posted on my local DSM group for a loaner ECU to test out that theory.

 

[fuel]

I think you should check for boost leaks.

 

[beaner]

Quoting mitsuturbo:
If it were a boost leak, the factory "boost gauge" would likely light up all six bars. So that's probably not it.


Explain.

I still think the bov is not staying closed. That or a clamp is loose or rip in a coupler.

/ubbthreads/images/graemlins/dunno.gif

 

[SouthCaliVR4]

Quoting 656of1000:
It sounds like a clogged exhaust to me... either a clogged cat, muffler, or collapsed flex section.



This!!!

 

[fuel]

Quoting Beaner:
Quoting mitsuturbo:
If it were a boost leak, the factory "boost gauge" would likely light up all six bars. So that's probably not it.


Explain.

I still think the bov is not staying closed. That or a clamp is loose or rip in a coupler.

/ubbthreads/images/graemlins/dunno.gif


I guess because the factory boost gauge isn't an actual manifold pressure gauge, it 'estimates' the boost by the amount of air through the AFM which would mean any leak after the AFM would be consuming as much air as it would be when boosting.

 

[mitsuturbo]

Quoting 656of1000:
It sounds like a clogged exhaust to me... either a clogged cat, muffler, or collapsed flex section.



This is super easy to check. Drop the 2 bolts for the downpipe and test drive. Although i have serious doubts about this being the issue. It wouldn't be a "collapsed" flex section, but the possibility remains that a catalytic converter could be clogged.

Fuel is exactly right about the factory boost gauge. It simply runs off the airflow the MAF sensor is reading.

 

[JCorbo25]

I picked up a known working ECU out of a 1991 Galant VR4 and will test that out tonight.

If that doesn't work, I'll go in this order:
1)unplug the BCS
2)drop the cat out
3)test the TPS

Of course, depending on how much time I have.

 

[JCorbo25]

Swapping in a known good ECU didn't do anything. But my 'rebuilt' ECU looks like it's leaking caps or someone did a piss poor job of soldering...



Also, disconnecting the BCS did nothing.

Next up:
1) drop cat, check for clogged exhaust
2) test TPS
3) check spark plugs, wires, and coil pack?

Any other ideas?

 

[grocery_getter]

Quote:
A TPS failure will often accompanied by hesitation. If you are just losing power, but not hesitation, or the engine chugging back and forth then most likely your tps sensor is fine. The best way to troubleshoot a TPS sensor is with an old school multitester with a neddle display, not digital display. Black to ground and red to tps feedback wire. Open the throttle with hand very slowly in a linear fashion from all the way close to all the way open position and observe if needle display also moving in the same linear fashion or if it is jumping around or hesitating.

Other possibilities:
If you still have a cat, maybe a clogged cat.
If you still have old plug wires, they could be bad.
If you have a wideband, observe afr may be getting lean which might indicates not enough fuel or poor spark problem.

 

[JCorbo25]

pulled the CAT off and the car boosted fine /ubbthreads/images/graemlins/applause.gif

But when pulling the spark plugs, i found a TON of oil in there. Must have a leak in the valve cover seals for the spark plug wells. Guess I know what I'm doing next weekend!