I have been dealing with a power loss issue randomly for a few months. I got a p0171 lean code a few months back. Changed the O2s and it seemed to go away. Now it's back. Everything seems fine until I have been driving for over 20 minutes or so. The stft will jump to %50 then slowly drop to 0. If I let the car idle from cold, all the numbers look normal until its warm at that point sometimes the numbers jump to %40 on stft.
If I am at WOT, trims go to 0, like they should.
So far I have:
cleaned iacv
cleaned fit
replaced both 02 sensors
replaced tps sensor
replaced plugs, wires, coil
replaced basically every engine part you can.
I have a msd6al
CAI
valves are shimmied correct
Greddy exhaust
timing belts and pump replaced
throttle body clean.

car has 320,000 miles so everything has basically been replaced.

The stft will almost always rise when I am going up hill, like to 40-50%. The engine continues running smooth, but a little weak.
When I am driving sometimes the car bucks a little or just dosent accelerate quick. When this happens the stft will go to -20%.

Any help would be appreciated!

 

It is a F22B1 with a 5 speed manual. And I have attached more pics from torque.

 

Has anyone else ever had this happen? I have had this car for almost 10 years.

 

P0171 is a lean code indicating excess air is entering (intake air leak) or reduced fuel delivery ( partially blocked injector or low fuel pressure). Improvement in stft at high engine speed w/ low load suggests intake air leak. Intake air can leak from PCV, ECR, brake booster, cruise control, intake manifold. A smoke test or water spray test can detect intake air leaks.

good luck

 

Thanks for the suggestion Texashonda.
I have already smoked the engine and I replaced the few leaks I found in the vacuum lines. PCv, egr, have been replaced and cleaned. Fuel pressure test showed I was good. The regulator and fuel filter were also replaced. That was all done and the p171 code is gone. I also replaced a bad injector at the time. The injector was ok but it had a bad oring that was impossible to find.
I have not had a CEL for months it just seems like something is going on when the stft fluctuates suddenly. The car drives like it should until I see the stft go to -20% outta nowhere. It is usually when I'm moving from a stop or going up hill in a low gear. I think it might have something to do with the load on the engine. Could a vtech solenoid cause these problems. I have redone all the gaskets but maybe it is oil pressure in the head doing it? Maybe the leak will only show after I have driven the car for an extended period of time?

 

Have you checked crankshaft to camshaft timing? Did the problem arise after Timing Belt change.

I would suggest checking cylinder compressions.

good luck

 

I did check the timing and everything is good. I have not done a compression test recently. I just dont see how compression could show up that intermittently. I can literally watch my stft randomly jump up to +50% and hear no difference in the idle. Then it drops to 1% and it still sounds the same

Last best guess is the o2 sensor was a dud. It is a Bosh but I guess even they make bad ones. I even tried putting a zip tie on the o2 plug connector to make sure it wasnt wiggling loose. I have noticed that my o2 will drop to 0 volts for about 30 seconds then spring back to life somehow. Could it indicate a bad sensor?

I do roadside assistance so my car will run for about 8 hours straight sometimes. Could that kill a new 02 sensor in 3 months though?

 

Are the intake air temperatures close to the outside air temperature?

Can you put the status of open vs closed loop on your scanner to see if you are going into open loop?

 

O2 sensor going to zero, would cause a sharp + increase in stft. A wiring or connector defect is more likely than a defective O2 sensor. You can't rule out ECM defect either.

good luck