95 MTX - No power, low mileage, computer reset restores power?

[bazacko]

I have an odd problem with my 95 MTX. It bogs very badly and has no power, doesn't run smoothly, sometimes runs rich, gets 160 miles to a tank, and when I turn on the climate control (any setting) the rpms periodically dip to about 500, occasionally stalling.
I've cleaned the MAF and pulled codes - I only got 157 (MAF is/was low/grounded) and 542 (thrown when engine stalls).
The 157 is probably because I unplugged the MAF a week ago to see if it would run better - it did, for about 10 minutes. However, this isn't always the case. Today I unplugged the MAF and it ran a bit worse.
The strangest thing is that for the first 5 or 10 miles after a computer reset (unplug battery for 15 minutes with lights on) the thing runs great, with all the power back (as far as I can tell).
Does this point to a bad MAF, bad computer, or something else? Any help is appreciated

 

[beaudeen]

Had similar symptoms a few years back...ran like crap once she warmed up...good cold...changed coil pack...same..same...turned out to be DIS module..buy a used one for $20...just might fix your problem..!!!

 

[Mr Anonymous]

Next time it starts happening, just shut the car off and re-start. See if that fixes it (even if only for a minute or two). If so, you may have EMI from the coil skewing the MAF signal.

If it doesn't fix it, my first inclination would be to try another MAF, preferably a known good one. Although based on your description and my experience, I would also eventually suspect the DIS module.

One issue is that you're allowing 15 minutes to clear the computer and that's giving the components time to cool down which is going to make finding the offending component harder. You can just disconnect the ground lead to the PCM for about 30 seconds to obtain the same result without waiting.

 

[bazacko]

Had similar symptoms a few years back...ran like crap once she warmed up...good cold...changed coil pack...same..same...turned out to be DIS module..buy a used one for $20...just might fix your problem..!!!

Yes, the cold/hot issue is also present in my car. I'm pretty sure a shop changed the coil pack a few years back too.
Is there a way to test the DIS?

 

[bazacko]

Next time it starts happening, just shut the car off and re-start. See if that fixes it (even if only for a minute or two). If so, you may have EMI from the coil skewing the MAF signal.

If it doesn't fix it, my first inclination would be to try another MAF, preferably a known good one. Although based on your description and my experience, I would also eventually suspect the DIS module.

One issue is that you're allowing 15 minutes to clear the computer and that's giving the components time to cool down which is going to make finding the offending component harder. You can just disconnect the ground lead to the PCM for about 30 seconds to obtain the same result without waiting.

Where is this ground wire? I looked behind the glovebox and in the engine bay but I can't figure out which wire to unplug.

 

[I'll sho u]

I think it is on the pass side inner fender just forward of the powersteering resivor

 

[bazacko]

Well I replaced the MAF, no difference. It has been running better lately for some reason - it no longer feels like it's running on 3 cylinders, and doesn't smell like gas so much. But it's still got no power.
It can't be something like timing or clogged cats though, right? Because a computer reset sometimes fixes it.

 

[SHOZ123]

If a computer reset fixes it it's because you are going back to base tables for fuel.

This points to a bad MAF or O2s.

It only takes a few seconds to clear the KAM in the PCM. Try just disconnecting the battery for 30 seconds or so.

How long does it take after clearing the KAM before it all goes to *** again?

 

[bazacko]

If a computer reset fixes it it's because you are going back to base tables for fuel.

This points to a bad MAF or O2s.

It only takes a few seconds to clear the KAM in the PCM. Try just disconnecting the battery for 30 seconds or so.

How long does it take after clearing the KAM before it all goes to *** again?

Sometimes it actually doesn't help a thing, but when it does, it only takes a few minutes of driving to go back to normal (poor) performance. Would you recommend changing the O2s next? Thanks for the help:wave:

 

[SHOZ123]

I would think bad O2s would throw a code. Clearing the KAM will set the fuel tables back to stock. It should take a bit before the car starts to run poorly again if they were the problem IMO.

Sounds like some hardware problem not fixable by the PCM. Hows the fuel pressure?

 

[bazacko]

I would think bad O2s would throw a code. Clearing the KAM will set the fuel tables back to stock. It should take a bit before the car starts to run poorly again if they were the problem IMO.

Sounds like some hardware problem not fixable by the PCM. Hows the fuel pressure?

Fuel pressure was ~12 psi with key on, ~25 idle. Those numbers are probably quite low though, because the gauge I used couldn't completely press down the valve.

 

[Mr Anonymous]

Fuel pressure was ~12 psi with key on, ~25 idle. Those numbers are probably quite low though, because the gauge I used couldn't completely press down the valve.

Don't forget that in order to properly test fuel pressure, you must remove the vacuum line from the FPR (fuel pressure regulator), plug the hose and leave the FPR vented to atmosphere.

Running at idle you should see 39psi. After shutdown it should hold at least 36psi for 10 minutes or so.

 

[bazacko]

Don't forget that in order to properly test fuel pressure, you must remove the vacuum line from the FPR (fuel pressure regulator), plug the hose and leave the FPR vented to atmosphere.

Running at idle you should see 39psi. After shutdown it should hold at least 36psi for 10 minutes or so.

Ah, I didn't know that. Thanks, I'll try to properly test it tonight.