How to diagnose and resolve engine issues using Durametric.

[jb92563]

Trying to apply logic which never seems to work with car problems like this:

The Facts:
Car runs perfectly at times and then suddenly it runs like crap with wandering idle, hesitation on acceleration, stalling at idle.
It seems that after it stalls and restarts it could go either way running good or crap again.

No Engine light is triggered.
Codes thrown are; P0102 MAF Low Input (connections/supply?),
P0507 Idle Speed too high (Wandering idle?).
P1571 Immobilizer - Open Circuit / No Signal

Since its my second new MAF I think I can rule out a faulty MAF as the source of the problem,

A faulty ground on the MAF or electrical is still a possibility but a low probability based on common issues I read here. Also I drive over some pretty bumpy roads and the faults do NOT correspond with vibrations making/breaking electrical conductivity so I'll rule that out as well for now.

Replaced AOS which had died and perhaps precipitated these issues?

Replaced Pre CAT sensors but no change there.

New Spark plugs and Coils look good and would be causing missfires if damaged and I am not getting misfires so cross the ignition section off the list.

New Fuel Filter, Checked Fuel pressure in the shop but not while driving and experiencing the hessitation so Fuel Pump is still a possibility.
The Fuel Pump relay can also be added to the potentials list since it is related.
Fuel flow is also good in the garage so that eliminates obstructed fuel lines and filters.

New Air Filter, better check the duct work for any obstructions just in case.
I have heard that turbulence at the MAF can cause problems and is why EVO intake folks sometimes experience MAF problems.

The battery had died while in the garage so it might have been weak, but its replaced now.

The computer ECU seems to work fine in every respect and the car still starts so the Computer is not fried,
however cold solder joints in the computer or loose ground connections to sensors is still possible but a low probability.
I did jiggle all the connectors leading into it and no changes were evident.

Vacuum leaks and smoke testing did not reveal any obvious leaks but that does not mean there is not a crack that could open up under real driving conditions and pressure, however nothing blatant was revealed as it was smoked from the intake side and through the Oil filler side with no leaks showing up under a few psi of pressure.

The only high probability items I can think of is the Fuel Pump and Ignition switch as many folks have done it from what I have read.

Those items don't seem to be monitored by any fault codes either so perhaps those should be my next efforts.

I have read that ignition switches going bad can produce all manner of strange issues but have absolutely no evidence or history pointing to the switch as suspect.

I have found a diagram showing the MAF pin-outs so I think I'll check that before buying more parts just in case its a faulty sensor ground connection or an out of spec supply voltage.



Looks like I'll have my 90,000 (Its only 72k on my odometer) mile service done by the time I replace all the wear and tear parts !
Should be good for another 10 years if the engine holds out.

[wawa]

I had change the fuel pump without any change. I had been told it usualy is not faulty, but I didnt want to take the chance.

You could try passing a second ground wire and run it for a time to see if it still happen?

Later

Wawa

[jb92563]

Originally Posted by wawa

I had change the fuel pump without any change. I had been told it usualy is not faulty, but I didnt want to take the chance.

You could try passing a second ground wire and run it for a time to see if it still happen?

Later

Wawa

Being that it is intermittent and seems to be all or nothing, working as normal or running bad, its hard to imagine a fuel pump failing in that way, unless there is an obstruction in the tank.

Perhaps its worth a look at least as I have heard of one fuel pump that broke free from its brackets and was hanging loosely in the tank by its hoses.

You never know if someone has shoved a plastic bag up the fuel noozle so the next person pumping gas gets it in his fuel tank.

[jb92563]

The saga continues and I'm near the point of giving up and taking it to an indy and letting them try.

I read some stuff about testing the MAF for a bad ground so yesterday I was fiddling with the MAF and trying to get my
multimeter hooked up so I could test the ground in situ.

I used sewing pins in the top of the MAF harness to make the connections but something slipped and the
MAF ground pin touched (shorted) the Supply 12v pin.

I heard the throttle plate make a hard smack at the same time and feared I damaged something
with the momentary short.

I then started the car and the Egas throttle was unresponsive, although the car started and idled.

I checked all the fuses and they all seemed fine.

I reset the computer disconnecting the battery, no luck, still no gas pedal response.

I checked the codes and the Egas Potentiometer codes are now present with implausible reading,
as well as the throttle position sensor codes and the MAF code that was there before.

I hope I did not fry something.

I took the throttle body apart and looked at the potentiometer and it looks fine and does not smell burnt.

I'll need to find the Egas potentiometers next and see if they look OK.

I hope the ECU is ok, as the car runs and otherwise functions properly.
Just no gas pedal response.

I wonder if the ECU has its own fuses?

It still acts like the ground is bad for the MAF so I read that the C9 pin at the ECU is the MAF ground
so will check that as well.


I found these helpful but I need to add a DSO scope to my toolkit.
https://www.youtube.com/channel/UCrf6f8hn5oy4alB2WXJCIqA

[jb92563]

Ordered a working Throttle body and Pedal module from a dismantler.

Hopefully that will fix my "Mistake/Accident" issue.

If not then I'll have to take a look at the ECU to see if it got damaged.

I also bought an ECU, Immobilizer, Ignition/key assembly matched set in case i need to try the ECU replacement, only $265 delivered for all 3 for my exact model year 2001 S.

I also discovered/read about another set of high amp (60A+) fuses hidden away in the car but I doubt these have anything to do with my problem.

I'll try the Throttle body first, then the pedal, ECU is a last resort.

[jb92563]

Update -

I tried swaping out the Throttle Body and the E-gas pedal potentiometer/sensor and still no luck.

The car starts and idles ok but does not respond at all to the gas pedal.

It just seems like there must be a fuse somewhere thats blown but all the fuses look good except the drivers seat adjustment, which has an issue that I know about.

I also found some more relays and fuses in the trunk but the fuse there looks fine as well.

I also disconnected the ECU in the trunk and used contact cleaner on the pins.

I took the ECU apart and nothing looks burned or fried. Solder joints look good.
I was surprised the ECU is not even a sealed unit, and looks cheap. Any moisture in the trunk would be a bad thing for sure.

As a last resort I have a matched used ECU/DME/Ignition assembly for a 2001 S same as mine, so I'll give that swap a try and keep my fingers crossed.

If no luck then I need to find a very talented Indy with the right skills and tools to figure this out.

Still the same codes for the egas potentiometer, Throttle Body and MAF but those are symptoms, not the root cause, as my swaps have proven.

No Check engine light suprisingly.

[woodsman]

Wow- just read the whole thread. It's been a while-- have you taken it to a pro???? If not keep up the good fight! Either way I appreciate that you've detailed your efforts...