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Discussion Starter · #1 ·
Hi all,

This is my first post. This seems like a nice forum though so I may stick around. I'm having some electronics issues with my car and wanted to bounce ideas to see if I'm headed in the right direction and get new feedback. I appreciate any you can offer. I have a 1993 Mustang LX 2.3L Automatic with about 157k on the clock. There's nothing fancy about it. I'm just trying to keep it running and stay on top of the maintenance to do so.

The last couple times I've driven it, I got a CHECK ENGINE light after a couple minutes of running and an erratic reading on the tach, like 400 RPMS when the engine still seemed to be running fine, it would sometimes stumble like it wanted to stall. After just being driven it would crank strongly but not start. I got stuck in the walmart parking lot (close to home luckily) with it but waited a couple hours and it started fine. I searched around and found that this is probably the DIS (ICM) module. I replaced it with a new part. It started and ran fine after completing the job.

I tried starting it the next day though and like before it would crank but not start. The difference now is that I no longer hear the fuel pump running when I turn the key to ON. Can everyone else hear it whine? I know I can.

I ran a diagnostic last night (have a reader thankfully) and got:

KOEO:
543 - Fuel pump secondary circuit fault.

Continuous Memory:
223 - Distributorless Ignition System - loss of dual plug inhibit (DPI) control
224 - Erratic IDM input to processor
543 - Fuel pump secondary circuit fault.

The stored 223 and 224 tell me I was probably right with replacing the ICM. I guess I'll find out later though. What exactly is the 543 secondary circuit though?

My fuel pump relay went bad a couple years ago so I opened the IRCM and soldered in a new one. My first step will be to check my work there in case it went bad. I'll also try jumpering the pins in the harness to see if the pump circuit actually works. It seems weird that the fuel pump would stop working so soon after replacing the ICM though. Are these systems related at all or is it just a fluke?

It may be unrelated but my Air Conditioning no longer cools. There's refrigerant in the system but it seems that the compressor clutch isn't engaging. I hear that relay is also in the IRCM. I wonder if they're all starting to go bad and it needs replacing.

Sorry for the long post. Better to be thorough up front, right? Any other ideas? I'd love to hear them. Thanks!
 

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ok i MAY be wrong on this but i'm pretty sure that the primary circuit for the fuel pump is the one that keeps it running while your car is on and the secondary circuit is the prime feed that runs it for a couple seconds before you start it... again i may be wrong but i think i came across that somewhere..

you should DEFINITELY be able to hear the pump prime when you turn the key

on the self test connector under the hood there is a terminal that you can ground that is a self test for the fuel pump.. so i guess its one way to check to see if the pump runs to test the wiring.. also you could go under the car and do some poking around with a power probe or test light.. the power probe would be nice because you could power up the pump and see whats going on..

definitely check the relay out and your soldering job.. energize the relay and test resistance across the contacts of the switch and there should be very low ohms then de energize it and there should be OVERLIMIT displayed on the multimeter like infinite ohms because it is detached.

someone else should be able to tell you more than i have but i guess its somewhere to start.. if you noticed that the relays controlling other stuff on the same control module stopped working than your assumption may be correct.. definitely check for faulty wiring or corrosion on terminals etc.

again sorry i couldnt give you more definitive help, i dont have much experience with DIS as i deal mainly with 5.0s but i do have alot of experience in general diag and am a ford mechanic by trade.. this is definitely the place to post your problems though, there are alot of people who have the same car as you and have 'been there done that'

good luck
 

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Discussion Starter · #3 ·
ok i MAY be wrong on this but i'm pretty sure that the primary circuit for the fuel pump is the one that keeps it running while your car is on and the secondary circuit is the prime feed that runs it for a couple seconds before you start it... again i may be wrong but i think i came across that somewhere..
Very interesting. I'll look into that.

you should DEFINITELY be able to hear the pump prime when you turn the key
Thanks for the reality check. I never knew if it was normal or not.

on the self test connector under the hood there is a terminal that you can ground that is a self test for the fuel pump.. so i guess its one way to check to see if the pump runs to test the wiring.
There are two connectors grouped together that get plugged into the OBD-I reader. The one has like 4 or 5 terminals in it but the other only has 1 terminal. I should ground that 1 terminal and listen for the pump?

again sorry i couldnt give you more definitive help, i dont have much experience with DIS as i deal mainly with 5.0s but i do have alot of experience in general diag and am a ford mechanic by trade.. this is definitely the place to post your problems though, there are alot of people who have the same car as you and have 'been there done that'
It's all helpful. Thanks for the response. I have a feeling I'm in the right place. :bigthumbsup
 

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Discussion Starter · #4 ·
An update for anyone interested or that has the same problem down the road. The issue was internal to the IRCM.

I removed it to test the replaced fuel pump relay. When applying 12V to the signal terminals, a trace on the circuit board burned up. That makes me think something else was going on with it. Since the smoke was properly let out of it, I replaced the board with an Airtex part from Rockauto (~$100). That solved the problem and it runs just fine now with no issues or check engine light.

The A/C still doesn't cool so I'll have to figure that one out. At least it moves now. :)
 

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Discussion Starter · #6 ·
Thanks, Maurice. I know just enough to get into trouble. Understanding relays goes a long way with respect to the IRCM. Thanks for the links also. The pdf will definitely be helpful in the near future.

It seems that all my problems are not solved though. :( Driving to work today, it would just shut down every 3-4 miles. The furthest I got was maybe 8 miles. The lights and dash would still stay illuminated though so it's not like all of the electrical system would die, just the ignition it seems. I would have to pull over and shut it off, wait a minute, crank a little more than usual, then everything was fine for a few more miles.

I'm thinking the IRCM is fine and that this is contained to the ignition system. A consistent intermitent failure like this sure seems like something is overheating. Maybe I installed the DIS incorrectly? I used thermal grease (for computer chips) on the back.

I'll run a diagnostic to see if it's throwing codes. I don't think there was a check engine light but I could have missed it while trying to manually brake and steer. (ugh!) If that doesn't pan out I'll try replacing the computer grease with some proper automotive thermal grease. At least I can get KOER codes now (since it runs).

Maybe I got a bad DIS. Is there a way to test it off of the car. I think there was a post somewhere that said an auto parts store could do it. Is that right? It seems pretty specialized.

Besides that, I'll probably have to take it to the shop. :( I hate gremlins.

Are there any other common failures I'm missing? I know coil packs can go bad but this doesn't seem like that. Maybe the main ECM? That's under the passenger seat, right? Maybe the ignition switch isn't making good contact and shutting off?
 

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Discussion Starter · #7 ·
A consistent intermitent failure like this sure seems like something is overheating. Maybe I installed the DIS incorrectly? I used thermal grease (for computer chips) on the back.
Turns out this was exactly the problem. I read the haynes manual and it was very clear to use "silicone dielectric grease" and nothing else so I replaced the heatsink grease. It seems to have done the trick as it idled in the driveway for a good 10 minutes yesterday and made it 12 miles to work today without issue.

I guess the HS grease couldn't keep up with the heat output of the ICM. Seems weird but if it works I'll go with it.
 

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Awesome letting us know this makes it searchable for a solution for someone else and also educates us all. Everone learns. Maurice
 
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