1995 Mustang Gt Cranks But Will Not Start

[dredd0822]

Update: I got my wife to crank the car, and I confirmed that the light blue/orange wire is showing 12 volts at the CCRM.
So I think that rules that out.

The last thing is the dark green wire/yellow wire. It's still not getting power at the CCRM when cranking, and I tested by cranking the car that there's no voltage at the green wire that connects to the inertia switch. Since that wire goes from the PCM to the inertia switch to the CCRM, I imagine that wire must be bad? But how could it be, since, when we applied voltage to it from the CCRM connector, the fuel pump came on?

 

[jozsefsz]

Hey there, personally I'd ignore everything back from the CCRM at this point. As you mentioned, jumping voltage to dark-green at the CCRM eliminates problems all of the way back. Focusing on the inertia switch and what-not is just complicating the problem for you.

The light blue w/ orange wire should be GROUNDED when priming or running, the fact that it's showing 12v tells me that we're on the right track -- there's a problem in that ground circuit.

There are some other light blue wires, but only one is light blue & orange. It may be hard to tell the difference between the others, so it's the one on CCRM pin 18.

You're correct, this same wire at some point branches off to the test port. That's why grounding the test port should cause the fuel pump to run all of the time (when the ignition is switched on). Yours did not, so again it might be a problem in that same wire.

As I'd suggested before, please attempt to run a ground wire directly from battery negative to light blue & orange (CCRM pin 18). If the problem is in that ground circuit from the PCM (I believe it might be), your fuel pump should begin to run (ignition should be on, doesn't need to be cranking). This will eliminate everything but a problem in the ground wire.

 

[dredd0822]

Man, you were so right. I applied ground to the light blue/orange wire at the CCRM, and it fired right up! So now, for SURE it's a problem with that ground wire.

My next step is to apply ground to it from the PCM and see what happens, but I need to wait for someone to get home to run that test.
But from what I just described, what could it be? What would make a wire pass voltage instead of ground?

 

[jozsefsz]

Awesome! Remember, the relay inside the CCRM is just a switch, with a + side and a - side. It's showing 12v on what "should be the negative / ground side" because the + side is being energized by the wire coming from the EEC relay inside the CCRM, and that voltage is just passing through the switch (as it should be, this just demonstrates the relay has good continuity). It's not a problem at all, other than the ground wire being broken somewhere!

So the problem is absolutely with the ground wire from the PCM. It might be broken anywhere along the way, so you can run it all the way back to PCM pin 22 to be certain, and that's your permanent fix.

If you're like me and you don't like messing with the PCM, one thing to try first is connecting the other end of that jumper wire that you connected to the CCRM to the test port you'd previously jumped to ground (that weird connector by the strut tower) instead of to battery negative. Why I'm suggesting that is that grounding that test port previously didn't help the situation, so it's my guess that the break in the wire is somewhere between that test port and the CCRM. If you connect that test port to the CCRM light-blue, you should have a good connection all the way back to the PCM. Which is easier than running a wire all the way back down into that darned kick-panel. If you do it this way and it works, it's also a permanent fix, you've by-passed the broken wire and the computer will control the fuel pump properly (priming, etc., as you'd expect).

Give that a try and if it works, all you've got left to do is permanently connect that wire to where you've temporarily jumped it. And return a few unused CCRM's for some Christmas $ back in your pocket.

If it doesn't work, you'll have a little more wire-running to do to get back to the PCM, but you now know where the problem lies. Congratulations!

 

[dredd0822]

FINALLY! It turned on!!!!!!!!!!!

So, when I went to look at the light blue/orange wire at the test connector, this time I looked more closely at the test connector itself, and I noticed a lot of battery-type corrosion in the wires right at the connector. I removed the metal plug that the light blue/orange wires connect to from the test connector, and they were full of corrosion.

When I removed the corrosion with a wire brush, one of the wires started coming off from the metal plug. At this point, I simply cut both wires from the plug, took a little bit of wire wrap off each one, then joined both of them in a twist. When I went to turn the key, it turned on! WOOHOOOOOO! Now I need spend several hours putting many things back together on the car, and it looks like the timing is off because after it turned on it now stumbles every 3-5 seconds, but that's most likely due to the new distributor I had installed.

So, for posterity, in case anyone else runs into this problem in the future, please know this about the LIGHT BLUE/ORANGE wire that provides ground from the PCM to the Fuel Pump relay:
Based on this diagram (http://sbftech.com/index.php?action=dlattach;topic=311.0;attach=2650;image)
The light blue/orange wire is split into two parts:
1. The first part of this wire goes from the PCM straight to the datalink connector (VIP test connector)
2. The second part of this wire connects to the first one via a metal plug that goes into the test connector. This second light blue/orange wire then goes from the test connector straight to the CCRM

So if you ever run into an issue where the light/blue orange wire is not passing ground to the Fuel pump relay in the CCRM, check out the test connector. There might be corrosion there that is preventing these two light blue/orange wires from communicating. Really, bottom line, it's good to check out these obvious things and rule them out first, before you go spending money.

In my case, the two positives about this taking forever to resolve is that, first, I got to know my car, and specifically the electronics, very well. In case I ever run into electrical issues in the future, having the knowledge I have now will give me a head start. Second, since I replaced a lot of electrical components on this bone stock car in my effort to fix it, these are components I won't have to worry about for a very long time (I hope!!).

A humongous thanks to jozsefsz for being patient and sticking with me throughout this ordeal. Could not have done it without him.
I hope I can repay this in kind to a fellow 'Stang owner in the future.

Off to put my car back together and enjoy it!

 

[jozsefsz]

Congratulations buddy, this makes a nice Christmas Eve resolution, and you're very welcomed. And you're right, almost everything you replaced is a good maintenance item on a 20 year old car, and some (like that fuel pump) set you up for the mods you'll one day want to make. Enjoy your car, you've earned it, and as you suggest pay it forward as you get to be an expert! Not giving up will get you there.