no CEL / no start, cranks fine

[mr cribb]

SOLVED: no CEL / no start, cranks fine

I have been working on my 92. My wrecked parts truck donated all the power accessories, as mine was originally a manual everything truck.

Part of my engine harness was burned so I started swapping harnesses, 2 days later, I have a complete 1991 power everything harness.

I will have you know, that the main connecting plugs DO NOT match on a 4/91 and 11/91 build date trucks. I am running the 4/91 harness now.

THE ISSUE:

No CEL, no start, cranks all you want. I do NOT hear fuel pump cycle when turning on the key.

WHAT I HAVE CHECKED:

Inertia switch - it is NOT tripped
power to distribution box - all maxi fuses have power.
relays (by distribution box) are all swapped with known working versions.
ignition control module - is swapped for a known working version.
The PCM is from my 92 model truck.

All I have is a test light, no multi meter.

I am almost certain I secured all the harness grounding points.

I can tell you that the wrecked truck did the exact same thing, before I stripped it.

I do know that no CEL, means PCM isn't communicating to fuel pump, but what do I check?

I have a few days before my wife goes out of town, and I am without a ride.

 

[Anime]

What 'main connecting plug' is it that doesn't match? The plug to the power distribution box?

The plug doesn't need to match, you can use any harness with any plug, if you just swap over the wires to the correct locations in whichever plug it is that the power distribution setup requires.


Strong cranking but not starting sounds like fuel issues.

No fuel pump priming sound means the fuel pump relay circuit isn't getting power, or the fuel pump isn't getting power.

Since the other truck with this harness had the same issue, and assuming your vehicle didn't have the issue prior to the harness swap, you can limit your troubleshooting to only what was swapped in.

If that's just the harness at this point, you should check and double check that the wires that are supposed to run to and from the fuel pump and ECM relays are in the correct locations for each terminal, and inspect the wiring for any damage, shorts, etc. that would cause issues.

My guess would be since the plugs aren't the same, the wiring is slightly different and two or more wires are just in the wrong locations, so the fuel pump isn't getting power. In my experience, just the fuel pump relay and ECM relay have anything to do with the fuel pump not priming. If it's not the relays themselves, it's the wires to the relays or from the relays to the fuel pump.

 

[mr cribb]

By plugs not matching I mean square connectors and round ones. XL model truck has less wires than XLT versions.

The wire colors match underneath the truck that go to fuel pump, Abs, and whatever else is under there.

So it seems like I need to look into the fuel pump relay area or even pcm power.

 

[boominXplorer]

Just FYI the fuel pump will only run for 2 seconds when you first hit the key. If you start probing wires you will only see power for the 2 seconds after you turn the key. I would try jumping the relay to see if you have power and a connection to the fuel pump.

 

[mr cribb]

I can tell you that no cutting or splicing was done except for along the frame where the wires go by the fuel tank to the fuel pump and anti lock brake sensor. This was only done because of the wiring harness is snaked in really tight between the fuel tank and frame. The leaf spring shackle is in the way hindering harness removal.
Same color and amount of wires.

Initially I was going to use just part of one harness to get what I needed, but it ended up going the other way.

I know we can rule out the computer, because it did this exact same thing with the 91 computer.

Are or is there a fusible link or diode built in the harness to power the pcm?

 

[mr cribb]

Just FYI the fuel pump will only run for 2 seconds when you first hit the key. If you start probing wires you will only see power for the 2 seconds after you turn the key. I would try jumping the relay to see if you have power and a connection to the fuel pump.

Yes I'm aware. That's what I'm not hearing is the priming part followed by relays clicking.

I know my problem is in this specific area. I'm wondering if there's a fusible link in this area or not.

 

[boominXplorer]

The fuse for the fuel pump is fed by a larger fuse in the fuse box that usually powers half the box. If the fuel pump is the only thing not getting power that is probably not your issue. If I had to guess you have an issue energizing the relay from the ignition.

 

[Roadrunner777]

[

I am working on a diagram for the fuel relay control part. In essence, the relay has to have 2 things to operate. First is +12, which arrives via the ignition switch. The other is ground, which is provided by the PCM.

If you pull the relay and turn on the key, you should get +12 on 2 terminal sockets. If you don't then you have to chase that. One is from the battery through the path I diagramed above. The other is from the ignition switch. There may be a schematic on the side of the relay showing you which terminal is what. Otherwise, look on the internet, it is very common. So, with this, you can check and fix the +12.

The ground comes from the PCM. You can bypass that with this:

http://www.explorerforum.com/photopost/data//500/odb4_port_location.jpg

http://www.explorerforum.com/photopost/data//500/odb4_port_connector.jpg

http://www.explorerforum.com/photopost/data//500/odb4_port.jpg

The fuel pump terminal shown goes directly to the ground of the fuel pump relay, therefore bypassing the PCM. If grounding this fixes your problem, then you have a PCM or PCM connection problem. This is an excellent diagnostic tool because, if you ground this, with the key on, the pump runs continuously, and you can use your test light more easily.

 

[mr cribb]

I need to see why the pcm isn't making everything else wake up.

By using my test light all the huge fuses in the distribution box have power. There is power from the fender solenoid to the distribution box.

There's some kind of failure between the distribution box and the pcm.

 

[Roadrunner777]

Ok, if you are correct, then grounding the terminal I describe should make the fuel pump run when the key is on. And, given everything else is good, the engine should run.

I guess I would ask you to physically verify that this is the case.

If so, then, just my opinion, but for temporary travel, I would ground the terminal and leave it that way. The relay is still controlled by the ignition switch.

If not, then we need to step back a few steps.

 

[mr cribb]

I will have to look at this after work. It sounds simple enough and hopefully your theory works.

 

[L.A.X]

Check your PCM ground

 

[mr cribb]

Grounding the test plug or jumping it did nothing.

 

[mr cribb]

All my grounds are secure.

Power at FP relay
Power at test plug all 3 spots.

 

[mr cribb]

11.59 volts at all relays and fuses in distribution box. I borrowed a multi meter from my neighbor.

I tried deciphering the schematics I have to determine which wire is power wire to pcm. I have Haynes and Chilton 's to go by, and neither are clear and concise in telling me what I need to know.

Could someone please tell me which wire or wires are my power to pcm. I'm still thinking it is a computer not getting power problem.

 

[Roadrunner777]

I don't have my book where I am now, but there is a PCM relay, I think. You could look at that. If the CEL lights when you turn on the ignition, it is getting power.

But, I'm having trouble making myself clear, I guess. Grounding that lead rules out the PCM entirely. The PCM grounds one side of the relay coil. That same lead goes to the diagnostic port. By grounding that terminal, you have provided ground directly to the fuel pump relay, bypassing the PCM. The other side of the coil goes hot with the ignition switch. I'm getting this straight from the Ford Factory wiring diagrams. Frustrating... if I were there with a test light, I could find the problem in less than 10 minutes.

I'll get the diagrams scanned, probably tomorrow night. You are close.

 

[MrShorty]

Grounding that lead rules out the PCM entirely.

Not necessarily. If the PCM is not getting power, not only will the PCM not command the fuel pump to run, it will also not be able to fire the fuel injectors, the ICM (which controls the coil/spark) will have no power. Getting power to the fuel pump will get fuel to the engine, but if the injectors don't fire, nothing gets into the cylinders, if the coil never fires, nothing combusts, and so on. If I have followed this correctly, no CEL with the key on indicates to me that the PCM is not getting power or ground, and I would probably focus on that.

Next to the fuel pump relay should be the PCM/EEC relay -- make sure that is closing. The red wire that comes out of the PCM relay (and goes into the FP relay) also feeds power to the rest of the engine management system including the ICM, PCM, injectors, and various solenoids and other components. If that red wire is not getting power, then make sure the PCM relay is closing.

 

[Roadrunner777]

Yeah, I meant that in the context of running the fuel pump.

I don't think the PCM relay feeds the fuel pump relay though. I believe the fuel pump relay coil gets 12v from the ignition switch directly. <- I was wrong here. mrshorty is absolutely correct.

I'm glad you said something mrshorty, you got me to reread the post...

I assumed there was CEL with ignition on. Can we verify that yes/no?

Fuel pump power goes through fuse #18 which is not a MAXI, but a 20A mini, a yellow one. You should have constant 12v there.

 

[mr cribb]

The relays have 11.59 volts as well. The red wire that ties all of those relays together does have power and all of those relays were swapped with known working relays from my original harness.

Phil- no, there isn't a check engine light illuminated on the dash with key on.
That's how I know there's a problem. I know with the CEL on at first start that is like an all systems good to go command.

 

[Roadrunner777]

Re-united with my manual, yea!

+12V supply to PCM is Yellow wire at position 1. It is protected by fuse #4 in the power distribution box, keep alive power, should be hot always.

+12V should be on red wires when the PCM power relay is closed. The source of the +12V is fuse #4 . So, battery -> Fuse #4 -> PCM Relay -> PCM red wires.

The PCM should be on with the ignition switch. Ignition switch -> diode at position 14, to the coil of the PCM power relay.

There are a lot of ground connections on the PCM connector. My first choice would be power ground at pin 60, black with white stripe.

These two connections are in the corners of the connector.

The ground looks like it's going to be tough to get to. It is way up in the passenger side kick panel, above the PCM. I only have a line drawing but it looks like it is almost by the glovebox.

I need to start work. I'll probably get scans of this up tonight, but it is difficult to follow in the manual because it jumps around on different pages.