why does my car keep blowing the #5 20amp maxi fuse (eec/fuel pump)

[94gts]

tonight i was driving my car to my hockey game and it just SHUT OFF while in gear at 60 mph. tried to start with key and nothing. tried popping clutch and nothing either. in the middle of the road at 1 am i determined that my fuel pump is not arming. so i look in the engine bay and the #5 maxi fuse is blown. its labled as the eec/fuel pump fuse, but there is also another one just for the fuel pump but that one is fine.

i got a ride to my job and grabbed 2 new 20 amp fuses and went back to the car. i put the fuse in, turned the car to accessory and the pump still wont arm. i go back to the fuse and see that it is blown again. this happened twice. I had to have a family member tow the car to my job (garage/gas station)

so, the car doesnt run at all. what would cause the car to blow this fuse like that? it sucks seeing your car on a flatbed

 

[HISSIN50]

Kyle, Has anything recently happened or been worked on with the car?

It seems to me that you actually have a PCM wiring or CCRM wiring short (if it was the FP, there's a chance it would blow the FP fuse instead).

I'm trying to think of a simple way to do diagnostics and it's not coming to me. If you disconnect the CCRM wiring harness, you disco' the EEC relay, so you really cant even differentiate a CCRM vs PCM wiring issue that way.

 

[kendoo130]

My car did that when my fuel filter was completely clogged

 

[94gts]

i have not done one bit of work to the car since may. the car has been driven 10k since then with 0 problems

i did the h/c/i, fuel filter, pump, etc. all of the sensors i left alone. the ccrm and eec are the only things on my car that is original ford

i thought maybe a pump problem too, but like you said idk how to diagnose it if i cant even turn the car to accessory

i have a spare pump lying around. i guess ill throw that in and see if that changes anything.

 

[HISSIN50]

I'm not sure I can find a correlation between a clogged Fuel filter and a circuit overload. Not that it can't happen, but I'd hate for someone to swap pumps, filters, etc and have the same issue at hand.


Something I might try (do at your own risk, etc etc) : Pull all fuses relating to the circuits involving the affected EEC fuse (I'd pull the fuel pump fuse, the cooling fan motor fuses, ignition fuses, etc). Put the EEC fuse back in and hope it doesnt blow. Then you could try installing one fuse at a time (leaving the fuel pump fuse for last) and note which fuse installation causes the ECU fuse to blow.

Also visually inspect the wiring harness to the CCRM and look for chafing.

That's the best I got at 3 something in the morning.

Good luck Kyle.

 

[tjh566]

the only way I could see that happening HISSIN is the fuel pump trying to push the fuel and it not going so it puts a higher load on the pump, causing it to pull more amperage, then blowing the fuse, its possible, but idk...

 

[mo_dingo]

the only way I could see that happening HISSIN is the fuel pump trying to push the fuel and it not going so it puts a higher load on the pump, causing it to pull more amperage, then blowing the fuse, its possible, but idk...

As JT said, start by looking at the ccrm, injector harnesses, and diverter valves for some obvious signs of wire chaffing. If nothing show up, then you are in for some fun.

According to this diagram, we have many things that get fed from that main 12V coming in.

Here is what I would do first. Buy a bunch of 20A fuses as well as a auto-reset 20A fuse with the regular size ATC blades that match the 20A fuses . It looks like this. Also called a atc circuit breaker. Before you use the breaker, touch one blade of the fuse to the hot terminal of the battery, then with you test light, see if the other blade is hot. If it is, the fuse is working properly and can be used to diagnose this problem.

Disconnect the main ground, then the ccrm. It, like the pcm, has ground all the time, so it is the likely culprit. Then replace the 20A fuse with the auto reset one and reconnect the main ground wire. With a test light, see if the fuse is passing power though. If it is, the CCRM or something after it is shorted/overloaded. If not, then the CCRM and everything past it is fine.

If the fuse is not passing power through, leave the ccrm disconnected, remove the main ground again and disconnect the PCM. It's behind the passenger side kick panel. Go back to the battery and reconnect the ground and see if the fuse is passing power through. If it's passing power through, the PCM and after is the culprit. If it isn't passing power through, repeat the same procedure for the transmission control sensors and solenoids if you have an auto transmission.

If you have removed the pcm, ccrm, and trans connections, and the fuse still wont pass power through, put a regular fuse in and see if it blows, which it should. You now know that your problem is with the 12V+ wiring that feeds each of the items in the diagram and you need to start tracing wiring for problems.

Give us an update later after you are done with above. And remember, if you disconnect the ccrm and the short goes away, that does not condemn the ccrm. It just tells you where to start looking, essentially narrowing the problem down by 2/3.
Scott

 

[94gts]

crap, i figured it wasnt going to be something simple. looks like i have to catch up on my electrical skills

 

[94gts]

also, just to rule this out....

would this problem be happening if another fuse was already blown?

not sure but i figured id try and cover the basics first

 

[94gts]

well all off my fuses are good exceptfor this one.

tomorrow, i am going to swap out the pump and filter just because it is easy.


but now that i think about it, there is fuel in the rails, so why is the car not starting?

its gotta be electrical

 

[HISSIN50]

You need sufficient pressure to spray decently and run (as an example, some Fords are very picky. Spec can be 56 PSIG and the car simply wont start at 50 PSIG).

Scott's advice is wise - you gotta gotta gotta go step by step and methodically to troubleshoot this stuff (someone can get lucky by tossing a part at something, but I'm not much of a Vegas-goer).

For the fuel pump or pressure situation mentioned earlier, it should be a near dead short to ground blowing the fuse so quickly. And the FP fuse itself should blow. To rule out the pump itself, I suppose one could trip the inertia switch. If the ECU fuse still blows, it's not the pump because the pump never received power with the inertia switch tripped.

The issue with that ECU fuse being the issue is that it's on the front side of several major systems. It is almost analogous to saying that as soon as the battery is connected, a fuse blows. Otherwise, no fuses blow. Well duh.

I'd almost start to disconnect items powered by the ECU fuse and see which one stops the blowing (it's something Scott hit upon but I didnt really because it's a little more involved). This is how we'd troubleshoot any other fuse that was blowing - you're just dealing with major players on this circuit.

None of us are debating other than to try and save ya some time with diagnostics so you can get up and running as fast as possible.

Good luck.

 

[mo_dingo]

Scott's advice is wise - you gotta gotta gotta go step by step and methodically to troubleshoot this stuff (someone can get lucky by tossing a part at something, but I'm not much of a Vegas-goer).

I'd almost start to disconnect items powered by the ECU fuse and see which one stops the blowing (it's something Scott hit upon but I didnt really because it's a little more involved). This is how we'd troubleshoot any other fuse that was blowing - you're just dealing with major players on this circuit.

None of us are debating other than to try and save ya some time with diagnostics so you can get up and running as fast as possible.

Good luck.

My thoughts exactly. Throwing parts at something usually results in returning a lot of parts...lol.

When I have a fuse popping short, I always like to narrow things down. You don't need a whole problem, you need a half of a problem, and half of that problem, etc.

Starting by eliminating the 2 of the 3 major feeds to the fuse will take 2/3 of the problem away instantly. Then, once the major feed is established, you can start with the destinations of that feed source.

A great way to find a short to ground, is to take a DMM and test for continuity between a 12v+ wire and any ground (i.e. battery ground terminal). This method helps to isolate a short to ground when you need to find a shorted wire among 20.

Note: This test only works when there is no light bulbs hooked up to that wire; as all lights are a high resistance short to ground. But ignoring the tone from the DMM and looking at the ohms value of resistance can show you that. Also, if there are circuit boards hooked to this wire, you will get some continuity to ground, almost always.
Scott

 

[GRGT1994]

I had the exact issue you describe after doing my HCI. Not that that means anything. But in case this saves you swapping out random parts . . . try this.

Sounds like a short to me. Mine was at one of the injectors. The way my trickflow upper sat put the injector harness for 1 or 2 of the injectors close to the intake. That sucker gets hot when running. One of the leads to an injector made contact with the underside of the intake, and melted through the insulation. And bang, there's my short. I searched and searched for it. Had a hell of a time finding it. Finally took it to a shop. They messed with it for a while. When they were bout to give up, the tech gave a pull on the harness and bang, another short. Popped the upper intake off, and sure enough it was plain to see.

So you might want to start by replacing the fuse. Then just go around and move the harness in every spot you can think of. Try to force the short again. If you find it, you can narrow down from the spot you were yanking on when it went. Or, maybe you just start by looking in the same spot I had (driver's side, under upper intake).

Good luck.

 

[94gts]

well its not the fuel pump

time to get into testing some of the other fun stuff

 

[virgostang94]

I had the same problem.

Did you also check the fuses under the dash of the car? I had the same problem after I replaced my rack and pinion. I ended up clamping tyhe +12volt wire going to the starter in-between the washer and head of the bolt holding the rack and pinion in. So check your starter wires. That's my advice.

 

[94gts]

well today (yesterday i guess, i havent gone to bed yet) i diconnected the ccrm and it did NOT blow the fuse when i cranked it.

so does this mean that the ccrm is bad or that i need to follow the ccrm wiring?

 

[HISSIN50]

It does not necessarily mean the CCRM is the culprit. This is what Scott, I and others were getting at, where it gets dicey because you're dealing with the big players and their power sources. At this point, I'd almost want to trace down the EEC relay circuit. The EEC relay is inside the CCRM, and it supplies half the sensors and solenoids with power (see Brad's post above - that is not a super-uncommon thing to have happen). Just about any wire on that circuit shorts out and it blows the fuse (it would almost be like having a huge fuse in between the battery and the underhood fusebox. Any time an underhood fuse would blow, instead it blows the big fuse between the battery and PDC. The issue is not the PDC but something powered from it. Same kinda deal here).

I haven't looked the CCRM harness to see if you can remove the pins. If you can, I'd pull the EEC relay control and current wires and see what happens.

Here's a diagram of the CCRM.
Not being able to remember if the pins come out of the CCRM connector limits what else I might say (if they come out, you should be able to narrow this down rather quickly).

Good luck bud.

 

[mo_dingo]

Here is a wiring diagram for the ccrm. It shows where power is distributed from the ccrm.

I had a thought. The ccrm has a ground wire (black/white stripe). That is its only source for ground. What if you cut or remove the ground wire from the plug? If the ccrm is shorted out internally, and you disconnect the ground, there is nothing for it to short out to internally. So if you were to plug it back in and test the fuse, and the fuse popped, then you know the short is after the ccrm. If it doesn't short, then the ccrm is bad (or part of the ccrm anyway).

Does that make sense? Don't try this yet until someone has confirmed my thoughts but I think this is a plausible method.

Good luck Kyle.
Scott

 

[94gts]

scott, my only question about that is that if you disconnect the ground, isnt that basically the same thing as remving the plug itself? because if theres no ground to pass through, would power even get to all of the components of the ccrm?

 

[mo_dingo]

scott, my only question about that is that if you disconnect the ground, isnt that basically the same thing as remving the plug itself? because if theres no ground to pass through, would power even get to all of the components of the ccrm?

Yeah I am not sure to be honest. You are probably right and it will not work. I was hoping that with the hot side still hot, it would pass current through, but w/o ground, the ccrm relays may be dead.

Yeah so omit my previous thought.

What you could do, is locate all of the output wires (looks like 7 from the wiring diagram below) from the ccrm that feed the PCM, data link connector, a/c system, etc and unpin them from the plug, and plug the ccrm in. If the fuse still blows, then you know the ccrm is shorted out internally and you need a new one. If it doesn't blow, then hook up the wires one by one and see which one shorts out the fuse, and now you now where to look.

If you can't unpin them, then you can cut them. I would try unpinning them; You may need a molex tool to get them out of the connector but I believe autozone sells them.

If you get stuck or have any questions, PM me.
Scott