[Intarsian]

It all started one day when I hit a pothole really hard. The fuse blew and fuel pump stopped. I changed the fuse and was good to go until recently when it started blowing again.
Now, everytime I am under a load, like plowing through snow, the fuse will blow.
This past weekend, my fuse blew again but this time I can't get it to stop blowing. Everytime I turn the ignition on, I blow the fuse.
The fuse is located in the slot marked ECMI.
How do I find out if it is the pump, the relay, or anything else?
I am assuming there is a short somewhere. I thought maybe I pinched a wire and am arcing out somewhere.
There is one black wire and two other wires coming off the tank where I am assuming the fuel pump is. The wire tester just barely has a dim light on one of the wires and nothing on the other. The problem is when I turn the ignition on to test the wires, I blow the fuse.

Any suggestions?
Thanks.
Rob in Wisconsin.

 

[MrShorty]

Year and engine would be useful information.

On my '98, the ECM -1 fuse feeds power to the PCM and parts of the engine management system. The PCm controls the fuel pump. If you are blowing one of the ECM fuses, the short could be in any number of places other than the fuel pump circuit.

 

[tbplus10]

Could be as simple as a loose or bad ground wire, I'd check those first.

 

[30 Yr GM Tech Burn-out]

short and sweet
If its blowin as soon as you turn the switch on..........( a really good thing..Its doin it!)
Disconnect wiring at your pump. If it quits...BINGO Reconnect the wiring, and blow another one....You got ti for sure! Replace the pump.

 

[Jonnyp]

I have a 94 GMC and am having the same problem, however when I unplug the harness it still blows as soon as I turn the key to on.

 

[RayVoy]

I assume, you are unplugging at the pump.

You probably have a pinched wire, somewhere it may be rubbing on the frame.

Without looking it up, I'll suggest the PCM circuit is commanding the fuel pump relay to operate. The relay then operates the pump. Two separate circuits. The fuse that is blowing is the one that operates the relay, not the pump circuit.

Again, without looking, there are two posibilities:
- power goes to the ECM and gets switched back to relay, or,
- the relay always has power (key on) and the ECM switches the ground.

 

[evenstevens]

Old school method I always use in these instances is replace the fuse with a higher amp re-setting fuse like on electric window motors or electric seats! I start out with a small amp then increase it progressively until I find the problem! The wire will get heat up between the fuse and the problem! Can't say it's not a ground problem, but have never solved a blown fuse problem by fixing a ground, and never considered that a ground can cause a fuse to blow! Current through the fuse causes it to blow! Grounds don't carry current! Last resort, I loosen the battery terminals, pull out the fire extinguisher, bring up the garden hose, make sure I can access all of the vehicle underneath, ( jack it up or have it on lift raised so I can get under it) and connect a straight wire from the positive post to the wire running from the blown fuse! Intermittentingly, I touch the jumper wire to the fused wire! The wire will get hotter and hotter, depending on the length of time you keep it jumped! Sooner or later, one of three things usually happens: the short breaks loose and the fuse stops blowing; the wire gets so hot the insulation starts to melt up to the short; and if you just throw the power to it and hold it there, and the shorted wire is strong enough, the insulation on the wire will ignite! Then you have to disconnect the battery and break out the water hose or fire extinguisher! It has only happened to me once where it caught fire. And I wasn't chasing a short! I was taping up naked wires under the dash on an 71 ElCamino I had bought and I connected one of the naked wires to ground taping up a naked wire! The insulation on these wires ignited fast!! I wasn't expecting this, so had nothing handy to put it out! Unhooked the battery and beat it out with a shop rag, and went and bought another roll of tape!!! Keep in mind that once you heat the wire up to right before it ignites, in the wiring harness, all the wires making tight contact with it will have their insulation heated up as well! So if the insulation is melted on the suspect wire, whether it's already melted or gets melted from your test, you either have to check the suspect wire visually from the point of the short all the way back to the fuse box to ensure everything is okay in the harness, or keep your attention on everything closely for a few days watching for something functioning irregularly. A clue some more wires may have been effected by the suspect wire. Hope this helps! Not as dangerous an operation as it sounds, long as you keep your attention on what's going on. The vehicle will not burn up unless you allow it to! Only said anything about it in the first place because anything is possible! Not because there is a high possibility that it will happen! It's never happened with me and I've successfully used this procedure many times. Not just once or twice. And it has only failed to work once! I had a Chrysler that was blowing the fuse and with it straight wired around the fuse, nothing happened! Smoke will appear first if you straight wire it. I got no smoke, nothing! Never figured this one out! GOOD LUCK!!

 

[30 Yr GM Tech Burn-out]

Evens advise was the stupidist ive ever read! He needs to try that on his house too! Just look for the magic smoke! LMFAO!

 

[xPosTech]

Yes the proverbial smoke test. And the ground carries exactly the same amount of current as the positive.

Ted

 

[RayVoy]

The correct, and the only approved way to find a short is with a meter.

The only other way to find it is with your eye balls, trace the wiring and inspect it.

Btw, I read all other posts (except for that real long one) and I did not give you complete info in my last post. I talked about the relay circuit and suggested the problem was on that circuit; sorry, as I read it, I realized if it is the fuel pump fuse that is blowing, it is not the relay circuit you need to look at, it is the pump circuit that has the fault. The relay contacts are the switch that sends juice to the pump.

 

[RayVoy]

Well, I just went back and read the long post; yep, @30 Yr GM Tech Burn-out , you are right. That is the worse piece of advice I have even read.
And, as usual, Ted @xPosTech is right, grounds carry the same amount of current as the hot wire. But, guys, I do agree with that poster, poor grounds will not blow fuses. A grounded hot wire is what blows fuses.

 

[evenstevens]

Evens advise was the stupidist ive ever read! He needs to try that on his house too! Just look for the magic smoke! LMFAO!

The home-town mechanic that told me how to smoke a short, Dr. Webb, (may he rest in peace) was a 50 year seasoned auto mechanic, best mechanic I've ever met for fixing automobiles, not working on them! He clued me in on this 35 years ago! I've used it over and over, in many cases, as the last resort. Never had any unfavorable incidents yet! Glad you got a good laugh out of it! Peace and love!!!

 

[evenstevens]

Well, I just went back and read the long post; yep, @30 Yr GM Tech Burn-out , you are right. That is the worse piece of advice I have even read.
And, as usual, Ted @xPosTech is right, grounds carry the same amount of current as the hot wire. But, guys, I do agree with that poster, poor grounds will not blow fuses. A grounded hot wire is what blows fuses.

RayVoy, I knew when I wrote this, there would be difference of views on it! After working at Caddy, GMC, Ford, Chrysler, Lincoln, and Mercury dealerships as there electrical repair nerd, I've read numerous dealer prescribed procedures for fixing electrical problems! Won't find this procedure in any of them! But it works and is unsafe only if a slumber-minded individual trys to do it! But my past experience has uncovered few of these types trying to do electrical! I've replaced more melted wire, and more factory connectors on vehicles as a result of loose connections on load bearing wires. (Especially those quick crimp splice connectors) I feel comfortable to say I've smoked over a hundred undetectable shorts and have never had fire as a result! The high amp re-setting fuse is first choice! I feel the wire and as it heats up it will lead you to a bad short! Also got to mention I've replaced a couple of miles of wire that had been smoked because tin foil used by a vehicle owner! There was no fire involved here, either! Fire start-up is only a remote possibility! A 12 volt battery will melt a clothes hanger in two in about 8 seconds, if the battery is hot! The hanger will turn cherry red in bout 5 to 6 seconds, and pop into two pieces in the next 3 seconds! (I know this first hand. Or maybe I should say two-handed. The two of mine that had deep burned lines in them that was holding the hanger to the post) So a fire could be started! But never have had it happen! NEVER! By the way, have to add, every auto repair manual lists the first step of every operation on a vehicle as: Unhook the battery before doing any thing else! I don't do this, ever! Unless removing the starter or alternator! So my advice don't count for too much, huh! Best wishes to you and good luck to you in everything you do! And may your ice cream always be topped with two cherries!

 

[RayVoy]

@evenstevens this is not the place to get into an argument over someone's credentials.
That is an extremely damaging, not to mention dangerous, way to trouble shoot. I am just very glad you never worked on any of my vehicles.

And, the only reason I'm responding is to try and keep others from trying it.

 

[xPosTech]

I'm biting my tongue. You're right Ray. Not the place.

Ted