ECM-IGN fuse keeps popping

PATA · #1 11-19-2004, 02:28 PM

I have a 1989 K2500 4x4. Problem started all of a sudden.... truck ran horrible one day (not driven every day, plow and boat tow truck.... dump runs etc.) and then stopped all together. I figured it needed a tune up (cap/rotor, wires, plugs etc.). Oh, almost forgot... I had some fuel line problems stemming from a rotten fuel tank sender unit and since I dropped the tank I also replaced the fuel pump.

When I tried to start it after all that it popped the ECM-IGN fuse. When I replace the fuse and try again it pops again. It runs for a second and then quits, the fuse is popped.

Where should I start and what to do after!!!...

Thanks!

Cam7 · #2 11-20-2004, 06:20 AM

Did you replace the wirring in the fuel pump inside the tank? Also since you hand the problem right after you changed the pump check to make sure that there are no wires shorted out bare wires that are touching. Might have to pull the pump back out to see if any wires are touching in the Tank. Try checking the harness connections first.

PATA · #3 11-20-2004, 08:32 AM

The whole fuel tank sending unit is new, not just the pump. When I turn the key the pump cycles and is ready to go... I then turn the key to start and it will... for a few seconds and then the fuse pops and there is no go. If I turn it completely off and then try again (without replacing the fuse) the pump cycles like normal but of course wont start at all.

I need to know what that fuse controls .... what parts will be popping the dang thing.

Cam7 · #4 11-21-2004, 05:32 AM

Try the fuel pump relay!

Fireplug · #5 11-21-2004, 05:17 PM

Blowing fuse is in most cases is a hot wire short(bare wire hiting a ground).
Re check all the wires that you worked with and look for a hot to ground wire , pinched wire or something like that. The only other thing that will cause a fuse to blow is the system pulling to many amps. A very badly corroded wire will incress the resistence and cause a high amp pull and blow a fuse. By looking at the fuse that has blown does it look melted or like exploded , melted high amp load, exploded short to ground

PATA · #6 11-21-2004, 06:30 PM

Ahhh.... good post... the fuse doesnt look melted but rather blown. Ok, here is a thought, I replaced the fuel sender and pump and the ground wire for the sender unit was not easily accessable so I cut it and crimped the new gorund to it. Now the pump works through all this trouble BUT could that be the problem?

Also, the pump always works AFTER the fuse pops....

This is very frustrating!!!

Fireplug · #7 11-21-2004, 08:11 PM

I think you have 2 different problems. If the pump still runs then the chances are you have a good ground for the pump.
Now the ecm fuse when does it blow/ as soon as you turn the key to the on position or to the crank position or just after the engine starts.
Check the ign switch on the bottom of steering coloum for any melted wires on the switch . If I remember that switch is the ecm power feed. Let me know what you find.

PATA · #8 11-21-2004, 08:39 PM

the fuse pops after the engine runs for 2 seconds... litteraly 2 seconds. I will look for the wires being melted where you said.

Thanks!

PATA · #9 12-27-2004, 12:55 PM

I have a thought...... Unfortunately I have not persued this and now we got hit with a Nor-Easter yesterday..... over a foot of snow. This dang truck has my plow on it... I need to figure it out NOW!!

If I disconnect the ECM will the pump still cycle up? and if the fuse does not pop maybe that will point to the ECM itself?

And if that is a good idea... where is a good place to purchase an ECM?

skipr · #10 12-27-2004, 10:41 PM

Get a self-powered test light and start probing the wires (first isolate wires to be tested from power) ground the test probe lead and start punching wires, you get a light, you got a short. Just make sure the wire your testing isn't a ground wire because that will show a short (because it is supposed to be shorted)

PATA · #11 12-30-2004, 10:07 AM

Skipr... what wires... any and all? whoa... looking at your profile you live in LA... nice and warm. Here in Boston if we start poking wires we open the wire to the elements... Salty roads and Salty air (forgot to say I live on the ocean like you). The salt will eat my wiring from the inside out.

Let me ask you this... I read some of your other posts... Is there a schematic that will tell me all components that may pop that fuse? or is it simply everything will pop it?

I am one step away from taking it to my local wizard... I think it is the ECM itself and wish the dang thing could be tested. Can you tell me this... if I disconnect it and my fuse doesnt pop... would that point to the ECM being bad?

skipr · #12 12-30-2004, 12:59 PM

Well I have schematics that give a detail of wiring harness routeing and color code, If you are comfortable using schematics, they will pinpoint the wires needed to be testing from fuse 3 to the loads. I could even highlight the ones that should be isolated from ground. Problem is I have paper manuals for that old of a truck so I would have to mail them to you like I did for "Broughty84". And I don't mean E-mail, Old fashion Postal service mail.

Oh I forgot to say, the test light has a needle piont end (to probe with) you back probe connectors and even if thts not a option stabbing the wire with a pin will not open it up to elements. I usally put a peice of Super 33+ (by 3M) tape around puncture.

Fireplug · #13 12-30-2004, 01:48 PM

Ok sorry it took so long to get back to you.
The next thing I would do is .
If you have the owners manual where it show what is on that fuse. I think the ecm is all by its self but I could be wrong.
I would also go and get this tool its a circuit breaker with test leads on it and install it in place of the fuse. Now when you turn the key on and start the truck the circuit breaker pops then resets
it gives you more time to find the problem.
Also check the wires by the ecm and ign switch for any signs of melting. To pop the fuse its a hot short to ground. Was anything do to this truck just before the problem started ?? Anything???

PATA · #14 12-30-2004, 06:05 PM

Nothing else was done to the truck.

I am gonna get that "circuit breaker" fuse. It fits right in the fuse box like the regular fuse? THAT is a great gadget!!

I will check around the ECM and Ignition switch. Key still turns the engine.... just that dang fuse pops.

skipr · #15 12-31-2004, 01:02 AM

Quote:

Originally Posted by PATA

Nothing else was done to the truck.

I am gonna get that "circuit breaker" fuse. It fits right in the fuse box like the regular fuse? THAT is a great gadget!!

I will check around the ECM and Ignition switch. Key still turns the engine.... just that dang fuse pops.

Yea it's great gadet to save you from burning fuses up left and right. But you still need to find the cause. So you rather check around the ECM and tear open the harness wrap looking for a wire you have no idea which one? I guess thats better than having a schematic which tells you exactly what fuse and where it goes and which color to look for.

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