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Username Post: ECM-B Fuse keeps blowing, 1990 1500 Suburban 5.7L        (Topic#141040)
Posts: 94

Loc: 'Burbs of Chicago
Reg: 03-19-03
09-25-06 03:08 AM - Post#1008206    

Well, the truck is dead again....

In my prevous post (1990 Suburban won't start...fuel related?) I went from condeming the fuel pump or the fuel filter to discovering the true reason for the no-start problem....a blown fuse on the ECM-B circuit.

Well, this fuse keeps blowing.....and the truck won't start. When I try to insert a fuse into the fuse block, there is a spark that occurs at the connection, causing the fuse to instantly blow.

First of all, what is the ECM-B circuit all about??
Secondly, is there something in the design of this system that is a known problem or a "typical" problem that causes the fuse in the circuit to blow?

Also, for what it is worth, the truck is a 2 wheel drive, gas engine 1990 1500 series Suburban.

Wish I had a wiring diagram....anyone have one that they can post or point me towards?


LMC Truck
Posts: 224
Reg: 05-07-06
Re: ECM-B Fuse keeps blowing, 1990 1500 Suburban 5
09-25-06 06:41 AM - Post#1008207    
    In response to Greaseball

if it blows right when you insert the fuse i would look for a bad wire. You might have a wire grounding out somewhere. Not sure about how your wires and all are ran but its a start i guess.

75 ShortBed 4x4

Senior Member
Posts: 341
Loc: Elizabeth, Colorado USA
Reg: 04-08-02
Re: ECM-B Fuse keeps blowing, 1990 1500 Suburban 5
09-25-06 03:35 PM - Post#1008208    
    In response to Raceman

OK, I had this problem with a 1990 V3500 truck with a 454, same body style as your sub. The shorted wire turned out to be on the back of the cylinder head, passenger side, just past the distributor. Do the "wiggle" test. Grab hold of the wiring loom and wiggle it, maybe pull it away from the engine. Now insert the fuse and see what it does. If not there, "wiggle" elsewhere. Just insert the fuse after each time to see where the short is. You'll find it eventually.

Big Blocks=Life

"14th Year" Gold Supporting Member
Posts: 17142
Loc: Colorado Springs, CO
Reg: 08-08-04
Re: ECM-B Fuse keeps blowing, 1990 1500 Suburban 5
09-25-06 04:46 PM - Post#1008209    
    In response to c502cid

It sounds as if you have a short somewhere in the fuel pump relay circuit.

Although I don't know for sure, ECM-B is probably dedicated only to the fuel pump circuit. There might be something else tacked on it, but it's primary function is probably to supply power to the pump.

Since I have had some experience with fuel pump circuits and relays, I would probably guess that the relay failed and shorted out that particular circuit. Fuel pump relays actually draw a lot of power, and relays that are used in high power situations tend to fail on a regular basis (especially BOSCH high power relays).

Posts: 94

Loc: 'Burbs of Chicago
Reg: 03-19-03
Re: ECM-B Fuse keeps blowing, 1990 1500 Suburban 5
09-26-06 02:20 AM - Post#1008210    
    In response to Vaughn

I've looked at the wires near the engine, and did the "wiggle test" as suggested above. Still no change.

Vaughn, I think you are onto something with the relay in the fuse pump circuit. Where do I find the relay for the fuel pump??

Super Senior Member
Posts: 6501

Reg: 07-03-01
Re: ECM-B Fuse keeps blowing, 1990 1500 Suburban 5
09-26-06 06:28 AM - Post#1008211    
    In response to Greaseball

The fuel relay is at the underhood electrical center, pass. side firewall. Look carefully and you should see the labels for each item molded into the plastic cover.

The diagram shows an orange wire, from the ecm-b 20 amp fuse, to the ignition switch, which has circuits from there to the a/c. The same orange wire from ecm-b/20 amp, intersects with another orange running into the fuel relay.

Wire colors shown for the fuel relay are: red for the fuel pump prime connector, then orange, gray, dark green/white stripe, black/white stripe.

hth ~SS~

Posts: 29

Loc: Alberta, Canada
Reg: 04-02-03
Re: ECM-B Fuse keeps blowing, 1990 1500 Suburban 5
09-27-06 03:33 PM - Post#1008212    
    In response to SuperSport

I had this same problem on my 87 1/2 ton, ECM B fuse would blow as soon as I stuck it in. I traced the problem to the valve underneath that switches fuel tanks from side to side. There must have been a short to ground in the solenoid. I don't know if the 90 burbs have dual tanks, but I bet the problem is in the fuel pump circuit somewhere. Maybe this will help.

Steve 1997 Chev Blazer AWD 1987 K10 Chev Silverado Shortbox 4X4

Posts: 94

Loc: 'Burbs of Chicago
Reg: 03-19-03
Re: ECM-B Fuse keeps blowing, 1990 1500 Suburban 5
10-01-06 06:54 AM - Post#1008213    
    In response to SuperSport


There is no fuse box or relay center on the passenger side firewall on this truck.

I found what appears to be a relay hanging off of 5 wires. I found it dangling off the back of engine. The wire harness coming into it is well sealed and it has provisions for a slide mount cast into it although I cannot find where or what it is supposed to mount to. One of the 5 wires is a red wire with a female spade terminal, the others are orange, green, black and grey. I cannot find where this relay was supposed to be hung from and I cannot find the male terminal to the red wire (I suspect that it is grounding out and causing the problems).

Does someone have a picture of the fuel pump relay and its location for my particular truck (seems like there have been many variations on locations through the years based upon the replies).

Thanks again

Posts: 57
Loc: Lakewood, WA
Reg: 08-03-05
Re: ECM-B Fuse keeps blowing, 1990 1500 Suburban 5
10-03-06 07:10 AM - Post#1008214    
    In response to Greaseball

I had the same fuse blowing out on my 91 suburban. I found the short behind the distributor in the giant wiring harness that runs along the firewall. Chevy or the previous owner had installed some cheap connectors in there. One of the wires (orange) coming from the oil pressure sensor mates with 2 other orange wires in that harness. There was nothing covering the connection and the plastic loom was ripped around that point. The dist. was the cause of the ground. I never had that fuse blow again after I fixed that connection.

91 Sub (almost finished)
90 Sub
Functional 98 Ford Van
Ugly 99 Cougar
Sweet 06 Charger

marks 66 bu 
Posts: 43

Reg: 02-26-06
Re: ECM-B Fuse keeps blowing, 1990 1500 Suburban 5
10-03-06 07:46 PM - Post#1008215    
    In response to jameswingate

look around the oil pressure sending switch, they tie the fuel pump relay into it, no oil pressure, no fuel relay, also, use a 12volt test light in place of your fuse, hook to bat pos, it should burn on the shorted side of the fuse block, when the short is removed, the test light will go out. I'll look at my mitchell info and see if I can find you a wiring diagram.

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