ECM-B fuse blown, no start!!

[SoCalSlaughter]

So the truck is 90' Suburban V2500 4X4 5.7lt. Today I was driving to work and every few minutes the radio would cut out, engine light would flash and truck would stumble, then the ECMB fuse blew, pulled over and put a new fuse in (same amp) did it a few more times. Then on my lunch heading home, I was backing into my parking spot and the truck just shut off. Tried to turn it over and would crank but no start. ECMB fuse was ok, after following the fuel pump wires from pump up to cab, didnt find anything shorting. Changed fuel pump relay, same no start. Went inside to research some online, went to truck to try and start and blew ECMB fuse, blew 4 more times til it finally held and would try and turn. Unplugged fuel pump and fuse would still blow. Unplugged oil sending unit, relay and pump and would still blow sometimes. Also, the night before I was driving to the store and got a code 42. That went away after turning truck off and back on. Finally plugged everything back in, took fuel filter off and tried to turn motor over and no fuel. So now the fuel pump isnt running. Could the pump be causing the ECMB fuse to blow? The pump is about a year old. Im about to push the truck off a cliff. Haha

[SoCalSlaughter]

Update, fuel pump is not turning on. Good fuses and relay is good. Just finished dropping the tank. Lets see if a new pump fixes the problem.

[Thetuneman]

On my 94 , it did the same thing, couldn't figure it out. Finally, after a lot of cussing, I found out the little round coil ( Don't know what they really call it) in the very bottom of the distributor was bad. you have to remove it and disassemble the distributor, taking the shaft out and replace that part. and it fired right up after assembly. May not be your problem , but that's what happened to mine.

[SoCalSlaughter]

The new pump doesnt turn on still! The distributor is only about a year and a half old. And the pick up coil? I wonder if that would keep from turning the pump on, cause the truck cranks but the pump wont turn on so its not getting fuel

[ChevyTech]

Your truck is a square body so you posted in the wrong section of the board. It is a different body style then the trucks in this section and that may be why you are not getting more help.

You said you found a code 42, so you must have checked codes, and if it had a fuel relay problem it would have set a code 54.

The distributor is only about a year and a half old. And the pick up coil? I wonder if that would keep from turning the pump on, cause the truck cranks but the pump wont turn on so its not getting fuel

The distributor has no control connection to the fuel pump running or not, but ECM needs to receive a distributor reference pulse from the distributor module to trigger the injectors.

If the injectors are not spraying fuel it does not tell you there is no fuel pressure. The injectors may not be opening.

The ECM controls the fuel pump relay.

The truck has a fuel pump relay that supplies power to the fuel pump when:
- Anytime the ECM receives a distributor reference pulse. (Engine running / engine cranking)
- The key is turned on engine not cranking – relay applied for 2 to 20 seconds (most trucks 2 seconds), depending on emissions equipment. Trucks over 8500 GVW and some other vehicles have and electronic Fuel timer module that allows the pump to run up to 20 seconds.
The key must be turned off for a certain amount of time before it will prime the system again when turned back on.

There will only be power to the fuel pump for a few seconds when you first turn the key to the on position. If you are turning the key on then walking around the vehicle testing for voltage to the fuel pump circuit there will be no voltage and should not be power to the pump.

The ECM should store a code 54 if the fuel pump relay fails.

A code 42 is set when the ECM loses communication with the distributor.

Code 42 can be set by a bad distributor module, a bad ECM or wiring problems between the ECM and distributor.

A code 42 will get set when the set timing connector is unplugged to set the timing. Make sure you clear the codes after setting the timing.

A bad distributor module is a common cause for this code.

Many stores like NAPA in my area will test the module for free if you bring it in.

Make sure when you install or reinstall the distributor module that you use heat sink compound/grease under it. The grease helps dissipate heat from the module. Without it, the module will fail.

Here is a thread you may want to read:
http://67-72chevytrucks.com/vboard/s...d.php?t=495054

You may want to do a search and do some reading.

You need to find out if the truck has spark or not.
You need to see for sure if the fuel pump runs or not.
If the fuel pump does not run, you need to check it for a code 54.

CT

[SoCalSlaughter]

Sorry about posting it in the wrong forum, I mostly post from my phone and cant see the whole title. And no code 54. Only code 12 and 42. Truck has spark, turn key to on and everything seems normal, I can hear the fuel pump relay click but no buzz from the fuel tank. Have changed pump out to confirm and still no fuel. Ive taken the fuel filter off and tried to crank and no fuel. ignition control module is working. I work at AutoZone and tested the module and it passed (Tested 4 times)

[ChevyTech]

It sounds like a wiring problem to the fuel pump.

Don't overlook the ground side of the circuit.

The body style after the square bodies has a fuse between the fuel pump relay and the fuel pump.

[SoCalSlaughter]

Ive checked and rechecked all grounds in the cab, frame and motor and all are good. Hooked up a 12v current to the fuel pump and it will run, but the truck will not make it run. Tested voltage on fuel pump wires and getting 8.45v with key on.

[ChevyTech]

Originally Posted by SoCalSlaughter

Ive checked and rechecked all grounds in the cab, frame and motor and all are good. ...

How about the ground wire to the fuel tank sending unit?

Originally Posted by SoCalSlaughter

... Hooked up a 12v current to the fuel pump and it will run, but the truck will not make it run. Tested voltage on fuel pump wires and getting 8.45v with key on.

What voltage, on what color wire?

One wire should be a ground and have no voltage.
One wire is for the gauge.
One wire is for the fuel pump and should get battery voltage, but only during the prime cylce that lasts a couple seconds.



The truck has a fuel pump relay that supplies power to the fuel pump when:
- Anytime the ECM receives a distributor reference pulse. (Engine running / engine cranking)
- The key is turned on engine not cranking – relay applied for 2 to 20 seconds (most trucks 2 seconds), depending on emissions equipment. Trucks over 8500 GVW and some other vehicles have and electronic Fuel timer module that allows the pump to run up to 20 seconds.
The key must be turned off for a certain amount of time before it will prime the system again when turned back on.

There will only be power to the fuel pump for a few seconds when you first turn the key to the on position. If you are turning the key on then walking around the vehicle testing for voltage to the fuel pump circuit there will be no voltage and should not be power to the pump.

[SoCalSlaughter]

Ground wire on sending unit is good, cleaned it and reinstalled. And I tested the voltage on the brown/wht wire going to the pump. When i turn the key to ON, all the dash lights come on, I can hear the relay click, then a few seconds later click again (the prime i think) Ive check ECM, pick up coil, ignition module and pump relay and the pump still wont run.

[ChevyTech]

The brown/white wire is for the fuel pump and should have a full 12 volts during the few second pump prime.

If the relay is not appyling power to the fuel pump wire, the ECM should set a code 54.

If the wire has a problem on the way back to the pump the system would not set a code 54.

[SoCalSlaughter]

What would be keeping it from getting a full 12v?
Posted via Mobile Device

[ChevyTech]

Originally Posted by SoCalSlaughter

What would be keeping it from getting a full 12v?
Posted via Mobile Device

A bad connection.

Corrosion at a connection.

Corrosion in the harness from having been probed in the past.

Have notice any marks from the wire having been probed in the past?

Have you found the fuse?

The later model trucks have problems with poor connections at the junction block under the hood on the power supply circuits.

[SoCalSlaughter]

The fuel pump is hooked into the ECMB fuse and its not blown. Ive checked all wires from the pump to the fuse block and everything is good. New distributor, ignition module, ecm, fuel pump relay and the pump still wont turn on.

[ChevyTech]

Below I have attached a link of a schematic that may help you understand the circuit.
According to the schematic the system would set a code 54 if the inline fuel pump fuse was blown.

I am not positive this schematic is accurate for your truck, but I think it is.
http://www.justanswer.com/chevy/1om1...-350-just.html

Look at the schematic and notice if you put power into terminal G of the ALDL connector with the KEY OFF the fuel pump should run. This is a good test to see if the wiring and grounds are ok all the way back to the fuel pump.

This link will show you which terminal to put power in.
http://www.obd-codes.com/faq/read-gm...codes-free.php

[SoCalSlaughter]

Well I was having a problem with the ECMB fuse blowing, and when it would blow the ECM would lose all codes, but I have fixed a few grounds and the ECMB fuse doesnt blow anymore, still no prime or run from pump, turn key on, engine light flashes once then stays on and I can hear the fuel pump relay click.. then a few seconds later click again. But the night before the truck stopped running I had gotten the code 42. Then just shut off in reverse and pump will no run. Everything else seems to work. maybe the fuse block inside had bad connections?