1987 Silverado fuel issue

[hamm]

Hello. Out of desperation, I joined this forum for help. Been struggling with this issue for a couple weeks now. Was driving the truck and it suddenly shut off and would not start. This has happened once before and I replaced the fuel pump only to realize that the old pump was not actually bad. However, the truck ran again after switching out the pump. That was 2-3 years ago, and no problems until now, when it just stopped again. I have looked at the fuel relay plug and schematics and I don't seem to be getting power to where it should be. I have juice to one pin all the time, but I don't get any to the second pin when turning on the key. I have put 12 volts to what I believe is the fuel pump test pin and I get nothing. I put 12v to what I believe should be a direct output from the relay to the pump, and nothing.

Also, the fuel gauge seems to have stopped working at the same time. I have seen that there is an oil pressure switch, but I don't see how it could keep power from reaching the pump when I turn the key on. I had an old ECM which would work until it got hot, then worked again when it cooled off. Put that in as a test. No change.

Suggestions?

Hamm

 

[Bextreme04]

In the resource library, there are manuals for every year truck. If you go into the 1987 manuals and look at the emissions and drivability manual, you will find a step-by-step troubleshooting procedure for this issue.

http://www.mediafire.com/download/i...Fuel_and_Emissions_Including_Driveability.pdf

 

[Snoots]

The oil pressure switch will shut the fuel pump off if you have no oil pressure. This is only bypassed when cranking. Check your oil pressure connector pins for corrosion.

 

[Redfish]

The oil pressure switch will shut the fuel pump off if you have no oil pressure. This is only bypassed when cranking. Check your oil pressure connector pins for corrosion.

Actually...no. That is not what it is for. It provides power to the fuel pump if the primary electrical circuit fails. I thought exactly what you said, but the electrical schematic plainly shows it in parallel, not in series.

paging @bucket for an amen...

 

[Bextreme04]

The oil pressure switch will shut the fuel pump off if you have no oil pressure. This is only bypassed when cranking. Check your oil pressure connector pins for corrosion.

Absolutely not

Actually...no. That is not what it is for. It provides power to the fuel pump if the primary electrical circuit fails. I thought exactly what you said, but the electrical schematic plainly shows it in parallel, not in series.

paging @bucket for an amen...

This is correct. The oil pressure switch is a parallel power supply that will keep the engine running if the fuel pump relay fails while the engine is running.

 

[bucket]

Actually...no. That is not what it is for. It provides power to the fuel pump if the primary electrical circuit fails. I thought exactly what you said, but the electrical schematic plainly shows it in parallel, not in series.

paging @bucket for an amen...

Amen brother

 

[hamm]

OK, I'm back. Thanks for the replies. Been busy. I'm also trenching in a new water line to my house right now - dug by hand. Yikes...

I finally found the ALDL connector. Out of 12 possible contacts, it seems to only have 4 that are active. From the upper right, it has contacts in A, B, C, blank, and D. All the rest are blank. Does this seem right at all?

 

[hamm]

No. Correction. Blank hole is where "D" would be, so the other existing contact would be "E".

 

[hamm]

Jumped from A to B and it ran a diagnostic. I don't have a "scan tool" that they refer to in your diagnostic advice. I got a code of "44". According to a chart I found on line, that means: "44- oxygen sensor or circuit - lean exhaust detected". Could that cause the engine to shut down and not restart?

 

[Rusty Nail]

My suggestion involves dropping the tank and repairing the chafed wires on the top of it.

Lemme attach a pic of the ARMOR I insulated my **** with after replacing the pump - after repairing the rubbed bare spots.

You can do it!

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[Ricko1966]

Actually...no. That is not what it is for. It provides power to the fuel pump if the primary electrical circuit fails. I thought exactly what you said, but the electrical schematic plainly shows it in parallel, not in series.

paging @bucket for an amen...

Which will be very obvious because if you are relying on the op switch for fuel pump power you will have an extended crank condition. Engine will have to turn over long enough to build oil pressure before it starts. Threw this in for anyone with mystery extended cranks that's following this.

 

[hamm]

Thanks for the suggestion Rusty Nail. I'm not sure that is my problem because I already reached over the tank and wiggled the wires with the key on. If there was an issue there I think the pump would have come on, but it didn't.

 

[hamm]

I have put my fuel supply issue on hold while travelling for work. However, I believe I determined that I'm not getting any power to the fuel pump relay when I turn on the key. Not sure what could explain that, given that no code was shown which would seem to explain it. I also jumped 12v directly from the battery to the relay connector lead which, I think, is supposed to energize the pump as a test point. Still nothing from the pump. Any ideas are welcome.

 

[KnuckleBuster]

When you initially turn the key to the run position the ECM will only power the relay for 2 seconds and then will shut off. To power it again you would need to turn it off, wait approximately 10 seconds, and then turn it on again. The ECM will provide constant power to the relay when cranking or with the engine running.

Here's what I would do:
Use a fused jumper to get 12v to the pump circuit. It will probably spark a little if the pump runs. Go back and listen to the tank and try to hear whether or not the pump is running. It may help to remove the gas cap and listen there. If you hear it humming, you probably have a good pump. You'd have to check pressure to confirm this.

If it doesn't run, disconnect the pump connector and check for power and ground. Seen plenty of these with loose terminals, so you'll need to watch for that.

Another possibility: Side tanks had a baffle that would sometimes come loose and knock the pump and level sensor out of place.

 

[KnuckleBuster]

OK, I'm back. Thanks for the replies. Been busy. I'm also trenching in a new water line to my house right now - dug by hand. Yikes...

I finally found the ALDL connector. Out of 12 possible contacts, it seems to only have 4 that are active. From the upper right, it has contacts in A, B, C, blank, and D. All the rest are blank. Does this seem right at all?

No. Correction. Blank hole is where "D" would be, so the other existing contact would be "E".

Jumped from A to B and it ran a diagnostic. I don't have a "scan tool" that they refer to in your diagnostic advice. I got a code of "44". According to a chart I found on line, that means: "44- oxygen sensor or circuit - lean exhaust detected". Could that cause the engine to shut down and not restart?

I think you're barking up the wrong tree trying to check ALDL circuits. Except for checking for trouble codes, you can pretty much ignore it unless a trouble chart sends you there.
The code 44 just means that the ECM believed the system was running lean. I don't think it's going to be of much use with your no-start condition.