1987 Silverado fuel issue

*or open.

The Crank fuse is ECM related. Any reference that said it has to do with the starter cranking the engine is incorrect.

bucket said:

The Crank fuse is ECM related. Any reference that said it has to do with the starter cranking the engine is incorrect.

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OK. Thanks. I'll keep that in mind. I have an old ECM which would quit working when it got hot. I already tried putting that one back in and it didn't help, but that was before I found the blown crank fuse. On the other hand, I don't seem to get 12v to the fuel pump connector by the fuel tank when I put 12v to the test lead at the fuel pump relay. That could not be due to the ECM, so I'm still baffled in general.

Well, all heck broke loose around my house last fall and I had to leave this project to sit all winter and spring. Now I'm back to needing to get this truck running. I'll review this thread, since I have forgotten a lot of where I was on this issue. I know I was in the process of jacking the tank back up into the truck, because the fuel pump seems to be fine. I do see that, in my last post, I had discovered that I am getting no voltage to the pump, even though I had changed out the crank fuse, which I found to be blown. After replacing that fuse, I believe I began hearing the fuel pump relay click, whereas I had not before. I believe I noted that the wire coming to the fuel pump is a different color than the one leaving the fuel pump relay. That would indicate that there is a junction or something in the circuit so that the wire is apparently not a direct full run to the tank from the relay. I'll try to figure that out starting tomorrow.

As before, any suggestions are welcome.

Cheers!

October the 6th is my kid sister's birthday.

Rusty Nail said:

October the 6th is my kid sister's birthday.

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I'll definitely bear that in mind.

I went back to "refresh" my memory...u been gone a long time it seems.
We missed you a bunch.

bucket said:

Amen brother

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I was going to tell him Amen.

Rusty Nail said:

Aww come on man that's no fun..be a sport!

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Omg that's hilarious!

This a great thread. What were we fixin?

Rusty Nail said:

Omg that's hilarious!
This a great thread. What were we fixin?

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I believe there was some debate back there about slapping wives. Whether to use open or closed hand or a mallet. You can review to find it.

On the other hand(so to speak) I reviewed and recalled that I did have spark - would start with a prime. I think I'm back to trying the old ECM (which worked when cold) after having replaced the crank fuse, OR whether there is an open circuit to the fuel pump due to a bad connector somewhere. Weather is a bit cooler today, so I'm out there checking things out.

When I follow the troubleshooting instructions found on this site for the fuel system, It says I should get an error code of 54 for a "failure in the fuel pump circuit". I didn't get that code. It also says there that there is a terminal for testing whether the fuel pump functions. I have a red pigtail hanging off of the harness, and other sources have spoken of a red pigtail existing for testing purposes. When I jump from the battery to that red pigtail, I do not get any voltage at the connector leading to the fuel pump. Can anyone confirm my understanding on this?

PS: I am back in the situation where after turning on the ignition to "run" (not start), there is about a 2 second delay and then I hear a "click" from the fuel pump relay. My understanding is that the fuel pump should be energized for about 2 seconds after turning on the ignition (until the engine starts). Does any of this make sense to anyone? Why would there be that delay before I get the "click"?

PPS: Now I see in the troubleshooting info that the fuel pump should run for 20 seconds after "on", not just 2 seconds. I'm not sure which is correct.

hamm said:

When I follow the troubleshooting instructions found on this site for the fuel system, It says I should get an error code of 54 for a "failure in the fuel pump circuit". I didn't get that code. It also says there that there is a terminal for testing whether the fuel pump functions. I have a red pigtail hanging off of the harness, and other sources have spoken of a red pigtail existing for testing purposes. When I jump from the battery to that red pigtail, I do not get any voltage at the connector leading to the fuel pump. Can anyone confirm my understanding on this?

PS: I am back in the situation where after turning on the ignition to "run" (not start), there is about a 2 second delay and then I hear a "click" from the fuel pump relay. My understanding is that the fuel pump should be energized for about 2 seconds after turning on the ignition (until the engine starts). Does any of this make sense to anyone? Why would there be that delay before I get the "click"?

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If you apply 12v to the red test lead, you should have 12v at the connector to the pump. The test lead splices in downstream of the relay per the wiring diagram. you can also apply 12v straight to ckt 120 on the harness with the relay disconnected and get 12v at the connector at the pump.

you should be able to put 12v on the pump test lead and put one end of your meter at the relay connector on the ckt 120 wire going to the fuel pump and the other lead of your meter to ground and see 12v at the meter, right? But that won't tell you if you have an open from the relay to the pump...only that the test lead is connected to the circuit.

The red test lead actually just goes right into the relay connector and should supply whatever voltage you provide. As I recall from my previous attempts last fall, that connection makes a bridge to another contact point in the relay, which should, in turn, run the pump. I now remember jumping across inside the connector, with it unplugged, from a good 12v source inside the connector. That should accomplish the same thing. I still get no voltage at the connector near the tank from doing that, or using the red pigtail with the connector plugged in.

The only other connector I could find in between relay and tank is one which plugs into a unit which I believe switches between the two tanks. It is a large-ish metal block with fuel lines routed to it, I think. It's dark now and I can't look again to confirm. I did pull that connector out of the block and all contacts look clean and good. It seems hopeless to trace the entire path of wiring from the relay to the pump. Too many junctions and hidden/confused passages.

Tomorrow I can check if voltage is making it to that intermediate connector spot. Not sure what else to do. Still don't understand why the "crank fuse" originally blew when it quit running, but replacing that fuse did not fix the problem. Thanks for the input.

PS: Maybe I should just throw a new ECM at the thing?

Hamm

this is from the 1990 manual. but I'd suspect your 87 is a similar setup except you might have the complexity of 2 tanks.

Fascinated but can't follow! It all seems so crazy once you start digging in.

Running on passenger tank only and one day hope to use both again....
-Sam