1987 Silverado fuel issue

[YakkoWarner]

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

If you're getting that click at 2 seconds, then most likely the ECM is working properly in that aspect. Putting 12V directly onto that red pigtail from the battery should feed 12V right back to the fuel pump - if you're not getting any juice back there, you're not getting pump action period. I would absolutely solve that first before messing with anything related to the computer. The fact that it fires off when primed indicated your ECM is at least doing the basics correctly.

I'd start at the fuel tank selection switch (my truck is single tank so I don't have one but my friend Dave had problems with his). I'm pretty sure the red pigtail will feed power only to whichever tank is selected.

 

[hamm]

Yes, I recognize those charts. Seen them before. What I have decided to do is finish putting the tank back in place and re-connecting it and put in some gas. Then I might run a 12V line directly to the pump, bypassing everything, and see if I can get the thing to start that way. I just cannot figure out why I'm not getting power back to the tank.

I did check for power at that intermediate connector spot. No power is reaching there either, even when putting 12V to the red test pigtail. I have no idea where the interruption could be.

 

[hamm]

I'd start at the fuel tank selection switch (my truck is single tank so I don't have one but my friend Dave had problems with his). I'm pretty sure the red pigtail will feed power only to whichever tank is selected.

Now THAT'S a good idea! You're right.. it should only feed power to one tank at a time! I believe I tried looking at that switch last fall, and broke the mount. I think it's hanging inside the dash now. I'll look at it tomorrow. Finally, something new to go on. Thanks!

 

[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.

Yes, as YakkoWarner suggested, it's going to be different with 2 tanks. I'll try to find a schematic for the setup with 2. That selector switch is an obvious possible disruption point.

 

[hamm]

Yes, now I remember where I was last fall on the tank selector switch. I had tried to pull it out of the dash, but the front, with the rocker part, broke off. Now, the rear part should come out, but the wiring seems too short to pull it. I think I have the back part of the switch mechanically in the correct position to activate the right tank, but can't get to the wiring to check voltages, etc.

I was in the process of pulling the ashtray, to get to the back of the switch and the wiring, but the ashtray frame seems too big to come out of the dash. It must have been installed from the back, and it looks like I have to remove some heater duct work to get the ashtray out. Sigh...

PS: It looks like there is just enough wire so I can pull the switch over to the ashtray opening, with the ashtray pushed to one side, and get to the switch connector and test it for voltage. Yay.

 

[gmbellew]

you will find the service manuals for the 87 in the Reference Library on this site. they will have test procedures, schematics, etc to help diagnose the selector switch

 

[hamm]

you will find the service manuals for the 87 in the Reference Library on this site. they will have test procedures, schematics, etc to help diagnose the selector switch

I have that. Thanks. Too hot out there now to continue until evening. "Shade tree" mechanics don't work well when there's no shade tree.

 

[CountKrunk]

On the subject of hitting things with a hammer.

i had a positive experience hitting my starter when truck no lights no crank on me in the middle of nowhere.

Carry on

 

[YakkoWarner]

On the subject of hitting things with a hammer.

i had a positive experience hitting my starter when truck no lights no crank on me in the middle of nowhere.

Carry on

Isn't that just basic percussive maintainence procedure?

 

[hamm]

Isn't that just basic percussive maintainence procedure?

Shock and awe. Let it know who's boss.

 

[hamm]

Been busy with other things the past couple of days. Further study has shown that the crank fuse should only see power when ign switch is in the "start" position. How could that fuse blow while driving, as that seems to have happened simultaneously with whatever is keeping voltage from reaching the fuel pump? Doesn't make sense.

I suppose the crank fuse could have been blown before my current situation, and be unrelated. I have read that the engine may start without it. Going to troubleshoot my tank selector switch today.

 

[hamm]

Well, kids.... it seems that maybe it was the tank selector switch all along. I pulled the switch and it would not make continuity between any of the lugs, regardless of switch position. So I sprayed DeOxit into it and worked it back and forth a bunch. Then I started getting continuity. I finished putting the tank back in, remade all the connections and put a couple gals of gas in. Dark came. I'll try starting it tomorrow.

 

[hamm]

Yep. It was the tank selector switch. Pump now comes on for a couple seconds with ign. to "run". Primed it a bit and it started instantly and seems to run just fine. Have not driven it yet.

I dropped the tank twice and replaced a working fuel pump, along with getting towed home, before figuring this out. Had no idea the switch could suddenly just stop making internal contact. It seems I could have just wiggled the switch and it might have run again.

I'll order a new switch. I think the spring gets weak in them as well as the contacts getting dirty. I just have to put the stuff back together that I tore apart in the dash after I get the new switch. Thanks for all the help, guys.

PS: I don't know what the crank fuse has to do with any of this. It may have been blown for a long time, for whatever reason. Apparently the thing will run without it.

 

[hamm]

My next issue is that the oil pressure gauge maxes out after I turn the key on - before starting. Any ideas?

PS: Actually, it stayed maxed-out after shutting the engine off, but I thought I saw it registering somewhat lower before I started the engine today.

PS: I did drive the truck. No more fuel problems.

 

[JamesSam]

My next issue is that the oil pressure gauge maxes out after I turn the key on - before starting. Any ideas?

PS: Actually, it stayed maxed-out after shutting the engine off, but I thought I saw it registering somewhat lower before I started the engine today.

PS: I did drive the truck. No more fuel problems.

From what I understand the guages are negative reads so it is disconnected or a ground is out if it is beyond maxed out.