1988 Chevy dually fuel pump troubleshooting

[=River Perfection=]

See below

 

[monkeyswrench]

I'd go selector valve module under the cab...and where are the pics?

 

[Sleek-Jet]

There is a module that lives in the distributer that energizes the fuel pump(s) on GM TBI systems. I've fought the same problem in early 90's K1500 before. There is a way to check that it is working but last time I bought one it was like $15, so it was just as easy to replace it.

 

[Sleek-Jet]

Thank you both for the feedback. I was gonna grab two new relays on way home and try those. Do u think the module in the dist would cause the tanks not to register?

I was think of replacing the selector valve also if that does not work.

It shouldn't, at least in the trucks I messed with the gauge still worked.

 

[rivrrts429]

Need to get some better pics, very nice truck. Was literally in a barn used as a horse hauler. Have alcoas for it need to get them on it. Body and interior are both 9 out of 10. Paint is a 7 but cleaning up well.

Don’t be modest Geoff. That truck is so sick in person. It’s going to be even better with the upgrades you’re doing.

 

[rivrrts429]

I hope so bud!!! Damn old trucks...

I feel as old as this tuck sometimes...... wait a min....

Know what a better plan would be? Let’s drink beers on its tailgate and talk about what the fuel issue could be but do less work and more drinking

RDP will figure out the problem. I’m sorta with you on this one and guessing but someone here will definitely know.

 

[warpt71]

Lived in a barn, check the wiring for chewing from rodents. Unfortunatly my square is an 86 and still has a q-jet and mechanical fuel pump.

Anthony Ervolina might be a good person to ask as well, I think he is still on here

 

[monkeyswrench]

That truck's beautiful! Usually not a fan of original red, because they've usually been oxidized to hell. Is that a 454 truck? I've run into 2 in the past couple years that were factory small blocks...didn't even know they made them!

 

[coolchange]

I’m chasing one of those now. 3/4 ton. 69,000 miles

 

[monkeyswrench]

Off chance, as I've never had a low mileage one, but what about the ignition switch on the column? Sounds like it hasn't been used much, and wondering if the contacts that slide in the switch are oxidized? The problem with that though, is the ignition circuit and gage circuit are separate I believe...but the TBI trucks use an ignition feed to light off the pump relays.

 

[monkeyswrench]

This is a 454 yes, Id love to rip all the smog bullshit off but would prob kill value? It just passed smog too. Where I have it registered it does not require a smog test any longer.

I have no idea about value with the smog stuff. I'd pull it and box it up...for the next guy. I spent the first 35 years of my life in Cali, the past 10 in non-smog part of AZ, and I honestly couldn't tell you what it should have for smog. I'd guess the egr plate and air injection into the manifolds? Stuff has always been gone!

 

[69hondo]

Eaxct same truck I used to have. I think I have another throttle body on the shelf you can have.

 

[=River Perfection=]

Eaxct same truck I used to have. I think I have another throttle body on the shelf you can have.

hey man I appreciate that.!

 

[bonesfab]

The gauges and pump are wired through the selector valve. Just because you replaced with new doesn't mean it is better than what you took out. I would start with the selector. About 80.00 on summit. And make sure you get the right switch. Carb and efi trucks take different switch.

 

[HALLETT BOY]

I seem to recall you have to order selector switch using VIN . On part # does not fit all

 

[SBMech]

Everything runs through the valve unit if I remember right.

Pretty easy to trouble shoot if you understand circuits. A PowerProbe works wonders for quick troubleshooting stuff like this, since you can energize and ground things when you poke em lol.

The relays on the firewall are a constant source of intermittent failures too, they are cheap, just replace them.

 

[trucker507]

The new selector switch is right... it did work both tanks... until recently. UGHHH lol

My dad had same problem he said the wire for switch runs next to exhaust and melted, might be something to look into

 

[LHC Kirby]

24 replies in and no one gives the obvious advice.

Have you tried a different prop ?



* I’m going with electrical either chewed, fried, broken, poor connection.. let us know what works

 

[pull-on]

schwiiiiing. Sweet square.

 

[bagged97taco]

Can we get some pics of it and the flat behind it!!

 

[=River Perfection=]

Can we get some pics of it and the flat behind it!!

Soon!

 

[=River Perfection=]

Update..... lol. So last night replaced the tank selector switch and both fuel pump relays. The tank fuel gauges seem to respond now. Still no fuel pumps.

This am.. the left tank fuel pump went on at key turn and stayed on for a while.. weird. The right fuel pump I could not get to turn on. You can hear them kick on usually when key is turned on( r/l whatever one is selected) standard primer function. Could the heat be doing something here.... this is killing me.

 

[monkeyswrench]

Update..... lol. So last night replaced the tank selector switch and both fuel pump relays. The tank fuel gauges seem to respond now. Still no fuel pumps.

This am.. the left tank fuel pump went on at key turn and stayed on for a while.. weird. The right fuel pump I could not get to turn on. You can hear them kick on usually when key is turned on( r/l whatever one is selected) standard primer function. Could the heat be doing something here.... this is killing me.

Do you have a power probe? If you do, pop the relays and check the pumps manually. That will let you know if the problem is dash/trigger related or the pumps themselves. You can then check the plug side, and make sure they're getting 12v from the battery. If all that seems good, check the "trigger" wires with the switch, and see if they get a constant.
Heat shouldn't be an issue, but grounds for the pumps may be. That could also effect the sending units in the tank.

 

[HANDY]

thank you guys for the reply!!

The left pump did run once yesterday when I turned the key over for about 20 sec, then it quit, right tank nothing.

I could not get it to go back on with the key or with 12v to the jumper wire at the relay( R or L pump). I did replace the relay and the dash switch after I started having issues with the right pump not working. I also replaced the under truck fuel switch valve this week. Nothing has helped.

I have power at the relay, the orange female terminal in the relay harness lights up on my test light key on or off. The OIL pressure gage is pinned for some reason yes, wich is strange. I have checked all fuses daily and they all look good. Everything works on the truck and the battery is new and 100%

The wiring for the switch where it passes through the fire wall can loosen and cause intermittent problems.

 

[SBMech]

Found this, it may help you some.

At least help you track down where the problem lies.

 

[24 Sleekenforcer]

One thing about this system is the switch only has power for a few seconds when the relay is energized. There should be a pink wire at the relay with a blunt end connector that you can jump to battery voltage and power up the fuel pump that it is switched to .

 

[24 Sleekenforcer]

Some more info to go with the schematic posted above.

 

[SBMech]

Some more info to go with the schematic posted above. View attachment 1136705 View attachment 1136706 View attachment 1136707

What's great is that flow chart matches the diagram, can't ask for more than that!

 

[monkeyswrench]

Damn, hitting the archives
Those books are the real deal. I've managed to find the GM transmission books for the 700r and the 4l60...books written by the guys that put the stuff together!

 

[24 Sleekenforcer]

Damn, hitting the archives
Those books are the real deal. I've managed to find the GM transmission books for the 700r and the 4l60...books written by the guys that put the stuff together!

You would be surprised on what I have, working for the same dealership since 1983.

 

[monkeyswrench]

You would be surprised on what I have, working for the same dealership since 1983.

Lucky! I've been digging up books here and there over the years. Usually, they're books I'd looked at in friend's collections when I was working on old stuff. I figured if I needed it once, could need it again. When I see them now at swaps or used book stores, I grab them

 

[=River Perfection=]

Have a guy putting new fuel pumps in it, not sure why but the other ones went out from sitting around I guess. tanks and pumps are brand new.

This thing is for sale. Not sure price yet. I have a nice set of alcoas going on it, just got back from the polisher. 48k original miles. Interior ia 9 out of 10 just needs a head liner. Paint is ok, a good cut n buff will make it better, body is straight, a/c does not blow cold.

909-670-8058 Geoff

 

[liv4riv]

Check the wiring under the bed at the frame rail where the get smashed going to the fuel tank.

you may need to loosen the bed bolts and jack the bed up in the area on drivers side to move the wires.

 

[H20 Toie]

Have a guy putting new fuel pumps in it, not sure why but the other ones went out from sitting around I guess. tanks and pumps are brand new.

This thing is for sale. Not sure price yet. I have a nice set of alcoas going on it, just got back from the polisher. 48k original miles. Interior ia 9 out of 10 just needs a head liner. Paint is ok, a good cut n buff will make it better, body is straight, a/c does not blow cold.

909-670-8058 Geoff

when i put new pumps and tanks in mine i had one fail within the first hour, replaced it and its worked for years

 

[white tortilla]

when i put new pumps and tanks in mine i had one fail within the first hour, replaced it and its worked for years

Saw you on the freeway yesterday @H20 Toie

 

[=River Perfection=]

when i put new pumps and tanks in mine i had one fail within the first hour, replaced it and its worked for years

No shit... well I'm over dropping those tanks before I'm even started lol.

The guy that did it now tells me hes just too busy lol. Anyone in the upland area know someone who wants to do this???

 

[H20 Toie]

View attachment 1255133
Saw you on the freeway yesterday @H20 Toie

damn i cant hide anywhere lol