Lift pump not getting power!! Please help I’m stuck in a parking lot

[Diyeli]

I have a p series 1994 6.2l Chevy diesel motorhome (possibly 6.5l) I’m not at all a mechanic but am very mechanically inclined. One day it just didn’t start sounded like it was struggling for fuel, I changed the fuel filter still nothing, no fuel comes out when I try to bleed it either. So I assumed it was the lift pump or wiring for that. I have the new pump it before I install that I tested the wiring and it’s getting no power. The plug was pretty damaged I replaced that, still no power. I can’t figure out which/relay or fuse goes to the pump. There is no cover with diagram and there is no diagram in the manual. Any suggestions? Please forgive my ignorance I’m just trying my best to solve the issue… I’m stuck in a parking lot until I can figure it out.. please help me out

 

[ak diesel driver]

Don't know on the p series but trucks LP get their power from the oil pressure sending unit. A good IP will suck past a dead LP

 

[dbrannon79]

Welcome to the forum @Diyeli

on your truck you have the relay and fuse up on the drinkers side of the firewall next to the junction block above where the AC accumulator is. also your OPS can cause the fuel pump not to work. OPS= Oil Pressure Sensor located in the rear of the block in the valley of the engine. it's a PIA to get to with the factory fuel filter behind the intake.

On the OPS connector there is three wires. iirc there should be an orange wire that has 12v power all the time and a grey wire which goes to the fuel pump. you can make you a jumper and cross these two pins in the connector and check if the fuel pump has power I will try looking up the OPS connector pinout and verify which wire is which.

 

[ak diesel driver]

P series should have a dog house and make the OPS easier to get to

 

[dbrannon79]

Here is a link to a guy that did a diy relay mod on his. this is something highly recommended. Leroy sells a complete wire harness kit for this. but this link confirms with wires to cross to test your fuel pump. the fuel pump will only operate with there is oil pressure, it's also wise to add a bypass push button switch in the harness so that you can prime filters and test the pump. Leroy's harness also has this included and is all plug n play.

OPS Relay Mod Install (1992-1995 OBDI Trucks)

www.dieselplace.com

 

[Glagulator]

Does your R/V have a turbo?

 

[MrMarty51]

Yes, welcome to TTS @Diyeli
If You get the OPS removed then go to a parts store, or hydraulic shop and have an extension hose made that will get the OPS up out of the valley.
My K3500 truck I had it made about two foot long and with one of those wiring/hose P shaped clamps fastens to the bolt that holds the underhood light connector.
I know Your van dont have such an aminal but it gives You an idea of where the OPS can be fastened to so it aint just flip flopping around under the engine compartment.

 

[jrsavoie]

Here is a link to a guy that did a diy relay mod on his. this is something highly recommended. Leroy sells a complete wire harness kit for this. but this link confirms with wires to cross to test your fuel pump. the fuel pump will only operate with there is oil pressure, it's also wise to add a bypass push button switch in the harness so that you can prime filters and test the pump. Leroy's harness also has this included and is all plug n play.

OPS Relay Mod Install (1992-1995 OBDI Trucks)

www.dieselplace.com

Don't cut and splice. If you make your own relay harness, get the connectors and make it plug and play, like Leroy’s.

I posted the numbers for the connectors, years ago.

 

[Will L.]

I highly doubt your problem is just a lift pump.
As mentioned the injection pump can suck past a dead lift pump by design.

crack open the bleeder screw at the fuel filter and cycle the key a few times to see if you are getting fuel up to the filter via the lift pump.

What injection pump do you have- ds4 is electronic so the throttle is electric.
The db2 is mechanical and has a throttle cable like the 60’s &70’s cars.
Post pics if you aren’t sure.

 

[jrsavoie]

I highly doubt your problem is just a lift pump.
As mentioned the injection pump can suck past a dead lift pump by design.

crack open the bleeder screw at the fuel filter and cycle the key a few times to see if you are getting fuel up to the filter via the lift pump.

What injection pump do you have- ds4 is electronic so the throttle is electric.
The db2 is mechanical and has a throttle cable like the 60’s &70’s cars.
Post pics if you aren’t sure.

I never understand this advice.

Why not jumper it or install a toggle switch to run the lift pump on demand?

I frequently install a toggle switch and inline fuse on jumpers. It just seems easier to me.

Saves all that climbing in and out of the cab.

You're also introducing air before you even start
If you jumper the lift pump, by whatever means, you should be able to hear it run.

If you can hear it running you can crack the T drain and run fuel out into a pickle jar, noting the flow and looking for crud.

 

[Diyeli]

Welcome to the forum @Diyeli

on your truck you have the relay and fuse up on the drinkers side of the firewall next to the junction block above where the AC accumulator is. also your OPS can cause the fuel pump not to work. OPS= Oil Pressure Sensor located in the rear of the block in the valley of the engine. it's a PIA to get to with the factory fuel filter behind the intake.

On the OPS connector there is three wires. iirc there should be an orange wire that has 12v power all the time and a grey wire which goes to the fuel pump. you can make you a jumper and cross these two pins in the connector and check if the fuel pump has power I will try looking up the OPS connector pinout and verify which wire is which.

Thank you.

 

[Diyeli]

I replaced the relays, still no power to lift pump. I traced the wires they go back above the gas tank and splice into another plug. There was power there. Do you think it could be a bad OPS that would be cutting off power to the lift pump? I’m just at a loss of what to do.

 

[ak diesel driver]

Run a temporary power wire to the LP to eliminate that aspect. If that cures it then you can zero in on it at a more convenient time.

 

[Diyeli]

Welcome to the forum @Diyeli

on your truck you have the relay and fuse up on the drinkers side of the firewall next to the junction block above where the AC accumulator is. also your OPS can cause the fuel pump not to work. OPS= Oil Pressure Sensor located in the rear of the block in the valley of the engine. it's a PIA to get to with the factory fuel filter behind the intake.

On the OPS connector there is three wires. iirc there should be an orange wire that has 12v power all the time and a grey wire which goes to the fuel pump. you can make you a jumper and cross these two pins in the connector and check if the fuel pump has power I will try looking up the OPS connector pinout and verify which wire is which.

Per your advice I used a jumper and by passed it and got power to the lift pump again!!! Do you think the OPS is bad or could that just be cause by an oil leak? Thank you guys so much for the help!

 

[dbrannon79]

99% of the time it's the OPS. without a relay on the OPS they burn out. the factory relay only activates during crank, then once the engine starts, the OPS takes over. if it's leaking oil, there's a good chance it's gone fubar.

 

[Diyeli]

Run a temporary power wire to the LP to eliminate that aspect. If that cures it then you can zero in on it at a more convenient time.

I bypassed the OPS by using a jumper wire and got power

99% of the time it's the OPS. without a relay on the OPS they burn out. the factory relay only activates during crank, then once the engine starts, the OPS takes over. if it's leaking oil, there's a good chance it's gone fubar.

Thank you so much!! Also when I by passed it, the fuel pump kicked on and then fuel leaked out of the bottom on the filter housing.. now do I have another issue there or do you think it leaked out just cuz I was forcing it to pump fuel?

 

[dbrannon79]

leaking is a problem! did you loosen anything on the FFM? make sure the cap is tight as well as the bleeder.

 

[Diyeli]

No I didn’t loosen anything that’s why I thought it was weird for that to leak randomly on top of everything else going on

 

[dbrannon79]

How bad is the leak and how far do you need to go to get home from the parking lot? it can be a fire hazard leaking also if there is an intake leak that can be disastrous too for a run away engine.

try and isolate it from being the seals on the filter housing or a fuel hose connection. fuel hoses that run under the intake from factory in that area will get brittle with time and heat.

in a pinch stuck in a parking lot (electronic injection pump) if you can access the fuel supply hose feeding the fuel filter housing. or even further back. run to a parts store and get you some fuel hose and an inline fuel filter (clear plastic one). disco the hose from the fuel filter housing and splice into it with the inline filter and run over to the IP inlet. prime the inline filter and new hose before connecting to the IP. then button that up, verify no leaks and drive home.

then I would say it's time to pull the intake off and replace all the rubber fuel hoses and seals on the fuel filter housing.

 

[jrsavoie]

Run a temporary power wire to the LP to eliminate that aspect. If that cures it then you can zero in on it at a more convenient time.

I've supplied power to the lift pump inline fuse on the 1994 trucks. On the trucks it's located passenger side by the load panel.

I remember seeing a picture with it labeled someplace.