Hey all,

My fuel pump is not always getting 12v. When it does get 12v the truck runs fine, but when it doesn't, it runs awful. I have a vegistroke kit installed, and it runs great when on veg. Could the #30 relay cause this? By the way, the WTS light always lights up. When the diesel pump is getting 12v the fuel pressure is fine.

When it first started acting up, I immediately thought the tank screen was clogged, but I happened to have it in the shop for something else, and the mechanic said the pump wasn't getting proper voltage all the time.

Are the fuel pump/PCM and the blower motor relays the same? If so, I thought about swapping them to see if that cures it.

Any ideas?

Thanks,
Brad

 

Here is the fuel pump electrical diagram from 1999 (don't know if there were any major changes from 99 to 01):



Power comes from fuse #19 (20A) through the fuel pump relay and the inertia shut off switch to the fuel pump motor.

Chris

 

also check for rubbed wire

 

Am I correct in thinking the fuel pump relay is #30 in the underhood fuse panel?

I'll check the wiring too!

Thanks for the replies!

Brad

 

Fuses aren't typically intermittent, but it's always a good thing to check. Relays, connectors, and switches are almost always a good source of inttermittent power. I'd start simple with inspecting connector contacts, then I'd inspect relay contacts, then I'd see if I could find those switches and ohm them out. If the problem wasn't intermittent, I'd follow the missing voltage back with a meter.

 

I don't see a number associated with the relay, but the diagram says it's in the relay block, which I believe is near the instrument panel.

 

I found the relay block behind the radio. Searchs revealed this is the location for the fuel pump relay. There are a few bigger relays and a small relay. NAPA and the dealer numbers say the smaller relay is the correct relay for a fuel pump. The question is "is it the one for the fuel pump?" The truck started and ran without the relay in! Is that even possible - if so, I would like to know how.

Anyway, I replaced the relay. The truck ran fine most of the day, but decided to act up after switching back from veg last night. I switched back to veg and immediately back to diesel and it ran fine. I'm leaning towards the veg on/off switch is not making good contact when going back to diesel.

The switch is cheap enough that I think I'll throw a new one at it.

 

The engine will not run without the fuel pump relay in place. You should be able to identify it by listening or feeling for a click when the key is turned on (the PCM enabling the fuel pump) and then another click about 20-30 seconds later with KOEO (the pcm shutting off the fuel pump without seeing an engine start). You can also identify the relay with the engine running by looking for a loss of 12V at the fuel pump when the relay is pulled.

How is your veg/diesel system designed? Does the switch control a valve that selects fuel from the desired tank, or does the switch enable an entirely separate fuel pump?

Chris

 

Maybe this is old news to others, but I just stumbled onto this today:

"Inertia Fuel Shutoff" Allegedly, if your vehicle gets whacked hard enough - it shuts the fuel off and needs to be reset. I have not yet looked any deeper into this, I'm preoccupied with pulling the trigger on my Buck$Zooka today. I just thought this info was worth mulling over.

 

The veg system has a separate fuel pump. I'm going to look how many poles are on the switch.

The truck hasn't been in any sort of wreck or even a hard jolt while driving.

Thanks for responding - what did we do before forums?

Ok - gotta ask what is a buckszooka?

 

The Superduty Horsepower Intensifier Tool. I can't post the acronym, it gets edited.