Blowing fuel pump fuse

[oldpa]

The 10 amp fuse in the main engine fuse block keeps blowing and kills the fuel pump.
It’s kind of funny because it has happened once last year and all I did was replace to fuse and it was fine or 12,000 miles but now it’s blowing repeatedly.

In the fuse block, the fuse that keeps blowing is marked PCM/TC-1
Also with this fuse out the starter does not work
Any ideas on what’s going on?

Thanks, Greg

2003 Winnebago sightseer, Workhorse P-32 gas

[M&EM]

The pcm/tcm-1 10 amp fuse is shown in the service manual to be connected with the Power control module/Transmission control module. I'd be guessing but the power control module probably controls the fuel pump relay coil. The fuel pump main operating current is on its own fuse. The only connection I see in the manual from the pcm/tcm-1 fuse is to each of the 2 control modules! If it is not a short in the wiring, then either module may have a problem. The powertrain control module C2 connector pin #9 controls the fuel pump relay coil. Perhaps the relay coil is shorted. Try replacing or just removing the relay to see if it still blows fuses.

HTH.

Marty

[Daysu47]

Hopefully it is not the problem I had. Long story short.

Fuel pump fuse blew starting vacation, fuse blew in LA 3 times in 21 miles, replaced fuses, drove to Palmdale, had fuel pump and all grounds checked, drove 189 miles north, blew again, replaced fuse, drove 71 miles, replaced relay, drove all the way to Oregon and back to San Diego. Thought all was fine. 3 months later, after 2 weekend campout, needed other work done on it so drove to work in AM, POP goes the fuse, got to work, drove to luncheon, POP fuse blew, got it to repair facility that day. Explained situation, so between one of the best electricians in San Diego, Workhorse, and Winnebago "experts" and over a3 1/2 week period, they finally decided to replace ALL of the wiring from the fuel pump, they also replaced the fuel pump, all the way to the fuse block, which they replaced too.

Sooooo, all is well 3 years and 36000 miles later.

It really baffeled everyone, they spent hours and found no cause.

So, as said, I hope you situation is a simple fix.

Good Luck,

[M&EM]

Quote:

Originally Posted by Daysu47 Hopefully it is not the problem I had. Long story short. Fuel pump fuse blew starting vacation, fuse blew in LA 3 times in 21 miles, replaced fuses,---- ---------------Workhorse, and Winnebago "experts" and over a3 1/2 week period, they finally decided to replace ALL of the wiring from the fuel pump, they also replaced the fuel pump, all the way to the fuse block, which they replaced too. Sooooo, all is well 3 years and 36000 miles later. It really baffeled everyone, they spent hours and found no cause. So, as said, I hope you situation is a simple fix. Good Luck,

A while back when I had a class C, I had intermittent fuel pump stoppage symptoms. I was able to speak with an engineer at one of the companies that manufactures fuel pumps. His take on the failure modes of fuel pumps back then was interesting.

Basically the pumps were centrifugal types. The impeller was a teflon disc with spiral grooves on one side and very close tolerances. Teflon has a high expansion co efficient and is relatively soft. In time small particles get inbeded in the disc. This causes extra friction which loads the pump which increase current flow. On a warm day, and with warmed recirculated fuel heating up the fuel tank, expansion further increases friction and current. Either the motor brushes will finally fail or the the motor locks up and stops or draws excessive current and pops a fuse. Time allows cooling down like in during replacing a fuse which allows for resumed pump function and repeated pump shut downs.

Back then I opted to replace the fuel pump. No further pump issues occurred.

Marty

[JonBrazel]

Specifically when is it blowing now when you say repeatedly? As soon as you place the fuse in, as soon as you start the engine or once you start driving a little ways?

[oldpa]

Well it’s fixed!
A small loop of wire somehow was protruding out from one of the main wiring harnesses on top of the engine, so that with vibration a small, very small part of insulation wore away and caused a short in that circuit.
As Marty said, that fuse is not the main fuse for the fuel pump but does control the fuel pump relay. With that fuse out-no gas to the engine.
Thanks for all of the replies and a big thanks to James at Advantage Automotive in Albuquerque who put other work aside to look at our motorhome and also took the time to track the short down.

Greg