24vCTD

Went to start my truck up this morning and didn't hear the FASS system running or see pressure on my FP gauge so I didn't crank it over. Bumped the key, nothing. Checked the inline fuse for the FASS system; it wasn't blown but the plastic on it was melted (I've had that fuse blow once or twice but have never been able to find the cause???). Replaced the fuse with a fresh one, nothing. I rigged up a toggle switch on the FASS system relay plug between the 2 terminals that normally go to the N.O. relay switch contacts, turned the switch on, and the FASS started running. Tested the relay; it clicked when I applied 12v to the coil terminals and I had continuity through the appropriate switch teminals. Plugged that relay back in then went into the Power Distribution block and pulled the fuel system relay in there and connected my toggle switch to the terminals in the block that go to the N.O. contacts on the relay...flipped the switch and heard something click in the injection pump so apparently this relay has nothing to do with the lift pump circuit. I've run out of places to look for the problem; can anybody explain to me where the stock lift pump/FASS system relay coil get their power from? Does this mean my PCM is shot? The wiring diagram in my Haynes book apparently doesn't cover the entire lift pump system so if anybody can provide more diagrams that would be outstanding. If it comes down to it for reliability's sake I'll permanently install a toggle switch in lieu of the relay to turn the FASS system on & off manually--I've already had to replace my VP44 once and that was certainly enough. BTW, I always check my gauges before shutting the key off and I was showing 12 psi fuel pressure so whatever quit working did it while the truck was parked overnight. Thanks in advance for any suggestions or diagrams you guys can help me out with...

george7941

LP is powered directly by the ECM, there are no relays involved.

The VP44 is powered by the ignition switch thru a relay

24vCTD

Thanks for the reply. I went out last night and put the FASS system relay back in and the dang thing started working again... I hate troubleshooting intermittent problems. I posted a thread about this on another board as well, and somebody replied back saying the lift pump drivers in the ECM are prone to failure, so I very well may just replace the FASS system relay with a manual switch so as to avoid replacing the ECM over this. Or if nothing else I could wire the switch in parallel with the relay contacts so if I'm driving and see the FP drop off I can hit the switch quickly to get it back. What's the cost on an ECM anyway?

VFIMechanic

It is not the face that the ECM is shot, it is probably just "footprinted". Which means that when multiple things happen all at once then the truck is shut off sometimes it dosent save all the changes ect. When you hook up the computer via the ECM plug it will probably come up with a note saying ECM is footprinted and just needs a reflash.

Diesel-Dan

See if this helps.....sorry i missed your post until now....

ALSO....instead of a new ECM....you can take the control away from the ECM by this fix: https://www.dieseltruckresource.com/...1&d=1207764088

24vCTD

Thanks Dan!

I like this fix a lot better than my toggle switch idea...so would anybody that happens to buy the truck from me down the road. Any idea why the FASS fuse keeps blowing or melting? Too little voltage causing high current draw maybe?

Diesel-Dan

What is the SN of your kit...i want to get a gauge of how old it is.....

24vCTD

Can't read it with it installed on the truck and can't seem to find the owner's manual which I wrote the info down on... I bought it from a diesel performance shop that is somewhat local to me about the end of February '07 and he didn't have it in stock so he ordered it from DPP about that time if that's any help. I'll keep looking for the SN & let you know if I find it.