03 isx, fuel issue?

[mikestrucks]

First time issue, trucks wouldnt fire. would spin but nothing. fuel filter fine, tried diesel rag against air filter, even little starting fluid, nothing worked. got mechanic out, he didnt find anypower to lift pump and it didnt seem to be making any sound before starting( someone told me it should hum or something) tried running hot jumper wire to it ( the lift pump ) and it started! it started several more times with original wiring hooked back up. set over night and started again today. so mechanic thinks we should try lift pump first! sound reasonable? any other ideas? and lift pump had power after starting but not with just the key on!

[Hammerhead]

(03-06-2018 )mikestrucks Wrote:  First time issue, trucks wouldnt fire. would spin but nothing. fuel filter fine, tried diesel rag against air filter, even little starting fluid, nothing worked. got mechanic out, he didnt find anypower to lift pump and it didnt seem to be making any sound before starting( someone told me it should hum or something) tried running hot jumper wire to it ( the lift pump ) and it started! it started several more times with original wiring hooked back up. set over night and started again today. so mechanic thinks we should try lift pump first! sound reasonable? any other ideas? and lift pump had power after starting but not with just the key on!

After initial Key On the lift pump should have +12v power for 2 minutes. After initial 2 minute prime to purge any and all air from the fuel system, lift pump power is discontinued from ECM until next Initial Key On.
So IF the 2 minute +12v power cycle is functioning correctly, and you have no audible mechanical buzzing, then, YES, I would suspect lift pump failure.
However you are saying after applying power directly to the lift pump, the truck started. So did direct power make the lift pump function? Diagnose and determine correct lift pump power cycle BEFORE throwing parts at it.
If the lift pump power cycle is correct, and the pump is operating as intended, I'd suggest further investigation, starting with the Anti-Drain Back Valve.
If you haven't yet, sign up for a Quickserve account and you can find the procedure there to properly diagnose your issue.

Your initial description was leading directly towards a malfunctioning lift pump. However this jumped off the tracks when you said that after applying power directly to the lift pump the truck started? If it was a NFG lift pump this wouldn't have made a difference. This leads to a malfunctioning Anti-Drain back valve, however after sitting the truck would lose prime and not start...unless the lift pump IS functioning properly and can overcome the volume of ADV fuel loss...see why I say to properly diagnose before throwing parts at it?

[Rawze]

On my CM871, there is a relay in the wiring harness that operates the lift pump. Make sure it is good too.