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Spent 4 hours chasing a no-start on a 5.9 Cummins, turns out it was the fuel heater relay
I mean, I was ready to pull my hair out. The truck would crank but wouldn't fire, and I checked everything - pump pressure, injector pulse, even pulled the valve covers to look at the rockers. My buddy kept saying 'check the stupid little stuff' but I was convinced it was something major. After 4 hours, I finally looked at the wiring diagram and saw the ECM kills the lift pump if the fuel heater relay grounds out. One $18 relay later and it fired right up. Has anyone else had a tiny electrical gremlin eat up a whole afternoon?
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theajohnson14d ago
Have you checked if the fuel heater relay is even doing anything useful on your truck in the first place? A lot of guys just bypass them completely since they're prone to failing and causing issues like this. I pulled mine out last year after it kept throwing codes, and the truck runs way better now with the lift pump on its own circuit. Honestly, those relays are more trouble than they're worth in warmer climates, so maybe that's a permanent fix for you.
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wendy_lee4814d ago
Oh man, that exact thing happened to my buddy Tom with his '06! He spent a whole Saturday chasing his tail, swapped out the ECM, new lift pump, the whole nine yards. Finally called his old man who drove two hours over with a multimeter and found the fuel heater relay was toast in like five minutes. Tom was so mad he just ripped the relay out and wired around it permanently, hasn't had a problem since haha. It's always the cheap little part that makes you feel dumb for not checking first.
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