Ford Truck No Start Fuel Pressure

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WILDSAILER
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  • 1 POST
I do not have any test equipment so trouble shooting is difficult. my 4.9 straight 6 wont start. It has fuel at the rail and spark.with the key in the run position the pump does not shut of after a few seconds.if i shoot it with starting fluid it will start and run, however not smoothly .it will continue to run until turned off. by the way that is with either tank.
Thanks for your help, wm.
Feb 21, 2007 at 11:40 PM
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KASEKENNY
  • ✓Experienced Mechanic
  • 18,907 POSTS
Even though you have fuel at the rail doesn't mean it is making it to the cylinders where it needs to be. There is something that would need to be clarified which is, when you spray the starter fluid and it runs poorly but starts, does it continue to run when you stop spraying starter fluid? If it does not and the only way to keep it running is to continue to spray starter fluid then this is normal. We don't want to have it continue to run on starter fluid, just see if it starts the engine.

If it does start and run then I suspect you have a weak fuel pump. It continues to run with the key on because it is not building the proper amount of pressure but it is building just enough to keep it running (poorly) after you give it a little help with the starter fluid. It's almost like you are just priming the system on a carburetor vehicle.

I know you said you don't have tools but we need to confirm this by testing fuel pressure. If you have access to a parts store, most of them have tool rental programs and you can get this and hook it up and prove this out.

You should have about 55 PSI when you just turn the key on. I would guess you have around 25-35 PSI. Everything you are stating points to this.

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

Please come back with questions. Thanks
Mar 25, 2020 at 9:46 AM

Suggested Repair

Rent a fuel-pressure gauge and measure pressure with the key on. Expect about 55 PSI; a weak fuel pump is likely if pressure is only about 25-35 PSI.

Conversation Summary

The owner of a Ford truck with a 4.9 inline-six says it will not start. Fuel is present at the rail and there is spark, but the pump does not shut off after a few seconds with the key on. Starting fluid gets it running poorly until it is shut off, on either tank. The expert says fuel at the rail does not prove delivery to the cylinders and suspects a weak pump that is not building proper pressure. The recommended next step is to rent a gauge and confirm about 55 PSI with the key on.

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