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Tim's Auto Repair
Tim's Auto Repair, mechanic
Category: Chevy
Satisfied Customers: 15573
Experience:  Have owned a repair shop for 25 yrs.
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03 chevy 3500 silverado 6.0 engine fuel pressure problem. Truck

Customer Question

03 chevy 3500 silverado 6.0 engine fuel pressure problem. Truck has P0300 multable cylinder misfire and hard start/rough idle. Has 50 psi fuel pressure (normal 55-62 psi?)at idle new fuel filter, new pressure regulator and a 2 year old delco fuel pump. When i clamp off the fuel return line the pressure goes up to 70 psi so i assume the pump is supplying enough pressure. When i do clamp off return line idle smooths out. Thanks for your help.
Submitted: 6 years ago.
Category: Chevy
Expert:  Tim's Auto Repair replied 6 years ago.


i would think the problem is still the fuel pump..these must have no less the 60psi .even though you have 70psi when you shut off the return..i think it is not delivering enough volume


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Tim's Auto Repair, mechanic
Category: Chevy
Satisfied Customers: 15573
Experience: Have owned a repair shop for 25 yrs.
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Customer: replied 6 years ago.
I replaced the fuel pump and the truck starts and runs a lot better but still has a slight rough idle which I can live with. The only concern I still have is that the fuel pressure only increased to 52 psi from 50 psi with old pump. It supposed to be 55-62 psi. It has new fuel pressure regulator, fuel filter and fuel pump. What else could be causing the low fuel pressure?
Expert:  Tim's Auto Repair replied 6 years ago.

this still isn't right..the pressure needs to be 60psi..nothing else can cause the low pressure other then the pump or regulator


Customer: replied 6 years ago.
Relist: Incomplete answer.
Expert:  Michael Moore replied 6 years ago.
How many miles on the truck?

Does this happen only when cold or all the time?

Does the p0300 come back of has the check engine light stay off?
Customer: replied 6 years ago.
135,000 miles, happens all the time and p0300 code is active and light comes on if truck idles for any length. I did find out that the fuel pressure regulator only has 15" of vacuum and when i unplug it from regulator the fuel pressure goes up to 60 PSI. Hose is not leaking. Engine only has 15" of vacuum anywhere you check. Could the problem be low vacuum? I sprayed carb cleaner around everything but no sign of a leak. Could it have an "internal vacuum leak?" How else can you check for low vacuum?
Expert:  Michael Moore replied 6 years ago.

You may have a vacuum leak at the intake gaskets. The vacuum leak is hard to find because the leak is under the intake, not on the top. GM has had problems with the intake gaskets on these engines, so much that they redesigned the gasket in 2005. If the intake gaskets have never been replaced before on this engine its a good place to start. The old gaskets are orange and the new ones are green. The only way to tell if you have the new gaskets is to remove the intake, which is not a hard job. The orange gaskets go flat and cause the vacuum leak. This will cause a rough idle and a few codes to set such as the p0300 and p0171/p0174.

The fuel pressure seams to be OK, if your pressure gauge is off by 5%, then you would have a normal pressure reading.

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