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Discussion Starter #1
would a bad fpr cause my truck to get crap mileage, idle rough and run rough above 70 it sounds like heavy bass coming from the stack and it starts to vibrate a bit. i dont want to have to replace it if its not bad i just got done putting 7k into the truck
 

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Check for codes-!

Clean the MAF sensor!

Change the fuel filter!

Check the air filter-!

Have you checked the wire FICM wire harness, where is is attached to the bracket by the alternator.

All of these can affect the engine operation and fuel mileage.
 

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Discussion Starter #3
newer filters only about 1k on each and had the harness replaced my wires did rub though but had that fixed, i will check my maf
 

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Why do you assume the FPR?

Have you monitored your desired vs actual fuel rail pressure?

I would check harnesses, LLY is known for ice pick fix and rub through on harness. I'd start there.

Any codes?
 

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Discussion Starter #5
i dont have any way of checking fuel pressures or injector rate. i'm just thinking its a fpr from reading about it on here ive been chasing problems on this truck sence i bought it last year and im new to diesels so im not real sure on how it should run
 

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How old is your Edge Juice W/Attitude? If it has the newer screen you may be able to monitor actual vs desired fuel rail pressure.

I think you are doing yourself a dis-favor by trying to assume what the failure is without the proper tools to test. My recommendation is to take it to a shop or find the proper tools, without them you could create new problems burying the underlying initial issue.
 

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You should do the bottle test, just to eliminate that-- it will check the FPRV and LLY engines do have a problem with a weak spring in the valve. --

At the rear of the driver's fuel rail, there is a "U" shaped hose-- remove the hose from the rail fitting, and plug the hose. Attach a long hose to the rail fitting and put the end in a bottle. Now drive the vehicle hard-- if you have fuel in the bottle, the FPRV is bleeding off rail pressure. You need to shim the valve spring, or replace it with a race valve [plug] that will not bleed pressure.
 

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Surging is more of a symptom of a bad FPR that rough idling is. That sounds more like a bad injector but there could be alof of other reasons for it so before you go throwing parts at it, start running tests to narrow down the possibilities. Bottle test above is free and easy. You can check demand vs actual fuel rail pressure with an Edge Insight and that can also help you check your injector balance rates as well.
 
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