signs of bad pressure relief valve on rail???? - Dodge Diesel - Diesel Truck Resource Forums

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signs of bad pressure relief valve on rail????

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Old 02-29-2008, 11:19 AM
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signs of bad pressure relief valve on rail????

what are some signs of a bad pressure relief valve im trying to figure out a hard start issue and was woundering if the relief valve would have anything to do with it. the injectors are good i know this is a common problem. the truck cranks for a long time before starting but once started truck runs fine.
thanks is there a check valve anywhere in the fuel supply side of the fuel system. any advise

danny
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Old 02-29-2008, 04:29 PM
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Here's some advice from a DTR member I just got yesterday on my boost issue but relevant to your question
If your not getting enough fuel, or rail pressure you'll also be low on boost.
You can easily check the rail pressure releaf valve. It the long cylinder going to the fuel return hose by the MAP sensor on the rail. If you unbolt that & start up the truck, look to see if you have fuel coming out of that. If you do, you have a bad releaf valve. This will cause low injection pressure & low boost.
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Old 02-29-2008, 04:41 PM
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you dont even have to start it. just remove the connection(engine off) if there is fuel present, the valve is bad.
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Old 02-29-2008, 06:18 PM
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Take the banjo bolt off the top of the valve on the rail? I would like to test mine.
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Old 02-29-2008, 07:33 PM
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I respectfully dissagree with the above "test" of the rail relief valve.

The top of the valve is also the fuel return from the rear injector that goes to the filter cannister, when there is fuel that needs to be returned it will still sit on top of the valve. Giving you a false test.

Solution is to test it like the FSM ( I have no idea ) or have a gauge befor and after you place a test bolt in the top and compare the numbers.

I had a false test when it was believed that my valve was bad when infact it was A-ok and a bad programmed xzt was the offender.

Believe what you will, just be informed and do your research, that is it.
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Old 02-29-2008, 10:14 PM
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Originally Posted by Dwitt0187 View Post
the injectors are good i know this is a common problem. the truck cranks for a long time before starting but once started truck runs fine.
danny
I would say TRIPLE check the injectors....but I am just saying that because I am recently coming off a looooooong battle with a cold start/hard start issue, that ended up being the injectors (I did have the relief valve replaced, it didnt do anything for the cold start).
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Old 09-20-2015, 03:04 AM
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I've seen a lift pump go bad and send stuff through the rail and stick in the relief valve. The truck will start but will have no rail pressure that may not be the case here. I would check that first though.

JOSH
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Old 09-20-2015, 10:57 AM
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You need a special tool to check this valve, Miller 9013

Fuel Pressure Test Adapter | SPX Miller Special Tools | 9013
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Old 02-26-2018, 06:05 PM
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Big iron do you use that Miller 9013 in conjunction with a Miller 6977 gauge kit?
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Old 02-26-2018, 07:10 PM
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A quick way to check if it is bypassing continuously is to start the engine cold and let it run for minute or two. If its bypassing through the PRV it will get hot in a short time. Be careful it can get really hot if it has a bad internal leak. This wont tell you if the pop off pressure is low but I haven't seen one with low pop off pressure that wasn't getting hot. They seem to go hand in hand most of the time.
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Old 02-27-2018, 09:47 AM
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At about 2:50 in this video they show testing the relief valve.


I would also say remeasure the injector return flow, even if you are sure they are good...
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