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Fummins

Problem holding rail pressure

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Been noticing i cannot hold rail pressure. Yesterday while driving to seattle, my RP was only about 7000 psi @ 75 mph. Couldn't get much over 12k under heavy acceleration. I stopped to fuel up and after starting it back up, my pressures were better but still down. Thinking I popped my PRV, any thought?

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Been noticing i cannot hold rail pressure. Yesterday while driving to seattle, my RP was only about 7000 psi @ 75 mph. Couldn't get much over 12k under heavy acceleration. I stopped to fuel up and after starting it back up, my pressures were better but still down. Thinking I popped my PRV, any thought?

Fill out your signature so we know what you have on your truck..........mods, miles etc. How was the truck running under these conditions though???? Normal or no power???? Normally you're not gonna pop the RPRV unless you are over about 26,000psi of RP. Before you check into the RPRV, check your fuel filter/filters. If they check out, then check your lift pump. If that checks out, then do a check on the FCA (Fuel Control Actuator) on the back of the CP3. If the truck was running fine otherwise, is could be the RP sensor. I would look into those things before digging into the RPRV. That's a start.......please provide info on your truck in your signature though..........we can help you better.

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Oh yes, I forgot my sig!I have a 2002 Ford F350. I just put in a 2004 5.9 CR that I rebuilt. I have 100hp injectors, arson cp3 kit, 63mm turbo and an airdog. Motor has about 1500 miles so far.I did just take the banjo bolt off the PRV and there is diesel in it.

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Oh yes, I forgot my sig! I have a 2002 Ford F350. I just put in a 2004 5.9 CR that I rebuilt. I have 100hp injectors, arson cp3 kit, 63mm turbo and an airdog. Motor has about 1500 miles so far. I did just take the banjo bolt off the PRV and there is diesel in it.

I'm not a 100% believer in the backside of the RPRV test..........because of backfeed thru the system. Unless someone can prove to me otherwise, I don't think breaking the banjo on the topside of the RPRV is a "true" test of it. However, I believe it's TS Diesel that makes an aftermarket RPRV that'll be made to your specifications and will undergo multiple "blow offs". Since this is a rebuild, check the injector return lines.......they could be bleeding off fuel..... This is fairly common on rebuilds and injector installs.:smart: That, along with what I said above..........some other members here should be chipping in here shortly and may provide more insight for you!! Welcome to the site!!!!:thumb1::thumb1:

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I would think that if it was that low it would be running horrible. What gauge are you using, some don't read too well! Is your CEL operational?

Negative Sent from my Droid using Tapatalk

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Are there any codes?

I just went and hooked up Smarty.. No codes present (at least that are related to rail pressure).

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Well I borrowed a good working PRV and installed it. Truck seems to be happy again, back up in the mid 20's on rail pressure again :hyper:

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I was wondering if the prv is a possible problem, could you replace the bolt in the banjo fitting with a solid bolt just to see if it helps the rail pressure and possible diagnose the problem. Maybe this is not a good idea:shrug:. let me know your thoughts. On that note I'm glad you were able to borrow a prv and solve the issue.

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I was wondering if the prv is a possible problem, could you replace the bolt in the banjo fitting with a solid bolt just to see if it helps the rail pressure and possible diagnose the problem. Maybe this is not a good idea:shrug:. let me know your thoughts. On that note I'm glad you were able to borrow a prv and solve the issue.

I ran a "capped" rail for about 50,000 miles. Not one problem. I'm not running anywhere near max RP though. If you're running near max RP, with a capped rail; the possibility exists of blowing out injectors. Especially in and then out of the throttle where there is microseconds of RP that is off the scale and very damaging.
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I was wondering if the prv is a possible problem, could you replace the bolt in the banjo fitting with a solid bolt just to see if it helps the rail pressure and possible diagnose the problem. Maybe this is not a good idea:shrug:. let me know your thoughts. On that note I'm glad you were able to borrow a prv and solve the issue.

Not sure you can just replace the banjos bolt, that fuel line coming off the prv is part of the return system

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I ran a "capped" rail for about 50,000 miles. Not one problem. I'm not running anywhere near max RP though. If you're running near max RP, with a capped rail; the possibility exists of blowing out injectors. Especially in and then out of the throttle where there is microseconds of RP that is off the scale and very damaging.

Many folks are removing their capped rails as the injectors react twice as fast as the CP3 and you can get pressure spikes that double the rail psi. I find it really interesting that 5.9's are using less capped rails, and the 6.7 crowd is starting to use them... History always repeats itself.

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