Losing prime overnight/fuel pressure problem

[Skman]

I've been trying to figure out an issue with my isx2250 the last couple days.
The other day after the truck sat overnight for about 10hrs...my driver went to start it and it would only turn over...no fire.
I got down to take a look and my PACCAR fuel/water separator was almost empty.
We tried priming it with the lift pump many times and it wouldn't start. The lift pump was changed a couple months ago because it was weak so I was pretty sure it wasn't the problem.
Eventually, I had to use a little starting fluid and got it to fire and it started running and sounded good after about 10-15 seconds.
Driver went out to work and he said that it had hardly any power on even small hills.

Today I went over and wouldn't start again.
Here's what I did today:
1. Changed both filters. PACCAR bowl filled up instead of being almost empty like before.
2. Bypassed the fuel water separator and primed from a Jerry can.
I can hear fuel running to tank during the priming process and after I shut off the key.
Still wouldn't start after priming about 10 times before trying to start.
3. Cracked the nut on the relief valve (about 3 months old) and it started dripping/trickling out pretty good. Probably a cup or two of diesel came out.
I didn't have another relief valve handy so I put it back together.
4. Tried a fuel decay test in InSite. Measured would NOT go past 13,000psi. But when I turned off key....it would hold within a couple hundred PSI.
5. Used a little ether again to start it and ran cylinder tests. Each one made a noticeable difference when cut-out.

Any ideas what to do next?
I thought maybe a bad relief valve on the rail but even though it doesn't build to 29,000 on the test...it does hold at 13,000?

[walterk]

Not sure if 2250 is the same as 2350, but 2350 should easily build 30000 psi during the test, at least mine does. So, if you have a high pressure rail system, that would be a good start.

[tree98]

You must be getting a check engine light? Probably a 0559 for low rail pressure right? You need to get it to run and pass that leakdown test properly.

You mentioned loosening the relief valve on the end of the rail while it was pressurized........

DO NOT LOOSEN FITTINGS ON THAT RAIL WHEN ITS PRESSURIZED!!! THERE'S ONE SPECIFIC FITTING YOU CAN LOOSEN, YOU'LL FIND IT ON QUICKSERVE. THAT LEVEL OF PRESSURE CAN SERIOUSLY HURT YOU!!!

Did you take the pump head off and inspect for damage?

Replace the relief valve if it's the original.

Replace all the guts in the high pressure pump if it has 400k or more miles on it.

Do you have the injector caps for testing injector leakage? If not go buy them and start capping injectors 3 at a time.

[Skman]

(06-24-2024 )walterk Wrote:  Not sure if 2250 is the same as 2350, but 2350 should easily build 30000 psi during the test, at least mine does. So, if you have a high pressure rail system, that would be a good start.

Yeah it should get up to 29-30,000.
A few months ago I tested it...and it got up to 30k But then it would drop like a stone so I changed the relief valve and it was better.
Now it won't build that high.

[Skman]

(06-24-2024 )tree98 Wrote:  You must be getting a check engine light? Probably a 0559 for low rail pressure right? You need to get it to run and pass that leakdown test properly.

You mentioned loosening the relief valve on the end of the rail while it was pressurized........

DO NOT LOOSEN FITTINGS ON THAT RAIL WHEN ITS PRESSURIZED!!! THERE'S ONE SPECIFIC FITTING YOU CAN LOOSEN, YOU'LL FIND IT ON QUICKSERVE. THAT LEVEL OF PRESSURE CAN SERIOUSLY HURT YOU!!!

Did you take the pump head off and inspect for damage?

Replace the relief valve if it's the original.

Replace all the guts in the high pressure pump if it has 400k or more miles on it.

Do you have the injector caps for testing injector leakage? If not go buy them and start capping injectors 3 at a time.

I had an inactive 559 code. I cleared it to see if it would come back but it doesn't. Even after getting it started and running it....though it's not under any load sitting in my shop.

[Rawze]

do an injector leak check on it, as per the video, and make sure it passes.
ref: http://rawze.com/forums/showthread.php?t...3#pid75483

If it will not get to 29,000 psi then the pump (or its regulator on the back side of it) is bad.

as far as fuel draining back.. the check valve in the Davco is failing?.

[Skman]

(06-25-2024 )Rawze Wrote:  do an injector leak check on it, as per the video, and make sure it passes.
ref: http://rawze.com/forums/showthread.php?t...3#pid75483

If it will not get to 29,000 psi then the pump (or its regulator on the back side of it) is bad.

as far as fuel draining back.. the check valve in the Davco is failing?.

I think I have a problem with my parking brake switch because when I tried to do the injector test in InSite...it won't let me. Says the parking brake needs to be engaged even tho it is.
I'm not sure if that's messing with the fuel leak down test as well? It'll let me do the test but maxes out at 13,000. When I was doing the rail leak down test it will sit at 13000psi...but if I slightly press the throttle during the test... it'll go up to 28,000.
Also, there is next to no leak after turning the key off/on. Over a few minutes I lost about 400psi.
I'm going to run a clear hose test to see if I'm sucking air somewhere from the tanks next.
I have a PACCAR fuel/water separator so I'm not sure if they have a check valve? I know my Davco on another truck does.

[Skman]

Did clear hose test with the fuel/water separator inline and also with it bypassed.
No air in the hose while priming or truck running.
But when you shut engine off...can hear fuel running into fuel tank. Also, the clear hose will run back and empty out.
Fuel rail stays at same pressure (within a couple hundred PSI) when fuel is running back to tank.
After turning key...it takes a few seconds for fuel to start running through it again toward the priming pump.
Almost seems like air getting into system somewhere...but there's no external leaks anywhere.

[Rawze]

(06-25-2024 )Skman Wrote:  

(06-25-2024 )Rawze Wrote:  do an injector leak check on it, as per the video, and make sure it passes.
ref: http://rawze.com/forums/showthread.php?t...3#pid75483

If it will not get to 29,000 psi then the pump (or its regulator on the back side of it) is bad.

as far as fuel draining back.. the check valve in the Davco is failing?.

I think I have a problem with my parking brake switch because when I tried to do the injector test in InSite...it won't let me. Says the parking brake needs to be engaged even tho it is.
I'm not sure if that's messing with the fuel leak down test as well? It'll let me do the test but maxes out at 13,000. When I was doing the rail leak down test it will sit at 13000psi...but if I slightly press the throttle during the test... it'll go up to 28,000.
Also, there is next to no leak after turning the key off/on. Over a few minutes I lost about 400psi.
I'm going to run a clear hose test to see if I'm sucking air somewhere from the tanks next.
I have a PACCAR fuel/water separator so I'm not sure if they have a check valve? I know my Davco on another truck does.

you should not have to rev engine up to make more fuel pressure. if so then the pump is not providing proper flow at idle. when doing the fuel leak test ... add the commanded fuel pressure to the monitor list along with the fuel measured. See if it is being commanded to 30,000 psi during the test at idle. If it is and it is not reaching it... then the pump is basd.. or you have a problem with the pump.

The difference between command and measured should always be within than about 300 bar or so... even at idle.