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Old 10-02-2022, 09:12 AM   #1
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5.9 stumbles at idle slow acceleration

1998 RV275 5.9 less than 10,000 miles on rebuild. New bore, pistons, head machined, new injectors, new lift pump, and new injection pump.
Seems like there is a rough idle, and, from a start it takes a while longer to take off.
Once the turbo kicks in it seem to be fine.
My EGT's seem to be a little lower. My fuel pressure is right where it has always been(15 lb's) I am constantly watching my EGT's and fuel pressure while traveling.
The only thing I can think of is running some injector cleaner..
Any other advise would be greatly appreciated..
Thx
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Old 10-02-2022, 12:09 PM   #2
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You've got a fuel pressure gauge on the lift pump & ETG ; do you have a boost pressure gauge ?

From your description , I think that there is a possibility of low boost pressure at low RPM.
Turbo waste gate not closing properly ?
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Old 10-02-2022, 02:04 PM   #3
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Quote:
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You've got a fuel pressure gauge on the lift pump & ETG ; do you have a boost pressure gauge ?



From your description , I think that there is a possibility of low boost pressure at low RPM.

Turbo waste gate not closing properly ?
Thx, I will look into that
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Old 10-04-2022, 06:25 AM   #4
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What can cause it to run on 5 cylinders at an idle??
I am 3 hours from my house. It seemed to run great. It slowed down more on hills(about 10 miles an hour). EGT's stayed low(1000 max).
Fuel pressure 15lb's. I showed up where I was going, left it at idle. And did a walk around. To my dismay the engine was bouncing around a bit.... The actual exaust looks clean. No unburnt diesel..
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Old 10-04-2022, 10:12 AM   #5
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Partially plugged injector , would be my first guess , for a rough idle .
It's possible injector cleaner could help.

I'm assuming your coach is on a Freightliner chassis , and there has been an issue with a fuel strainer in the supply line to the engine ; but if your getting consistent good fuel pressure that shouldn't be your problem .
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Old 10-04-2022, 06:55 PM   #6
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Partially plugged injector , would be my first guess , for a rough idle .

It's possible injector cleaner could help.



I'm assuming your coach is on a Freightliner chassis , and there has been an issue with a fuel strainer in the supply line to the engine ; but if your getting consistent good fuel pressure that shouldn't be your problem .
I ran injector cleaner from the start of this trip 165 miles.. yes it is a Freightliner..
Thx
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Old 10-04-2022, 10:00 PM   #7
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I'm scratching my head ; all the way back to my 1998 1/2 Dodge Cummins ISB training , on the VP-44 injector pump . I don't believe there is an easy way to isolate a bad injector electronically ; like the HPCR system .
If memory serves it's a messy job , requiring cracking the supply tube at the cylinder head to see if the engine's idle gets worse .

I left all my training manuals at the dealership when I retired in 07 ; I'll see if I can track down info to confirm my thoughts .

Engine was just rebuilt , you need to get the valve cover off to make sure a valve bridge hasn't flipped off , and that all valve adjustments are correct .
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Old 10-04-2022, 10:01 PM   #8
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Water in fuel can cause a myriad of problems, plus ruin a modern high pressure diesel fuel injector: 1998, not sure
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Old 10-04-2022, 10:08 PM   #9
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5.9 stumbles at idle slow acceleration

yep 3/4 wrench to loosen 1 injector at a time, they’re mechanical and pop open on high pressure so loosen keeps it from firing but messy for sure.
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Old 10-04-2022, 11:12 PM   #10
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yep 3/4 wrench to loosen 1 injector at a time, they’re mechanical and pop open on high pressure so loosen keeps it from firing but messy for sure.
Eye protection and a rag to cover the fuel spray .

But check valve adjustment first.
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Old 10-05-2022, 08:40 AM   #11
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yep 3/4 wrench to loosen 1 injector at a time, they’re mechanical and pop open on high pressure so loosen keeps it from firing but messy for sure.
Thx Skip and Jon,
These injectors have roughly 10,000 miles on them. I just figured they would last Alot longer then that.. I am going to isolate it soon.. I am not sure if I have a 3/4 wrench with me...
I did pull the valve cover and everything looks the way I left it...
As for water... it has a fuel water separator, and, I opened the drain on the bottom of it.. no water came out (just a drip or 2 of fuel).. it also has a water sensor in the actual fuel filter.. it has not come on.....
Thx again! And I will keep you posted on what cylinder is not cooperating...
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Old 10-05-2022, 11:20 AM   #12
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Thanks for the update .
I'll continue to follow your posts .

I had to ask about the bridge being properly in place ; as one of the Cummins engines I had to replace in my 14 years of Dodge/Cummins repair was due to a washed down cylinder, caused by the bridge flopping off an exhaust valve .

3/4" = 19mm. just in case you have metric wrenches with you .
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Old 10-05-2022, 11:34 AM   #13
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Hmmm.... While You are at it..
Check fuel lines from the tank to the filter[s] to the pump for degradation causing it to suck air..
Causes a loss of power and rough idle.

This is a known issue with the older fuel lines up to around '08 or so mfg.
Those fuel lines are not compatible with the ultra low sulfur/Bio Fuel blends and they "rot" from the inside out.
We replaced ours ['02] last year...[ also affected the operation of the generator and the AquaHot].
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Old 11-05-2022, 08:40 AM   #14
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Finally found some time.. cylinder #3 has no pressure from the vp44. I made a short 9 second video but can't post it here.. the only thing I can think it to be is my injection pump?? I bought and installed it in March on 2021... I also installed an aftermarket lift pump so my injection pump would last... I have put approx 10,000 miles no it.. last 1000 it has had this rough idle and slowed down on grades...
What does everyone think??Click image for larger version

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