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Question and hoping someone here can help out.
 
We have a 2008 Monaco Diplomat with a Cummins 400 ISL with 67K miles and have a problem we hope someone may have experienced and resolved in the past.
 
We we're on the road and go to accelerate, she acts as if she wants to stall out.
 
Our mechanic says the diagnostics show she wants 23K psi of fuel pressure but it drops to about 11K psi when he goes to accelerate. The turbo does not factor into his diagnostics.
 
We've replaced filters, fuels pumps, adjusted the injectors (mechanic thinks they may be suspect) and he just change the PCM control module (made the problem come up in about 10 miles where as he was having it come up previously in approximately 200 miles and no he's not taking it camping), checked fuel quality (it's fine) but all to no avail.
 
He's trying to get Cummins to assist but claims they are on COVID19 slow down.
 
Hopefully someone may have had the same issue to deal with in the past and can provide some insight.
 
Thanks for your time and all be safe.
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I’m sorry, but your repair person is sending  out RED FLAGS to me. MITE be this or that .   Hopefully you aren’t  being charged for he’s gusting. There must have been a code that came up when this first started ? Do you know what . 

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Hello Harald,

I live in the heart of Cummins Country in Southern Indiana.  I called a Cummins-buddy of mine (an IT guy not a engine expert)  and asked his advice on your situation.
He said, call 1-800CUMMINS and that he checked... the lines are still open.

Hope this helps.

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I had Cummins do a compression check and they found a small leak in the block causing it to loose power especially up grade.  Just a thought in not a mechanic. 

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Howdy, We had something like that and it ended up as a leaking exhaust manifold gaskets and an intake boost sensor bad. Repaired by Crosspoint Cummins in Knoxville, TN and has run perfect ever since. 75,000 miles then and now is around 130,000 miles. 

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When your mechanic is using the Cummins Insite software while driving the coach he will be able to see and record the engine computer commanded fuel pressure vs the actual fuel pressure.  Is this what he did?  Is this problem intermittent?

Has your mechanic used the Insite software to command high fuel pressures while at idle and will the fuel pump meet the target pressures?

If not, you likely have a fuel flow blockage, a failing fuel pump or a leaking fuel rail pressure relief valve.

Hope this helps.

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Sorry before I said engine compression when I meant exhaust manifold leak.  I dsys I wasn't a mechanic. I was identified by a very experienced 18 wheel driver who heard it when next to me in the fuel slot. 

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I have one more thought.  If this is an intermittent problem and the coach pulls grades at full turbo boost and the engine is throwing no trouble codes you might have a sticking turbo electronic actuator. 

To find out, the next time you lose power keep your foot full on the accelerator to see if after about 15 seconds it will turn on the check engine light with a turbo electronic actuator code error. 

When going from no throttle to throttle, the VGT will rapidly cycle from the braking mode to pressure boost.  If it sticks in the braking mode you get low fuel pressure, no boost pressure and no power.  If this situation lasts for a short time, it will not turn on the check engine light and act like the engine temporarily lost power.

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We have seen mechanics that were not aware that there are actually two fuel filters on your coach. Did the mechanic change both fuel filters. The secondary fuel filter is often overlooked and could be plugged. We have a 2006 Diplomat and the secondary fuel filter is located to the right of the radiator when facing forward from the rear (passenger side). Remove the panel that covers the hydraulic fluid tank and look down. It should be there.

 

Edited by Bob Nodine
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12 hours ago, Joel Sheriff said:

Sorry before I said engine compression when I meant exhaust manifold leak.  I dsys I wasn't a mechanic. I was identified by a very experienced 18 wheel driver who heard it when next to me in the fuel slot. 

Noted Joel. Going uphill does not exacerbate the problem.  It happens on a flat run when he goes to accelerate.

55 minutes ago, Bob Nodine said:

We have seen mechanics that were not aware that there are actually two fuel filters on your coach. Did the mechanic change both fuel filters. The secondary fuel filter is often overlooked and could be plugged. We have a 2006 Diplomat and the secondary fuel filter is located to the right of the radiator when facing forward from the rear (passenger side). Remove the panel that covers the hydraulic fluid tank and look down. It should be there.

 

Thanks for the input Bob. He and I have changed both filters on numerous occasions and well aware of both of them. We always carry spares as well.

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12 hours ago, Frank McElroy said:

I have one more thought.  If this is an intermittent problem and the coach pulls grades at full turbo boost and the engine is throwing no trouble codes you might have a sticking turbo electronic actuator. 

To find out, the next time you lose power keep your foot full on the accelerator to see if after about 15 seconds it will turn on the check engine light with a turbo electronic actuator code error. 

When going from no throttle to throttle, the VGT will rapidly cycle from the braking mode to pressure boost.  If it sticks in the braking mode you get low fuel pressure, no boost pressure and no power.  If this situation lasts for a short time, it will not turn on the check engine light and act like the engine temporarily lost power.

Good thought.  The warning light comes on even when stopped.  The lift and high pressure pumps are new and he's verified them more than once. He's verified the fuel lines for blockages and leaks, the tank vent, the injectors and changed the PCM.  The good thing is he's determined to resolve this on his dime.

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By warning light I'm assuming you mean check engine light.  Please post the history of both active and inactive check engine code numbers.  If your mechanic is not using the Cummins Insite software and Cummins engine service manuals for troubleshooting your problem, it's time to find another mechanic.

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I had almost the same thing every time something was done I'd get 200 to 1000 miles and would happen again a lot of money chasing this problem around. So anyway Monaco added a Raycor-Parker fuel filter (primary) in line first then to the Fleetguard (secondary) supplied by Cummins. I spoke to a old  Monaco tech about it he said they had lots of trouble with the Parker filter and to bypass it and see if the problem persisted. So of course 1000 miles from home and in the rain I was removing the brass elbow out of the housing and found the inlet side packed full of rust, this raised my curiosity and started to pick it out to look into the housing and as I was doing this a piece of solder fell down. Yes a 1/4" piece of flat solder some how was in my tank and found it's way all the way to the filter. When work was done and the pressure released it would fall down and lay flat then when ever it decided to flip up and block my inlet it would. I cleaned it all out and never had a problem again (Aug 2016) .That said I know that was a freaky  problem but there might be something to the parker filter failure the Monaco guy told me about. I made my bypass out of brass from Lowes  5 or 6" 3/8" nipple ,2 couplings ,and a bushing. For some reason one side is different size from the other but the brass elbows out of the housing are standard pipe thread. Using those fittings is easier the trying to make a bypass of the flared hose ends.

Just food for thought     

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19 hours ago, Frank McElroy said:

By warning light I'm assuming you mean check engine light.  Please post the history of both active and inactive check engine code numbers.  If your mechanic is not using the Cummins Insite software and Cummins engine service manuals for troubleshooting your problem, it's time to find another mechanic.

Frank:  Karen had snapped this when we first brought it in.

I'm thinking it's the PRV on the fuel rail but I'm no mechanic.

Thank you for all the suggestions/recommendations.

 

98453734_2673560776237875_3061795195050786816_n.thumb.jpg.a142e6abaffd9e1f03ac27ada516898d.jpg

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Thanks for posting the trouble code.  Very often low fuel pressure is due to plugging fuel filters.  Algae growth in the fuel tank can plug filters in under a hundred miles.  But once plugged, you will lose more and more power under load.  It's not an intermittent problem.  Attached is a picture of my cut open fuel filters after about 10,000 miles of use.  These show minimal debris.

The fuel pressure on your engine is controlled by the engine computer.  If memory serves me right fuel pressures operate between about 10,000 at idle to about 30,000 psi at full load.  Your mechanic can "command" the engine computer to operate at max fuel pressure while at idle to see if the system can achieve full pressure.  He can then shut off the engine and monitor the leak down rate over time.  My engine will hold fuel rail pressure for hours with minimal pressure loss.  Excessive leakdown or inability to reach max commanded fuel pressure are issues that must be resolved.

From your description, it sounds like you are having an intermittent problem.  If that's the case, your mechanic can setup the Cummins Insite software to record engine parameters in real time so he can see all engine parameters when you get the problem.

When I was having a hesitation problem with no trouble codes, I had to use real time data recording while driving to finally identify a sticking turbo actuator as the source of my problem.

A good mechanic using the Cummins Insite software should be able to solve this problem without throwing parts at it.  I sure hope that your mechanic followed the Cummins service manual procedures and checked the fuel rail pressure relief valve and internal block injector connections for leaks before replacing the injector pump and the engine computer.  If not, I suggest you might want to find another mechanic.

Hope this helps.

IMG_20150719_141019238.jpg

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