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Old 09-15-2019, 09:00 AM   #15
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Originally Posted by Kenny Hughes View Post
As of today 9/15/19 I sincerely hope to have solved the fuel problem on my Cummins 400 ISL engine after being towed to Cummins in Savannah Ga and diagnosed with fuel flow problem and other guessed at problems and $8000.00 diagnosing and replacing High Pressure Fuel Pump and telling me it was fixed. Drove it 60 miles back to Hilton Head with a few stumbles and no water temp gauge working. Called them and was told probably a little trash in fuel should clear up and not there fault or much concern about temp gauge. -- This was all the last week of May 2019. After three months at Hilton Head mandantory evacuation was ordered for hurricane and I left Thursday Sept.5,19 and had terrible engine stumbling and made it about 30 miles to A-1 Towing and Service in Ridgeland SC who started diagnostic the next day and off and on eliminating flow areas were led to restriction in tank. Removing or sliding tank out and removing pick up tube more testing done with tube being examinied and cleaned put back in and more restriction and air testing led back to tank problem, so removed again and looking at pick up tube, discovered by measuring tube it was resting flat on bottom of tank. Cut off 1 inch of tube and replaced and to amazement fuel flowed great. On road test up to 85mph and 20 or so miles "no problem" ran great. Another $2000.00 and wondering if the Cummings Engine folks diagnostic work and repairs were even needed after this. I hope this is the end of this story, plan to not sit idle and do a little driving soon to see. Also the wire left off my temp. sending unit was found and replaced and temp gauge back working.
Whether you needed the pump work is a tough call. The injection pump can fail if there is a fuel restriction but finding the cause of the failure is as important as fixing it.

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Old 09-16-2019, 11:58 PM   #16
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Odd how this came down. 2004 is a long time for an engine to run without problems, when the fuel pickup tube was not providing any clearance from the bottom of the tank...

But between the new parts, and the shortening of the fuel pickup - you are running good now... So go have some fun,

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Old 10-30-2019, 02:41 AM   #17
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Kenny_Hughes: Did you experience any other symptoms or just poor acceleration.

This happened to me in the beginning. I thought it was time to change my fuel filters since I had 12,000 miles on them. And when I changed my fuel filters I was able to accelerate and travel over 35 MPH.

I have a 2004 Itasca Horizon 40AD with a Cummins-ISL-350HP engine and CAPS injection system. So while our engines are similar they are not exact.

Your other problems and nightmares are exactly what I experienced; and over time I found I was replacing fuel filters more often.

Then a year later my engine would start and then stop 1-2 minutes later. I even thought I might have a fuel tank venting problem for a while.

Finally, I was stranded in my Montana campsite... and after much effort and help from TR4 & BigLar368 I diagnosed my problem to be... 3 loose lift pump bolts... that broke the gasket seal at the Lift Pump Manifold... and that allowed air to be sucked into the line.

In a CAPS Injection Pump System: A stock Cummins (Carter Type) Lift Pump only runs for 30 seconds to prime the Injection Pump. Then a low pressure gear pump (which is part of the Injection Pump System) sucks fuel from the tank and passes fuel to the high-pressure side of the Injection Pump. Then in my CAPS system it goes to an Accumulator before metered fuel is distributed to each cylinder.

...and if you measure the vacuum pressure you will find it to read -4 or -5 PSI.

This is the minimum Cummins specifies for their ISC engine. Therefore, any vacuum leak in the lines will cause your your injection pump to loose fuel flow and time-and-time-again your injection pump will get starved fuel/lubrication... until one day it fails.

Thinking back to my symptoms/problems, I also know know cold temperatures can exacerbated the problem, because I had 2 incidents after a freezing night... when the next morning my engine would start and then stop about 1-2 minutes later.

...And when I changed my fuel filters, the day warmed up and the partial restriction in the 5,000 mile filter I just replace was removed. This allowed my injection pump to build up enough pressure to keep my engine running.

...And after my engine got hotter the air leak diminished and all was fine again, with one exception. Occasionally, my check-engine light would go on. But it would sometime go off after I pulled over; turned the engine off; and then turned the engine back on. What is this you ask? I think I'm describing a "Soft ECM Code". And while the ECM would clear the code it would sore it in my history.

This also lead me to replace my Key Ignition Switch which I also describe in this thread. And I recommend everyone do this after 75,000 miles or so as a preventative measure:

Why Did My Cummins ISC-350HP Motor Run Better After Changing The Key Ignition Switch

Note: Many will think replacing the key-ignition switch is unnecessary, but I have seen too many car/truck problem come about due to a worn-out key switch. And in my case, my RV key was getting "sloppy!" ...But I swear my engine was running stronger after I replaced my key switch.


FYI, I think it's hard to find anyone at Cummins who can rebuild these injection pumps anymore. Only the old mechanics know how the injection pump works and there was a day when they rebuilt them in the shop.

Of course, there was a day when a mechanic would rebuild alternators in the shop too, but those days are gone. In fact, the only reason I agreed to have Cummins replace my entire CAPS inject pump was because I did not trust their ability to overhaul mine. (Sad but true.)

Believe me when I tell you I really caused a stink working with Cummins in Colburg, OR and I will NEVER, NEVER GO THERE AGAIN!!! !!!! !!!!!

Also note: All the problems I mentioned above (and in the thread below) occurred after I replace my CAPS injection pump and ECM to the tune of $9,200.


I think in both our cases, our stock/OEM fuel delivery system operates "on the edge of failure." Sure an injection pump can last 50K or even 100K miles; and there are going to some who brag about how they are over the 200K miles and never had any problem with their injection pump. And to the latter, all I can say is: "You will."

These injection pumps are built to very tight tolerances and many of us our seeing hard failures at under 80,000 miles. The cost can be $6,000 to $10,000 and a lot of this is due the difficulty in getting to an injection pump in a Freightliner Chassis. You Spartan owners have it a bit better, but not much. Also, when your injection pump blow you often have to replace your ECM too. So don't forget that part!

This is because sooner our old fuel lines and/or Lift Pump and/or Lift Pump Manifold Gasket is going to develop a vacuum leak we cannot often detect. And we drive... And drive on. ...Check that!

Often the warning signs are there. We just don't pay attention to them! We ignore a check-engine light when it goes out, because we feel "lucky" when we dodge a bullet. We change our fuel filters prematurely and think we got a bad batch of diesel fuel. (NOT SO!) And yes... I bet sometime the mechanics replace parts unnecessarily, and then tighten your lift pump bolts, and then send you on your way. (Happy your engine is running again!)

...in my case all I needed to do was tighten 3-lift pump bolts and maybe none of my problems and nightmares would have occurred!

...And ULSD fuels are why many of CAPS owners use additives like Howe's or PS-Diesel.


Me and other CAPS owners are upgrading to a FASS lift pump. I wrote I ton about this subject here:

Cummins ISC - Engine Starts But Then Quits & Why We Upgraded To FASS TS Pump!!!!

I'm not saying and ISL-400 injection pump is identical to my ISC-350 injection pump. Maybe Smitty77 or TR4 can clarify that for us, but what I am saying is that I think the only real solution is to upgrade to a FASS or AirDog electric fuel pump.

Sorry to hear about your nightmare, but thanks for sharing!
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2004 Itasca Horizon ISK-40AD, ISC-350HP Cummins
... and the best of 3 Diesels I have owned thus far!
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Old 10-31-2019, 11:01 AM   #18
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Originally Posted by Smitty77 View Post
Odd how this came down. 2004 is a long time for an engine to run without problems, when the fuel pickup tube was not providing any clearance from the bottom of the tank...
My first thought as well.
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Old 10-31-2019, 10:20 PM   #19
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Wouldn't shortening the tube also mean you will run out of gas above the "E"? That is to say, if you know where your lower limit is, now it would be higher?

On only a few occasions have I got real close to the "E" so I'm guessing there is some downside to shortening the draw-straw. (Is that what we are talking about; or maybe I'm missing something?)

2004 Itasca Horizon ISK-40AD, ISC-350HP Cummins
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