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Old 10-18-2020, 07:56 AM   #1
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Diesel engine stumbles....

Our coach travels about 4000 miles/year, so it sits alot next to the house in the shaded yard. 150 gallon fuel tank is kept full, to the point that I add fuel until it dribbles out the fill-tube, in order to minimize air in the tank.

Fuel/Water separator has 5,000 miles on it and is two years old. I've loosened the drain nut on the bottom, and only diesel comes out.

Despite all of that, the coach began to stumble during our last drive up to Montgomery (no steep grades, level driving). I'll change the filter when I get a quart of fuel at the next diesel station, but what else can I look for in order to prevent this?

Oh, the CEL was On during the last hour of the drive. Engine oil is fine, all gauges read normal.
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Old 10-18-2020, 08:18 AM   #2
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Changing the Fuel/Water separator filter plus a biocide treatment will likely solve your problem.


If you have 2 fuel filters I would change both of them.



I use Valvtect Microbiocide which is available at most marine stores.
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Old 10-18-2020, 08:26 AM   #3
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Don't know what engine you have in your coach, but if it's a 2002 series Cummins ISC, check under your coach for diesel fuel spotting.

You could have a failing lift pump....notorious for these engines. One of the symptoms is what you're describing.
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Old 10-18-2020, 08:34 AM   #4
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I should have said that we have an ISL400 with 63K miles (2003 model), if an ISL is susceptible as well, would failure be immediate or gradual?

We can either go another 500 miles to finish our trip, or can divert and head home for a 200 mile route. What does the brain trust say about how severe a lift pump can be?
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Old 10-18-2020, 08:37 AM   #5
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Some have had lift pump leak as described above and tightening 3 bolts can help. The rubber gasket shrinks due to ULSD, the gasket only is conveniently discontinued . I'm not the expert other guys are on what years engines or chassis have what but I think this is gasket reproduced.
https://www.ebay.com/itm/122561159521
The injector pump sucking air is bad check any fuel residue at lift pump.Some swear by upgrading to Airdog or Fass lift pump systems to protect the injector pump.
CEL possible ,low coolant level in tank possible. Limp mode due bad sensor or reading.
Other less ordinary things engine brake sticking,poor air flow collapsed filter rodent/bird nest , blown or collapsed CAC/turbo hose.
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Old 10-18-2020, 08:47 AM   #6
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Yes, it happens on ISLs also. And as 153stars said, it's due to the ULSD and the contraction of the seals.

There is a lot of reading on the topic. I'm not sure if it's serial number related, but on the ISCs it was all of them.

Wish you luck and hoping for the best.
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Old 10-18-2020, 09:03 AM   #7
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Would you expect that it is probably OK for another 500 miles, or should we beat it back home and get it to a shop ASAP?


We felt it gradually, usually on an up-hill, but maybe 6 times in the last hour, with no symptoms for the first 3 hours.
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Old 10-18-2020, 09:07 AM   #8
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You have a Cummins CAPS fuel injection pump. Here’s a great thread to read, it explains a common problem with this pump.

https://www.irv2.com/forums/f123/rep...lp-289659.html

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Old 10-18-2020, 09:30 AM   #9
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I made edit in case you did see Sunday of course so going to be hard to read code
CEL possible ,low coolant level in tank possible. Limp mode due bad sensor or reading.
Other less ordinary things engine brake sticking,poor air flow collapsed filter rodent/bird nest , blown or collapsed CAC/turbo hose.
At least 20 people have been able to tighten pump bolts but dont fixate on one thing
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Old 10-18-2020, 09:32 AM   #10
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Would restriction or impending problems with the pump or CAPS be the cause of the CEL coming on?


Also, could I have a show of hands for whether you would choose to drive the coach either 200 or 500 miles in 75 degree weather on flat ground?

We have about 2 hours to make a decision.
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Old 10-18-2020, 09:37 AM   #11
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If you are able to locate the lift pump, inspect it. I suspect it is dirty and diesel soaked, maybe even dripping fuel to the ground. Not a lot of fuel, but enough to make a wet spot over a few hours.
If you can, use a 10mm socket on an extension to tighten the three bolts that have their heads pointing up. They hold the part of the lift pump that looks like a carburator bowl. I suspect those three bolts are loose and causing the lift pump to suck air. If left un attended, I have read that it will ruin the injector pump to the point of a costly replacement.
I replaced my lift pump for the same symptoms that you describe. The problem went away. It is not a hard job, just frustrating as there is very little wiggle room.
The pump is located on the passenger side of the MH near the front of the engine.

You asked if you should continue your trip or head home. That is a judgement call, either way, I would tighten the bolts before continuing. But, that is just me.
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Old 10-18-2020, 09:39 AM   #12
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Yes, you have the CAPS system on your engine and your symptoms are consistent with a failing lift pump or, a failing main injector pump. Lift pump runs around $400, main injector pump around $3000, and that's just for the part.

Your CEL light is on so that should be addressed immediately, IMO. Any truck service center or mobile tech can read the codes and tell you where the issue might be. The fact the CEL light is on also points to a more serious CAPS pump issue rather than a lift pump leak as it generally will not light unless the main pump is showing significant low injector pressures.

My advice, do not drive home without first getting the codes read. If they show probable issues with the main pump or injectors, any continued use could damage the main pump, if it has not already been damaged. Might be a bad injector which is much cheaper to repair than a whole new main pump.
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Old 10-18-2020, 09:45 AM   #13
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Forgot this one hidden inline filter/strainer again not sure of exact years but i think Freightliner was on list not sure if just the chassis if could be on spartan
https://www.irv2.com/forums/f26/the-...er-328852.html
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Old 10-18-2020, 09:48 AM   #14
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from above link
This happen to my brother dutchstar with the same Cummings. The same pattern or work and no fixes. He finally called his son back home and had him ask his mechanic Had he experience these problems before. Back up a little the call to Spartan chassis about any unknown filters they said no not in that model.
The mechanic back home call the service manager and told him exactly where the unknown filter is located. the tanks drop sterilized fuel was polished put back in the same scenario as above. His bill was little over $5600 total from all the different service areas he went to.
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