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Cummins ISX problems

Question:
Hubby's been having problems with this engine off and on for several months now. It will run fine for weeks and all of a sudden starts spitting and sputtering, smoking, will run no more than 45 mph. The check engine light comes on when this is happening.
First time it happened, the company told him to add some fuel treatment and see if that helped. It did. A couple other times at the first sign of running rough, he added fuel treatment and it seemed to help. BTW, fuel filters are changed every 20,000 mi or so.
Last week the problem started up again. He added fuel treatment and this time no go. The car was due for a service so he took it in. They changed air filter also. It ran good for a few hours until we stopped for the night and shut it off. Upon starting the next day, same old problem was back. BTW, car idles smoothly (as smooth as an ISX can apparently) only gives probs under load.
He took the car to Kenworth and they said the codes were indicating a bad fuel pump. They said the fuel pump was only putting out about half pressure. So they changed it and also did the overheads while we were there (390,000 miles). The car then ran like a dream, never heard that engine so quiet. It idled much smoother, had a lot more power.
That lasted until yesterday. We sat for a few hours without idling and when we got ready to pull out of the parking lot, no go. It was doing the exact same thing as before. Hubby drove down the road a few exits in hopes it would smooth out but no go.
He took it to the only close shop, a TA where they checked a few basic things like to see if the fuel line was sucking air, the air to air clamps, and the turbo and said all looked fine. However, they dont have the equipment to diagnose the engine codes for Cummins. BTW, it magically fixed itself this time but its done that before too.
He plans on taking it to company shop ASAP to let them have the headache or get another car because this is just too unpredictable and is getting old.
One thing I have noticed is a link between times it is shut off for a period of time and allowed to cool off and the rough running. At least twice I know of that was the case immediately before the problems, a lengthy time of not running.
Any suggestions since it doesn't look like the mechanics have made any progress so far?

Answer:

At my company, most ISX motors need the fuel filters changed at 15k mile intervals. The ISX motor really heats up the returning fuel, and this creats a lot of deposits in the fuel filters. But, since I'm sure you changed the filters, then we'll go onto problems # 2 an #3:
The second problem is with the EGR valve. These tend to fail at somewhere over 300k miles, and they give just the sort of engine problems as you describe. It may be this, and/or the next problem.......
The pressure differential tubes often become clogged in motors over 200k miles. These are the 2 tubes way down in front, bottom of the motor. They carry hot gasses, but they were not insulated in the early versions, which allowed condensation and gunk to form in them. Once they get clogged, the same problems will happen. They might need to be cleaned, or completely replaced.
You need to go to a Cummins shop that has an ISX certified technician. If you call Cummins RLS at 800 233 7373, they can tell you where you can take it.
BTW, I wouldn't trust any TA shop with anything more complicated than a brake job. I deal with TA shops every day at work, and they range from mediocre to awful. Go there for tires, oil changes and brake work, but nothing else. Even Petro shops are better, and that ain't saying much!!
(P.S.-my company fleet has nearly 1000 ISX motors, from 2003 to new, so I'm about as close to an expert on ISX breakdowns as you'll find on this board.)

Answer:

Thanks for the tips. I read some of your earlier ISX posts and saw some things on the topic but wasn't sure of symptoms EGR valve or tubes could cause.
Yes, we did change the fuel filter. That seems to be the first thing our road service people are quick to suggest, that and fuel treatment..
You gave us two good possibilities to suggest to shop next time we get in there.
Another question though? Would any of the above conditions cause a fuel pump or fuel system code? Of course, we dont know the engine is giving the SAME code as the one before the fuel pump was replaced but the engine is definitely acting the same.
I'm not a mechanic but makes sense to me if something was preventing fuel reaching the fuel pump it could cause a fuel pump code and also show low pressure from the fuel pump?
BTW, Kenworth did the overheads and fuel pump replacement. The company had us go to TA for help the other night since there was nobody else open on the weekend within miles of us.

Answer:

what do you think. do they work and what brand would be the best to go on a t600 kw n14.here in oz they are unheard of.thanks for any input.

Answer:

I had one of my 2004 T600's act up like that , turned out to be a faulty ECM after countless filter , fuel pump changes, change this try that they replaced the ECM reset everything to factory settings and that CUMMINS is HUMMIN along

Answer:

injector selonoid,
i have an N-14 that acts the same way, but it doesn't spit out any codes, so after discussing the problem with a cummins mechanic, we have determined it to be a faulty selonoid on an injector,
but mind you the ISX and N-14 have a different set-up, the selonoid is mounted on the side of the block on the ISX,on the N-14 it is part of the injector itself

Answer:

I have an ISX Signature 600 and have had a similiar experiance.
I had the check eng. light come on all of a sudden one day, and the car just stopped running.. like it was out of fuel. Apon closer examination, I had a flash code that said I had low fuel pressure (or somthing like that ,I had to call the cummings 800 hotline to get an explaination of the fault code as the manual in the car does not list the codes like Detroit does .... Go figure.. ).
I found that the supply line going to the fuel pump was the culprit. There was black tar like substance in the opening. I had to put a flashlight in there to see it. I took a small jewlers screw driver and picked out a fair amount of junk from there.. It's almost like seaweed, or decayed leaves.. slimey and dark brown / black...
I was told by Cummings that this is caused by thefuel being heated. The ISX's fuel gets abnormaly HOT! Any fuel will eventualy do this.. Earlier engines had a screen in the inlet and I was advised "to remove it and throw it over my right shoulder " if I still had one..hehe (I didn't have the screen).
I got it reprimed and it ran better than ever after... It still runs like a scalded dog now... I think this was partialy restricted since I bought the car because it has never ran so good! Ya might want to check this out on yours??
(I use nothing but Fleetguard filters, and change all filters at 12,000 mi. along with the oil).
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