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C9 missing

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Ken Sair:
I am experience an engine missing under certain conditions and am looking for ideas. 18 months ago I had a fuel injector on my C9 replaced. The symptoms were coach shudder under trhe slightest acceleration. Turned out the #4 cylinder fuel injector failed.

Then in march 2009 we were coming out of the Sierra Madre mountains in Mexico and used the exhaust brake exstensively for many miles. Upon reaching the bottom, and accelerating, I experienced the same MH shudder as when the fuel injector failed. Any attempt at acceleration caused the whole coach to shake. Again, it felt as if it was running on 5 cylinders. About 15 minutes later (with light acceleration) the symptoms disappeared.

Fast forward to last week (11 months later). We were coming into San Diego on I-8. There is a long stretch of over 13 miles with 6% plus grades. I used the exhaust brake extensively and all worked well. Again, at the bottom I accelerated and the coach began to shudder again. It had not done so for the past 11 months. Anyway, I limped it along for a few miles till I arrived at my destination and turned it off. 45 minutes later, we went to leave and all was well. We parked for a week and left today heading to Temecula. About the 10th hill (again, using the exhaust brake on the downhills) I accelerated and damned if it didn't shudder upon acceleration. Same symptoms, like it was running on 5 cylinders. I limped it to the next offramp and called CAT hotline who put me in touch with a Freightliner business in Fortuna CA. After a brief rehash he felt it was the fuel pump failing. he could not explain why it kinda fixed itself after setting for a half hour. Anyway, I was on hold with parts for over 30 minutes. Got fed up and decided to head to the campground. After 45 minutes the coach started and ran just fine.

Its done this twice in the last week. It then 'repaired itself' after setting for 30-45 minutes. The symptoms are identical to when the fuel injector faild 18 months ago. I am getting no engine lights etc. All temps and guages are normal. I checked the filters and no water was found. The problem is occuring after long extended use of the exhaust brake but goes away after a brief rest period.

If anyone has ideas, I'm listening. I will be taking it to CAT and check for computer codes. Just like to go in educated.

tx, Ken

Daryl Beck:
Could it be that the exhaust brake is not opening fully and causing the miss you are describing?  :)

Ken Sair:
The exhaust brake works fine. Turns off and on like always. Its after I turn if off after a long downhill and accelerate that the engine misses.

Edward Buker:
It seem like your problem is repeatable enough that you should be able to make it happen. I would consider getting hold of an IR gun and see if you can get a reading on each port of the exhaust manifold from the rear hatch. You could try this measurement with your engine at idle to get the technique down, then hot and operating normally. If you get the problem to reoccur you can then measure and see if one port is significantly lower in temp. That would most likely indicate an injector problem with one cylinder. Your symptoms are repeatable enough that someone at Cat should have seen this and have a definitive answer. I would be inclined to go to one of the largest Cat truck dealerships near you. They would have far more insight than most Freightliner dealers. If you are interested in trying the IR gun there are some at this site. One that has a decent high temp range up to 932F for $67 which seems reasonable. I have been told that a symptom of a failing pump is surging at idle and low RPM range. I'm sure there are other symptoms that I am unaware of. Wagner Cat truck dealership in Denver has an excellent trouble shooting team from my experience. Might be worth a call. Hope this helps.
http://www.arizonatools.com/tools/temperature-guns-and-probes/?gclid=CJXU6tephaACFRy4sgodRCO9mQ

Gerald Farris:
Ken,
From the symptoms that you described, it sounds like a fuel delivery related problem to me, but that is just a guess. I would say that the highest probably would be an injector, followed closely by a pump problem.

The Caterpillar repair shop should be able to tell what the problem is by reviewing the ECM (Engine Control Module) history if any fail codes were set. The down side is, if there are no codes set in the ECM  they might have to duplicate the problem to fix it.

A restricted fuel filter can cause an engine miss, but I assume that you have changed it, especially if you were in Mexico when the problem started.

Gerald  

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