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Cat Man
Cat Man, Cat Engine Expert
Category: Medium and Heavy Trucks
Satisfied Customers: 8414
Experience:  I am ASE Master Truck Certified.
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Mr Cat Man, Im in desperate need of some help as I have

Customer Question

Mr Cat Man, Im in desperate need of some help as I have never ran into this problem before. I have a c15 mbn engine that has been showing multiple injectors bad. Even after installing a complete set of new injectors i can run the test once and it may show #1 and #2 bad and the next time it may show #5 or #3. Its just really random. We have tried multiple injectors.....aftermarket which I have NEVER had problems and CAT OEM injectors also. We have install new injector wiring harnesses, new fuel transfer pump and tried multiple ECM that are identical to this one. Fuel pressure is good also. Can you give me any insight on this issue? It would be very appreciative and I guarantee a healthy tip if you can give me any help.
Submitted: 10 months ago.
Category: Medium and Heavy Trucks
Expert:  Cat Man replied 10 months ago.

Thanks for asking your question and requesting me. I will try and help you out.

I would like to ask you a few questions to better help me understand your problem. I hope that is OK.

When you say multiple injectors showing bad. Did you run a cylinder cut out test? Or are there codes for the injectors?

How does the engine run? Does it have low power or a miss?

Did it just start doing this one day? Or was there a repair done on the engine and then this problem started?

Customer: replied 10 months ago.

No codes. Only determine that by doing cylinder cutouts and by letting cat et run the injector test. When doing individual test some of the injectors hit but when I run the automatic test with et it may show the same ones that sound to be hitting good to be bad.

Engine has good power and only seems to be missing at an idle.

Truck originally kept blowing the tip seal on #6 injector. Customer had replaced that tip seal 3 times before it was brought to me. I don't feel the reoccurring tip seal blowing is related. I was thinking customer had just not cleaned the injector bore good.

Expert:  Cat Man replied 10 months ago.

Thanks for the information.

There are a few things I have seen cause this.

The first is to check that the correct 4 digit injector trim codes are programmed into the ECM. I have seen sometimes when they are wrong, it will cause the engine to run rough.

Second is a return line restriction. When there is a restriction it will cause the fuel in the head to get hit a aerate. This can cause the engine to run this way. I have seen injector o ring debris in the fitting on the back of the head, fuel line, and fuel pressure regulator.

Third is compression getting past an injector. To verify I like to install a clear sight glass on the fuel return line from the head. If it looks like beer foam. There compression getting past an injector.

Next is the parts department has given you the wrong injectors. I would double check and make sure they gave you the correct injectors.

Lastly is old software in the ECM. I have seen MBN engines with old software run like this.

Please reply back if you need more help or have more questions. I am happy to assist.

Expert:  Cat Man replied 10 months ago.

Hey. I just wanted to see how things were going. Please let me know if you need more help. I am happy to assist. If my information was helpful, please leave a good or higher rating so that I receive credit. Thanks.

Expert:  Cat Man replied 10 months ago.

Did you ever find the problem?

Expert:  Cat Man replied 9 months ago.

Hey. I just wanted to see how things were going. Please let me know if you need more help. I am happy to assist. If my information was helpful, please leave a good or higher rating so that I receive credit. Thanks.