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Cat Man
Cat Man, Cat Engine Expert
Category: Medium and Heavy Trucks
Satisfied Customers: 8725
Experience:  I am ASE Master Truck Certified.
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I have c7 acert that will not start. The truck came to the

Customer Question

i have c7 acert that will not start. The truck came to the shop running. It was brought to us because it needed the sensor harness replaced. we put the new one on and it would not start. So we put the old one back on and it still wouldn't start. We put the new one back on and now we are just trying to figure out what to do next. when I crank the engine it just barely runs for about 3-5 seconds smokes like crazy and then dies
rpm 667
inj actuation psi 1841
inj actuation output 76%
fuel psi is 20-30#
Submitted: 2 years ago.
Category: Medium and Heavy Trucks
Expert:  Cat Man replied 2 years ago.
Hi. Thanks for asking your question and requesting me. I will try and help you out.
Does the engine have any diagnostic codes in the ECM?
Customer: replied 2 years ago.
NO
Expert:  Cat Man replied 2 years ago.
Thanks for the information.
Since there are no codes, there are several things I have seen cause this.
The first is bad or poor quality fuel in the engine. Could be water or a mix of gasoline. I would check this first.
Second is a massive inlet restriction. If you havent already I would remove the intake piping.
Third is a engine speed timing sensor problem. They could be plugged up backwards. If one pushes hard enough they can plug up backwards. I have also seen them get rpm but not TDC. To verify I like to check AC to the injectors while cranking. If there is no AC, there's no good rpm and TDC signal.
Next is damaged injectors. They normally do not all fail at once unless bad fuel or water went through them or metal from the Heui pump contaminated them.
Lastly is a faulty ECM.
Please reply back if you need more help or have more questions. I am happy to assist.
Customer: replied 2 years ago.
THE FUEL IS GOOD
ALL THE INTAKE PIPING IS OFF
WOULD IT WANT TO START IF THE SENSORS WERE PLUGGED IN BACKWARDS
I WILL CHECK THE AC AT THE INJ
I'VE ALREADY TRIED A DIFFERENT ECM FROM ITS TWIN AND GET THE SAME RESULTS. I DID JUST HOOK UP TO ANOTHER KAL ENGINE AND MONITORED THE HEUI PSI WHILE IT WAS CRANKING AND IT SPIKED TO 2666PSI BEFORE IT STARTED. THE DEAD TRUCK NEVER GOT ABOVE 1750PSI
Expert:  Cat Man replied 2 years ago.
Thanks for the information.
Yes if they are backwards it will still try and start. The timing will be way off.
1750 is plenty of actuation pressure to start. The engine only needs 870 to run.
Let me know if you have Ac to the injectors while cranking.
Customer: replied 2 years ago.
HOW MUCH AC SHOULD THERE BE
Expert:  Cat Man replied 2 years ago.
Normally there is 20-40 AC during cranking.
Customer: replied 2 years ago.
AC IS ABOUT 15 ISH
Expert:  Cat Man replied 2 years ago.
That should be good enough. If the ECM was not firing injectors. There would be none.
Is starting to sound like an injector problem. If you have fuel pressure, good Actuation pressure, and power to the injectors, all that's left is failed injectors.
Unfortunately the only way to verify is to replace a couple of them. If the engine starts and runs on them. You'll know for sure its the injectors.
Expert:  Cat Man replied 2 years ago.

Hey Dan,

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!

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