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I have 2003 peterbilt 378 with a c15 cat,unit turns over but…

i have 2003 peterbilt 378...
i have 2003 peterbilt 378 with a c15 cat,unit turns over but will not start,put ecm on a different truck,ecm ok,checked all power supply wires are ok i have a ck engine light but can not ,get into ecm.
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Answered in 3 minutes by:
11/4/2015
Technician: Cat Man, Cat Engine Expert replied 6 years ago
Cat Man
Cat Man, Cat Engine Expert
Category: Medium and Heavy Trucks
Satisfied Customers: 10,344
Experience: I am ASE Master Truck Certified.
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Thanks for asking your question. I can help you with this.

Since the yellow check engine light comes on, this indicates the engine ECM is receiving power and functioning. There are several things that can cause a crank no start on this engine.

The first is a low or no fuel pressure condition. The engine needs at least 35 psi to start. If it is low, the injectors will not get filled and it will not start. If the engine has a hand priming pump, and it gets stiff when operating it, the engine has enough pressure to start. If there is no hand priming pump, I would connect a psi gauge and measure the pressure. If the pressure is low, I would change the fuel filters first if you haven’t already. If it is still low, I would suspect a failed fuel pressure regulator in the secondary fuel filter housing, a weak fuel transfer pump, or restricted fuel inlet line. The pump is located on the front of the engine.

Second is a failed engine speed timing sensor. Some engine have one, some have two. It depends on your engine serial number. If the engine speed timing sensor has failed, the ECM gets an RPM/TDC signal and will not send AC to the injectors.

Next is low battery voltage to the ECM while cranking. The ECM must have at least 7.5 volts DC to operate. I have seen weak batteries or a poor connection cause low voltage. You could have a poor connection at the batteries or starter.

Next is a faulty engine ECM. The ECM has an injector driver module inside. This is what powers the injectors. If it fails, the ECM will log injector codes for all the injectors.

Lastly are worn injectors. Over time the injectors can wear if they have a lot of hours on them. To verify, I like to check AC to the injectors while cranking. You should have between 20-40 AC while cranking. If you do, and you have good fuel pressure, the injectors are worn. If you do not have 20-40 AC while cranking, you have either a failed engine speed timing signal, low power to the ECM while cranking, ot a failed ECM.

Most often when these things are happening there will be diagnostic codes in the ECM. If your engine has cruise control switches, you can pull the codes. If you have never done this, let me know. I can get you the procedure.

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

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Customer reply replied 6 years ago

unable to get ecm to communicate with lap top

Technician: Cat Man, Cat Engine Expert replied 6 years ago

i see. Thanks for the information.

Have you checked the power on pins 52,53 and 70? The grounds are 65-67. 70 is the key switch wire. 52-53 are unswitched.

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Customer reply replied 6 years ago

yes I have power at pins 52,53 and key power at 70 grounds are good

Technician: Cat Man, Cat Engine Expert replied 6 years ago

Thanks for the information. If the ECM ran on another truck and you have good power and ground. You must have a problem with the data link wires that run from the ECM to the data connector causing your tool not to communicate. However a communication problem will not cause a no start. You most likely have a problem with one of the items I mention before causing the no start.

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

Cat Man
Cat Man, Cat Engine Expert
Category: Medium and Heavy Trucks
Satisfied Customers: 10,344
Experience: I am ASE Master Truck Certified.
Verified
Cat Man and 87 other Medium and Heavy Trucks Specialists are ready to help you
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Technician: Cat Man, Cat Engine Expert replied 6 years ago

Please get me you phone number please.

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Customer reply replied 6 years ago
tom
Technician: Cat Man, Cat Engine Expert replied 6 years ago

Calling now.

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Customer reply replied 6 years ago

no ac current to injectors

Technician: Cat Man, Cat Engine Expert replied 6 years ago

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

If there is no AC to the injectors. I must suspect low DC voltage to the ECM while cranking. I know you have tested for power on the correct pins. But if the voltage to the ECM drops down below 7.5 volts while cranking. The ECM will not have enough power to function. This low voltage can be caused by a starter pulling to much amperage, a poor connection on the battery terminals or starter. Could also be poor connection on power wires to ECM.

To confirm I like to supply the ECM with a separate 12 volt power supply. Cat makes a bypass harness to do this with.(###) ###-####is the part number. If the engine starts with the bypass on the ECM. You'll know the problem is low DC power while cranking.

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Customer reply replied 6 years ago

replaced battery wires to ecm fired up .thanks for your help.

Technician: Cat Man, Cat Engine Expert replied 6 years ago

You are very welcome my friend. I am happy I could help.

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