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I am upgrading my 90 KW truck from the early (3176) 40 pin…

I am upgrading my 90...
I am upgrading my 90 KW truck from the early (3176) 40 pin rectangle ecm plug to a 2002 70 pin C-12. The ecm plug that came with the takeout engine only uses to of the 101 power inputs in ports 52 and 53. Also only uses two grounds (229) ports 65 and 67. I hooked up my signal return wire (old harness wire 6202) to port 5 and unhooked it from the ground stud. The diagram for the 70 pin harness did not show it conected to ground. I then rewired the TPS with the power input from port 4 so it would use 8v instead of 12. Last Hooked up the clutch and brake signal wires to ports 22 and 45. last I hooked port 70 to the key switch. After that....No start. Not sure what I am missing. The old engine used a flywheel sensor in the bell housing. Is this the crankshaft position sensor. The c-12 didnt come with one in the bellhousing. Is it somewhere else?
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Answered in 10 minutes by:
11/24/2012
Technician: Cat Man, Cat Engine Expert replied 9 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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Hi. Thanks for using JA! I will try and help you out

The C12 has two engine speed timing sensors. One on the crank and one on the cam.

The C12 does not use a sensor in the bell housing.

Did you wire up the check engine light wire?

If so does the engine light come on when you turn the key to on?
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Customer reply replied 9 years ago

I have not hooked that up yet. I will in the morning.

Technician: Cat Man, Cat Engine Expert replied 9 years ago
I see. Thanks for the information.

I always like to ask because if the light is coming on, I know the ECM is functioning


It sounds like you have correct power to the ECM. Power is on 52,53, and 70. Grounds are 65 and 67.

If you power is correct the next thing is the light coming on. If it does, the ECM is functioning. Then all that is left is an engine speed timing signal. Then it should run.

You could check while cranking if the injectors are getting AC. If they are, the electronics are OK.


If they are not, the ECM is faulty or its not getting an engine speed timing signal.

Please reply back if you need more help or have more questions.
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Customer reply replied 9 years ago

No engine light. I grounded the harness side and the light works fine.

Technician: Cat Man, Cat Engine Expert replied 9 years ago
Thanks for the information.

If the light is not coming on and we know the ECM has correct power and ground, it sounds like there may be a problem with the ECM. I have seen this before. Sorry. I wish I had better news.


Let me know if you need more help.
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Customer reply replied 9 years ago

This was supposed to be a running take out, for the sake of not ruining a new computer, can you see that I might of miss wired this one.

Technician: Cat Man, Cat Engine Expert replied 9 years ago

I have run many engines out of chassis and powered up the ECM's to run the engine. All the ECM needs to run is power on the pins you have power on. 52, 53, 70.

 

As long as it has power, then gets an engine speed timing signal, the engine should run. There isn't anything else that can keep it from running. I am sorry.

 

It is possible that the ECM has just lost its memory. I have seen this several times over the years. You may be able to have the ECM reprogrammed. Many times the backup battery inside the ECM has failed and when power is removed from the ECM, it goes blank. When this happens, the check engine light will not come on.

 

Unfortunately, when the check engine light does not come on, it mean no power to the ECM or a blank/failed ECM.

 

I am sorry. I wish I had better news.

 

Let me know if you need more help. I am happy to assist.

Cat Man
Cat Man, Cat Engine Expert
Category: Medium and Heavy Trucks
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Customer reply replied 9 years ago

Still scratching my head. I unhooked all wires but the three powers, two grounds, and the eng. light. Engine light now comes on w/ the key and flashes every 6 seconds. Still no start, No attempt, Not even smoke.

Technician: Cat Man, Cat Engine Expert replied 9 years ago
Thanks for the update.

Have you checked to see if there is AC power going to the injectors while cranking? Normally there is 20 to 30 AC going to the injectors. If there is power going to the injectors, the electronics are OK.
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Customer reply replied 9 years ago

Going to do that. Thanks, 20-30V AC with injector plugged in?

Technician: Cat Man, Cat Engine Expert replied 9 years ago

Yes. I like to do this when I have an engine that is not starting. If there is no voltage while cranking, there is an electrical problem. If there is voltage, the electronics are OK.

 

Let me know what you find.

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Customer reply replied 9 years ago

It must be Monday! I'm off to town in the morning for a starter. Before it quit it seem to be only flashing about 2 or 3 volts.

Technician: Cat Man, Cat Engine Expert replied 9 years ago
So when you checked it, there was only 2-3 volts?
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Customer reply replied 9 years ago

Ok, so now I have a new starter and batteries, I was thinking that the starter draw was to much for the old weak batteries. But no... still 2 V Ac while cranking good.

Technician: Cat Man, Cat Engine Expert replied 9 years ago

Thanks for the update.

 

If you are getting 0 volts before cranking, then getting 2-3 while cranking. It sounds like the ECM is trying to start the engine.

 

It is possible that while cranking that the voltage to the ECM is dropping to low. If the voltage to the ECM goes below 7 volts while cranking, the ECM cannot function.

 

You may want to hold a DC meter on one of the power wires and see how low it is going.

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Customer reply replied 9 years ago

That's what I was thinking with the slow cranking starter and weak batteries. But now with new I'm holding about 10 volts while cranking. While cranking it flashes about 2 volts.

Technician: Cat Man, Cat Engine Expert replied 9 years ago

Thanks for the information.

 

When you say it is holding 10 volts, where are you checking this at?

 

Are you checking it on one of the power wires to the ECM?

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Customer reply replied 9 years ago

I will check that, I was going off the dash gauge.

Technician: Cat Man, Cat Engine Expert replied 9 years ago

No problem.

 

I always like to check it at the power at the ECM.

 

I know you have good batteries and starter, but there could be a low voltage condition caused by one or more of the power wires going into the ECM. It could also be caused by a poor connection or corrosion on one of the wires.

 

 

Let me know what you find.

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Customer reply replied 9 years ago


It had a leaking fuel pressure regulator. Runs good now. Thanks for your help.

Technician: Cat Man, Cat Engine Expert replied 9 years ago
That is great. I am glad you got it fixed. Great Job!
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