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99 3126 cat no start. Have 2 identical trucks, been swapping…

99 3126 cat no...

99 3126 cat no start

Mechanic's Assistant: How long have you had problems starting the vehicle? Do any lights still turn on?

Have 2 identical trucks, been swapping parts, swapped ecm, injectors, has new high pressure pump, 950 psi oil pressure while cranking, new sensor harness, new rpm sensors in front cover, no start

Mechanic's Assistant: What's the make, model, and year of your truck?

99 sterling with 3126 cat

Mechanic's Assistant: Is there anything else the truck Mechanic should know before I connect you? Rest assured that they'll be able to help you.

We have cat ET, rpm reading comes up to 38 while cranking, no higher

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Answered in 4 minutes by:
12/16/2021
Technician: Cat Man, Cat Engine Expert replied 11 months 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 you question. I will try and help you out. 

So you are able to communicate with the ecm? Are there any codes?

Does the yellow check engine light come on when the key is turned to the on position?

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Customer reply replied 11 months ago
One active code, engine speed signal not performed, sensors and harness are newOne status flag, no engine speedEcm works on different truck just fineWhen cranking, engine speed according to ET goes straight to 38 rpm no higher
Technician: Cat Man, Cat Engine Expert replied 11 months ago
Thanks for the information. 

Sounds like you have an rpm/tdc issue. I would suspect the  cam gear may have walked off the cam. When this happens. The ecm will not receive an accurate signal.

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

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Customer reply replied 11 months ago
I have front cover off now, cam gear is on like it should be. That was my initial thought also
Technician: Cat Man, Cat Engine Expert replied 11 months ago
Thanks for the information. Have you checked power to the injectors while cranking?
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Customer reply replied 11 months ago
We have done a solenoid check with ET all click as they should, but what is the best way to check them while cranking? Because I dont think they are firing
Technician: Cat Man, Cat Engine Expert replied 11 months ago
I like to remove the 12 pin connector going to the valve cover. While cranking you should see 20-40 ac while cranking. If you do not. You have either low power to the ecm, bad ecm, no rpm signal, or low actuation pressure. 

If you do have AC while cranking. The injectors are faulty or you have bad or contaminated fuel.

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Customer reply replied 11 months ago
I believe it is rpm signal, 6 injectors run fine in other truck, ecm runs other truck, timing sensors and sensor harness new from cat. Still only shows 38 rpm. Oil pressure is 1100 to 1200 psi when cranking. Checking ac voltage now40 voltsWont even smokeAny ideas?
Technician: Cat Man, Cat Engine Expert replied 11 months ago
I would suspect a compression problem in each cylinder. Most likely the engine has been overspeed and slapped all the valves. That’s the only way to explain good power to the injectors and good injectors.
Cat Man
Cat Man, Cat Engine Expert
Category: Medium and Heavy Trucks
Satisfied Customers: 10,344
Experience: I am ASE Master Truck Certified.
Verified
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Customer reply replied 11 months ago
Even when we give it a little brake clean, (we dont use ether, and pre heater disconnected) the rpm reading jumps to 38, and never goes higher.
Customer reply replied 11 months ago
We figured it out, not compression problem
Technician: Cat Man, Cat Engine Expert replied 11 months ago
Great
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