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Cat Man
Cat Man, Cat Engine Expert
Category: Medium and Heavy Trucks
Satisfied Customers: 8330
Experience:  I am ASE Master Truck Certified.
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I called earlier today with a 3126 cat problem. the

Customer Question

I called earlier today with a 3126 cat problem. the gentleman tried to help but did not know much about chevy trucks.i still have not got truck to stay running. I had no power to ecm terminal so I ran a jumper to power it up. engine started right up, ran for about one minute and died. now have 2500 lbs.of hieu pressure and 60 psi fuel pressure and it won't start.
Submitted: 4 months ago.
Category: Medium and Heavy Trucks
Expert:  Cat Man replied 4 months ago.
Hey. That was me you talked to.
60 psi fuel pressure is plenty. So is 2500 psi heui pressure.
Here is a complete list of all the things that can cause your engine not to run.
To me it sounds like you may have a faulty ECM. I have seen many faulty ecms do this. Here is your list of items.The first is a low or no fuel pressure condition. The engine needs at least 25 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 on the back of the head or a weak fuel transfer pump. The pump is located on the back of the HEUI pump.Second is a low injection actuation pressure. This is the high pressure oil system that activates the injectors. The engine needs at least 870 psi to start. If it is low, you have either a failed Injection actuation pressure control valve in the HEUI pump, a weak HEUI pump, a high pressure oil leak at an injector, or a faulty Injection actuation pressure sensor. To test the sensor, just unplug it. If the engine starts, the sensor is bad. It has 3 wires and is located on top of the engine near the front and screwed into the head.Third is a failed engine speed timing sensor. Your engine has two. They are located on the driver’s side of the engine on the back of the engines front cover under the HEUI pump. The bottom sensor is the primary start sensor. If it has failed, the engine will be hard to start. The top one is the primary run sensor. They come as a pair.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.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.
Expert:  Cat Man replied 4 months ago.
It sounds like the injector driver module in the ECM has failed. Many times when this happens, the engine may crank and run for a short period of time then shut off and not start back.
If the injector driver module in the ECM has failed. The ECM will have codes for all 6 injectors. Unfortunately you must have the ECM read with a service tool to verify.
If the injector driver module has failed. It's not replacable. The ECM would need to be replaced.Please reply back if you need more help or have more questions. I am happy to assist.
Expert:  Cat Man replied 4 months ago.
Hello are you there?

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