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I have a 1999 gmc 6500 with a cat 3126 7as64272 will crank

Customer Question
fine but will not start...
i have a 1999 gmc 6500 with a cat 3126 7as64272 will crank fine but will not start starts on ether check light comes on but air inter lights not working i check the solenold has power on one side + side check it off the engine clicks on and off outstide power source i probed the 2 wires going to solenoid while on engine has voltage on one side so i probed the other small wire to ground solenid kick on and light on dash crank eninge while probeing still no start does the ecm control the air intake solenoid
Submitted: 4 months ago.Category: Medium and Heavy Trucks
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Answered in 6 hours by:
7/26/2017
Technician: Cat Man, Cat Engine Expert replied 4 months ago
Cat Man
Cat Man, Cat Engine Expert
Category: Medium and Heavy Trucks
Satisfied Customers: 9,013
Experience: I am ASE Master Truck Certified.
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Thanks for asking your question. I will try and help you out.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 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.
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Customer reply replied 4 months ago
none of this answered my question about the intake heat solenoid
Technician: Cat Man, Cat Engine Expert replied 4 months ago
The ecm controls the inlet air heater. But if it's not working. It will not cause a no start. The heater is only for smoke reduction for emissions.
The truck sends 12 volts to the heater relay all the time. To turn on the heater the ecm just supplies a ground.Please reply back if you need more help or have more questions. I am happy to assist.
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Technician: Cat Man, Cat Engine Expert replied 3 months ago
Hey. 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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Cat Man
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