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I have a 2001 freightliner FL70 with cat 3126 wont start…

Customer Question
I have a 2001...

I have a 2001 freightliner FL70 with cat 3126 wont start check engine light and glow plug light flash intermittantly

Mechanic's Assistant: What's the make/model/year of your truck? Engine type?

2001 Freightliner FL60 with cat 3126

Mechanic's Assistant: Are you fixing your truck yourself? What have you tried so far?

Have found low voltage to starter replaced starter and cables, verified voltage, checked pressure at HEUI pump, checked power at ECM and yes fixing my self

Mechanic's Assistant: Anything else you want the truck mechanic to know before I connect you?

Not at the moment

Submitted: 3 years ago.Category: Medium and Heavy Trucks
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Answered in 8 minutes by:
2/1/2019
Technician: Cat Man, Cat Engine Expert replied 3 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 you 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 3 years ago
My computer is unable to connect to the ecm constantly, sometime does sometimes does not, also the truck does not have cruise control, voltages are proper and the check engine light flash with the glow plug light the whole time
Technician: Cat Man, Cat Engine Expert replied 3 years ago
It’s best to be able to read the ecm for codes. It’s the best way to troubleshoot
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Customer reply replied 3 years ago
Unfortunately we are unable to read codes in any capacity, cannot recognize or connect to the ecm, yet it is responding to rpm while cranking, however during cranking the tack recognizes then stops and continues to go back and forth
Technician: Cat Man, Cat Engine Expert replied 3 years ago
I see. Thanks for the information.
I would try a bypass harness to the ecm to read codes. Are you using Cat ET software?
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Customer reply replied 3 years ago
Where can I find a break out harness and why would the taco go up and down cranking
Technician: Cat Man, Cat Engine Expert replied 3 years ago
Cat sells the harness. The part number is(###) ###-####
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Customer reply replied 3 years ago
What about the tach? Unlike normal during cranking it reads rpm then loses it reading, tach goes up and down?
Technician: Cat Man, Cat Engine Expert replied 3 years ago
Tacos can be misleading. In a situation like this I would prefer to watch rpm on a service tool.
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