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Cat Man
Cat Man, Cat Engine Expert
Category: Medium and Heavy Trucks
Satisfied Customers: 8768
Experience:  I am ASE Master Truck Certified.
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Cat 3126 cranks but no start new high pressure pump new sensors

Customer Question

Cat 3126 cranks but no start new high pressure pump new sensors new solenoid ecm has all power to 3 pins two constant and one key switch and grnd on two pins
Submitted: 2 years ago.
Category: Medium and Heavy Trucks
Expert:  Cat Man replied 2 years ago.
Hi. Thanks for asking your question and requesting me! I will try and help you out.
I would like to ask you a few questions first to better help me understand your problem. I hope that is OK.
Does the yellow check engine light come on when the key is turned to the on position?
Do you know if there are any codes in the ECM?
Do you have a service tool to read the ECM?
Customer: replied 2 years ago.
Check eng light comes on there were injection actuation pressure sensor codes and the pump was reading 200 psi with gauge dead heading pump so I changed the pump
Expert:  Cat Man replied 2 years ago.
Thanks for the information.
How much pressure do you have now?
Customer: replied 2 years ago.
Now check eng light does not come on
Expert:  Cat Man replied 2 years ago.
Thanks for the information. The light should come on everytime the key is turned to the on position.
If the yellow check engine light does not come on when the key is turned to the on position and the engine will not start, there are only 2 things that can cause this.
The first and most common is the engine ECM is not getting the correct power and ground to function. The ECM should have power on pins 52, 53, and 70 of the rear most ECM connector. This is the truck side harness connector. 70 is the key switch wire. The grounds are on pins 65 and 67. You can remove the connector and check for power on these pins. If you do not have power on these pins, you most likely have a blown fuse in the electrical system. I would check all fuses first.
If you do have correct power and ground to the ECM, you most likely have a failed ECM. I have seen this many times over the years. To confirm the ECM is bad, you would need to install a known good ECM on the engine or you can take the ECM to the dealer to be tested. Unfortunately the ECM cannot be repaired. Replacement is the only option. I am sorry. I wish I had better news.
Please reply back if you need more help or have more questions. I am happy to assist.
nks for the information.
Customer: replied 2 years ago.
Now there is no keyed power anywhere
Expert:  Cat Man replied 2 years ago.
I see. If there is no power. There is most likely a blown fuse.
Customer: replied 2 years ago.
Starter was changed last week
Expert:  Cat Man replied 2 years ago.
So the engine spins over but does not start?
Customer: replied 2 years ago.
Now there is nothing then it comes back and cranks but then it loses power and does nothing again
Expert:  Cat Man replied 2 years ago.
Thanks for the info.
That sounds like a poor connection somewhere. Possibly at the batteries or at the starter.
Customer: replied 2 years ago.
Powers good now cranks no check engine light coming on but instrument cluster says no eng
Expert:  Cat Man replied 2 years ago.
Thanks for the information.
If you have power to the ECM and the instrument cluster says no eng, you most likely have a failed engine ECM. I am sorry. I wish I had better news.
Customer: replied 2 years ago.
No grnd at 65 67
Expert:  Cat Man replied 2 years ago.
I see. Thanks for the info. If there is no ground you could run your own new ground.
Customer: replied 2 years ago.
Found some bad grnds and now check eng light comes back on but still no start I have like 100 psi on fuel pressure and I have 1500 psi on the high pressure oil pump
Expert:  Cat Man replied 2 years ago.
Thanks for the information.
That is plenty of fuel and actuation pressure. There are only 3 other things that can cause this.
The first is no TDC signal from the timing sensors. To verify, I like to check AC power going to the injectors while cranking. You should have over 20 AC while cranking.
Second is a faulty ECM. If the ECM has failed there will be codes for all 6 injectors.
Third is failed injectors. Failed injectors are very rare unless contaminated fuel has entered them.
You can also try and pull the flash codes by using the cruise control switches. If you have never done this, here is how.
Use the following procedure to retrieve the flash codes from the check engine light:
1. Turn the ignition key switch to the On position/ Engine OFF.
2. Turn the cruise control ON/OFF switch to the OFF position.
3. Move the SET/RESUME switch to either position. Hold that position until the yellow lamp begins to flash.
The yellow lamp will flash in order to indicate a two digit flash code and the SET/RESUME switch may be released. The sequence of flashes represents the system diagnostic message. Count the first sequence of flashes in order to determine the first digit of the flash code. After a two second pause, the second sequence of flashes will identify the second digit of the flash code.
Any additional flash codes will follow after a pause. These codes will be displayed in the same manner. Flash Code 55 indicates that No Detected Faults have occurred since the ignition key switch has been turned to the ON position.
Let me know what 2 digit code you get and I can tell you what the problem is.
Customer: replied 2 years ago.
The timing sensors were put in on Thursday I'm gonna try a test ecm this morn then I'll do the codes if that doesn't work I'll let you know thanks
Expert:  Cat Man replied 2 years ago.
OK Sounds Good. Let me know if you need more help.
Customer: replied 2 years ago.
Flash code 28 56 49 42
Customer: replied 2 years ago.
48
Expert:  Cat Man replied 2 years ago.
Thanks for the information.
Code 28 is an throttle position sensor fault. This can not cause the engine not to start.
Code 56 is Customer system parameter fault. This indicates there are setting in the ECM that are not programmed. Depending on which ones they are, it could cause a no start.
Code 49 is an inlet heater fault. This can not cause a no start.
Code 42 is an engine speed timing calibration fault. This can not cause a no start. But could indicate an ECM problem because there is a code 56.
There is no code 48. Sorry.
Due to the code 42 and 56, you may have an ECM problem. They have been known to lose memory sometimes and cause a no start. To verify, you would need to have someone connect Cat ET and read the ECM.
Let me know if you need more help.

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