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How is your service priced? Cat 3126 in '99, Trying to! New…

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Mechanic's Assistant: What is the complete model and serial number of your machine?

Cat 3126 in '99

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

Trying to! New speed/timing sensor, new fuel transfer pump, checked power to ecm (from harness side), pin 70 has 9.8 to 10 volts when cranking, Fuel restrictor at back of head works, with no sign of metal fragments. Also, sprayed contact cleaner on both ECM pins and sockets. This cat 3126 is in '99 GMC. Engine serial #7AS79444. Oh, cannot check flash codes as vehicle does not have cruise control.

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

That's enough for now. Was curious about the cost of your service.

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Answered in 3 minutes by:
12/2/2016
Technician: Cat Man, Cat Engine Expert replied 6 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.
Verified
Thanks for asking your question. I will try and help you out.
Can you elaborate on your problem. Is it a crank no start condition?
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Customer reply replied 6 years ago
Crank no start. Did you get the information I submitted a few minutes ago or do we need to start over?
Technician: Cat Man, Cat Engine Expert replied 6 years ago
I did. Thanks for the information.
Does the yellow check engine light come on when the key is turned to the on position?
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Customer reply replied 6 years ago
Give me 5 minutes and I will check.check engine light comes on when key is turned.
Technician: Cat Man, Cat Engine Expert replied 6 years ago
OkThanks for the information.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 6 years ago
The following has been installed or performed: new fuel transfer pump, new speed/timing sensor pair, new fuel filters, good voltage to ECM injectors were recently removed and checked and re-installed with new cat o-rings. Fuel pressure with hand pump is approx. 25 psi and descends over about 5 minutes. Will the gauge that I installed next to the hand pump also show cranking fuel pressure? If it is below 25 psi with new Cat pump is there any possibility that the drive gear on the HEUI pump could be slipping? Is there a port on the head where I could install a high pressure gauge to check oil pressure?Some background information: After running at highway speed with heavy load engine cut off when it went to idle, got it started with ether. It did it twice more coming home empty, but I was still rolling and it re-started. The final time it cut off at idle and would not start with ether; got towed home and it has not started since.I will try the IAP sensor test tomorrow. Oh, is there ay way to pull flash codes with cruise control?
Thanks,
Farmer Bob
Technician: Cat Man, Cat Engine Expert replied 6 years ago
Thanks for the information.
Yes it's possible the gear on the heui is loose and slipping. Over seen that many times.
To check high pressure. There are several Allen plugs on the head to install a high pressure gauge. At least a 5000 psi is recommended.
I would pull the valve cover and crank the engine. You could have a leaking injector. If one is leaking. You will see it.
Here is the procedure to pull the codes with cruise control switches.Use the following procedure to retrieve the flash codes from the check engine light:
Turn the ignition key switch to the On position/ Engine OFF.
Turn the cruise control ON/OFF switch to the OFF position.
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 two digit code you get and I can tell you what the problem is.
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Customer reply replied 6 years ago
Any way to pull these codes if I don't have cruise control? I don't have access to a Cat Electronic Technician.
Technician: Cat Man, Cat Engine Expert replied 6 years ago
Oh I see. Unfortunately there is not a way to pull them without cruise. Sorry. I wish there was a way.
Please reply back if you need more help or have more questions. I am happy to assist.
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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Customer reply replied 6 years ago
Still no start! Removed valve cover and cranked; nothing appeared to be out of order here. I am going to pick up a new fuel pressure regulator tomorrow. Could not remove a plug on head to test HEUI pressure. Removed new fuel transfer pump and shaft through the HUEI pump seems tight, so I assume drive gear is tight also. I planned to remove the pump, but the back bolt would require intake manifold removal. Poor planning on my part; I believe front plate removal would be easier. I guess the IAP valve and the ECM are the next things to check. I will not give up!
Technician: Cat Man, Cat Engine Expert replied 6 years ago
Thanks for the update. Sorry you are still having trouble. Let me know if you need more help.
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Customer reply replied 5 years ago
Still no start. I removed valve cover and saw nothing abnormal while cranking. Installed new Cat fuel pressure regulator, which made no difference. Removed front plate from engine and checked torque on nut holding gear on HEUI pump. According to specs. at 80 lbs I performed the IAP sensor test that you recommended, but still no start. I have rigged a high pressure gauge which I will use to test IAP pressure tomorrow. Do you have additional suggestions? .
Technician: Cat Man, Cat Engine Expert replied 5 years ago
Thanks for the information.
Have you been able to install a psi gauge in the head to test heui pressure?
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Customer reply replied 5 years ago
Tomorrow p.m.
Technician: Cat Man, Cat Engine Expert replied 5 years ago
Ok.
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Customer reply replied 5 years ago
Installed high pressure gauge and had 1500 psi while cranking. Interestingly, I show no fuel pressure when cranking. I can pump up to 25 psi with the hand pump and crank with no indication that it wants to start. Cranking fuel was the first test that I performed and because of no pressure I bought and installed a new Cat fuel transfer pump. Apparently shaft through HEUI is turning, so why no pressure? Is there anything related to the hand pump that could block flow from the transfer pump? Maybe a stuck check valve? Is this ituation pointing more toward the ECM ? Thanks,
Technician: Cat Man, Cat Engine Expert replied 5 years ago
Thanks for the information.
If you are getting 1500 actuation pressure. That's plenty and it means you are getting rpm.If you can get 25 psi with hand primer. That's enough to start.I must next suspect the ecm. To test I like to install a known good ecm. Not sure if you have one but it's the best way.Please reply back if you need more help or have more questions. I am happy to assist.
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Customer reply replied 5 years ago
Please refer to my previous question relating to fuel pressure. I am puzzled that with a new transfer pump I don't generate measurable fuel pressure when cranking, but can generate 25 psi with hand pump. Regarding ECM I am looking for a source to test it off the engine. I will call the nearest Cat dealer (40 miles), or maybe consider one of the companies on the internet.
Technician: Cat Man, Cat Engine Expert replied 5 years ago
Thanks for the information.
That is odd you can get 25 psi with the hand primer but not cranking. But if it still does not start with 25 psi from the hand primer. I don't think fuel pressure is the cause.Let me know how you make out with getting the ecm tested.
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Customer reply replied 5 years ago
ECM goes to Carter Cat in Ashland, VA on Tuesday.
Technician: Cat Man, Cat Engine Expert replied 5 years ago
10-4. Let me know how you make out.
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Customer reply replied 5 years ago
Took ECM to Cat dealer for test. ECM appears to be working, but due to earlier 164-11 and 164-2 codes that were retrieved, I was allowed one day with their test IAP valve. Installed it, but still no start. Three of their mechanics reviewed everything that I had done and didn't cone up with any more suggestions, other than to have the truck towed to their shop for in-vehicle analysis. I'll check the price of towing. Only bright spot was when I went to pay the bill; no charge Merry Christmas! One more question for you, when cranking should I be able to hear the injectors clicking? With or without the valve cover in place.Thanks,
Technician: Cat Man, Cat Engine Expert replied 5 years ago
You are very welcome my friend. I am happy I could help.
That was nice of them. Don't see that a lot.
No. Normally you can't hear the injectors while cranking
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