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Old 09-16-2017, 04:50 PM   #1
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3126e NO Start Resolved

Posted this over on the FL forum and thought it might help someone here too.

Hello Folks,
Getting our FL chassis Discovery ready for a trip to find it started but kicked, bucked and idle was ruff. Hit the accelerator pedal and it ran smooth at 1,500 rpm. So, a definite fuel supply issue, I thought! prefilled a new fuel filter installed and same issue. Attempted to start her back up a third time to not even fire this time. Wonderful!!!!

Noting, this engine has had pampered life, 44,000 miles, having oil changes at 7,500 miles along with fuel filter. Stored inside, washed and waxed annually. My heart sunk.

Being an engineer I put my experience to work searching the internet, calling FCC, calling local CAT dealer to find one answer: "Tow it in". What? seriously, I was a little put back that these "support" resources wouldn't take a moment to listen. I should clarify, FCC did listen to my pain but really had no experience with a 3126 to help. CAT, I couldn't get past the "gate keeper" to speak with a guy that probably has some insight.

SOLVED!! I researched the fuel handling system on the internet and how the system functions regarding several sensors feeding back to the ECM.
Not having a code reader to pull any codes, I studied how the system functions and what could cause this condition. (Let me say that this engine has never even farted. It has run like a dream from day one) That said, it may not be your specific issue but well worth testing without spending a dollar.

Cat uses a IAP sensor (injection activation pressure) to monitor the high pressure oil that opens the injectors. The HEUI pump takes engine oil at 60-65 psi and amplifies it to 1,200 psi at starting to 4,000 psi relative to the engine demand/load. The IAP sensor feeds back to the ECM indicating that the pressure is at desired pressure called by the ECM. The IAP is supplied with 5 vdc and feedbacks a linear voltage to the ECM. The IAP is a fancy name for a pressure transducer. IF and when the IAP fails to feedback to the ECM, Fuel is shut off to the injector supply port.

So, I unplugged the IAP. This "fooled" the ECM to think pressure was low. She started up and idled perfect. (((NOTE: I would NOT advise extended running/driving because the ECM will not provide proportioning fuel to the system under high load conditions))) However, this proved the sensor was defective. Went to my local cat dealer, picked up a new IAP sensor and oring.
Took ten minutes to install. Our baby is back to purring. $165.00 w/tax.

Location: The IAP is located on the front left side of the engine and screws into the head just to the right of the HEUI pump. Has a 10" wire harness with a triangular 3 pin connector. Google "3126 sensor locations" for some clear pictures if in doubt.

I hope this helps many that may some day experience this issue.

Travel Safe.
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Old 09-16-2017, 04:57 PM   #2
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Quote:
Originally Posted by discovery39s View Post
Posted this over on the FL forum and thought it might help someone here too.

Hello Folks,
Getting our FL chassis Discovery ready for a trip to find it started but kicked, bucked and idle was ruff. Hit the accelerator pedal and it ran smooth at 1,500 rpm. So, a definite fuel supply issue, I thought! prefilled a new fuel filter installed and same issue. Attempted to start her back up a third time to not even fire this time. Wonderful!!!!

Noting, this engine has had pampered life, 44,000 miles, having oil changes at 7,500 miles along with fuel filter. Stored inside, washed and waxed annually. My heart sunk.

Being an engineer I put my experience to work searching the internet, calling FCC, calling local CAT dealer to find one answer: "Tow it in". What? seriously, I was a little put back that these "support" resources wouldn't take a moment to listen. I should clarify, FCC did listen to my pain but really had no experience with a 3126 to help. CAT, I couldn't get past the "gate keeper" to speak with a guy that probably has some insight.

SOLVED!! I researched the fuel handling system on the internet and how the system functions regarding several sensors feeding back to the ECM.
Not having a code reader to pull any codes, I studied how the system functions and what could cause this condition. (Let me say that this engine has never even farted. It has run like a dream from day one) That said, it may not be your specific issue but well worth testing without spending a dollar.

Cat uses a IAP sensor (injection activation pressure) to monitor the high pressure oil that opens the injectors. The HEUI pump takes engine oil at 60-65 psi and amplifies it to 1,200 psi at starting to 4,000 psi relative to the engine demand/load. The IAP sensor feeds back to the ECM indicating that the pressure is at desired pressure called by the ECM. The IAP is supplied with 5 vdc and feedbacks a linear voltage to the ECM. The IAP is a fancy name for a pressure transducer. IF and when the IAP fails to feedback to the ECM, Fuel is shut off to the injector supply port.

So, I unplugged the IAP. This "fooled" the ECM to think pressure was low. She started up and idled perfect. (((NOTE: I would NOT advise extended running/driving because the ECM will not provide proportioning fuel to the system under high load conditions))) However, this proved the sensor was defective. Went to my local cat dealer, picked up a new IAP sensor and oring.
Took ten minutes to install. Our baby is back to purring. $165.00 w/tax.

Location: The IAP is located on the front left side of the engine and screws into the head just to the right of the HEUI pump. Has a 10" wire harness with a triangular 3 pin connector. Google "3126 sensor locations" for some clear pictures if in doubt.

I hope this helps many that may some day experience this issue.

Travel Safe.
Thanks! No longer have a 3126 but it's always good to learn stuff !!
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Old 09-16-2017, 07:28 PM   #3
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George,
OUTSTANDING write up. I cannot give you enough praise for diving in head first in a situation like this. We have an '04 Itasca Horizon 36GD with the CAT C-7 330HP. It's pretty close to your 3126 with some differences. I read your write up with great interest. Our coach, and or engine, has also been one outstanding performer. Not even a hiccup. We just finished a 6,400 mile trip around the U.S. and, while not relevant to this thread, I'm surprised the engine is still mounted in the coach, with the seriously LOUSY ROADS in much of this great country.

Anyway, I really want to thank you for taking the time to put this kind of info out, at least for us DIY types. Sometime, I ought to tell you about my issue with the J1939 Data link system that our coach has and what happened.
Scott
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Old 09-25-2017, 06:08 AM   #4
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been there and solved this intermittent issue back in 2007. This was after listening to CAT and FL in the Phoenix.
My cost ? sensor, o'ring and 15 minutes.
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