Community Forums

maddogrdhg · 06-27-2018, 11:16 PM

On a long trip and suspect I may have gotten bad fuel. It began to lose power on long/steep hills. Bucks and chugs under heavy incline loads. No check engine or fault codes I can find. Put fuel cleaners and conditioners in tank. I changed primary and secondary fuel filters. Was only able to change primary first as my wrench wouldn't fit secondary. Later changed secondary. Ran worse after each one. Kept driving and it smoothed out with much improved power after 150 miles. Still not normal but may be getting better. If an injector goes back/intermittent does it always send a code or check engine? Ideas what to check? Fuel pressure regulator, ohm out each solenoid, ?? 5000 miles from home and worry dealer will just start swapping expensive parts. Thanks for your feedback.

Skip426 · 06-28-2018, 12:25 AM

Bad fuel , can take , multiple filter changes to correct.
The fuel system returns unused fuel to the tank so by the time you use a tank of fuel it's been, back into the tank then , trough the filters several times .
Filters will plug up quickly and after a tank of bad fuel ; often.

2 Stroker · 06-28-2018, 10:55 AM

What year C-9
How many miles on the oil, HEUI pumps like clean oil and fuel.

May have to change filters again, if you prefill only use the small holes to fill.
Do you know what kind of boost you have on the grades.
How clean is the air filter?

2 stroker

diesel car · 06-28-2018, 12:23 PM

Sounds like you got a bad tank of fuel. As stated, multiple fuel filter changes will b necessary. I always use HOWES fuel treatment with every fillup. Today's fuel offers little or no lubrication for the the injectors or your fuel pump. ULS fuel also doesn't burn as hot...

maddogrdhg · 06-28-2018, 01:54 PM

5500 miles on oil. Boost at 26. Seems like starving for fuel. Bought fuel again today at newer high traffic location. Added Howes and bit of diesel kleen. Running worse immediately after fuel fill.

maddogrdhg · 06-28-2018, 01:56 PM

Pulled air filter and appears clean. Only about 7000 miles on it.

GreaTOne65 · 06-28-2018, 07:09 PM

Hey Maddog, check the hose clamps on the intake pipe before the CAC. I was checking on a few things yesterday, and found another hose clamp broke! That makes 2 one on each side of the hose connection. Had it happen 2 yrs. ago, just outside of Albuquerque. I couldn't find spring clamps so settled for 3 regular 4" hose clamps that have stayed put so far. I ordered 4 new T bar clamps yesterday.

Good luck!

tankcj · 06-29-2018, 09:57 AM

My coach did the exact same thing. Started chugging/bucking at about 21 pounds of boost anything above or below it ran fine. A couple hundred miles later a check engine light came on and I’ve got a bad number six injector. But it runs fine and no chugging/bucking. This is the second injector that spit out a code that it’s bad but the coach always runs fine. Now I am waiting for the new style injector. Since the old style is obsolete there’s none to be found.

discovery39s · 06-29-2018, 08:37 PM

Quote:

Originally Posted by maddogrdhg

On a long trip and suspect I may have gotten bad fuel. It began to lose power on long/steep hills. Bucks and chugs under heavy incline loads. No check engine or fault codes I can find. Put fuel cleaners and conditioners in tank. I changed primary and secondary fuel filters. Was only able to change primary first as my wrench wouldn't fit secondary. Later changed secondary. Ran worse after each one. Kept driving and it smoothed out with much improved power after 150 miles. Still not normal but may be getting better. If an injector goes back/intermittent does it always send a code or check engine? Ideas what to check? Fuel pressure regulator, ohm out each solenoid, ?? 5000 miles from home and worry dealer will just start swapping expensive parts. Thanks for your feedback.

I had same issue with mine on a spring wake up call. Ill look up my thread and send it to you. Hold off replacing any part until you read it.
Get back soon

discovery39s · 06-29-2018, 08:47 PM

Here ya go. Hope it resolves your problem.

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.

discovery39s · 06-29-2018, 08:51 PM

Here ya go. Hope it resolves your problem. *** I have a 3126E. however it is my understanding the C7 and C9 used the same.

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.

maddogrdhg · 06-30-2018, 01:02 AM

Thank you. I will check into this.

maddogrdhg · 06-30-2018, 01:03 AM

Thanks, been remote area no net. Will check tomorrow.

maddogrdhg · 07-03-2018, 08:35 PM

Broke down and took into CAT shop. Initial discussion with tech he indicated my symptoms sounded like low fuel flow or pressure. I told him on cold start up it has a clacking noise for 5-10 seconds and never does it again that day. I had made a video of it and played for him. He said that was just the sound it makes when fuel prime/pressure not maintained after shutdown or air leak in line. Later they diagnosed #1 injector not firing. Pulled out and saw a spec of metal. Not sure if that was legit or what. Much discussion back and forth to pull all injectors and HEUI pump. I agreed to have them pull oil filter and inspect for metal fragments. They even cut open and peeled media out to inspect. Found no metal fragments. They decided best course of action was replace injector and see how it goes. NOTE - they did say they had to update firmware 3 levels as it had never been done from new. Tech also mentioned that the wire lead going to number 1 was tie wrapped too tight from factory and was trying to pull connector out. Replaced and motor runs smoother and on short trip back to park seemed better. Will know tomorrow when I hit the mountains. QUESTION I have is about the clacking....I started this morning and it still made that noise. What are your thoughts....