Recently truck started to "knock" during acceleration. It sounds almost like a gas engine with a timing knock. It will do it in spurts while accerlerating and then quite once crusing. Took it into service shop and they said it was fuel tempature sensor. Quoting the mech "with computer hooked up it showed perodically the fuel tempature sensor was readin 300 degrees plus and then the computer was adjusting to that causing the knock" Not to sure what the fuel temp should be reading but had them replace temp sensor and problem cleared up till now about 1000 miles later. Has any every heard of this before?

Fuel temp sensor is a pretty rare failure item. Is it setting that code again?

i dont have my own efi and i havent had it taken back in yet to the shop. I had dustin at diesel addiction tune it over a year ago. 20000 miles and no problems until about a month ago. Pretty sure not a problem with the tuning because it will "knock" on all 5 settings even the stock setting. Check engine light isnt on either.

I would have someone check the pigtails on your injectors.

Could be crappy fuel. Try running some Power Service fuel additive. You can find it at Walmart and truck stops. Made mine stop knocking.

Check the FICM harness at the alternator- the sharp corner, where it is tied down, will cut into the wires and cause all kinds of problems. :D

Check the FICM harness at the alternator- the sharp corner, where it is tied down, will cut into the wires and cause all kinds of problems. :D

X2 - to fix it, undo the zip-tie, fix any worn wires, re-tape, then insulate the whole thing with a split piece of heater hose... then zip-tie back in place. You won't have any more problems there... :thumb:

The FCIM was already fixed previously thanks though. Its not a fuel quality problem beings i just changed fuel filter and i use the best fuel in the area i belive ( fill up at local fertilizer plant that sells fuel an they use 2 micron filters also never jelled up last winter in weather below 0 without running additive). Got it back from the shop today an they found the ground wire for the fuel temp sensor was cracked/correded so they fixed the wire an told me to try that. Not gettin charged for nothin beings as truck went back in for same problem so the shop is takin good care of me i think. Also computer showed fuel temp was reading 300 degrees and above when it "knocked" so that would make sense for the "knock". To much air an not enough fuel. Thanks for the comments

i dont want to scare you,but that is exactly how my rod bushing startedhow many miles do you have on it?

137xxx approx. I doesnt do it everytime i drive it though so i would think its something electronic failure. If it was mechanical problem truck should "knock" all the time when accerleratin. I dnt no. Gna run her and watch it see if maybe the ground wire was the problem

Hope you found the problem keep us up to date. Was woundering does anyone know where the fuel temp sensor is located on theses trucks?

usmcbaer, I got an 04 LLY it has what I call a "peck". It kinda reminds me of valves chattering in a gasser. It does it when my tranny is out in od and you give it fuel. It recently has done it when the tranny is shifting out at high rpm's. Does any of this sound like your situation. I was kinda leanin to an injector starvin for fuel but readin your prob has got me to thinkin. Thanks for your help.

Just returned from a 10k mile trip. Mine did a similar thing out in Yellowstone. No CEL. Gauges OK. Only intermittent knock under light throttle. Eventually it disappeared. It happened a couple more times. Haven't heard it again for about 4k miles. Sounded to me like chunks of carbon going through the combustion chamber (possibly from EGR passage). Don't know if that's a possibility on a diesel. I know it can happen in a gas engine.

Thanks for the info. I am gettin ready to install an EGR blocker this weekend and stop any more carbon buildup in the intake. Does anyone know how much of a chore it is to clean all of the carbon out of my intake?

usmcbaer, I got an 04 LLY it has what I call a "peck". It kinda reminds me of valves chattering in a gasser. It does it when my tranny is out in od and you give it fuel. It recently has done it when the tranny is shifting out at high rpm's. Does any of this sound like your situation. I was kinda leanin to an injector starvin for fuel but readin your prob has got me to thinkin. Thanks for your help.

Kinda like that it will do it in all gears regardless if you are pushin pedal lightly or flooring it. Speakin about the EGR plate though i belive my egr is disabled but i dont have a plate on it. I will have to get a hold of dustin at dieseladdiction to verify if he did that. I wonder if that could be part of the problem?

Also truck is back in shop still actin up. I believe they are going to replace fuel temp sensor again to verify it wasnt a faulty part.

Mine does something similar, but only when the coolant temp is between 120 ish and 180 ish. Sounds like valve clatter from possibly a single cylinder on the passenger side. Only under light throttle though, give it some more fuel and it quits. bugs the hell outta me.

Sounds similar to my situation. Talked to a friend who is a GM mechanic and a fellow LLY owner and he said that he is pretty sure that it is an injector sticking open. Gonna try to get it in his shop next week. I will keep you posted. Thanks for all of your input.

Having the same problem, just started today.Just under light throttle and comes and goes. Going to give the dealer a call and schedule an appointment since its still under warrenty. Keep us posted maybe its the new winter blend. Mine started to do it right after I filled up.

Kinda like that it will do it in all gears regardless if you are pushin pedal lightly or flooring it. Speakin about the EGR plate though i belive my egr is disabled but i dont have a plate on it. I will have to get a hold of dustin at dieseladdiction to verify if he did that. I wonder if that could be part of the problem?

Also truck is back in shop still actin up. I believe they are going to replace fuel temp sensor again to verify it wasnt a faulty part.

My girlfriends 04.5 LLY does the same exact things your describing. I have her EGR turned off with EFI but no blocker plate. Her truck has done it since she bought it used. I can't narrow it down for nothing! I have changed fuel filters, put a LBZ FPR and that didn't help any either. Checked injector balance rates and they are all ok.. It will do it in all gears no matter how much throttle your giving it. Does it louder just driving normal. Its not as bad if your WOT but still does it a little. If you guys figure it out LET ME KNOW!! Oh and it has never thrown any CEL so its gotta be something minor causing it if its not normal

This is killing me ,its the only vehicle I have since my wifes van took a crap. I dont want to drive it and cause more damage so I'm forced to bring it somewhere to get checked.

This is killing me ,its the only vehicle I have since my wifes van took a crap. I dont want to drive it and cause more damage so I'm forced to bring it somewhere to get checked.

I don't think its causing damage! My g/f's has been doing it for quite some time. Its more aggravating then anything

any word on anyone elses mystery knock

update on truck:

knock still occurs under light to heavy throttle. Shop told they wouldnt do anything else to truck because they werent to sure what the problem is. When they orginally fixed the problem the code was PO168 Engine Fuel over Temp. Anybody got any insight on this?

Mine has no codes at all....

Mine has no codes at all....

u have used efi or had a shop hook up to computer and still no codes? Maybe your edge wont show this code. I dont no just askin maybe we have the same problem. i will watch my coolant temp when truck does it again and post

Does this knock sound like a gas motor "diesling"? If so, I noticed mine running louder lately, and when I get on the throttle, there is a point that it makes this sound. So now I am curious, after reading this post. I have dropped of a few MPG's as well, but colder weather is coming in too.

Does this knock sound like a gas motor "diesling"? If so, I noticed mine running louder lately, and when I get on the throttle, there is a point that it makes this sound. So now I am curious, after reading this post. I have dropped of a few MPG's as well, but colder weather is coming in too.

ya kinda a gas motor with a timin knock. I have dropped a few mpg's too even when it was warm out

My truck is doing the very same thing, Im pretty sure it is an injector, I can brake stand the truck, load the engine hard, and cancel out injectors on my scan tool, the noise goes away when I cancel out #8. Im guessing that an injector is not spraying correctly, something like that. I have tried alot of additives, nothing helps, but a heavy dosage of ATF

Got mine in the shop now. EFI is showing code for #4 injector. Hopefully it may only be an electronic issue. I just want it to quit that knockin. Will keep you giys posted.

Mine was doing something similar, ran a few tanks with Diesel 9-1-1 and cleared everything up. That was prob. 5k ago.

What is 9-1-1?

diesel additive.turns out my mystery knock was crappy fuel, drained the tank,changed the filter and refilled,no more knock.

I would find someone with EFI and datalog the truck, just quickly looking at the injector balances doesn't tell you enough. I had to drive around with my "Black Box" and datalog before I found out that it was the injectors wiring harness. Ice Pick tricked worked on 4 injectors.

any word on anyone elses mystery knock

I have 7200 miles on my 09 LMM and i have the same problem and a CEL. Banks iQ kicks me a code PO181 and PO182, all related to Fuel temp. Sensor. Was given no help from the dealer. I keep clearing the code and it keeps coming back. Read a lot of posts on PO181, all they say is clear the code and forget about it. I'm not sure about any body else but a knock can not be a good thing. It seems like these things are all related but have not read one thing hear on how to take care of it other than, Clear it and forget it. Its hard to forget when i can hear it and a CEL is staring at me.
Is there a fix ?????:confused:

diesel additive.turns out my mystery knock was crappy fuel, drained the tank,changed the filter and refilled,no more knock.

Shooting in the dark here, but do you think this could be throwing these codes(PO181 & PO182) I have just switched to a cheaper diesel station
about two fill ups ago since this started, also I have been running Standany (performance) with every fill up.