Dan s

Can someone explain what fuel knock is. I know this sounds dumb but I need it clearified

edwinsmith

On gasoline engines, it's called pre-ignition. Once the fuel is ignited by the spark plug the pressure increases rapidly which causes unburned fuel elsewhere in the combustion chamber to explode before the flame from the properly ignited fuel gets there. This causes an even more rapid increase in pressure and the knock.

Something similar may be happening in a diesel. Maybe if you have crankcase oil spray in the cylinder from leaky rings or maybe a leaky valve seal that could be exploding early before the fuel is injected causing the knock. Just my educated guess.

Edwin

patdaly

Sorry, just grabbed the first Google link I found..... def. didn't mean to sleight anyone.

Dan s

Just an update. I've quit looking for my "knock". I e done everything except pull the head. The knock is still there even after several road trips and pulling my camper 6 hours back to Georgia. The following is a list of what I've done and found nothing. Oil sample. New injectors. Pulled trans to inspect flywheel (flexplate). Turned fuel back down to factory settings. The oil pressure is still holding 50psi when loaded and unloaded. Idle it will drop to 30psi. Took the factory lift pump off the truck and put a plate on side of block. Put a new water pump on it (old one started to leak out the weep hole). I gave up about a month and a half ago and have just driven it. I just wanted to update this thread because as I researched this I found several threads just never gave any answers or just never got updated. I really appreciate all the help everyone here on this sight tried to be. If it does ever show it's ugly face I'll be sure to post it here.

bigragu

Thank you, for following thru

mknittle

Glad to see you a here again Dan. Noises can be a PITA to find.

NJTman

Not according to my wife. She says she hears it all the time when I'm around her, and that they usually are accompanied by some sort of horrific smell...



Geesh !


Just can't make them happy no matter what, eh ?

MrFusion

Dan, Install a stupidly loud exhaust or sound system...then the knock won't be as noticeable or might go away entirely.

Dan s

That's pretty much what I did. Lol. Next trip is from Atlanta to just south of Orlando. Then back home somewhere around thanksgiving. Got some cash put back just incase it finally lays down but I don't think it will. It just runs way to good. That is unless it's a wrist pin that lets go. But I'm prepared for that

edwinsmith

I have no muffler on my truck. I just tell the wife that diesel's smell like that. I don't think she buys it though.

Dan s

I FOUND IT. I bought a botescope over Labor Day and pulled all the injectors. All piston tops look good. All cylinder walls look good except number 3. It has some very light vertical marks. Not dug in like a groove. I'm glad I found it it but now I gotta do something about it. I can't make a decision till I get the head off so I can really see it. I have been looking at options for a rebuild kit. Looked up some stuff about boring the cylinders in case I have to. Then of course what if the head has a crack somewhere. The bad thing is that it is work season for me and I don't have time to work on it myself. That means I would have to hire it out and that can get expensive quick. Not to mention that finding someone I trust to do the work. I have noticed that after it is warm it gets a lot quieter. Hope all is well.

patdaly

Around here it is far cheaper to just buy another engine and replace it than to even consider a rebuild. YMMV, but most of the trucks die long before the engines even reach half-life status.

Dan s

I have considered that option. But finding a good motor that u can hear run in my area is kinda hard. And if u do the price is still pretty steep. At least what I consider steep for a used motor. Don't bet me wrong. If I find one that will be the way I will go. And considering it is work season for me I will continue to use the truck. Which means by the time I get home sometime around thanksgiving I could have totally messed up the block. I don't think it will but it is a possibility. If I'm lucky I'll find one n Florida while I'm down there working. The next task would be to find some one to install it. But my luck usually goes not so good with things like that.

deere country

I don't know how a stratched cylinder wall can give you a rod knock type sound. If you beleive the tops of each and every piston look to be undamaged I don't see how you could have had something mark up a cylinder wall.

Generally if a turbocharged diesel has a valve type failure by the time you think you hear something out of place in your engine the pieces from the failed cylinder end up in all other cylinders not just the one with a valve failure.

If you have a mark in your cylinder wall I would suspect it made its way in through a compromised air filter via sucking in dirty air. I have never seen a dusted Diesel engine with a rod type knock.

Dan s

I thought maybe piston slap. It tends to get quieter when it warms up. I've Been driving this thing almost a year and nothing has come apart. It's not getting louder. No loss of power.