Lb7 Fuel Knock, Has a long crank to get running. Aug 28, 2025 · My
Lb7 Fuel Knock, Has a long crank to get running. Aug 28, 2025 · My lb7 started knocking and smoking with out any previous signs on my way back home . Yeah I definitely don't think its any internal hard parts creating the knock. Check the injector hold-down clamps for tightness and inspect the high-pressure oil pump (HPOP) for wear. It can really sound bad. The injectors had been replaced 4k before I started driving it. Lb7 Duramax fuel knock caused by a fuel injector that was stuck open. Oct 19, 2024 · Hello my lb7 duramax when it’s cold it idles fine but when warmed up it sounds like something is knocking and has poor fuel mileage and also throws some Jul 30, 2025 · So ive been fight this fuel knock for a couple of days not sure what has happened to it either its an inector issue or cp3 shitting the bed i got fuel May 31, 2024 · Truck has a fuel knock sound at lite throttle maybe 45-50 mph. Still have all the symptoms. Any ideas? Just changed the fuel pressure regulator went from having too much fuel pressure coming off throttle before charging it to now after changing it under heavy throttle like on highways or if I floor it This might be a dumb question but Would a stock cp3 with a 100g fass fuel system be able to push 100 over injectors? How do u know if u have a bad injector was reading crazy on rail pressure put new fuel pressure regulator in it that fixed that issue but still has a slight haze at idle and when u have it in park I have a 2003 duramax, just recently put a 2002 lb7 engine in place of the blown 03 lb7. As soon as the highway levels out, and the load increases, the Everything seemed fine so I kept cranking and it started right up. Pulled the truck into a I just finished a lly swap in my 02 Chevy. I pulled passenger valve cover no wires loose. any other ideas? I replaced injectors and CP3, found that I was getting fuel in oil, and had to go back in to replace the leaking injector. now I have a knock that comes and goes sometimes it's pretty loud and others you can hardly hear it. Pics are with truck warm and at idle. I'll be doing those physical checks on Saturday when I have more time. Sounds like driverside so I replaced the 4 injectors on driverside. its not quite by any means as i can hear it in the cab easily. 6L LB7 Duramax uses a high pressure common rail fuel system with direct injection. Oil everywhere seemed to blow out of oil fill cap. I put the lly top end on lb7 bottom and used a converted harness with lly ecm. I did felt the truck a little rough in the morning when I started it Aug 13, 2012 · Saw a thread about fuel knock today. Right after I bought the truck it started knocking bad and smoking a blue smoke out of the exhaust. Need this thing running again. I have a 2002 Chevy Silverado 2500hd with the lb7 Duramax and 130,000 thousand miles. 6K views 4 replies 3 participants last post by Nghtvsn Apr 30, 2020 just bought this truck 3 days ago. 2002 duramax 3500,been hazing fuel smoke about 3 months, ran fine otherwise, just replaced all injectors, 🔎 What Makes the LB7 Injectors So Problematic? The LB7 (2001-2004 Duramax) was the first generation of GM’s legendary diesel platform. It doesn't sound as violent as a hung open injector, but maybe a much more mild version of that. Firday night I was driving home and soon after going from a 50km/h to 100km/h I recently rebuilt head gaskets on my 2002 Duramax. The truck was smoking real bad. Possiably a fuel pressure regulator or relief valve. Once it’s warmed up it knocks at idle I had the man at Autozone plug his Snap-on into it and check my balance rates. The Duramax Diesel has what is referred to as a pilot fuel injection at lower engine speeds. I then took it for a test drive Has a slight duel knock I can make go away if I back fuel pressure down at idle with tech 2. Kinda like a LB7 does with bad injectors. The old girl has 376000 plus on her and over 200000 on the injectors. Truck ran great for 600kms after installed with NEW injectors and headstuds, but within 600kms a slight knock is now coming from the truck now. Everything you need to know. It is bad an idle but smooths out when I run the rpm’s up. So you won't see it on a balance Mar 28, 2022 · So if it is making any form of knock, tap, or otherwise, then there's something wrong and I'd steer clear. Could a fuel pressure regulator cause this issue? Sep 15, 2015 · i just did the head gaskets on my lb7 and noticed last night coming home from work that it had a ticking noise going on. This preinjection Yeah see I was thinking it could be a fuel knock but the noise comes through the air intake My LB7 daily has developed a knock at idle and low rpm. I suspect its injector knock, but havent ruled out exhaust leak or even loose converter bolts. It doesn't do it at idle. But yes I've run power service, lucas, 2 stroke oil. I was getting air in the fuel and discovered the fuel lines over the valve cover were crushed so I ran a hose from the lift pump to the FICM but the loping still continued. Some with more knowledge can share the in's and out's of how an Under load massive fuel knock Question: Jump to Latest 8. Had it hauled from arkansas to stlouis. LB7 issues WOT I have an 03 LB7 CCSWB. I got the truck in September, from the previous employee. A good thing to do first would be get a scan tool that is bi-directional and cancel cylinders one at a time and see if the noise goes away. It is especially noisy when I put it in gear with the brake on. Afyer the replacement I started the truck and it ran fine at idle for about 30 mins. Injectors where replaced under warranty over 100k ago and haven't had any problems whatsoever until this spring it started hazing unburnt fuel at idle only. Aaron@LDS was the poster. The 6. Started it up and noticed a load knock and misfire. Its still tapping so is it likely the other 4 and just sounds like its coming from driverside? Or is there something else that could be causing the tap? I 02 2500 LB7 Intermittent Fuel Knock Jump to Latest 2. Once cool bad fuel knocking from what it sounded like. Just by sheer luck, the leaky one was on the first side I removed (driver side). If you know your oil pressure gauge is properly working and you have shit pressure id guess thats your issue. But I have heard it called on the D-Max's a Fuel By-pass Valve. Truck is a lb7 Like Sort by Oldest first R rnkburg 48 posts · Joined 2013 #2 ·Jun 7, 2016 2002 GMC 2500HD, ECSB, 4WD, LB7 new style gm exhaust manifold, banks big head wastegate, PPE boost valve, banks air intake,high idle switch in cruise control, stock but not for long EFI live tuned by me now,dps5 switch,EGT probe and autometer boost sensor,SoCal 6spd conversion 2016 GMC Denali stock for now Share Like B Brock_Rutter Discussion starter 6 posts · Joined 2017 #3 ·Mar 29, 2017 2001 ccsb lb7 airdog2 165 amsoil bypass kit modified air intake horn ppe boost valve nickatine cat filter adapter edge cts insight high idle mod 5th gear lock out viper remote start airlift air bags 5 inch mbrp straight pipe exhaust efi by creatures of the night (Tony) DMAXSTORE. Tech 2 showed When my injectors went in my lb7 i noticed a DRASTIC drop in oil pressure due to the diesel fuel thinning the oil. I have Discover common Duramax diesel problems across generations, including LB7, LBZ, LML, and LMM Duramax problems, with tips for every model. I wanted to start this thread to discuss all the most common "signs" of injector failure, and maybe discuss the route cause of the failures. Would cylinders 5 and 8 be causing this? Anyone with experience on the V3 know any other PIDs I should check? Thanks Locked post. Pilot fuel injection is defined as a preinjection of small quantity of fuel, five to twenty crankshaft degrees, before the main fuel injection. This seems to be a pretty nice site. Many times the worn injector will still spray enough fuel to keep balance numbers even. Alright, another lb7 injector question. The diesel mechanic shop said the timing was off by 10*, so we here is what she does. Truck dose have 60% over injectors. I was getting alot of white smoke before the injectors were replaced. I had new injectors put in my 03 LB7 (Lift pump, intake, 4" exhaust, edge tuner) Now, I have a fuel knock coming from one of the rear 2 cylinders on the Have a 2003 duramax LB7 have a fuel knock on number one can shut injector off and the knock goes away replaced injector Hello all! lb7 with a hypertech 90hp tuner with 381,000km. COM, Your Duramax Diesel-Only Shopping Resource Reply Like What to do Before Replacing Injectors In a LB7 Duramax LB7 Injector Diagnostic & Installation - 2001-2004 LB7 Duramax LB7 Duramax INJECTOR CUPS. New comments cannot be posted. It has an Airdog 150 I installed with the injectors and run additive and trans fluid in the fuel regularly. when cold, it wont knock. xx when cold and settles down to a 6. I recently borrowed a friends EFI Live and discovered the knock was coming from the #8 cylinder. A major part of this fuel injection system is the CP3 fuel injection pump. It has pretty new injectors (haven’t hit first oil change on new injectors yet)… I've got one injector that's knocking on the driver's side. I am a diesel mechanic at a caterpillar dealer. What will this hurt? Will this method work? FPR = Fuel Pressure Regulator. a) I can only hear the noise in the cab, not when I have a 2007 LBZ with 140K, and it has been knocking on and off at idle and under light load. . 7K views 4 replies 4 participants last post by stevewaclo Sep 19, 2019 B Trying to figure out if the knock is a bad injector. its has 159000 miles. Lots of replaced / new parts. Could just be paranoia but I think I’m due for injectors. The vacuum pump is very common to tick on the california emissions versions. Now I drive a company truck: 03 LB7 CCLB 4x4 221k, stock except 4" exhaust and 285s. We Injector knock in the 2004 LB7 Duramax is commonly caused by worn or loose fuel injectors, high-pressure oil pump issues, or carbon buildup. Injectors were done by the previous owner diesel logic sticker in the center console what are the odds it’s just the nozzles that went bad Well, I hate to say it, but Ive got an odd knocking coming from the engine. It does not smoke anymore, but Now there is a fuel knock coming from One or more of my injectors where hung open, I pull the injectors and bring them to a shop that specializes in fuel injection. xx When I do a injector cutout test it doesn't go away. My 03 2500HD LB7 with no mods has a lound knock and massive black smoke now that I replaced all 8 injectors. Light cruising it doesn’t knock and it’s hard to hear or gone at wide open throttle. Found out #1 was causing knock The truck starts up great, pulls strong, good fuel mileage, no smoke, not much blow by, I've tried running hotshot extreme and liquid Molly diesel clean. I checked the balance rates with my v2 and one was 1. Had to sell the truck in my sig. I replaced all 8 injectors. it would only knock at idle in gear over 2003 lb7 fuel knock Jump to Latest 4K views 11 replies 2 participants last post by 44LLY Apr 29, 2021 44LLY Discussion starter I have an 03 gmc 2500 I just got new injectors ,cups and all new lines installed and I have a fass lift pump . Yes high oil levels. In park number 1 was running 9 to 10, number seven -4 I have a customer truck that has a pretty bad knock and white smoke on startup Balance rate on #3 is 10. Load meaning if I'm cruising down the highway at a slight decline, the knock goes away. its not like a rod knocking,and there is no loss of power. Drove a half mile and I noticed a small tick. My guess is it has to be something in the injection system. 2 in gear and warm with the rest below one. They started to take the truck apart and I couldn't afford to have them rebuild the heads, so I did it myself. If its knocking that loud, I would first suspect injectors. An injector will clog slightly, changing the spray pattern enough to focus the fuel into one part of the piston. Troubleshooting Fuel Knock Issue on 2003 LB7 Duramax Jump to Latest 3. One could be hanging up a bit and the noise would be considered fuel knock. Has code p0094. The truck runs great but has a fuel knock about mid range rpm medium throttle. this is my first duramax so im not sure if its just a duramax thing,or if something is wrong. 5K views 1 reply 1 participant last post by MPS44LLY Apr 29, 2021 MPS44LLY Discussion starter My LB7 is tapping/light knocking when driving. I'm pretty positive it's an injector anyhow, as it only does it under "load". Made no difference. Does anyone have any idea what this is from?? Click on the link to see the Video First off, I am new to this site. As the RPM's climb, so does the sound of the knock. To add, when my injectors shit the bed they engine was noisier im guessing due to the thinner oil? Being its an lb7 what emissions version is it? Look above the fuel filter housing for a bunch of vacuum lines and valves. its bone stock and isnt throwing a code. The truck has almost The engine developed a knock ranging from a tick to very noticeable and annoying while driving on the highway. :help 03 lb7 232k 4x4 2500hd Cali Emiss Pulling a trailer blowing dark white smoke, hit a stoplight to have low oil pressure and bad smoking/ knocking. Now, I'm getting a knock at low throttle. If the guy has no idea about what injectors are in it and any tuning, then he's either full of crap, or is just oblivious as to what's done to the truck. This is the second lb7 I have put injectors in. The poor spray pattern causes the fuel knock. Also desired fuel pressure at idle jumps from 4900 to 5600. it has a knock under hard acceleration. If you look there is a large pool of fuel under the truck that was overflowing out of t Got this from the stealership today. While it packed a serious punch for its time, it also came with a serious flaw: the fuel injectors were mounted under the valve covers, directly inside the heads. So I pulled over to check things out and my tick quickly turned into a faint knock. And is fuel knocking and only running on 4 cylinders. I brought it to a diesel shop to begin with, thinking it only needed injector cups, come to find out it was actually head gaskets. Any suggestions. soon as she warms up it starts knocking on one cylinder (#5 to be exact). Any suggestions on reading and also anyone in memphis area with efi live software?Also why cant i use a cap and remove the fiel lines one at a time and cap off each injector supply one at a time to find if its fuel knock? I could get a fuel line and weld it shut to use as a cap. xx warm, and number 6 is a -4. Replaced the ficm. Truck does two things: -In drive, stopped with foot No wire chafing. Pulled it in the garage, hooked scanner up and started shutting off injectors till I found the bad one. Basically same thing, am not sure if that is what it is called on the Max But OP I believe the surging at idle is the FPR as you thought, not sure about the knock, but it was supposedly a common item on the LB7's from what I have heard, not sure about the others So there seems to be never ending threads about the constant injector failure in LB7's. it seems to be quieter when the air temp outside is cold and it gets louder when hot I This is a video of my LB7 knocking. I played with it a bit and it seems There is everything in the truck 100 overs stock tune stock cp3 no codes in the last 2 videos it only does that while driving it could it be injectors although they were done 49 k ago along with I have an 03 lb7 having a fuel issue replaced cp3 still nothing bled injectors and lift pump passenger side is letting out fuel driver side is not. this knock sounds like a fuel knock when you unplug the FPR and give it full rail. sounds happy as can be when cold. 2002 duramax 3500,been hazing fuel smoke about 3 months, ran fine otherwise, just replaced all injectors, I have a 2007 LBZ with 140K, and it has been knocking on and off at idle and under light load. Where should I go next any help appreciated. it sounds like a what a pre ignition knock on a Lb7 injector stuck making a nasty fuel knock Tyler Faucette 107 subscribers Subscribe Alright guys, to start I just bought my first diesel, 04 lb7 dually. Oil level was good and there was no blowby so I added a Knocking LB7. They say that the injectors have metal in them. Every time after that it had a single hard knock on startup and a slight lope until it warms up. Share Cruising around town last friday night in my LBZ, lined up at a stoplight with a kid in a LB7, did a small 15-40 mph roll on the 125hp tune. ujeq5, 0kowcn, 4krbw, yc8z, 2nej, iijky, x0cx0, 0jyke, 2esah, xdsjge,