fuel knock

[olegreen95]

hopefully find someone that can help, got i believe a fuel knock that i cant find it smokes and smells like raw fuel its not white or grey smoke the knock doesnt always have the same tone gets louder and quieter at no certain time truck has 300,000 miles is all stock and has never had anything added on it, its a customers of mine i found multiple wiring problems and had codes for injector 2 and 4 for circuit problems, found some injector connectors had been replaced at one time and some wernt replaced all eight due to pin problems and routing rub through problems when previously replaced all active codes are gone but still have fuel knock, checked all wiring esp at fuel computer where they commonally rub through, checked all pins and wiring at ecm, killed each injector none really changed it, checked balance rates cyl 1, around (6) cyl 2, around (4) all others are around 1 or less,replaced injector 1 and 2 still have knock swapped the two injectors out with each other cyl so all of the injectors have been swapped out knock is still there but seems slightly quieter checked balance rate again and cyl num 1 is around (6) even with the new injector all others are about right using stethoscope knock sounds louder at cyl 1 when placed on the injector only and cyl 1 has the lowest cyl temp, it is firing because it is obvious when killing that cyl the rpms are more affected when killing num 1 over any other cyl like that cyl is working harder then the others also fuel pressure is right around setpoint when raising rail psi with scan tool the knock starts to go away also using snap on scanner sorry so long but wanted to give as much info as i could any help or ideas would be appreciated

 

[IdahoRob]

Oh my god, my head hurts from trying to read that. What is the rail pressue and what codes is it throwing?

 

[Diesel Tech]

Have you checked the compression on each cylinder? With 300K on it you may have an issue.

 

[olegreen95]

sorry sounded better when i was typing it out, it is hard to read. i cant remember the codes, i have them wrote down at work i will get them tomorrow and i didnt check compression yet, also this happpen quickly customer said he was driving constant 55mph everything normal then started to knock with a little black smoke he pulled over and had it towed rail psi was 4500 to 4800 at idle but stayed close to setpoint

 

[IdahoRob]

Sounds like the typical LLY harness issue shutting down a bank of cylinders. Check the injector harness where it routes over the top of the altenator bracket, pull it up and look to see if it has rubbed through. Also the standard cyl. 2 and 7 harness problems.