Fuel knock??

[The_Jackale]

I have a slight knock/ping to my motor that has slowly developed. Fuel pressure is 16 at idle, 19 running down the road. Slight black smoke at throttle increase from idle. Noise can be heard bouncing off structures. Not really feeling a power decrease. Uploading a video. It sounds like an injector but quieter than any videos I have seen/heard.

 

Going to crack the injectors unless you guys think of something else to stop me. 

Going to be taking the truck on a 600 mile trip soon. 

[army_greywolf]

I had the exact same sound, cracking cylinder 5 killed the fuel knock completely.  Changed the injectors, ended up replacing crossover tubes too because they too were slightly leaking, enough to give me an extra quart or so between oil changes which really means 2+ quarts with normal consumption.

[The_Jackale]

1 hour ago, army_greywolf said:

I had the exact same sound, cracking cylinder 5 killed the fuel knock completely.  Changed the injectors, ended up replacing crossover tubes too because they too were slightly leaking, enough to give me an extra quart or so between oil changes which really means 2+ quarts with normal consumption.

 

 

Thank you for the reply. Going to get the lines cracked. Did you just go back with stock injectors? I really do not care about power gains, just long term reliability. This may be the reason I am seeing 12 to 13 mpg...

 

I also noticed I have white smoke/steam coming out of my oil cap now. So I may be doing a compression test soon. 

[Nascar]

22 hours ago, The_Jackale said:

I have a slight knock/ping to my motor that has slowly developed. Fuel pressure is 16 at idle, 19 running down the road. Slight black smoke at throttle increase from idle. Noise can be heard bouncing off structures. Not really feeling a power decrease. Uploading a video. It sounds like an injector but quieter than any videos I have seen/heard.

 

Going to crack the injectors unless you guys think of something else to stop me. 

Going to be taking the truck on a 600 mile trip soon. 

Your fuel pressure is low. You should have min 19-22 at idle & min 25-32 under load.

As for your knock....most likely inj's as army-grey wolf mentioned. When a injector(s) seat area gets worn or dirty, the nozzle can start dribbling ( usual cause of a fuel knock ) or spraying outside the piston bowl ( which can cause cylinder wash down....damages the rings, hard on the piston(s) & will cause excessive blow by over time ) or both.

[Mopar1973Man]

As injectors wear out the pop pressure drops to very low. This makes the injector fire early. Hence the knock. The other way to test this is hook up a live data tool if engine load at idle is less than 3% its time to replace. If the engine load is 0% and idle is not resting at 800 RPM it will be higher. This is most likely where your at typically this is roughly about 260 bar (3770.98 PSI)

 

Like my current injectors I idle about 10 to 11% yet being they were popped at 320 bar (4641.21 PSI)

 

Minimum pop pressure is 293 bar (4249.61 PSI) according to FSM book.

 

 

[Nascar]

4 hours ago, Mopar1973Man said:

As injectors wear out the pop pressure drops to very low. This makes the injector fire early. Hence the knock. The other way to test this is hook up a live data tool if engine load at idle is less than 3% its time to replace. If the engine load is 0% and idle is not resting at 800 RPM it will be higher. This is most likely where your at typically this is roughly about 260 bar (3770.98 PSI)

 

Like my current injectors I idle about 10 to 11% yet being they were popped at 320 bar (4641.21 PSI)

 

Minimum pop pressure is 293 bar (4249.61 PSI) according to FSM book.

 

 

Am I missing something? This is a 12v engine according to the forum & fuel pressure. Injectors popping off early will not create a fuel knock, as it is same as advancing the inj timing but at a lower pop pressure ( less atomization, which only causes a dirtier burn & less power & less mpg ). And no way that I know of to test live data on a all mechanical 12v ?

 

As mentioned, one or more of the inj's are dribbling (leaking down way out of the regular compression stroke) is most likely the cause of the fuel knock.

[Mopar1973Man]

Oops on the 12V... so there is little to give there.

[CUMMINSDIESELPWR]

leaky/weak injector. crack each line to find it. move it to one that isnt knocking to verify the problem moved by cracking the line where it moved to. if it doesnt move its further up. if it moves its the injector. i suggest rv275's