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Old 12-06-2010, 11:28 AM   #1 (permalink)
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knocking noise in cyl 6 Help!

Hey members, new here. I have a "knocking" noise in my 1990 Dodge 250 Cummins 5.9 engine. I bought this truck with no noise, but a leaky injector pump. I replaced a seal, put it back together and now have a knock in cly 6. I goes away when I loosen the injector line. It in NOT noisy on cold start, but makes the knock noise after about 30 seconds. It stays after that. (Checked rod and main bearings, and they look good. No metal in oil, bottom of piston not cracked or cyl wall galled, checked valve tappet clearance, no issues!)

I switched injectors with cylinder 2 and the knock is still at cyl 6. Advancing the injector timing makes it louder. (turning the pump toward the top of the head) and quieter when retarding it. (turning the pump toward the oil pan).

What am I missing here? What is this "fuel knock" I keep hearing about, but still do not understand completely. Any ideas anybody? Can I damage the engine if I keep driving it this way? Thanks again for any help! DeVere
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Old 12-09-2010, 12:20 PM   #2 (permalink)
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Quote:
Originally Posted by DeVere View Post
Hey members, new here. I have a "knocking" noise in my 1990 Dodge 250 Cummins 5.9 engine. I bought this truck with no noise, but a leaky injector pump. I replaced a seal, put it back together and now have a knock in cly 6. I goes away when I loosen the injector line. It in NOT noisy on cold start, but makes the knock noise after about 30 seconds. It stays after that. (Checked rod and main bearings, and they look good. No metal in oil, bottom of piston not cracked or cyl wall galled, checked valve tappet clearance, no issues!)

I switched injectors with cylinder 2 and the knock is still at cyl 6. Advancing the injector timing makes it louder. (turning the pump toward the top of the head) and quieter when retarding it. (turning the pump toward the oil pan).

What am I missing here? What is this "fuel knock" I keep hearing about, but still do not understand completely. Any ideas anybody? Can I damage the engine if I keep driving it this way? Thanks again for any help! DeVere
i seen a similiar problem with a 1256 international tractor. it was diesel as well. heard a knocking noise every time we ran it. when we had a mechanic look at it, we isolated it to the fuel system. about 6 months later we found it was actually something to do with the a fuel line (don't remember the specifics). i think we wedged a piece of rubber innertube against it. i'm not sure if you got the same problem but might be a place to start.

it ran for years after the noise starting and never had a problem with the fuel system. traded it off on a different tractor only because of its age and we wanted a loader.
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Old 12-09-2010, 12:45 PM   #3 (permalink)
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Thanks for the information... The 200 mile trip was delayed till tomorrow.

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Originally Posted by bloyet03 View Post
i seen a similiar problem with a 1256 international tractor. it was diesel as well. heard a knocking noise every time we ran it. when we had a mechanic look at it, we isolated it to the fuel system. about 6 months later we found it was actually something to do with the a fuel line (don't remember the specifics). i think we wedged a piece of rubber innertube against it. i'm not sure if you got the same problem but might be a place to start.

it ran for years after the noise starting and never had a problem with the fuel system. traded it off on a different tractor only because of its age and we wanted a loader.
DeVere here again about the 90 Dodge Diesel knock noise.

The noise seems to be coming back, but not as loud. I will check more after I drive it a bit. I am still perplexed as to what exactly this noise is. Anybody have any good information about "fuel knock", that is mentioned in various places, but not explained? Thanks again.
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Old 12-09-2010, 08:47 PM   #4 (permalink)
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If you switched the injector to a different cylinder and the knock didn't move then I would assume fuel knock is not the problem.

A damaged piston could change in sound with the advancement or retardation of the injection pump.

If the valve train was out of adjustment or damaged it could change in sound also.

Exhaust manifold cracks and or loosened exhaust manifold bolts.

Issues with the injection pump. Though I do not believe this to be the problem.
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Old 12-10-2010, 02:57 AM   #5 (permalink)
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Update on knock...

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Originally Posted by kstinson View Post
If you switched the injector to a different cylinder and the knock didn't move then I would assume fuel knock is not the problem.

A damaged piston could change in sound with the advancement or retardation of the injection pump.

If the valve train was out of adjustment or damaged it could change in sound also.

Exhaust manifold cracks and or loosened exhaust manifold bolts.

Issues with the injection pump. Though I do not believe this to be the problem.
Thanks for the information. It seems more and more that maybe it is the piston pin or piston slap. What I do not get is that it takes 30 seconds to even make the noise cold, and it was not there when the injection pump was leaking on the case seal. I simply replaced the seal, put it back together and had that darn knock all of a sudden. When I listen to the number 6 injector line by itself, it is making the same knock and is louder than the others, although they all are very loud. I checked the rod and main bearings and they are fine, with no metal in the oil, Yet that knock is still there! I am driving this truck on a 200 mile trip towing a trailer, so I will have a chance to see how the switched injector and advanced timing help it, or not. After a test ride tonight hauling back 425 gallons of water, it ran better then ever before with the injector switched and the timing advanced. Anybody know how far is too far on that injector timing advance? The knock is still there, just different and not as loud as before. Weird stuff here... Thanks for all who are helping me think this all over. I will try putting a rubber hose over the injector line to see it that helps with dampening any harmonics or vibrations.

DeVere
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