Need help before I Really mess up

[Rob4]

I posted a thread a while back and thought things have changed somewhat that I should just start a new thread. I have recently installed a low mileage 2002 military surplus AMG/GEP 6.5 in my 1994 one ton. It ran just great with a very faint knock mixed in with the normal engine noise. However it was quite loud inside the truck down low by the heater. After about 40 miles the noise seemed to become somewhat louder and on the advice of some TDP members I have done the following:

Verified that the noise was from #8 by loosening each injector line one at a time.

Swapped out the injector on #8 twice with known injectors

I had replaced the metal coolant line that runs along side the passenger side of the engine with a regular rubber hose when I installed the double thermostat crossover and had zip tied the hose to the #6 and #8 injector lines. When I pulled the hose away from the lines the noise inside the truck stopped. (so much for rubber Isolating vibration?) It had no effect on hearing the noise outside the truck.

I ran a compression test and all read around 410-420 PSI.

I pulled the pan ( after pulling the front differential ) checked all the rod bearings and all are fine.

Inspected as best I could the bottom of the pistons and skirts as well as looking for any scoring of the cylinder walls and could not see any obvious problems

I pulled off the rocker/valve cover and again could not see anything wrong.

Before I haul off and pull the head, am I missing something really obvious??? I'd hate to continue to tear down an engine that so far looks just perfect inside and than ask questions. The noise from the #8 injector line being picked up by the heater hose worries me a little... Would a knocking noise inside the engine cause a knocking noise from the injector line, or the other way around? Is it possible the noise could be coming from the IP? The IP worked great when I switched it over from another engine. Prior to tearing down the engine I put the truck under a load and the knocking sound seems to decrease, or at least it's not as noticeable. The sound doesn't seem really deep. By ear, it sounds like it is above the crank, so I ruled out a main bearing----?. Doesn't a bad wrist pin produce a double knock? I need input from the members. Any ideas?

Thanks in advance for any input.

[john8662]

Nothing should be allowed to touch any of the injection lines on the engine, including the heater coolant line.

Ensure that all the lines are not touching anything and that they all have sufficient clearance from the valve cover or brackets holding them to the valve cover. When they touch a surface, the pulse of the injection event can cause a knocking noise that you'll certainly hear from the cab.

Can you record the sound it makes externally (after fixing any line issues)?

Although, not really likely, a crossed injection line can cause a knocking noise, and a miss, this is something to verify is correct as well.

Your compression is great!

J

[tommac95]

Sorry to bother , but is this an electronic DS4 pump , or a mechanical (DS2?)?

I maybe should not say this , since i'm not expert , but i think that characteristics of a bad valve in the line at the output of the FIP might be another cause of knock. [of course you said the pump was OK]....

[DmaxMaverick]

Sorry to bother , but is this an electronic DS4 pump , or a mechanical (DS2?)?

I maybe should not say this , since i'm not expert , but i think that characteristics of a bad valve in the line at the output of the FIP might be another cause of knock. [of course you said the pump was OK]....

That could be the problem, if the IP were an inline pump. The axial pumps, such as the DB/DS pumps, share the plungers (pistons) with multiple cylinders. It is possible the head (inside the pump) could be damaged at one cylinder port, which could cause a pressure drop at that one cylinder. Not a likely scenario, though. Not that it couldn't happen, just that I have never heard/seen it. Usually when the head/rotor starts to go (other than progressive wear), they go together, effect all cylinder injection events, and worsens rapidly (self destruction).

[Rob4]

The IP is the electronic DS4 type. It came from the old engine we pulled out, which ran great until the #6 piston cracked.

About the injection lines touching something... Will that cause a knock from within the engine? I could understand them causing a tick or rattle where they touched, but I've crawled all over this thing listening to it and the knocking sound is coming from within the engine. Near as I can tell, from the head at #8, or a little lower.

I'm reasonably sure I don't have any lines crossed. I think it runs too good for that. No miss, just the sound.

I've done everything I listed above and this engine looks perfect, except for this sound. This thing is driving me nuts! I'm afraid I'm going to end up completely dismantling it and not find anything wrong.


Thanks for the replies so far. Any more ideas?

[DmaxMaverick]

If an injector line is touching ANYTHING, it can send the event pulse to sound like it is coming from just about anywhere. And, it can be quite loud. The lines should be touching NOTHING, but the isolators, and they should properly secured.

Your noise could be any number of things. If it's there, no matter what you do (including injector line isolation), then it could be an exhaust leak, or a rocker arm retainer button has broken (they're plastic, but easily repairable, if it isn't too late). If the engine still has "normal" power and is smooth (as smooth as it's ever been), then it's likely not serious. A wrist pin noise will usually change with differing power load levels, either silent at idle and noisy at higher RPM, or noisy at idle, and silent at higher RPM. If it's really worn out, it will be very noisy at any RPM, but the sound will change as load increases. Another possibility is a broken valve spring. No biggie, it can repaired with only valve cover removal.