Engine/Transmission (1994 - 1998) intermittant Knocking

[Earlschultz]

alright guys I am in desperate need of some help. The truck is a 1996 12v 4x4 5speed #10 370s afc 3/4 foward bhaf 4inch exhaust. Ok now the problem the truck is developing an intermittent knock that has become not so intermittent.

it knocks most at cruise speed light load sometimes after a run down the tollway it knocks very loud for a few minutes. i've changed the lift pump the overflow valve, replaced the return line, new fuel filter,cleaned and replaced gaskets on the heater and replaced the little 90 degree fuel hose. i did a compression test and had 450lbs on all cylinders. if you listen under the truck it sounds like its gonna throw a rod but the knock has been around for quite awhile. i have also noticed that the knocking quiets way down when it warms up outside I am at a loss and getting pretty scared. I just threw a rod on my jeep with 33000 miles Iam gonna be wheel-less pretty soon . oh yeah i also have some black goo around my exhaust manifold gasket on cylinders 3 and 6

 

[Forrest]

If it was a rod @ the crank, then oil pressure would be way low ... wonder if it could be @ the piston?

 

[Earlschultz]

i thought about that it has seen a few 1500 temps but only for a few seconds is that enuff to hurt it? Piers told me that if it was a rod bearing it would go rather fast maybe a wrist pin? oil pressure at 2000 is slightly over 40 at idle it falls to the low side of the 40 notch

 

[NCovey]

Does the truck ever shake when this knocking starts, could it possibly be from a cylinder that isn't firing, like maybe an injector plugging up? Just a thought without hearing it. -Nicholas

 

[Earlschultz]

no vibration when knocking present idles smooth runs strong but i wont git on it till i know whats up. Engine noise cackle or clatter has markedtly increased. I've checked for exhaust leaks but cant find any. Thinking this might be the cause.

 

[Whiskey]

Wrist Pin Maybe

whiskey

 

[NCovey]

The quieting down when the outside temp warms up is what throws me. I would think if an internal componant were going bad, it would sound the same no matter what the outside temp was. Have you noticed any debris when changing the oil?-Nicholas

 

[Earlschultz]

no debris in oil last oil sample good next one goes this weekend . I also wonder if its a fuel related issue fuel knock maybe? could a injector be bad? and if so both sets ? I switched back and forth to see if it went away. It didn't

 

[Vaughn MacKenzie]

Maybe it's a separated crank pulley damper?



I would check oil pressure with a mechanical gauge. Should have a lot more than 40psi at 2000 RPM, more like 60-70 I would think when warm.



Vaughn

 

[BPonci]

Try pushing in on the primer pump button. It could be your lift pump ticking or some concider it a knock.

 

[NCovey]

Earl, is there any chance you are near me?-Nicholas

 

[Earlschultz]

Nicholas



i would love to say yes in hopes of some help but alas no addison illinois

 

[ABorchard]

Sorry to say it but I had one knocking like you explain a few years back, having the injection pump rebuilt fixed it.



Before you go that far I'd have the injectors popped tested first.

 

[NCovey]

Sorry, I can't help you out more, I will try to rack my brain and see if I can come up with something else. -Nicholas

 

[Jschafer]

My oil pressure has been just like that from day one A little over 40 at rss or cold a little under 40 warm and idle.

 

[Earlschultz]

could this be a fuel knock ? maybe air in the lines ?could the ambient temp changes cause gaps somewhere letting air in? how would i check for this ?

where would i put the sight glass return or feed or both? if it is the pump (p7100) are they temp related finicky? oh by the way the truck has 132000

miles 100000 of them on 285/75/16 size tires the math slips me at this point but it is a bit more. the lift pump was replaced not long ago due to weak/falling fuel pressure under load.

 

[acook]

I agree with A Borchard. After working in a Cummins distributor for the last 11 years, I have seen this several times. ( P7100 fuel pump) If nothing is showing up in oil samples or if no metal is found when cutting open the filter, I would not think rod or main bearings. This type of failure will show up a copper color in the filter and you would find fragments. If the engine has been overheated at some point and you think scored piston, this will show up as excessive blow-by out the breather tube, usually followed by oil leaks. The easiest way we would locate this is to run on the dyno under load and have someone by the engine listening. This maybe an expense now, but a lot cheaper than a major engine failure. I would not keep running the truck and take it somewhere and have it checked out.

 

[Earlschultz]

alright then can anyone recommend a reputable repair facility in northern illinois or indiana?

 

[BigPapa]

Mine's doing something similar. It's not quite a "knock". More like the engine is pulling a cylinder that's not pulling it's own weight, if you know what I mean. I've had 2 different shops say it could be an injector going down. It has been a while since my last fuel filter change, I'm going to take care of that first. If that doesn't fix it, I think I'm going to go to some 370's. I think I can handle the labor so I'd rather spend my money on the 370's than paying someone to test my stockers. I was really planning on a plate and GSK first, though.



Scott

 

[mechanic]

alright guys I am in desperate need of some help. The truck is a 1996 12v 4x4 5speed #10 370s afc 3/4 foward bhaf 4inch exhaust. Ok now the problem the truck is developing an intermittent knock that has become not so intermittent.

it knocks most at cruise speed light load sometimes after a run down the tollway it knocks very loud for a few minutes. i've changed the lift pump the overflow valve, replaced the return line, new fuel filter,cleaned and replaced gaskets on the heater and replaced the little 90 degree fuel hose. i did a compression test and had 450lbs on all cylinders. if you listen under the truck it sounds like its gonna throw a rod but the knock has been around for quite awhile. i have also noticed that the knocking quiets way down when it warms up outside I am at a loss and getting pretty scared. I just threw a rod on my jeep with 33000 miles Iam gonna be wheel-less pretty soon . oh yeah i also have some black goo around my exhaust manifold gasket on cylinders 3 and 6

I would check for a bad injector before doing anything else. A leaking injector will hammer like a rod bearing. But a rod is quiter when cold. Just loose the injecter line to each cylinder and see if the knock disappears. If it does, pop check those injectors.



A piston will get quiter when hot, but unless you have overheated the whole engine or used an oil filter on the "do not use list", I doubt that you have a problem there.