Engine/Transmission (1994 - 1998) Got a new 12v truck and has a knock??

[JCurry]

I have a 01 24 valve cummins. I just bought a 12v 96 cummins 4x4 5 speed 3500. I have a knock in the truck and the more load i put on it the louder the knock gets. Other than the knock, the truck runs great, plenty of power pulling my 10k lb trailer, idles great and starts right up. I have put 500 miles on the truck since i got it and the knock is still there but has not gotten worse, or better. I have tried lucas injector cleaner, power service, changed the oil, cut open the filter to make sure there were no metal shaving in there (from rod bearing) and no luck. I just took the truck camping this weekend and it ran great the whole trip. The knock worries me because my 24v sounds nothing like it so i know its not just a "diesel" thing. Any help would be greatly appreciated, i hate to keep driving it like this but its my daily driver.

 

[kenny61]

The 12valves are noiser than the 24v



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This thing got an 01 24valve in it...





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[JCurry]

Is it normal to hear a knock inside the cab with the windows up? Is it normal to hear it with the windows down about 60mph? I can hear it over the wind, if its normal im fine with it but that just seems like a little much?

 

[kenny61]

Without hearing it I do not know if its normal or not. I'm just saying that 12v are noiser and knockier than the 24v's. My 12 v is noisy as hell in the cab. You kinda have to shout to have a conversation due to the engine noise coming thru the firewall. If your 12v sounds like the one in the above video it is normal. If it is knockier there may be something wrong. heres 2 examples of inside noise



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[JCurry]

Mine definitely has a louder knock than both of those. You can hear it until the turbo kicks in and seems to get quieter the higher in rpm you go. Anything over 2200 you can just hear the straight pipe. Anything under you can hear it knocking on every fire the faster it runs the more knocking you hear, if you go down a hill and let off throttle, you can harley hear the knock til you hit the throttle again.

 

[RyanStewart]

Have you tried checking the valve lash?

 

[kenny61]

from reading these threads knock can be a lot of things from a bad fuel filter to a bad cylinder. since you just bought it I would change the oil and fuel filter. cut the old oil filter open and look for metal also the drain plug and waste oil. I would check the valves as well. after that try loosining the injector lines 1 by one see if the noise is limited to one cylinder

 

[ata]

It sounds like you have a hurt piston. Warm the engine up and crack the injector lines at the injectors one at a time with the engine running. Make sure you have a face shield on and gloves. If you find one that makes the noise change or go away that will be the clyinder to look at.

 

[JCurry]

Ok i did cut and check my filter and there was no medal in it. I will check the valves this week and try cracking the injector lines tomorrow to find the cylinder. If it is a bad piston my bet is it is #5 or #6. I can hear it more in the cab than i can outside the truck. If it turns out to be a bad piston do i need to remove the motor to fix it? Will i end up needing more work if i keep driving it with the bad piston? What is average cost to fix a bad piston? I just noticed today that there is some sort of fix leak or something in the radiator fluid i can see small copper pieces floating in it. Thanks for all the help guys i want to try to do most of the work myself if possible. Other than the knock the truck runs awesome.

 

[JCurry]

Sounds like this YouTube - Cummins knock

 

[kenny61]

If your gonna burn a piston it is usually no 6 they run the hottest on these motors. you gotta remove the oil pan to get to the connecting rod bolts and i am not sure if there is enough room to pull the piston under the cowl. You might be able to do it but i would pull the motor. the block may also require machuine work to clea up the cylinder depending how bad it is. depending what is broke yes you can do more damage by continuing to drive it. you might have one of these in there. Do the injector test and tell us what you got #ad

 

[kenny61]

thats a tap not a knock, this is a knock <object width="425" height="344"><param name="movie" value="http://www.youtube.com/v/u_Uh0Y_cTJk&hl=en&fs=1&"></param><param name="allowFullScreen" value="true"></param><param name="allowscriptaccess" value="always"></param><embed src="http://www.youtube.com/v/u_Uh0Y_cTJk&hl=en&fs=1&" type="application/x-shockwave-flash" allowscriptaccess="always" allowfullscreen="true" width="425" height="344"></embed></object>



Actually its really hard to tell from the audio on the video but it does sound more like a tap. I have read a bad lift pump will tap but do not know how loud. if the injector test doesn't do anything check that next

 

[SFPADGETT]

One other source of a Loud Knock is a bolt backing out of the torque convertor, it will sound like a rod is knocking. You can check the bolts through the inspection plate on the transmission. Much cheaper to repair, and easy to check

 

[champspa]

I could be the lift pump , the spring can lose its' tension and it hammers like a rod . a new pump kit or stretch the spring just to give it a check. I'll bet this is what your hearing

 

[MMiller]

I could be the lift pump , the spring can lose its' tension and it hammers like a rod . a new pump kit or stretch the spring just to give it a check. I'll bet this is what your hearing

I agree with this one first. If it was a burnt piston, he would have metal in the filters, and it would get worse very quickly. Do you have any idea where the timing is set at?



Michael

 

[JCurry]

Which spring do i stretch? Is it the one on the overflow valve or inside the lift pump? For the price of the lift pump that would be great if that is all that is wrong. I have no idea what the timing is set at or how to check it? Is a lift pump change fairly simple to do for the average joe?

 

[champspa]

stretch the overflow valve spring . sometimes the rod on the pump wears and you have to get a new pump (about 80 bucks) your fuel pressure should be about 20 to 35 lbs. I stretched mine real far and it came back to 32 psi , then I ordered a new valve.

 

[JCurry]

I stretched the overflow spring (it was a little less than 1/2"). Truck does seem to run a lil better but have the same noise. It has not got any worse or better stays about the same. Any lift pump better than the other? I would rather get a good one the first time then have to buy another next year. Any sponsors want to sell me one? PM ME!

 

[Dieselnut59]

One other source of a Loud Knock is a bolt backing out of the torque convertor, it will sound like a rod is knocking. You can check the bolts through the inspection plate on the transmission. Much cheaper to repair, and easy to check

His truck is a 5 speed. The pressure plate can rattle a little as the bushings wear. Does the noise change depending on what gear you are driving in? Does it change if you disengage the clutch?

I agree on the lift pump. My '96 has a loud "ticking" under the driver side cab area, where the plastic section of the fuel lines "cavitate" with the pulses of the transfer pump. It is less noticeable with a higher amount of cooking oil, so I do not worry about it.

 

[MLee]

Does'nt look like this has been suggested yet. Get a piece of rubber hose 3-4' long and put one end to your ear, and the other use it like a listening tube, place it in the areas that you think mite be making the noises. You can also purchase a mechanics stethoscope for a few dollars. After listening to your engine with this you just might decide to ride a bicycle.