Bad engine rattle when warm
 

Howdy all. New guy here. Just wanted to say I appreciate all of the great info here and the time you all put into helping people like me out. Between working and trying to farm a little on the side I don't have much free time but hopefully I can be of some use myself.


Anyway on to my issue. I have a terrible rattle when accelerating. It typically happens in the 1200 - 1700 rpm range under light throttle. It is nonexistent at idle and goes away with moderate to heavy acceleration or higher rpms. It started about 6 months ago and sounded like valvetrain rattle. Finally got around to running the overhead, it was out a little but not bad, but made no difference in the rattle. It has since been getting progressively worse. I have researched it till I am blue in the face and cant seem to get it figured out. Obviously my biggest fear is losing an injector and burning a piston. No other injector related issues though. Easy starting, no white smoke, a very little pre boost black smoke on hard acceleration. I should mention I have reman injectors with +/- 50k on them. Rail pressure seems to be ok. 7k idle 17-18k cruising 20-21k WOT. Have "re clocked" cp3 gear twice with no real change. Had a local shop run the contribution test which showed a range of 96%-105% if I remember correctly. Finally the thing that has me stumped is that it only occurs when engine is warm. It is nonexistent until engine reaches 140 - 160* and then slowly starts getting louder until engine reaches normal 200* operating temp. I was under the impression that if it were injector/combustion related it would be louder when cold.


Sorry for the long post, just want to give as much info as possible. Curious to see what you all think. Thanks is advance!

Without actually hearing the noise, I will take a wild guess and say that it sounds like piston slap or wrist pin noise.

Suggest that you get an oil analysis done and see if that tells you anything.

Thanks for the reply. I did have an oil analysis done and it came back good. Ive not had time to study the results but it didn't flag anything as being too high. As far as describing the sound the best i can do is like spark knock/detonation from low too low of octane in a gasser as it is warming up. Almost pinging like. Then after it is warmed up fully it becomes more metallic like. More rattle like though than rod knock like. I know what a rod knock sounds like but not sure bout the wrist pin or piston slap.

Rattle
 

Leaking injector will cause a rattle sound . I had high fuel rail pressure . Causing injector leak and a rattle sound . But if you had oil checked , no fuel in oil that may not be your issue .

I would check all the injector line clamps. I had 1 come loose and it drove me crazy for about a week before I found it. Was almost identical to what you describe

Thanks again for the replies, I really appreciate it. Been busy mowing hay all weekend but finally got around to checking the injector line clamps. Found #4 was stripped. Must have done it when I replaced #4 line several years ago. Anyway found one size larger bolt and got it to thread in good and tight. Made no change in the rattle. I am really starting to worry it may be something internal as it seems to be getting progressively worse. Best I can tell the noise is coming from underneath the truck, oil pan/bell housing area. Hard to tell though as there has to be a light load on engine for it to rattle. I cant think of anything clutch related that could cause this. I would think throwout bearing would only act up when clutch was engaged correct? By the way I have gotten rid of the dual mass flywheel, have a solid one now. Have not ruled out injectors either. The thing I am having a hard time with is the fact that engine has to be at operating temp for it to occur. In my novice opinion this would point to something that is oil lubricated. Am I thinking correctly? I would assume that if it were injector related the warmer the engine the better it would combust fuel lessening the injection rattle?? By the way I have been running diesel kleen for several tanks as well as the ashless 2 stroke oil and the noise has only gotten worse since. I may try to find a good diesel mechanic and have him look at it, as I don't want to start throwing parts it without knowing what is wrong. Just hoping to save some money and diagnose it myself. Any more input would be greatly appreciated!

I recommend to connect a real oil pressure gauge and monitor oil pressure.
The factory oil pressure gauge in the dash cluster is a fake and should be ignored.

An injector kill test with a high end diagnostic tool or disconnecting one injector at a time may help to narrow down the rattle to 1 cylinder.

Keep and eye on the engine oil level in case this is an injector. Not for going down but for going up.

Ill try to connect an oil pressure gauge soon. Is there an empty port I can tap into or will I have to tee off of factory sensor? I hauled some hay last night and man its hammering bad. Im afraid its time to park it till I get something figured out. If I drop the oil pan will I be able to check the condition of the rod/main bearings and wrist pin or do the pistons have to come out? Also I have had the kill test done but cant tell anything because the knock/rattle is not present at idle. Any more insight would be much appreciated. Thanks!

Also I am not making any oil, actually using about a quart between 5-6k oil changes.

Another wild guess as part of the process of elimination.

Check the harmonic balancer at the front of the engine for any signs of rubber deterioration. Also go over the exhaust system for any loose clamps. Doubt if it is any of these, but check anyway.

Sorry, can't tell you where to tap into the oil system on your engine, but it probably is the easiest to just use the oil sender port.

Thanks for the reply. Ill definitely check those things. Just throwing something else out there. I pulled a U0019 code that I cant clear. Seems it is related to the tipm. My tipm is toast, ac issues, trailer turn signal issues, ect... but I don't think the tipm is related to my problem, just throwing it out there just in case.

Figured Id post an update. I have checked everything on truck that could possibly rattle with no luck. I did find that the clamp on the turbo elbow to the downpipe was loose. Tightened it and no change. So I am confident it is either a fuel/injector issue or internal motor issue. I am leaning towards injectors because I don't see a stock 191k Cummins having bottom end problems without having burnt a piston or something, but definitely not out of the realm of possibility. Anyway my plan of action is to get a fuel rail test cap and kill one cylinder at a time to hopefully narrow it down to one. Once I find the culprit Ill switch injectors with another cylinder to see if the noise follows injector or remains at same cylinder. If noise follows injector it is obviously the injector. If not then time to look deeper in motor. Just wanted to post up and see if this course of action makes sense.


By the way I know that this is basically the same as having the kill test done with scan tool, but I figure the cap will give me a little more flexibility to rev motor etc... as I cant hardly hear noise at idle.

Check the FCA if fuel pressure fluctuates more the 500 psi from set point at idle then most likely the fuel control actuator.

I watched my rail pressure closely yesterday while driving. At idle I'm fluctuating 400 psi at the most. 7000 to 7400. When accelerating it seems that pressure spikes very quickly. If I just barely roll into the throttle it jumps to 17-18k immediately and that is where I hear the rattle. If mash on it pressure drops for a split second then back to 17-19k. Having a hard time seeing 20k even at full throttle. However the rattle instantly goes away with more throttle. Am I spiking pressure too quickly at very light throttle causing the injectors to rattle like crazy? In summary my truck rattles like crazy under light throttle with rail pressure at 17-18k only when engine is warm. I would be thrilled if it were only there fca.

hello im wondering if you ever found what was creating this rattle?