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Help!! Engine knocking?

17K views 20 replies 8 participants last post by  Russ2500 
#1 ·
Howdy guys, Just posted this in the incorrect forum so reposted here...

I'm stumped. I have a 97 Dodge ECLB 4x4 with 211,000 on the clock. Due to some unfortunate circumstances I rebuilt the engine 5,000 miles ago and had the short block and head assembled at a local reputable machine shop. 1,000 miles ago the tranny went and I just replaced that with a remanned 47re.

NOW TO THE ISSUE. Two days ago I was accelerating under light load in town (20 mph) and heard a couple metallic sounding knocks. These immediately went away so I figured I ran over something. 2 minutes later as I pull away from a stop sign (1700 rpm and maybe 25mph) the metallic knocking returns loudly and I immediately pull over. I have it towed to a transmission shop thinking maybe a bolt backed out from the recent swap but they say nothing is wrong. So i now have it at my house and need help.

The knocking is loudest in the cab and under the truck, but up under the hood it is difficult to hear with the other engine noises. In the cab or to the side it is certainly loud enough to make you cringe and yell "shut er off!" It is in time with the RPM's and although I haven't tried driving it yet, I have brought the engine up to 2200 and the noise stays consistent with engine speed and only gets louder. I also found out that the tranny guys never dropped the tranny to physically look at the flexplate and instead only "listened" and knew it was an engine noise.

Tonight I pulled the injectors and inspected them. #6 had decent carbon build up so I cleaned them all (completely disassembled and cleaned) and also switched #6 with #1 to see if the sound changed areas... No change. Checked oil and it didn't appear to have any fuel mixed in with it. Using a stethoscope, I can't seem to pinpoint the noise but I'd swear it's coming either from the rear bottom area of the block or the bellhousing area.

Injector knock? Even though I cleaned and switched the "bad" looking one.
Cracked flexplate?
Rod bearing? (on a "bran new" short block??)
Rod??

Any help would be appreciated. After just rebuilding this pig i'm REALLY not wanting to tear into her again. Tomorrow I will try to inspect flexplate and also see if I can get a borescope and take a peak at the cylinders and pistons... If it's a bad rod or bearing are there other signs I would see aside from noise?

Cheers.

Edit: I forgot to mention that the engine seems to idle and run perfectly. No smoke. No miss. And the little I drove it (to move it for the tow) it seemed it still had plenty of power... Aside from the loud clanking/knocking, it still seems to run like the new engine it is...
 
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#2 ·
My 94 did this and it was a rod bearing. It was a loud knock and the knock macthed rpm. I pulled the head and i could slide #6 up and down. Pulled the motor and stripped it down to the block and in the process of rebuilding it now.
Hope you have a warranty.
 
#3 ·
Unfortunately I do not have a warranty because I performed most of the rebuild myself. I had a local machine shop rebuild and assemble the head as well as the short block. I had them install bearings, rods, and pistons specifically because I did not have the experience to feel comfortable doing that (being that if something went wrong, you have to rebuild...)

Anyways I will be in contact with them tomorrow hopefully and ask them what they might be willing to do if it is in fact a rod bearing... What would cause a rod bearing to go out in barely 5,000 miles??

I'm still holding out for a cracked flexplate, but after reading some other posts, its looking grim. Is there any tests I can perform to help diagnose whether it is specifically a rod bearing? I.e. drain oil and look for shavings, etc? Would I not feel the engine run rough?
 
#5 ·
All the rod bearings I've had go out on me have just been noisy, but for a rod bearing the noise should at least get quieter under load. They're noisiest when there's no load either way through the engine, and engine smoothness would not likely be affected unless it was ready to send a rod through the oil pan.

If it were a manual, I'd suggest blocking the wheels, putting it in 5th gear, starting it up and revving to well above idle, then slowly let the clutch out, just enough to drag and load up the engine and see if the sound goes away, gets quieter, or changes in some other way.

I'm not sure of the best way to duplicate this with an auto aside from getting it in lockup and roll into the throttle, as much/hard as you can without triggering a downshift.

If it's unchanged, look into the lift pump. Of course, they run off the camshaft so the clanking would be at 1/2 engine speed.
 
#6 ·
Update

Ok guys here's an update. After letting her run just a it in the shop and getting second pair of ears, we've determined it sounds like it's coming from rear and middle of the block (middle of #5 or #6...) and NOT the bellhousing. :banghead:

Yesterday I drained the oil to look for metal shards and didn't see any. If a rod bearing or something went out, would there not be metal shavings? I will probably cut into my oil filter tomorrow and see what I can find...

I then filtered the oil through 2 layers of a white t-shirt to catch anything that I may have not seen... Oil appears perfectly clean and I can't even feel any grit when I rub it between my fingers. To my surprise though, a lighter colored ring formed on the border of where the oil had soaked into the shirt. After looking, smelling, etc. I am about 99% sure this is diesel fuel in the oil...

Wouldn't that be consistent with injector issues? Could the lift pump allow oil into the crankcase? I've cracked the injectors one at a time and with my ear I have not been able to hear a difference, but would there necessarily be a major difference? :confused013:

I called some places in Topeka and I think I'll make a trip over there on Monday to see about getting my injectors tested and possibly an oil analysis done.

Thoughts?

Thanks in advance!
 
#7 ·
The two most apparent direct pathways between fuel and crankcase *to me* would be the lift pump or injection pump, but I've not been into either one so I don't know how likely that is.

I've had a couple bad rod bearings in my life, and both times found surprisingly little in the way of visible metal particles in the oil. One I replaced with the engine in-frame and it was only after removing the pan that I saw a thin layer of glitter on the bottom of the pan. I had a flattened cam once that gave me glitter actually suspended in the oil, that was a major disaster. I have never cut an oil filter apart before so I couldn't tell you what to expect in there.

I read back through the original post and what stands out to me is that neither of my rod bearings went that quick. They gradually started making more and more noise over a period of time. That may not be a universal norm, just what happened to me.

I'd say oil analysis is a good idea at this point. If it is a bearing or something else mechanical, they'll get a metal particle reading off the charts, and may even be able to tell you what kind of metal it is, narrowing the list of likely culprits.

I would focus on the lift pump right now. What's your fuel pressure at? Can you stethoscope the lift pump itself? Is the knock occurring on every rotation of the crank or is it at 1/2 crank rotation?
 
#8 · (Edited)
Hmm that's a good point. I haven't had much experience with rod bearings but I do know the few I've dealt with have come gradually now that you mention it. I will pull LP tomorrow to inspect it... Also I have a hard time determining if it's 1/2 the rpm or every rotation of the crank, but to ME i wanna say it is with every engine rotation... I'll double check tomorrow and see if I can't figure that one out. Feel kind of dumb I didn't listen closely enough earlier.

I was actually in the process of putting a pressure gauge on it, but time hadn't allowed me to finish it before the knock occurred and I put it in my shop. :doh: Maybe tomorrow I will try to install the gauge and see what pressure i'm pushing for fuel... From what I've seen on other threads I install it on the banjo fitting going TO the injector pump (not the return line), correct? We will see how my drilling and tapping skill are.

Once things open up on Monday I'll make a trip to Topeka and get the oil analysis going as well as see about testing injectors. How much should I expect to pay for testing injectors? I haven't been able to get a straight answer from a shop yet... with 211,000 on the injectors, would it be better money spent to just order a set of remanned ones and put them in... not knowing 100% if that's the problem?

Like always, thank you so much for you wisdom and advice! It is really appreciated.

Caleb
 
#9 · (Edited)
Correct on the banjo bolt. You want the one on the bottom rear of the IP, you'll have to pull your intake horn to get to it. NPT ports are among the more forgiving of tapping exercises. They're tapered so they are pretty good at self-aligning and you'll need to put thread sealant on it anyways, so it's not the end of the world if you start the tap -eyed. When cutting the threads, use lots of lube. For this, WD40 or used motor oil will do. Cut 1/4 turn, then back off 1/2 turn to evacuate chips. Advance to the point of cutting, then cut 1/4 turn, back off 1/2 turn, etc. A tapping wrench is highly recommended. Cut threads a little at a time, pull the tap out and thread in the actual fitting you intend to use to gauge your progress, I like to stop when there are 2 or 3 threads still showing with the fitting as finger-tight as you can get it. Make sure it's CLEAN of chips before you put it back in, that would nuke your IP in a huge hurry. 3 wraps of thread tape on a 1/8 NPT fitting works best for me.

Your IP will be empty of fuel after pulling that banjo bolt out, so loosen the OFV to let the air purge out easier while cranking, and tighten the OFV when you see evidence of fuel burbling out.

As far as the injectors go, I was under the impression they lasted a lot longer than 200k, but I could be wrong. As far as putting new ones in, I would investigate one avenue at a time. Lets see where the lift pump gets us. Oil analysis may be a non-issue after tomorrow. :thumbsup:

As for listening, something you might try (no idea if this will work) is feeling one of the injection lines as the truck idles. You might be able to feel the injection pulses, which occur at 1/2 crank rpm. If that doesn't work, try one of the soft lines between the IP and the lift pump, as the lift pump cycles at 1/2 crank rpm as well.
 
#10 ·
Dauntless, Thanks for the advice. I just got the lift pump pulled and everything APPEARED ok... The plunger slides freely and the spring certainly seems to work (takes quite a bit of pressure to push the plunger in).

Would it be good to still replace this and see what it does? Or simply reinstall and begin focusing on injectors? Autozon3 has one for me but wants 150 for it and if I don't need to replace it I'd rather not... :confused013:

Caleb
 
#13 ·
Yeah unfortunately I don't have an extra pump laying around. Autozone had one so I took a look at it and compared to the one I pulled off. Plunger, spring, and everything else looked and felt exactly like the brand new one. Spring still required significant force and there wasn't any give that I could see.

Ok so I finally managed to get a video uploaded of the truck running. Also, Dauntless, I listened carefully and the knock appears to be 1/2 the engine speed )listened with the stethoscope to the lift pump and compared as well as used the injector lines as a guide. thanks for that advice).

Not sure how to upload the video to this post, but here is the link:
97 Dodge Cummins Engine Knock... Fuel knock? - YouTube

To recap:
- Significant knock that is 1/2 engine speed
- some fuel in oil
- no metal shavings visible (no oil analysis yet... Thanksgiving and all...)
- Tranny shop says not the flexplate but I haven't pulled tranny to look personally
- occurred suddenly and does not appear to affect the engine idle or power (haven't driven it much since it happened though)

Maybe this will give someone a better idea of what's going on. I switched up the injectors and the sounds seems like it COULD have moved cylinders, but even with the stethoscope I couldn't tell. I plan to call an injection shop that is semi-local tomorrow and see what they suggest.

Caleb
 
#14 ·
It's amazing how loud it is away from the engine...

Did you stethoscope *each* injection line? Was there one in particular that the knock seemed to be "in sync" with?

I've never heard one in person before, but it sounds like an injector when I compare your video against other videos of injector knock on Youtube. Listening to it now, I might have a very faint one in my truck.

Listen to this one, when the idle speeds up a little around 0:30 it sounds VERY similar. To me, anyway:
 
#15 ·
Dauntless, because it's a little more difficult to hear from up front I had a difficult time determining if it was in "sync" with the knock... But #4 (previously #6 before I switched up injectors) seemed louder by a little.

Also, thanks for the video comparison... I had seen this video a few days back but it hadn't dawned on me how similar mine sounded once it was on video... Thanks! I'm feeling pretty sure about it being a fuel knock so hopefully tomorrow the injector shop can help me button this issue up.

Anyways, I'll let you know what I find tomorrow.

Caleb
 
#16 ·
I know most threads die out before the answer is given, so here's at least my current answer.

I took the injectors and had them cleaned and pop tested. They all checked out. The tech said they were a little low, but all were the same and still popped a good pressure. Props to Injection Turbo in Topeka, KS... $10/injector and they were done in an hour. I put them back in the truck with new washers, o-rings, etc. and the knock was still there. I let it warm up for a minute then slowly brought the engine up to about 2000 RPM... Knock got louder and stayed with engine speed. Partly due to frustration, I hit the go pedal again (in P so no load) and brought RPM's up to about 2700... About as far as my truck lets me get. After holding it there for a few seconds, the knocking became random like something bouncing around a little. Scared, I let the engine go back to idle and shut her off. A couple seconds later I turned it back on and the knock was gone!

After a few minutes I could hear a faint knock and it is most prevalent around 1100 RPM, but to me, it sounds like a normal cummins again... May still be a faint fuel knock, but certainly bearable and doesn't sound like the truck is coming apart now. A video wouldn't record it probably.

Any idea why high RPMs would make it go random like a ball bouncing around then stop completely? I'm a little confused but happy. :party018: Maybe had something in an injector port that finally pushed through? Or maybe valves? I'll triple check valves tomorrow morning and see how they are...

I'll change out oil and switch to a Mopar filter since the old stuff had fuel in it and probably call it good unless it comes back. Speaking of filters, is Fram oil filters still not good to use on the cummins? I remember seeing a bulletin somewhere but didn't they fix the issues with it clogging the cooling jet?

Thanks for all the help! Definitely helpful information. :thumbsup:

Caleb
 
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#17 ·
Interesting.

Fram is a no-go, they've been known to get the guts pumped out of them from normal (well, Cummins normal) pressure surges. I run Fleetguard but there are tons of acceptable brands.

If the tech was paying attention, he should have noticed either pressure-related symptoms or visual indicators of a plugged port during the pop test (like 4 spurts of fuel instead of 5).

Your plugged injector theory is as good as any though I suppose, and it kind of makes sense that it went away as fast as it presented.

The next few times you drive it, don't baby it. See if it clears up more or comes back. Don't stomp it's guts out either but roll into the throttle a little more than normal.
 
#18 ·
check the push rod's we had a 12 valve 93 that sounded like a rod and turned out to be a bent pushrod
 
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