Hey guys. I got a pretty loud knock happening with the old Cummins and could use some help identifying it. My alternator went out on a business trip this week. In an attempt to limp the truck to the next town I ran it dead. I had a new alternator put in it and got it all charged back up. 

When I fired it back up it was smoking a lot I had a miss and knocked real bad. I put about 20 miles on it and the miss/smoke went away but the knock is still there. 

It changes up and down with engine speed. I have checked under the hood or tools left over belt issues and anything obvious. Boost fuel pressure and exhaust temp are all normal. 

No check engine light but I will pull codes next time I get a moment. 

Any help would be greatly appreciated!! 

What's your oil level...

Any codes?

Edited January 14, 20169 yr by hex0rz

hmmm... Knock to me sounds like injector or a rod/wrist pin problem unless the dying alternator killed something kinda crazy.  

As the batteries might be bad now from being pulled so low, I wonder if it might be that the batteries are flat.  These trucks do weird things with old batteries.  I know it is unlikely but it is better than a rod issue.  

I would bar the engine over using the alternator nut and pop it back and forth to see if I could get it to rattle.  

Those crazed libs out in that Missoula area are sabotaging your rig, that's my story and I am sticking to it.

 

Seriously though what was your fuel pressure just before the batteries died, possibly ran the voltage down to where you lost fuel pressure long enough to kill the VP and it is dying a slow death but just has not thrown any death codes yet, symptoms sound like they could be all fuel related.

 

Just spit balling here.

Edited January 14, 20169 yr by Wild and Free

Thanks for all the quick reply. 

Oil level good. Still not sure on the codes. As far as fuel pressure it had gotten down to about 12 psi before she died. It did hack and cough and smoke and sputter real good for about the first 10 minutes after starting again though. So I know there was a fuel issue. Maybe the pressure had dropped farther than I thought. 

I am still on my business trip as we speak. I have gotten about 200 more miles on the truck since the incident. No change in the knock at all. 

Sounds more like a vp issue to me. I'd pull the cables overnight just for the heck of it. Can't hurt!

Will disconnecting the batteries like that let things reset? 

I just checked the codes using the key and only got a P0217. Haven't had time to get my hands on a code reader yet. 

Got almost 300 miles on since the new alternator today. Got about 200 to go tonight to get home. Sound has not changed at all. Still the same. 

I still have not seen a check engine light yet though and all gauges are working as they should. 

0217 is an engine overheat... weird. I know unhooking the batteries doesn't erase codes, but maybe unhooking will reset something. Worth a try IMO

sounds like a fuel knock , you may have to find a dealer & have your ecm reflashed. not good to run it like that for sure. sorry to here of your troubles & good luck.

Yea, I wonder if you messed up the ecm or vp44 running the truck dead. Did you charge the batteries instead of using the alternator to do the work? I know you mentioned that they were charged, but how.

Edited January 14, 20169 yr by hex0rz

Disconnecting the batteries will no reset anything software wise other than APPS values that the only thing it dumps.

They used a battery charger while they were changing the alternator. I am not sure what amperage they used to to do it though. 

Is there a quick or easy way to check engine timing on these trucks? I would just like to rule out fuel knock or a timing issue. 

I found this video on youtube. It is not my truck but this sounds very similar to what my truck is sounding like. 

 

 

If this was your truck, where would you start to diagnose it? I just dont understand why I would get a knock after just running it dead and changing the alternator.

That is painful to listen to... Start cracking injector lines and see if you can narrow it down to a single cylinder.

Valve lash...

Very painful. I had to drive it like that for just over 400 miles to get home last night. Never got better or worse, just stayed the same.

I will try cracking the lines this weekend when I get more time.

Why would the valve lash all of a sudden be off? Ran fine and quiet until it died from lack of battery power. Ran like this ever since I got it started again. Not trying to be rude, just curious as to what the cause would be.

I agree, crack injector lines one at a time and see if it isolates one cylinder or quiets down or enhances it. I still think fuel issue caused by low fuel psi/flow from low voltage.

Very good possibility. Without any trouble codes from the VP is there any way to test it? Any way to see if it is firing correctly? I would hate to throw a VP at it if it wasn't a for sure problem. 

I will start by cracking the lines on Saturday. How much do they need to be loosened? Just so they spray a bit? 

Could it be something with that temp sensor messing with timing

That's too definitive to be a timing knock IMO.

Loosen them until you hear the engine start to missfire. You'll know when it's loose enough.