Knock while cold.

[Mopar1973Man]

I've got a member (Towhungerford) that called today and is having problems with a 2003 Dodge Cummins that has a knock while under load and goes away after it warms up. The injectors where just replaced and the knock came after the injector replacement. The injectors where replaced because of hard starting issues. But now there is a audible knock while under load cold but as the engine warms up the knock leaves. Got me scratching my head.

[bjytech]

Since the injectors were just replaced I would re-check the injector hold downs and make sure they are up to torque, my thinking is something isn't quite tight enough when cold but as things get warm everything expands and seats properly.

[cajflynn]

FCA?

[AH64ID]

Any codes?What kind of knock? Is it a ping like detonation on a gasser?Does he run Cetane boost?

[Mopar1973Man]

No codes that I've been told.He describes it as like a piston slap knock kind of.Unknown on the cetane boost I'll ask.

[AH64ID]

Is there a way to verify that 03/04 injector tips were used and not 04.5/07 tips?

[Mopar1973Man]

Just left him a message so I can get more feedback on this...

[dobienut]

Can't remember where I read it and I never did understand how it could be the cause, but I thought there was a TSB out on the 5.9 dealing with an engine knock under load, and it was caused by the thermostat

[Mopar1973Man]

I talked with him for a short time and it had something to do with air bubbles in the return line. This is what he chasing right now. There a pump on the back of the CP3 that he ordered.

[AH64ID]

Can't remember where I read it and I never did understand how it could be the cause, but I thought there was a TSB out on the 5.9 dealing with an engine knock under load, and it was caused by the thermostat

I beleive that was a 2nd Gen 24V issue.

I talked with him for a short time and it had something to do with air bubbles in the return line. This is what he chasing right now. There a pump on the back of the CP3 that he ordered.

Interesting. It could be the gear drive, but don't see how that would cause the knock only when cold.

[dorkweed]

Mike,Can you elaborate the "under load cold" statement???? IOW's is he starting the truck up cold with the toy hauler loaded to gills and driving away without a warm up????:smart:My normal routine when getting going in the AM is to start the truck, back out of my garage, turn around, back up and hitch up my trailer. I then close my garage door, lock it, get back in truck and drive away. Usually under 5 minutes.That said, even with the stupid hot/humid weather we've had here, my truck is not to operating temp...............but it has had enough time to get oil everywhere etc.!!! When I drive away, it's noticeably more "noisy" vs. when she's fully up to operating temp.Is this what he's hearing???The above is also true if I just back out of my garage, close it, lock it and drive away without a trailer. Truck is louder because she's not up to operating temp.:smart:Disclaimer....................This is my truck; your truck my vary!!!

[Mopar1973Man]

Empty truck no load. Manual transmission... All he's got to do is start up let it built oil pressure and drive away. By the time you shift into 3rd gear and roll into the throttle it starts knocking. He's got a theory that it might be a air issue.

[MnTom]

I had a Ford 302 that would sound just like a rod knocking when cold too. Once I got to the end of the block it would sound normal and not knock until the next morning. Never figured that one out. I also was running a 290 Cummins (1973 model) that had a knock in the auxillary drive gears (we thought) that sounded like a rod when it was run against the governor with no load. It ran over 80k miles like that and I quit so I don't know how much longer it was run like that. In other words some knocks can be very difficult to find and fix.

[towhungerford]

Hey guys sorry for the slow response things have been very busy at the shop and home. Anyway the sound i was hearing was most noticable cold and would hardly be audible fully warmed up. Truck came in for a no start issue and was diagnosed as high returns in the injectors. So we put a set in from Diesel Pump & Injector Service in Houston, Tx. I never noticed a knock after i installed the injectors, so customer picks the truck up and calls a few days later saying the truck had a knocking sound. So he brings the truck back and sure enough i heard a knocking sound when the motor was cold. I could put it 3rd and come off the clutch kinda fast and it would kinda sound like a fuel knock or a slight pinging sound. Also taking off hard throttle i could hear it too. I ran the overhead just for sh--s and giggles but no difference. I checked exhaust temps with an IR gun and all clys where even. So I called the place where we got the injectors from a he told me about another customer that had the same issue, he put clear lines to and from the cp3 and found aeration in the return from the pump. He replaced the lift pump on the back of the cp3 and fixed his issue. so I did the same test and got the same results. Replaced the lift pump on the back of the cp3 and the noise is almost completly gone. On a side note something thats still in the back of my mind is that the engine is an HO model and not sure if non HO injectors would cause the noise I was hearing. Thanks for all input and ideas on this issue.

[mopartechnician]

The ho and non ho are different injector nozzles. The ho has I think one more hole. I had a customer that told me he had a 04.5 ho motor, so I installed the injectors and this thing smoked like there was no turbo. Anyways, come to find out he has a early 04 motor and he thought he had a ho because it was a manual. So now I always look at the engine label. When I first heard about this, I was thinking bad injectors. That is how I used to find bad injectors was to put the truck under the load and listen for knocking like an old 12 valve, then with the star scan I would cut out each injector until the knock went away. I have never heard of the pump on the cp3 going bad, but I am always learning stuff everyday. I wonder why the pump is putting air into the rail and how its getting into the fuel system?

[AH64ID]

The ho and non ho are different injector nozzles. The ho has I think one more hole. I had a customer that told me he had a 04.5 ho motor, so I installed the injectors and this thing smoked like there was no turbo. Anyways, come to find out he has a early 04 motor and he thought he had a ho because it was a manual. So now I always look at the engine label. When I first heard about this, I was thinking bad injectors. That is how I used to find bad injectors was to put the truck under the load and listen for knocking like an old 12 valve, then with the star scan I would cut out each injector until the knock went away. I have never heard of the pump on the cp3 going bad, but I am always learning stuff everyday. I wonder why the pump is putting air into the rail and how its getting into the fuel system?

It sounds like you are using 04.5 as the HO designation, and that is not correct. 03-04 had a Cali, SO, HO motor and all 3 use the same injectors and nozzles. 2004 had 2 different HO motors, a early 305hp and a late 325hp. All motors from 04.5+ are called HO. The 04.5-07 motor does use a different nozzle. While there is a difference in the number of holes the main difference is spray angle. The 03-04's use a 143° spray angle and the 04.5-07's use a 124°. Use of 124°'s in a 03-04 piston will cause issues, to include knocking; however, a 143° can be used on a 04.5-07 piston with good results (time will tell, I'm not personally sold yet but it is becoming more common). I too don't really see how the CP3 is going to push air. I think some air in the return is normal, isn't the CP3 self bleeding and the return is where the air goes?

[dorkweed]

It sounds like you are using 04.5 as the HO designation, and that is not correct. 03-04 had a Cali, SO, HO motor and all 3 use the same injectors and nozzles. 2004 had 2 different HO motors, a early 305hp and a late 325hp. All motors from 04.5+ are called HO. The 04.5-07 motor does use a different nozzle. While there is a difference in the number of holes the main difference is spray angle. The 03-04's use a 143° spray angle and the 04.5-07's use a 124°. Use of 124°'s in a 03-04 piston will cause issues, to include knocking; however, a 143° can be used on a 04.5-07 piston with good results (time will tell, I'm not personally sold yet but it is becoming more common). I too don't really see how the CP3 is going to push air. I think some air in the return is normal, isn't the CP3 self bleeding and the return is where the air goes?

All of this^^^^^ is spot on, 116.93%, correct. I'm wondering now if the "knock" he's hearing isn't CP3 "phasing" related. As much as I hate to plug them.................go here for an explanation of CP3 timing/phasing. Wicked Diesel has most of the worth while posts. Many of the others just seem like idiots driving their Daddy's truck!!!! Here you go.............. http://www.cumminsforum.com/forum/3rd-gen-powertrain/23399-cp3-timing-results.html

[mopartechnician]

Ya i was going to put he 04.5 uses differnet nozzles that the 03-04 but I ended up wording it wrong. So i see where you get the confusion

[dorkweed]

Bump to the top for an UPDATE, if any!!

[Mopar1973Man]

I haven't heard anything yet...