Knocking after injector change

[Rupert8]

Hello all,

I recently changed out the fuel injectors (code B) in my 6.9. Job went smoothly. Took it for a test run and it purred like a kitten (albeit a huge ugly diesel kitten). I was amazed at the difference: Engine ran smoothly when idling, also super smooth when working - at speed and also when climbing the steep hill I live up. It was much more responsive. Just felt better overall. I drove it five miles, let it sit for 15 minutes while I ran an errand then drove it maybe seven miles home. The engine upper hose was hot when I got back.

Half an hour after getting home I fired it up to go get some firewood with my son, telling him how great the truck was now running..... How foolish of me: Started up and idled fine - until we came to the first incline close to the end of our driveway, not even a hill, when the engine started knocking as soon as it had to actually do anything. It's quite a discernable knock.

I turned around and took it home (less than half a mile). Home is up a steep, long driveway during which it knocked like anything.

I let it sit for another hour then tried once more to see if this was repeated. It was.

So... Why would it run so well when it first went out (up hill, up to 50 MPH and when idling) but now knock as it does when I take it out?

Oil level is good. No fuel leaks. Injectors are remanufactured from Pensacola Injection. (I know everyone has an opinion on their best and worst injectors suppliers, but Pensacola seem to get reviewed well.)

I'm not super technical so I'm not confident in my abilities enough to identify a bad injector - but, again - first time out it did great.

If I need to take it to get the timing looked at - is it going to be damaged if I drive it maybe half an hour?

Thanks, as always, in advance for the help on this.

Edit: there is a small amount of white smoke visible in the mirror when it is knocking. It didn't smoke at all before.

 

[onetonjohn]

Check the oil and make sure you dont have fuel in there or anything wierd going on. I found an issue by feeling all the injector lines while it was running. One of them was pulsing/ vibrating. Turned out the line was bad. Also heard people say to Crack the injector line on at a time and see if there is noticeable change. You should get change on cylenders that are good. Tighten them back up and move on. The one that doesn't change the engine if the bad one.

 

[IDIBRONCO]

Injectors are remanufactured from Pensacola Injection. (I know everyone has an opinion on their best and worst injectors suppliers, but Pensacola seem to get reviewed well.)

I think you just answered your own question right here. Reviews don't really mean very much. Most of the reviews are made in a short time after purchase and first use. If there's a problem, it's not too often that someone goes back to leave a different review if it's even possible. Pensacola Diesel isn't known for quality parts among members on this forum.

 

[Rupert8]

Thanks, onetonjohn and IDIBRONCO.

Couple questions: The truck sounds just fine when idling. If I crack an injector line am I going to hear enough to identify a bad injector? (Oil seems fine.) It only knocks - and knocks a lot - when moving, regardless of RPM.

Hmm on Pensacola Injectors.

Is it possible for an injector to be just fine one minute then causing a knocking sound the next time an engine is started?

Again, much appreciated.

 

[onetonjohn]

Hmmm. You can't Crack the injectors while you're moving g. If you increase rpms while not moving g do you hear the knock? If not maybe your newfound power broke something loose like a carrier bearing or something.

 

[Rupert8]

Hi,

Thank you.

Well, I have to rev it fairly hard when stationary to get it to knock. But it will knock. And when I'm idling down my steep driveway it doesn't knock, so I can be moving without it knocking I guess. But as soon as I start up the incline there it is. Does that rule out the carrier bearing etc. theory?

I don't want to exaggerate, I'm not about to win any F1 races in the thing now the new injectors are in but it was meaningfully more responsive and definitely running more smoothly on the test run.

Ugh, I didn't mention smoke! I'll edit my original post. Shoot. But there is suddenly light-color smoke when it knocks. Not a ton, but it's visible in my side mirror.

Hmmmm indeed. Thanks again for the input.

 

[IDIBRONCO]

It only knocks - and knocks a lot - when moving, regardless of RPM.

Well, I have to rev it fairly hard when stationary to get it to knock.

The above two make me think that it's related to the engine load, not the engine RPM.

Ugh, I didn't mention smoke! I'll edit my original post. Shoot. But there is suddenly light-color smoke when it knocks. Not a ton, but it's visible in my side mirror.

This is another symptom a fuel issue to me. Before anything else, did you check the timing after installing the injectors? Installing new/rebuilt injectors will change the timing.
Honestly, a knock isn't usually a timing issue, but I think it's best to rule it out first. Almost always, a knock that comes and goes is fuel related. A mechanical knock can get quieter and louder and change with engine RPM or vehicle speed, but it's always there.

 

[Rupert8]

Thank you. Well said - it does seem as though it knocks under load, not just at a higher RPM. (Steep learning curve here on Oil Burners, which is a good thing...)

I did not check timing - but please see below.

A couple questions based on your response:

*Not discounting it as a possibility, but if the timing were off with the new injectors, would that not have resulted in a knock during the initial (successful) test drive?

*Is it possible that an injector went bad after the first test run (when the engine performed and sounded great)?

*If I can't identify a faulty injector and so it looks like timing is the issue, I'll need to take it to a shop to get it checked out (I don't know where to start with timing and don't think I should work on it) . Since it seems like it's a fuel-related issue rather than anything mechanically wonky, will I likely damage the truck driving it the half hour in to town...?

(I'll buy a set of mechanic's stethoscopes today to see if I can find a faulty injector, and report back....)

Again, thanks so much.

 

[Brian VT]

There's not many mechanics left that are willing, or able, to time these.
Many of us have bought the timing equipment and are willing to help you in some fashion.
Maybe one is near you?
List of us here:https://www.oilburners.net/threads/timing-service-registry.70126/

Or you can get into it yourself. Gear will run you @ $200 on ebay (army Humvee surplus). Search DTI Tech Time 3300 (and also optional timing light @ $80).
Edit: I can't find one for less than $350 now. Ouch. I paid $172.04 shipped.

But...there's really not much point to timing it until everything else is working right.

 

[Black dawg]

Sounds like a pintle is sticking at higher lift. If you are unable to pinpoint which cylinder, I would try to lightly use it, avoiding making it knock. Might loosen up, or whatever is making it stick will flow through.

 

[Brian VT]

Sounds like a pintle is sticking at higher lift. If you are unable to pinpoint which cylinder, I would try to lightly use it, avoiding making it knock. Might loosen up, or whatever is making it stick will flow through.

I think you just answered your own question right here. Reviews don't really mean very much. Most of the reviews are made in a short time after purchase and first use. If there's a problem, it's not too often that someone goes back to leave a different review if it's even possible. Pensacola Diesel isn't known for quality parts among members on this forum.

On that note, it seems that many of the injectors available to buy are junk. Many have learned this the hard way and later bought again from one of 3 the recommended rebuilders here.

 

[IDIBRONCO]

(Steep learning curve here on Oil Burners, which is a good thing...)

As long as you're trying, that's the main thing. We understand that everyone has to start somewhere.

*Not discounting it as a possibility, but if the timing were off with the new injectors, would that not have resulted in a knock during the initial (successful) test drive?

This isn't an easy question to answer since fuel knock can be a very tricky thing. If the knock was caused by the timing being off, then it probably would have knocked on the first run when it ran good.

*Is it possible that an injector went bad after the first test run (when the engine performed and sounded great)?

Yes. Very possible.

will I likely damage the truck driving it the half hour in to town...?

Probably not. Especially if you take it as easy as possible, trying to drive with the least amount of knock possible. You'll get some, but less is better in this case.

 

[Rupert8]

Thanks again for all the varied input - from all angles. Hugely helpful, makes things seem manageable....

I probed around with my shiny new stethoscope and all the injectors are sounding very similar. Some variation front to back but it is even on both sides so I'm guessing it's the acoustics of the engine varying slightly. But nothing standing out at all.

Now, this was at idle, of course - when it isn't knocking. Actually sounding quite good. Slightly tricky to use the stethoscope when I'm driving along so I'm not sure if this really proves or disproves anything. I'm guessing that cracking the fuel lines would be similarly unhelpful since there isn't an audible/apparent problem when idling.

Tough one. Not sure what next steps might be. Maybe try a different set of injectors ($$$) or put the old ones back in to see what the result is: Still knocking?

Thanks again. Open to any and all ideas going forwards.

Good to hear I likely won't do any damage if I do find somewhere which will work on it.

(And I'll keep the list of folks with timing equipment. That's golden.)

 

[IDIBRONCO]

I know that Snap On used to ( maybe still do) sell something that they call an "engine ear". It was something that had different probes(?) for lack of a better term that you put at different locations around a vehicle to try to pin point where a noise is coming from while driving. I think that one of those would be absolutely perfect in this situation. It would be great if you could find someone who had one and would let you borrow it. Now that's absolutely ideal, not an expectation.
That aside, maybe you could find someone to help you here. You could crack open an injector line and have the helper rev the engine to where you can hear the knock while the truck's at rest. Or you could crack a line and rev it yourself. Putting the old injectors back in is a viable option. You know that there wasn't a knock before the injector change. If it's gone with the old injectors, that narrows it down. It's also better than buying more injectors before you know that you need them. If the old injectors don't knock, you can have the Pensacola injectors pop tested to check for pop (firing) pressure and spray pattern. I hate to ask someone to spend more money unless it's needed.

 

[KansasIDI]

I know that Snap On used to ( maybe still do) sell something that they call an "engine ear". It was something that had different probes(?) for lack of a better term that you put at different locations around a vehicle to try to pin point where a noise is coming from while driving. I think that one of those would be absolutely perfect in this situation. It would be great if you could find someone who had one and would let you borrow it. Now that's absolutely ideal, not an expectation.
That aside, maybe you could find someone to help you here. You could crack open an injector line and have the helper rev the engine to where you can hear the knock while the truck's at rest. Or you could crack a line and rev it yourself. Putting the old injectors back in is a viable option. You know that there wasn't a knock before the injector change. If it's gone with the old injectors, that narrows it down. It's also better than buying more injectors before you know that you need them. If the old injectors don't knock, you can have the Pensacola injectors pop tested to check for pop (firing) pressure and spray pattern. I hate to ask someone to spend more money unless it's needed.

My grandpa has one