Rough running with a slight knock.

[House Builder]

Ok, the 2000 Crew Cab 6.5 hits about 85K miles and starts to smoke badly and has a knock, so we run a compression test and find the #2 cylinder at only 250 psi. So we pull the head off and sure enough the exhaust valve is cracked, and while we have it all torn apart we replace both heads, and spend 3 days putting it all back together... here's our problem.

It runs somewhat roughly, and has what sounds like a little bit of a knock, we ran another compression check and all the cylinders are over 400, most over 450. We then checked each cylinder by cracking the injection line open a little and listening to the engine sounds. All the injectors sound the same but #8; the engine doesn't seem to change RPM or sounds when we crack it open. So at the moment it seems like we have one injector that isn't working right, though that doesn't explain the knock sound.

The question is why would the injector stop working between being removed and replaced? And how easily do they plug? Or is it something else that I am over looking?

Anyway, that

[JohnC]

The injector is extremly sensitive to dirt. If the dirt holds it open, the dribble can cause a knock and when it comes time to fire, it wouldn't be able to create any pressure, so, I'd have it tested or replace it or swap it with another one.

[DmaxMaverick]

Most of all knock issues with Diesels are injector problems. Before you go chasing a ghost, switch the #8 injector with #1, and check again. If the problem follows the injector, that's your problem. If not, there's a bunch of other things that could be suspect. Keep it simple and be optimistic for now. If it turns out to be the injector, don't mess with replacing just that injector. Replace them all with good rebuilds, or new. The miles are a little short for a failure, but not far from the average. Replacing only one will leave you with a poorly balanced situation, again. If you want to be cheap about it, and have time to mess around, a good injector additive w/ cleaner could clear up a fouled injector. JK recommends FPPF, and I have no reason to doubt anything is better.

[ronniejoe]

A malfunctioning injector can cause a knocking sound. If it is dumping fuel, not spraying to atomize, then the piston is trying to compress liquid fuel...that will knock rather loudly.

You should probably have the injector tested.

[House Builder]

I have another 6.5 on a stand I can pull some injectors from, so I will try replacing it first and see is that helps.

Thanks for the fast replys! I'll swap it out right away.

Ryan

edit, another thing is that the glow plug in the #8 cylinder was "wet" when I pulled it for the compression test.

[ronniejoe]

That possibly tells you that it is sending fuel to the cylinder, but not burning it. Another sign of a bad injector.

[House Builder]

ok, I'm not sure what to do now.

I swap a new injector into #8, it makes no difference!

so I think that it might be a bad injector so I swap #1 and #8,
the number #8 injector works fine in the number one slot,
and the #1 injector doesn't seem to work in the #8 slot.

and the #6 injector doesn't seem to work either! you can crack it and it the engine runs the same. so #6 and #8 aren't working.. even when a working injector is swaped in.

they are getting fuel to them, but I can't figure out why they won't work! I've double checked the lines and I didn't get them reversed at the pump.

I can't think of a reason for them not to work. it has compression, there is fuel to the injector, and the injector is good! yet it doesn't seem to be working. the engine is still running "rough" and there is a slight knock sound, not a metalic knock, it's a softer knock about the same as an advanced timing sounds.

anyway, I'm clean out of ideas, anyone have a suggestion?

thanks!
Ryan

[House Builder]

well we just checked the codes with a UBDII tool, and we had P0300, P0306 and P0308. basically it's misfiring on numbers 6 and 8. and we can't seem to figure out why.

Ryan

edit, is there any possiblity that the DS4 pump has gone bad and not firing correctly on #6 and #8 cylinders? it was replaced about 5000 miles ago under warrenty.

[diesel65]

Hopefully that you still have the intake manifold off, I would recheck all the injector lines and make sure they are in the correct firing order.
The firing order is 1-8-7-2-6-5-4-3

At work a fellow mechanic putting a new engine together managed to switch two injector lines, I don't remember whether it was 6 & 2 or 6 & 5

Looking at the lines on the pump, On the passenger side, would start from the top (clockwise) with #7, then 2,6,5.
The drivers side would start with #8 on top then 1,3,4 (counterclockwise)

[House Builder]

we've already double checked the lines, and they are on correctly.

this one really has us stumped.

[House Builder]

ok.. tried to take it for a short test drive.. it was very little power, is running very rough and dies in gear at an idle, not to mention smoking badly.

I'm going to recheck the injection lines, but it acts like notthing I've seen before.

Ryan