Pinging/knocking after injectors!?!

[HETvet]

R&Red some injectors on an M998. Got it running. Checked for any leaks at idle. Gave it some throttle. Took my foot off the throttle and it started pinging/knocking loudly. It will only do this off throttle. What in gods green earth is going on here? I vaccumed out each runner on each head. Taped them off, and only removed the tape to install the new intake gaskets and finish out the rebuild. To me it sounds like rod knock or piston slap.

 

[ken]

Sounds like dribbling injectors. Or the "pop" pressure is too low. Fuel is puddling on the piston. Then burning as the piston comes up on the compression stroke. This slams the rod into the crank when the crank is trying to push the piston up.

 

[Barrman]

Yep, the injectors are wrong inside. Did you by chance get some of the "marine" injector internals off an online auction site? They are for the shorter 6.5 injectors, not the 6.2 injectors. Just a little bit of size difference gives you that leak and noise.

 

[HETvet]

https://real4wd.com/store/Injectors

He got these injectors

 

[Stein12501]

Mine just started doing the same thing. Changed the fuel filter and primed still not getting fuel. Ordered a set of rebuilt injectors and will replace when it's running again. I figured mine had leaking injector(s) causing the knock and rattle. She always ran great until now.

 

[HETvet]

They now want me to talk to their technician. We will see how this goes

 

[Stein12501]

Good Luck!!!

 

[HETvet]

After talking with him, he said the injectors are fresh rebuilds and they get them from a third party. In his experience it's been cured by replacing the injection pump and lift pump. If that doesn't fix it, then it's piston slap, rod knock, and/or wrist pin slap. But it's nothing to be concerned about because he has pulled the heads on these engines and found rust in the cylinder and they run just fine. He recommended I do a compression check on all 8 cylinders.

 

[doghead]

Did this just start after you replaced your injectors?

Did it do it before?

 

[infidel got me]

You mentioned re-build... so the truck/engine ran with no knocking or pinging before injector replacement???

 

[HETvet]

Yes, this started after injector replacement. It didn’t do this before injector replacement. It was a process over 4 weekends. I used a shop vac with a plastic pipe attachment to vacuum out each intake runner and around the intake runners/valley before and after intake manifold removal, during and after gasket removal, before installing new gaskets, and before installing the intake manifold. Then I vaccumed out the intake manifold before and after torquing down the manifold bolts. Checked fuel going in to the filter, and discharge from the filter. Got a rough idle then tighten each file pipe at each injector one we had fuel flow.

 

[doghead]

Seems clear the problem is your injectors.

Replace them.

 

[HETvet]

The problem is I’m just the mechanic, the owner is already frustrated with the cost involved in it as of now. Plus this thing needs to be up and running in a month. My only available time to work on it is half days on the weekends

 

[Action]

Why did you replace the injectors and why were the intake parts removed?

See if the sound is coming from the torque converter area. I have seen the inspection cover rub the flywheel teeth. It sounds like a ticking sound.

 

[HETvet]

One had a cracked and leaking fuel pipe connection. Hard starting, black smoke, rough idle, and for $35/injector, the owner thought it was cheep insurance. Yes, I took iff the intake manifold to remove all the injector supply pipes for inspection, cleaning, and to make injector replacement easier

 

[cwajciec]

I’m no diesel mechanic, but could it be that you have a vacuum leak in the intake that is sucking in too much air under decel? I would think that could cause a knocking and since you removed the intake it could have messed up a gasket putting it back on?

 

[HETvet]

Diesels can’t have to much air for combustion. They actually run on a surplus of air tobegin with. In a diesel, your throttle pedal regulates fuel rates, where at in a gas engine, you regulate air flow via the throttle plate. Diesels don’t have a throttle plate.

 

[HETvet]

Update;

The injectors are new. The owner just text me and said it knocked at first when reving, but once it came up to temperature, the knock went away. Injectors are not the problem. I’m thinking piston slap

 

[infidel got me]

I call them EVER SINCE CUSTOMERS... Ever since you put air in my tire my alt. wont charge or my wipers don't work or...... You did o.k. overall, he only wasted a few days of your time chasing your tail!!!!

 

[HETvet]

What?