LB7 miss

[lutzjk913]

Ok guys. Sons truck is having an issue.

Stock motor. LDS 45 Sac injectors

Had a bad misfire/lope and pouring black smoke. Cylinder 3 injector is maxed out on balance rate. Shop diagnosed it as a bad injector. They could cycle the injector off and the fuel knock and smoke would go away. It would idle fine.

Called LDS. Started the warranty process. They got the injector back and said the roller was bad if I recall and replaced it. Sent me a new injector and the truck does the same thing.

Shop did a compression test on the cylinder and it came back good. Shop also swapped in a good ECM and FICM and truck still does the same.

Replacement injector was sent to S&S and tested fine.

Also under valve cover harness was replaced.

Shop has also ohm tested the harness. As of now they are going back over the harness a second time checking things over.

Any insight guys on where to go?

Thanks

 

[PureHybrid]

You probably don't want to pull the injectors back out, but maybe have it and a good one tested? Purrformance Diesel is reasonable

 

[2004LB7]

Make sure they are pulling the right injector. Cylinder number VS firing order. I've seen that mistake. Some scanners don't show the right cylinder number that corresponds to the one it's turning off. Tech2 is correct but EfiLive and maybe even snap on has shown this issue. They might need to prob the harness to verify the actual injector they are turning off that stops the noise. Then they can pull that one and not whatever the scanner says.

 

[lutzjk913]

You probably don't want to pull the injectors back out, but maybe have it and a good one tested? Purrformance Diesel is reasonable

Missed that part. The replacement injector was sent to S&S and tested good. Can’t believe I skipped that part.

 

[lutzjk913]

Make sure they are pulling the right injector. Cylinder number VS firing order. I've seen that mistake. Some scanners don't show the right cylinder number that corresponds to the one it's turning off. Tech2 is correct but EfiLive and maybe even snap on has shown this issue. They might need to prob the harness to verify the actual injector they are turning off that stops the noise. Then they can pull that one and not whatever the scanner says.

Passenger bank. Second cylinder back.

Not sure on what scanner. I believe it’s a snap on.

Also. The under valve cover harness was replaced. Also left that part out. My bad.

 

[lutzjk913]

Original post has been updated.

Sorry guys. Was trying to type that in a hurry at lunch.

 

[PureHybrid]

Wiring would cause a misfire, but smoke is going to be a hard part.

 

[lutzjk913]

Wiring would cause a misfire, but smoke is going to be a hard part.

Yep. And this thing looked like a locomotive.

 

[PureHybrid]

Yep. And this thing looked like a locomotive.

Hey some people pay good money for that lol

 

[lutzjk913]

Hey some people pay good money for that lol

Lmao

 

[lutzjk913]

Update

They swapped cylinders 1 and 3 and the issue stayed on 3. Rules a injector out

Shop is recommending replace both engine harness now

 

[2004LB7]

Update

They swapped cylinders 1 and 3 and the issue stayed on 3. Rules a injector out

Shop is recommending replace both engine harness now

Both?

A proper shop would be able to ohm out the wires and test if it's the harness or not. Could be the FICM, could be just the pin in the connector. If the harness is bad they should be able to show you exactly where in the harness. I hate parts swappers

 

[lutzjk913]

I’ve been all over the place and forgot to update this

I gave them a ficm to test.

And yes both harnesses. Supposedly both of them have been ohm tested twice and they can’t find anything.

 

[NC-smokinlmm]

Could the return line be clogged up and causing issues? I think I remember something along time ago about this same issue.

 

[Dallas S]

I’ve been all over the place and forgot to update this

I gave them a ficm to test.

And yes both harnesses. Supposedly both of them have been ohm tested twice and they can’t find anything.

Just because it ohms doesn’t mean it will pass a load test. See many guys get burnt with a multimeter…

 

[2004LB7]

Could the return line be clogged up and causing issues? I think I remember something along time ago about this same issue.

Unlikely to affect only one injector. The LB7 has that hard return line that connects all the injectors under the valve cover before exiting. If it was clogged then multiple injectors would likely have issues. Plus the LB7 is not as picky about the back pressure as the later years. Infact they can run without any back pressure. I believe the incoming pressure just has to be at least 1200 psi above the return pressure to operate the injector

 

[lutzjk913]

Just because it ohms doesn’t mean it will pass a load test. See many guys get burnt with a multimeter…

My thoughts also