LB7: low balance rate after replacement

[sweetdiesel]

On my friends lb7 we checked balance rates and #4 was -7 the rest where well within spec

So we swapped the number 4 injector with a brand new bosch injector from GM. We get it all back together and findout the balance rate is exact same

Yes we are sure we replaced the proper inj.

we checked compression and it was great,What would cause this

 

[SteveFord]

Compression test on just that cylinder or did you do all of them and it fell within spec?

 

[sweetdiesel]

Compression test on just that cylinder or did you do all of them and it fell within spec?

all cylinders where tested Steve.

 

[Vrabel]

If its the same, could it be electrical?

 

[sweetdiesel]

If its the same, could it be electrical?

ya.....good call! Im going to check that

 

[Vrabel]

I know its a suck job. but try swapping two around. if still the same then maybe harness screwed up.

 

[S Phinney]

I would recommend to double check glow plugs to make sure they are sealing up good. Even though compression is good on the test this could cause differences in balance rates. I had this occur once when I found a couple had loosened up even though they were torqued to specs.

 

[05smoker]

If it was an injector harness I would think you'd be in injector limp mode wouldn't you?

 

[DuramaxPowered]

I just did injectors on my LMM last Saturday, and the balance rates were way out until the engine ran for a while. I assumed it was air in the system since they are all good now. How long did the engine run after injector replacement?

 

[sweetdiesel]

I would recommend to double check glow plugs to make sure they are sealing up good. Even though compression is good on the test this could cause differences in balance rates. I had this occur once when I found a couple had loosened up even though they were torqued to specs.

They where tight

If it was an injector harness I would think you'd be in injector limp mode wouldn't you?

You would think,But we are going to swap the harness to that injector anyways

I just did injectors on my LMM last Saturday, and the balance rates were way out until the engine ran for a while. I assumed it was air in the system since they are all good now. How long did the engine run after injector replacement?

Not very long

 

[TrentNell]

For what ever reason Simon the computer thinks that cylinder is traveling down the hole too fast , and pulling fuel . A low compression would cause a + rate i would think . Did you re-use the nozzel ? i would assume no because the injector would have came with a new one . Only other thing is a fat chance but .................. reluctor wheel .................. dirty crank sensor ?

 

[05smoker]

Can you do an ohm test on the harness before you dig in? If it is bad or grounded on the valve cover it should read diff than the rest IIRC.

 

[McRat]

Odd. -7 should mean too much power.

IIRC, sometime the balance numbers don't always identify the cylinder properly. A problem in the injector right before, or right after, in the firing order can cause it.

 

[LBZ]

Odd. -7 should mean too much power.

IIRC, sometime the balance numbers don't always identify the cylinder properly. A problem in the injector right before, or right after, in the firing order can cause it.

Exactly!! One of the only proper tests to do to find out which hole it is when a compression test comes back good is a cylinder power contribution test. I'm not sure if the Tech II can do this or not, but this is how they check Ford's for missfiring or engines that run rough/lack power but don't smoke.

 

[sweetdiesel]

Ok so what does that mean?

We tested the ohms and they are the same as the other inj harness connections?

What now?

 

[Vrabel]

swap injector with another cylinder. maybe its a very long shot you got a dud one. Stuff happens sometimes.