LB7: Can Injectors be bad but still pass the balance rate test?

[TRUBBS]

buddies truck now is showing signs of bad injectors, 11mpg, lope idle, white smoke, raw fuel smell and overfull dipstick with smell of fuel.
but the BRates are still showing everything within spec.
wondering if maybe he could possibly have lost a cup rather then an injector itself?
or can the body/nozzle crack but still somehow pass the BRate inspection?

 

[Bustedknuckles]

Can't be a cup, they don't work that way. And yea, the pintle seats could be leaking and balance rates still look ok. Just go ahead and replace them.

 

[ThebigGids]

Yeah you can have bad injectors and still good rates. Balance rates are not 100% accurate measure for how your injectors are doing.

 

[02greysixer]

I am doing injectors on an lb7 this weekend that was making oil and had no power. Balance rates were dead on, all +/-1.5. They put them on the stand at work and one blasted fuel from a cracked body at low psi and 5 more were pretty far out of spec.

sent from a galaxy far far away

 

[TRUBBS]

That's kinda what I thought & all signs pointed to Injectors but wanted to double check my thought process first.

 

[Kappa9012]

fuel in oil is definitely an injector, but lopey idle may also be a shitty cp3 regulator, might have a bad cp3 in the works.

 

[TRUBBS]

fuel in oil is definitely an injector, but lopey idle may also be a shitty cp3 regulator, might have a bad cp3 in the works.

Mine lopes if I run without adding something to the fuel for lube, I add a gallon of 2 stroke per tank.

I think I've heard it to be common for them to start loping with bad injectors?
My LLY sounded like a machine gun meets jack hammer when I had mine go bad from rusty fuel.

 

[THEFERMANATOR]

Most people make the mistake when checking balance rates and not pay attention to what the fuel rate is when you check them. I know I learned this one the hard way, and is how I now know. If all your injectors are worn and worn about the same amount, then your balance rate will be dead on. Balance rates are nothing more than a measure of how far each injector is off from the average fuel flow. At a 680 idle and a hot engine in park, you should see a fuel rate of roughly 8-9MM3 of fuel. If you see say 4Mm3 of fuel, then you need to add 4 to the balance rates to get the true balance rate. When you do it this way, all of the sudden the balance rates can go from +/- 2 to 8 or more(seen one that was showing a negative Mm3 of fuel at an idle).

 

[MACKIN]

What he said above :thumb:

GM didn't replace injectors on a balance rate check BUT fuel return rate!

 

[OnTheFritz]

Sorry to hijack the thread, but on my CTS would that be pilot injection fuel rate? Mine is showing 1 mm3 in park when warm.

 

[THEFERMANATOR]

What he said above :thumb:

GM didn't replace injectors on a balance rate check BUT fuel return rate!

Balance rates were just meant as an indicator, not really a test. Most don't want to do a return rate test as it normally leads to engine teardown to do it.

 

[THEFERMANATOR]

Sorry to hijack the thread, but on my CTS would that be pilot injection fuel rate? Mine is showing 1 mm3 in park when warm.

Pilot injection amount should always be right around 1MM3 of fuel for an LB7. You need to look for the main fuel rate when you are at an idle. In park, A/C off, engine up to temp at a 680 idle, it should be around 8-9MM3 of fuel.

 

[OnTheFritz]

Pilot injection amount should always be right around 1MM3 of fuel for an LB7. You need to look for the main fuel rate when you are at an idle. In park, A/C off, engine up to temp at a 680 idle, it should be around 8-9MM3 of fuel.

Is it the same for an LLY?
Thank You

 

[THEFERMANATOR]

Is it the same for an LLY?
Thank You

Pretty close. I think the LLY can have a slightly higher pilot amount, but the idle amount should be pretty much the same.

 

[1978steven]

Mine lopes if I run without adding something to the fuel for lube, I add a gallon of 2 stroke per tank.

I've heard of adding some Tech 2 to quiet them down but a gallon per tank seems to be a bit excessive!

 

[TRUBBS]

I've heard of adding some Tech 2 to quiet them down but a gallon per tank seems to be a bit excessive!

oh it is overkill, i know.
but ohwell lol more lube in my mind cant hurt. its 2stroke so its designed to burn off unlike atf and some other stuff people use.

 

[tlange31]

I have injector balance rates of (-0.4,0.9,-0.2,-0.9,0.3,0.4,0.4,-0.3) on this truck I'm currently looking at buying. when you say +/-4 what exactly does that entail number wise

 

[2004LB7]

I have injector balance rates of (-0.4,0.9,-0.2,-0.9,0.3,0.4,0.4,-0.3) on this truck I'm currently looking at buying. when you say +/-4 what exactly does that entail number wise

the normal healthy main injection rate minus (or plus if the injectors are plugged up) the actual main injection rate. the +/-4 was an example of what one might find when checking the numbers. without knowing the main injection fuel rate in mm3 the balance rate of the injectors is pretty much useless