Fuel knock

[jmw1439]

Developed a knock yesterday I’m pretty sure a fuel knock had excessive black smoke also no codes. wasn’t far from home so went ahead and drove it back.
My question will unpluging the injectors one by one allow me to find the bad one should the knock clear up any help is appreciated

 

[Ron Nielson]

Sure, give it a try. If you have the ability to read balance codes, take a look there also. One may confirm the other.

 

[2004LB7]

Be aware that if it's leaking mechanically then pulling the electrical connector may not stop the fuel flow. But you can do it in a reverse elimination. The ones you pull do make a difference might be good.

And be aware that pulling the connector will put it in limp mode and shut down the two injectors tied together. So you might need to reset the codes or restart the vehicle between injectors

 

[jmw1439]

What’s your guys opinion I’m just shy of 250000 miles should I just think about replacing them all over just the one I’m thinking is bad and be done with it?

 

[2004LB7]

I'd diagnose first

Do you have a scanner? Something that can read balance rates? Might go a long way to saving you money in repairs and diagnostics

 

[jmw1439]

I don’t have a way to check rates I have an old Diablo predator tuner from forever ago that would record rates but can’t get it to work. But I had unplugged all but 5 and 6 number injector yesterday with no change. But when I unplugged # 5 today the knock disappeared and ran a little smoother still rough obviously but better so guess I’m gunna go ahead with changing # 5 out to start

 

[2004LB7]

That's a good start

 

[Bdsankey]

At 250k I'll be honest, an LBZ typically needs injectors due to high return rates. It'll show up as a low rail pressure code in my experience, especially when tuned. With stock trucks it's usually masked until it's extremely bad.

I'm not saying that in an attempt to sell you injectors, I'm saying that because I've seen 100-150k mile sets come back perfect except return rates were out of range.

 

[Ridin'GMC]

At 250k I'll be honest, an LBZ typically needs injectors due to high return rates. It'll show up as a low rail pressure code in my experience, especially when tuned. With stock trucks it's usually masked until it's extremely bad.

I'm not saying that in an attempt to sell you injectors, I'm saying that because I've seen 100-150k mile sets come back perfect except return rates were out of range.

He's not wrong, I have the same situation at 267k miles on it. It'll run fine driving normally but towing heavy or running WOT, you'll notice quick enough. My lift pump is basically band-aiding it along with the new cp3 I did while doing head gaskets. I know it's expensive but it's better to change all 8 of them with that many miles even if your balance rates are within spec. Mine is within spec and I know it has high return rates.

 

[68ss]

At 250k I'll be honest, an LBZ typically needs injectors due to high return rates. It'll show up as a low rail pressure code in my experience, especially when tuned. With stock trucks it's usually masked until it's extremely bad.

I'm not saying that in an attempt to sell you injectors, I'm saying that because I've seen 100-150k mile sets come back perfect except return rates were out of range.

Like the old saying buy once cry once. Been here done that. Mine popped the p0087 code. After looking at fuel pressure figured out it was injectors. Bought brand new Bosch stock injectors. Best thing I did.

 

[2004LB7]

Could always do a return rate test