Hey guys, first timer here. Here's the deal. Had a customer bring his LB7 in with injector issues. Found #6 & 7 both with high rates. I advised changing all injectors but the guy is tight for cash so I just changed the 2. This is the shitty part, I pulled all the injectors and resealed the cups as pr usual. Checked compression, all good. Buttoned everything up and I'll be damned if I can't get both the injectors to come even close to the rates of the other injectors. Ran it for a while and smoked like a pig. To be honest this is the first time I've only changed 2 and not 8. Especially 1 on each side. I can get #6 to come down to +8 but that's it??? Should I be doing all 8? (Don't answer that, I know the answer) But has anyone else seen extremely high rates after changing just one or 2? I've done just one or 2 Cat or Cummins injectors with no issues? WTF
High balance rates new injector
- Thread starter PMIPaul
- Start date
I got the injectors from the dealer as to avoid this issue. I hate billing customers for unnecessary work. Fuel rate was at 9mm. Balances were all within spec minus the 2 new. I can't recall rail pressure. I think I was more annoyed with the readings and the smoke :/
You checked compression on all 8 and they all built pressure in the same # of seconds cranking ? Check valves? Did the truck come in for smoke originally? Doesn't surprise me your 2 new ones are high with the other 6 being worn out. Remember balance rates are essentially just a comparison of the injectors to each other.
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Flash in the stock tune first, then rescan them. Why were they replaced? Just bad balance rates, making oil and or hazing?
Balance rates can be very misleading.....
For example, you assumed the 2 injectors with high rates were the bad ones.
However, what if those were the only good ones? The other 6 could be leaking/flowing excessive amounts of fuel, causing the main rate to drop mm3. So in order for the 2 healthy ones to flow the same as the other 6 sloppy ones, the balance rates appeared high on those 2.
I could be way off. But I've seen just as many bad injectors with good balance rates as not.
You were right in the beginning to tell him all 8. Should have went with your gut feeling on this one. Replacing anything less then a full set on an LB7 never seems to work out for anyone.....
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For example, you assumed the 2 injectors with high rates were the bad ones.
However, what if those were the only good ones? The other 6 could be leaking/flowing excessive amounts of fuel, causing the main rate to drop mm3. So in order for the 2 healthy ones to flow the same as the other 6 sloppy ones, the balance rates appeared high on those 2.
I could be way off. But I've seen just as many bad injectors with good balance rates as not.
You were right in the beginning to tell him all 8. Should have went with your gut feeling on this one. Replacing anything less then a full set on an LB7 never seems to work out for anyone.....
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Yes all 8 had identical compression readings. 300-350 then 400 and stayed. I did not set the valves. The original complaint was smoke at idle and on throttle. I suspected overfuelling. The only reason why I faulted the 2 instead of all 8 was that the balance rates for those two were the only two which showed high the others were all really tight to each othe +\- 0.5. I Know that putting one or two good injectors will give me funny rates to compensate for the others but 6 was +12 and 7 was +4 after changing them out.
Absolutely. I cut out 7 and 6 and both made no change in sound of engine. But you are right. I should check the smoking and see if I can isolate that way. Great tip!
Update: I put a full set of injectors in RH bank. Flashed up and ran smooth. Only problem is it hazes blue at idle and sounds like its overfuelling on a cylinder under load. Balance rates at temp are beauty but in drive #6 creeps up to the threshold. Pulled the glow plug on that hole and it was literally smoking from unburnt fuel. I believe I found another culprit. But this time I'm putting another 4 in. I would hate for this guy to come back in a couple of months needing the rest done. Tomorrow I will swap in the LH bank and post an update.
And do your shop a favour.... replace all eight injectors. I've burned up so many unbillable man hours on this job. Makes my head spin. And at the end of the day I still will hand him a 4500 dollar bill!
And do your shop a favour.... replace all eight injectors. I've burned up so many unbillable man hours on this job. Makes my head spin. And at the end of the day I still will hand him a 4500 dollar bill!