A cylinder kill test will do absolutely no good at determing if or whihc injectors is bad. All it does is shut off the injector at an idle to see if a miss goes or stays.

If you have a stock engine, no tuner, and it blowing black smoke driving around or a grey haze under hard throttle you have one or injectors over fueling for some reason. These engines do NOT smoke stock, you might get a little puff of soot from the muffler if you drive low load for a while but once hard on the throttle and it is gone.

You may be able to determine whihc ones are the worst with a contribution test and a rpm drop on shutdown but not much more thna you already know, a set of injectors is likely in your future.

 

if 5 of the 6 are working correctly, and he shuts them down individually, would it not become very noticeable when a good one is shut down, and not so/as noticeable when the poor one is, helping him identify a bad injector(s)? i'm not really farmiliar with these common rail injectors thought maybe he could get away with not having too pull them all and have them tested

 

kinda like this..

 

The problem is injector operation is dynamic depending on what each cylinder has to do to maintain idle, it will fluctuate as the ECU constantly adjusts for actual fueling.

Then, the whole concept of SOP on a kill test is so vague it is hard to tell what it really means. Shut down an injector and the sound doesn't change much, you have to define "much", and, then decide is that means the injector is just not contributing because it is bad and others are picking up the slack, or, is not contributing because others are too high and the ECU has pulled it way back to compensate.

Even just looking at the contribution test does not tell you exactly what is wrong. Rate reads 95% with 2 injector previous in the firing order are reading 104-106%. Is the 95% injector bad or pulled back to compensate for over fueling on the others?

Same with the 104-106% injectors, are they compensating for low injectors in the sequnce, or, compensating for wear and over fueling when the ECU adjusts the duty cycle of the solenoid? At a low duty cycle they don't delive rneough fuel, at a higher duty cycle it is too much fuel. The ECU is erring on th ehigh side trying to compensate and maintain 750 rpm.

When you look at the contribution percentages, run a kill test and record the rpm drop it helps a bit, but it is still a guessing game what is actually wrong.

Testing is hit or miss also, not all benches and operators are equal and it is not installed in the engine with all the entails.

We make an educated guess which and what is wrong thne either replace them all or try to find the worst one to replace.

 

glad to see someone actually explain themselves (and teach me something new!) rather than state their point and leave it at that! what does that really leave for us common rail guys when it comes too injectors on these trucks? not too hijack the thread here, but it just sounds like there is so many variables the safiest/ most time efficient decision is just throwing injectors into the motor

 

Even though the suckage factor is high that is the best solution, and new injectors is the only good choice. A reman is a crap shoot, Bosch is the best source and you still have to watch them to make sure you don't get some that are just not up to spec.

There is a range of specs applied to a reman injector and if the internals fall in that range they go thru rebuilding. The problem is as-installed they just may not perform well enough to be adequate. You get 1 or 2 injectors that are on the high side in return flow, still meet spec, and it starts ok. Get 4 on the high side and you have long cranks. They meet spec on return flow but in the truck no go. On a bench test all the nuances do not make themselves known.

I have done it both ways and if you do your own work it is cost efffective. Have had to replace some remans becasue they just would not balance with the rest.