Diagnosing injector problems

[KMinAF]

At idle there is a very slight stumble which I assume is caused by a leaking injector. I believe it is this stumble that is causing the high HC reading at idle. I have recently replaced the plugs and wires and performed a leak-down test ( just to verify the integrity of the rings and valves). The engine was completely rebuilt 13k miles ago. All plugs were a light tan with no signs of fouling.

Is there any way short of removing and visually inspecting or sending them out to be flow tested, that I can diagnose which injector is faulty?

 

[destrux]

Visually inspecting them will only work if they're leaking really bad. If they were leaking it would also cause hot starting problems, as it would flood one cylinder when you shut the car off, and if you try to restart ten minutes later, it will either be hydrolocked with gas, or run with a bad misfire (depending on how bad the leak is).

But yeah, there's a tool that you hook up to each injector individually while they're in the car to test for leaking ones or clogged ones.

http://www.otctools.com/products/fuel_injection_tester

How it works:
You hook up a fuel pressure gauge and this tool pulses each injector for a known amount of time, one at a time, to test the amount of pressure drop in the fuel rail. You re-pressurize the fuel rail by turning the key on between each test. If one injector has less pressure drop than all the others, you know it's leaking (this doesn't make sense at first, but think about it for a while, when you test the leaking one you're effectively eliminating the leak while that inejctor is open, as it was also leaking during the test of each other injector). Also, if one has less pressure drop than the others, it could be clogged. It's not the best way to test injectors, but it will show an imbalance.

You also need a good fuel pressure gauge to go with it, as in, a digital one. One with a needle won't suffice (unless the injectors are REALLY BAD, as you need accuracy +/-0.5psi to detect small leaks or clogs).

Once this tool shows you that you have a problem, pulling them all and sending them for a flow test and cleaning is the only solution (short of replacing them all with new ones).

Also... there's a schematic online somewhere to build one of these yourself for like $20. I built mine, because $400 is alot for a tool I rarely use.

 

[KMinAF]

Thanks for the info, I think I found the injector flow tester you mentioned http://www.youtube.com/watch?v=JZnSBkfwX4Q
Can anyone recommend a good place to send the injectors for servicing?

 

[AJ'S 88NA]

NAPA I believe still does them, or look on line in your area maybe.

 

[jetjock]

...At idle there is a very slight stumble which I assume is caused by a leaking injector. I believe it is this stumble that is causing the high HC reading at idle....

Fwiw I seriously doubt that's the case. Doesn't make sense.

 

[KMinAF]

I am not sure where else to look, I have checked for vac leaks, replaced all the plugs with Autolite, installed new NGK plug wires, set the timing, run snake oil through the tank, and checked all connections.
I considered the coil but there isn't any misfire under load, only at idle. Any ideas or suggestions would be appreciated.

 

[Turbo Habanero]

I can tell you i have a TPS issue somewhere and under load or even just driving it seems to feel like a missfire. What did you gap your plugs to?

 

[hvyman]

I am not sure where else to look, I have checked for vac leaks, replaced all the plugs with Autolite, installed new NGK plug wires, set the timing, run snake oil through the tank, and checked all connections.
I considered the coil but there isn't any misfire under load, only at idle. Any ideas or suggestions would be appreciated.

Those are crap. Swap them out for ngk coppper p/n 4644. Rock auto has them for a 1.61 each and there is a 5% discount code in there section on here.

Do you have any codes? Cps wires good?

 

[suprajztwenty]

i just swapped my new shortblock so i dont know if my problem has went away yet (only ran it for a few minutes to bleed the coolant and check for leaks)
anyways...
i always remember having this same issue. i can say that ive tried 3 different types of spark plugs and none helped the issue...not saying to stick with your plugs, id only use those as backups though.

i never had a code or cel either...is it possible the maf/o2 sensor could cause the ecu to dump too much fuel at idle? what about the cold start injector leaking?
i did used to have a fuel pressure problem after sitting over night, took a couple cranks to get to fire but after that initial startup i never had a problem all day.

i think youre on the right track, injectors could be the issue. well i planned on 550's or higher anyways, i guess its about that time.

 

[KMinAF]

O2 sensor is only a year old and didn't change anything. I am wondering if a coil is shorting out except I would think it would be more prominent under load. I too have to crank it i.e. cycle the key a couple of times in the morning to get it started, I just thought this was normal since it starts first try for the rest of the day.

It is definitely the slight and intermittent sputter/stumble at idle causing high HC reading which if I am am correct means raw fuel which is either a result of a weak spark or too much fuel.

 

[suprajztwenty]

ill be willing to try new coil packs/coil over plug setup...but id rather give the injectors a try since its technically a moving part and will wear out quicker and relates more to our "hard start after sitting". now, what size do we try? 550's seem to be the norm but for my overall goal with the setup i have now, i plan on 600hp and im thinking 750+injectors should keep me comfortable for idle and if i choose to go e85 they should be decent enough....though i havnt done much research.

my bottom end is built with wiseco and eagles...after 100 miles ive noticed my stumble is still there and in full force. i had bought a lex afm so i gave that a 30 mile run today, no change...well low idle untill the ecm learned it. still a stumble problem.

so, we're down to coil packs/plug wires, injectors/fuel pressure, o2/water temp sensor (or whatever ecu input that will cause a rich condition)
im leaning towards the o2 sensor right now, plus its cheap...well when you find the right one. i need a 3 wire, which driftmotion has the best price i can find...and the same goes for the coolant temp ecu input, driftmotion ftw.

i think first thing ill try is a fuel filter just because of price...may be a bitch to change but ive always been a preacher of cheap/simple first, in the diagnostic process (well if youre guessing)
next would be o2 sensor and THEN fuel pump/injectors, which will be upgraded in the future anyways, bad or not.

please, if you stumble upon the fix (get it, stumble...yea im drunk, i crack myself up sometimes) please pm me with your theory/fix for this problem...with a brand new motor its pretty embarrassing when it starts to miss when youre trying to show it off, and it drives me fucking nuts.

 

[KMinAF]

Today I swapped the coil pack, there was no change, the slight stumble is still there at idle. The car runs great and and clean off idle, it just exceeds HC limit by 130ppm when idling. I still think it is an injector issue, but which one? How can I determine which is the faulty injector?

 

[suprajztwenty]

try another set? basically like stated before you could hook up a fuel pressure gauge in the rail...jumper the fuel pump, and as you manually pulse each injector that pressure will change. after you write down each pressure change, then you can somewhat determine which is most out of whack...but i think itll actually be easier to buy a new set if youre looking to upgrade in the near future.

 

[suprajztwenty]

also id like to add that i just changed out to accell universal wires (8mm) and i relocated my coilpacks because im running n/a valve covers and mounting them became an issue. i relocated the coils to the lower intake manifold, this way i dont have to extend my factory wiring.

after swapping my new motor my stumble actually was just as bad if not worse...but after swapping plug wires it got a lot better, but like you describe, my stumble problem is still there.

i think new injectors are going to be next on my list, weather they fix my problem or not, ill need them eventually anyways.

 

[KMinAF]

This past weekend I adjusted the boost to max out at 8 (up from 5) and the miss/stumble is noticably worse under load. I am going to pull the Autolites and replace them with NGK to see if that changes anything.

 

[suprajztwenty]

hows your diagnosis going? i got my used injectors in today...im going to throw those in later, maybe tomorrow.

i put the lucas stuff through it and it got noticeably better but once i got through that and half of another tank, its baaaack...not quite as bad, but its intermittant, sometimes its really bad, other times its barely noticeable...and sometimes its gone completely.

if you find anything different please let me know