air injector flow too high after cleaning = problem or no?

[motuman]

Mercury 300xs, serial #1E051504 w/ 132 hours.

I just had my grey air injectors cleaned & serviced by a reputable company. (i.e. a company that Don has mentioned he trusts, and fwiw Integrity Injection was my first choice but schedule didn't work out this time around)

The injector service company states that 4 out of 6 injectors are flowing too much (fluid, as they can't measure air) after cleaning, and should not be used. The worst out of spec injectors are flowing about 8% over at idle-midrange, 5% at full throttle.

I had previously read an ongoing debate about whether Optimax Direct Air injectors flowing too much will air lean out an engine, or not. A third injector service company makes this argument in another forum:

If you calculate the volume of air injected into a cylinder per cycle by a direct injector, it is less than 1% of the total combustion air. And a "word on the street number" from Mercury purports the total volume of air ejected into a cylinder per cycle is less than 3%. So using Mercury's number of 3% in a hypothetical example...if a direct air injector is flowing 33% high (out of spec) that's 33% extra air on 3% of total combustion air, so only raises the overall A/F ratio by 1%. He goes on to state that the primary function of the direct injector on Optimax is to atomize and disperse fuel, not to modulate A/F ratio.

I can see both side of this argument on a hypothetical basis....i.e you want air and fuel injectors matched and flowing in the correct ratio. I could also see how the amount of air introduced by the direct inject is actually a small fraction of total combustion air. I just don't have enough real world experience to take a chance on the "slightly out of spec" high flowing air injectors.

Hopefully Don will have time to chime in, but very interested to learn if an air injector flow too slightly too high after cleaning is a problem or not?

[JOE54]

so if i understand this correctly "they" are saying its flowing too much fuel as well because fuel psi in an opti max should always be greater than air , so my understanding is engine will be rich do you agree ??? how many hours on this engine we speak of ???? so when you sent these off for cleaning howd this engine run must have been terrible ????

[motuman]

so if i understand this correctly "they" are saying its flowing too much fuel as well because fuel psi in an opti max should always be greater than air , so my understanding is engine will be rich do you agree ??? how many hours on this engine we speak of ???? so when you sent these off for cleaning howd this engine run must have been terrible ????

- The engine was running really well, I heard a very slight bearing knock and pulled the air compressor to inspect. Saw the beginnings of compressor failure. Purchased a new compressor from European Marine, and sent out the injectors and fuel system for cleaning.

- I'm told the air injectors were flowing OK when I sent them in. But now, 4 of my direct air injectors flow above spec after cleaning. Apparently it's common for air flow rate to increase as air injectors wear.

- An an FYI (new to Optimax, here to learn) it sounds like the air injectors are designed to flow about 4 times as much as the fuel injectors.

So the question is....do higher flowing air injectors lean out your mixture? Or is the amount of air being injected small enough (@ possibly 3% +/-), relative to total combustion air used, to not affect your overall A/F ratio.....given slight variances in air injector volumes.

[lpugh]

fuel injector pulse width determines the amount fuel for that cylinder, Direct injector atomizes and delivers that mix, even if the direct injector has a 25% additional flow rate the AFR will still be very close to optimum. Does not matter where the air comes from on a speed density system fuel charge will be the same as long as the pressures and injectors are working correctly assuming all other things are correct, so PCM send the correct pulse width.
I am amazed at the difference in flow rates of direct injectors, keep in mind that they are tested with a liquid, and they flow a vapor.
I would bet the actual vapor flow rate is not much different on the higher flowing direct injectors, though I do have concerns at about 15%
Would like to hear Dons take on this.
On a mass air flow system this would be a serious problem due to unmetered air.
Logic makes me think that excessive DI flow rate is like a mini very low volume super charger, meaning you would want to pair the highest flowing fuel injector with the highest flowing DI
These are just my opinions are in no way proven facts.

I would love to see the flow results on a couple of dozen brand new DI,s.

[DewRonInc]

I agree with the assumption that as long as DI injectors do not leak flowing liquid, they are golden as I would bet every single one is out of spec due to the design

[lpugh]

I agree with the assumption that as long as DI injectors do not leak flowing liquid, they are golden as I would bet every single one is out of spec due to the design

That would be a dangerous assumption, one of the big problems with DI injectors are stalling at very high RPM with a long pulse time. IE: wide open throttle

[JOE54]

^^^^^^^ + 100 never good at wide open end result can be catastrophic

[DewRonInc]

Yes indeed, but under testing and flow is off a bit but the have zero leaking and Ohm reading is correct, what ya think

[EuropeanAM]

1. A high flowing Direct/Air injector will be RICH (not lean), because ANY air leak (even too much air through a DI) will result in fuel migration to the air side of the rail.

2. An air injector that flows more than it should, especially at mid-part throttle, or idle parameters, will not close properly at WOT parameters, which will result in COMBUSTION GASES passing backwards into the rail. This causes a cascading effect of failing DI's (one of the primary reasons we see such a high mortality rate).

3. In addition to #2, the injector that fails to close between pulsewidth events opens the real possibility of raw FLAME entering the rail. Inspect a few lower-end fuel injector o-rings and you'll even find the burn marks.

4. Respectfully: 25% too much flow on a DI will never produce "optimal" fuel delivery or combustion. That would be a recipe to fail 4-6 other direct injectors within 50 (or considerably less) hours.

[juanclemons]

this one reason im sticking to the efi 3.0 liter lol

[JOE54]

[DewRonInc]

I know they are very picky for sure

[EuropeanAM]

I agree with the assumption that as long as DI injectors do not leak flowing liquid, they are golden as I would bet every single one is out of spec due to the design

VERY bad assumption. Based on Post #1 data, you should ABSOLUTELY, POSITIVELY replace those injectors. The REASON they flow too high is that they're not closing between pulses, meaning that raw flame and combustion gases can pass directly into the fuel rail.

This results in a cascade of failed DI's in a relatively short period of time.

Those parameters are more indicative of Part-Throttle and WOT. If you tested at idle parameters, the numbers would be north of 15%.

This is totally separate from the comments that Leon made. Air supplied through the DI's is there to ATOMIZE the fuel (not to supply the air-to-fuel ratio or stochiometric air volume).

[EuropeanAM]

this one reason im sticking to the efi 3.0 liter lol

Good luck... parts are going NLA faster than I can recognize and keep up with.

[DewRonInc]

About to flow and clean mine just to see where mine are, due to another problem

[basspro57]

Just curious...did the cleaning service just do a static flow of the direct injectors or did they do a pulsed flow? I see a lot of postings where the lab just does a static test (wide open) and that is not how they should be tested. They need to be pulse flow tested as I see a lot of injectors that appear to flow fine static but then do not flow when pulsed correctly (and they are pulsing in real life).