Optimax Air Injectors

**clayc** · 07-17-2022, 01:29 PM

Originally Posted by boostalmighty

i had a similiar situation to yours, all my fuel injectors were good, 2 air injectors were clogged beyond cleaning, and 2 were not pulsing at all. i absolutely could not believe it so i got them back and sent them to someone else, second company told me the exact same thing first company told me. he asked me who i sent them to first and when i told him he said vouched for them as well. long story short i ended up buying 6 air injectors from merten and they flow tested them before sending them over to me. also, fyi my engine was not showing any symptoms, i just sent them out as a preventative maintanence.

I’d just completed compression and leak down testing when I decided to remove belt and turn compressor pulley by hand. That’s when I found the dreaded compressor problem. Took compressor apart,, rod bearing and journal trashed. Piss poor design, in my opinion.

I’ve learned there’s a back order on direct injectors nationwide. I’ll be making lots of calls in hopes of finding 5 new ones.. You mentioned getting yours from “Merten”, who is that?

**kellytheaker** · 07-17-2022, 03:20 PM

I don't think you rebuild - you buy it new as assembly - could be wrong .

**InjectorService** · 07-18-2022, 10:21 AM

Originally Posted by clayc

Just called the Injector Svc back, had a long conversation. Said he fails a high number of air injectors. He also warned me about how many brand new / right out of the box air injectors that fail testing and Merc will not stand behind them. That’s BS at $700 each.

Curious…. Do most of you have the air injectors flow tested? Or just run em until you experience problems? Wondering if this air injector failure is as prominent as it seems and if there’s been any legal action against Merc over it!

This tells me almost all I need to know. I don't belive this for a second. Can I ask what shop this was? (you can PM me, I don't want to start a business trashing here)

EDIT: To add to this a little bit, I'd like to know what test they failed and how they were testing them. I've had this same conversation with people before, infact I've had it with injector shops as well, and it is largely misunderstood how and why to test these.

If I were you, I wouldn't go shopping just yet.
Blake

**2jz** · 07-21-2022, 10:30 AM

Originally Posted by InjectorService

This tells me almost all I need to know. I don't belive this for a second. Can I ask what shop this was? (you can PM me, I don't want to start a business trashing here)

EDIT: To add to this a little bit, I'd like to know what test they failed and how they were testing them. I've had this same conversation with people before, infact I've had it with injector shops as well, and it is largely misunderstood how and why to test these.

If I were you, I wouldn't go shopping just yet.
Blake

it is largely misunderstood how and why to test these
Would please explain in detail ☝️

**InjectorService** · 07-21-2022, 11:17 AM

will do, give me some time to make some sort of write up.

**XstreamVking** · 07-21-2022, 08:20 PM

Thanks for clearing this up..

**InjectorService** · 07-22-2022, 09:37 AM

I will start off by saying the Optimax fuel and air system is very misunderstood and misdiagnosed by Mercury dealers, repair shops, and injector shops alike.

I have this same exact conversation with people weekly, who have sent their air and fuel injectors to a variety of shops that have told them to replace nearly all their air injectors. So here's my 2 cents on the Optimax fuel/air system.

My opinion is that the flow rate on the air injectors DOES NOT MATTER. I know you're thinking, "Yes it does, you could lean out a cylinder if they are out of spec....." Here's why not:

Opinion 1 - Low flow can lean a cylinder out on fuel.
Easy numbers the direct injectors flow 2500+cc/min, and the fuel injectors 650 cc/min (numbers are rough for easy calculation) Thats nearly 4 times as much capability as the fuel injectors feeding them. You would have to have an air injector that was 75% blocked or out of spec before you would start leaning out on fuel. (remember fuel pressure is more than air pressure)

Opinion 2 - An air injector that is flowing too much will lean the motor out on excess of air:
Cylinder volume is 500cc. Direct injectors flow 1440cc/min @ 5000RPM with a 5ms pulse width @ 90PSI. Which ammounts to 0.12cc/revolution. (I can break that math down if you like) That equals out to .024% of the cylinders volume is injected through the air injector into the cylinder in a 5ms pulse width.

Now, keep in mind, my numbers for the direct injectors are in fuel, not air. The fuel/air mixture would be very tough to measure in actual volume and I do not have the equipment capable of that. But even if you take my numbers and multiply them by 10, that's still only .24% of the cylinders volume of air.

Now let's take this one step further, just for arguments sake. Word on the street says that Mercury claims that LESS than 3% of the total air for the Opti comes from the air injectors. (I have not seen this number printed anywhere but it may be) Now this number is obviously much higher than mine, but I'm sure they have engineers and calculations and other factors I can't or haven't considered.

So now we take 3% of the cylinder's air coming from the fuel injectors. In order to supply 1.5% extra fuel, or in other words lean out the motor by 1.5% you would need to have an air injector that was flowing more than 50% higher than normal. Alternatively if an air injector was 50% plugged, it would richen that cylinder by 1.5%. In either of these cases you would have a noticeable running issue and this would be easy to see based on a simple spray pattern test.

I have an injector test sheet from another company here that is stating to replace multiple air injectors because of a 12% imbalance. So if we take 1 injector at 12% high flow, that would mean that cylinder would be receiving .36% extra air on that cylinder. If it was down 12% on flow that would mean that cylinder would be .36% rich.

With all of the above information in hand, I want to reiterate that the air injectors will ALWAYS flow all of the available fuel supplied to them, unless they are blocked to less than ~650cc/min, at which point there would be a noticeable running issue. (Remember fuel pressure is higher than air pressure)

The point I'm trying to get across here, is that any possible way you calculate it the air supplied by the air injectors is so little it does not matter. The sole purpose of the air injector and air system is to atomize the fuel, not supply air to the engine for combustion.

I look forward to you guys reading this and imputing your own opinions on this.

Blake

**XstreamVking** · 07-22-2022, 10:13 AM

The times I have had air inj issues the cylinder was always very rich and the air inj would fail the ohms test. In my case it had zero ohms resistance and had completely failed. I replaced with some used ones and so far no problems. I feel as long as the running and starting performance is good that it might be wise to leave it alone

**InjectorService** · 07-22-2022, 12:41 PM

Originally Posted by XstreamVking

The times I have had air inj issues the cylinder was always very rich and the air inj would fail the ohms test. In my case it had zero ohms resistance and had completely failed. I replaced with some used ones and so far no problems. I feel as long as the running and starting performance is good that it might be wise to leave it alone

Correct me if I'm wrong, I think what you may be seeing is actually a complete lack of fuel to that cylinder, and you are actually reading oil on the plug. I see this a lot on the Etec motors, customer complains of over rich on 1 cylinder, which often turns out to be very lean, but because the oil is still coming from the crankcase the plug looks rich.

EDIT: But yes, ohms test is a straight fail regardless. Usualy you see that on a single cylinder though. What I am talking about above is failing 4+ injectors at 1 time based on flow rate.

**kellytheaker** · 07-22-2022, 12:50 PM

Thanks excellent Tech -

**clayc** · 07-22-2022, 12:55 PM

Injectorservice, Thanks for the write up. Even though I’m not an injector expert, I’m an old school gear-head that built some nitrous gulping big blocks w/ big tuned Holley’s feeing their appetite.

Before your post, I wondered the same thing. How can such a low volumetric “puff of air” create a lean-out on these engines. Are they that lean already! I also asked myself, if it’s not the amount of air being injected, but the pulse width widening, thereby holding the air injector open during ignition. Maybe that’s it. Then, that theory didn’t hold water. I finally thought about all the direct injectors in diesel trucks (like my ‘7.3 PSD w/ 340k) which are still running fine with way more hours than a 400 hr outboard.

I’ve settled on the conclusion of this: clean the air injectors to ensure there’s no contaminants or obstructions. If they’re opening, with no odd sounds, and the spray patterns are good, w/ good ohm tests. . Run’em!

**boostalmighty** · 07-22-2022, 01:16 PM

Originally Posted by clayc

Injectorservice, Thanks for the write up. Even though I’m not an injector expert, I’m an old school gear-head that built some nitrous gulping big blocks w/ big tuned Holley’s feeing their appetite.

Before your post, I wondered the same thing. How can such a low volumetric “puff of air” create a lean-out on these engines. Are they that lean already! I also asked myself, if it’s not the amount of air being injected, but the pulse width widening, thereby holding the air injector open during ignition. Maybe that’s it. Then, that theory didn’t hold water. I finally thought about all the direct injectors in diesel trucks (like my ‘7.3 PSD w/ 340k) which are still running fine with way more hours than a 400 hr outboard.

I’ve settled on the conclusion of this: clean the air injectors to ensure there’s no contaminants or obstructions. If they’re opening, with no odd sounds, and the spray patterns are good, w/ good ohm tests. . Run’em!

i dont think the 7.3 injector analogy is fair. totally different animal and if a diesel injector stays open then you can wash out the cylinder walls. everything else i do agree with though.

**kellytheaker** · 07-22-2022, 01:55 PM

All I can say is Blake - Injector services has been a great asset here and continues to easilly lay out the running questions on these Opti s . Gives me confidence when I send him stuff to check . I call him S.U.B - short for Super - Uber - Blake !

**clayc** · 07-22-2022, 05:42 PM

Originally Posted by boostalmighty

i dont think the 7.3 injector analogy is fair. totally different animal and if a diesel injector stays open then you can wash out the cylinder walls. everything else i do agree with though.

You’re right, 7.3 analogy isn’t correct. It was just what was rolling around in my head. Two different systems. Only 100% similarity is it both are in the combustion chamber.