I know this has been discussed and beat to death over the years, but I haven't been able to find anything that will answer my questions about this. I plan on deleting the OMP on my S4 NA soon, and wanted a general idea of what to expect before I dive into it.

1. Does the OMP block off need a gasket or RTV?

2. Premix ratio? I've seen the general consensus is 1oz per gallon.

3. If the car sits for awhile, I would imagine that the oil would settle either on top of the fuel in the tank. Is this safe for a car that has no other source of lubrication for the Apex seals? Will the proper amount of oil still get into the combustion chamber?

4. Will engine braking cause wear on the Apex seals? I would imagine not, because even with closed throttle at 6k rpm, the injectors are still firing. Any downsides here?

 

the car has a fuel system with a return line, even if it sat long enough for the premix to settle, the fuel system will mix it all back up pretty quickly

 

On the last question, if you're using the stock ECU (or an aftermarket unit and have decel/overrun fuel cut enabled), the injectors will be off during decel/engine braking, thus not delivering any fuel & premix oil. Is it enough to worry about? Don't know, I suppose that really depends on how often you engine brake from high RPMs.

 

You are absolutely right. I don't know why that didn't occur to me

 

Stock ECU, so I guess the injectors will be cut. There's no way they're ALL THE WAY off during decel, otherwise the engine would stall, or lean out, no?

 

Hey bubba, what's the reason for eliminating the OMP? Just curious

 

Less headache. My OMP is very much shot, and it's easier to slap a block off plate on there than to rebuild it. Also, less carbon buildup due to injecting crank case oil which isn't meant to burn

 

The oil metering pump rarely fails. They can be resealed and reinstalled and be as good as new. Their internal rotation is somewhat minimal and they don't really wear out. They will leak but will remain functional. I've never used premix on an SA, FB or FC and I've never had any issues. The system works well enough for a daily driver and I've seen original GSL-SE's with their original engine with over 300k miles and a stock oil metering pump. A dedicated track car will require a bit more and you will want to premix to ensure a constant oil supply at higher rpm.

Its more of a headache to eliminate the omp. You will have to remove the dynamic chamber and remove the oil injectors and block of the ports or you will have vacuum leaks there. While you're in there you'll want to replace all of the vacuum lines, coolant lines from the engine to the throttle body, and likely the fuel pulsation damper and injector seals. Of course its good preventative maintenance to replace that stuff anyways but may not be necessary currently.

I would suggest resealing the oil metering pump alone and keeping it in place. Then premix a half an ounce of premix oil per gallon of gas that you put in the tank. This way you will ensure that you always have an adequate oil metering supply to the engine be it from the pump or the gas.

 

Actually they cut to 0% duty cycle, completely off. So unless your injectors happen to be worn & leaky, nothing gets injected. You won't stall and leaning out is not an issue when engine braking, as you're not putting any load on the engine (max vacuum).

 

In all honesty, I'm not that worried about pulling the dynamic chamber to get the the OMP injectors. I've had it off more times than I can count. I've rebuilt the intake track with new gaskets, deleted the rats nest and all of their associated vaccum lines, EGR, etc. The only vac lines I have running are to the OMP injectors, to the injector air bleed, and to an adjustable FPR.

For me, I premix my fuel anyway, ½ oz per gallon. So having to remember to add oil isn't an issue.

Idk, it just seems like the benefits don't outweigh the downsides to keeping it.

 

That makes sense, okay.