There aren't really any great reasons to remove an OMP, but there area lots of good reasons to keep it whether you modify it for fresh oil or keep it stock drawing from the oil pan.

My REPU has no OMP because it was a real pain to tray and make it work with the mixture of engine parts I have and my carb. I had several setups for OMP in there and each time it was a leaky mess. I really hate that it doesn't have one. If you want to premix go ahead and do it even with the OMP, but sometimes you really don't want to have to pull out the funnel and oil then have to clean up your mess and keep that messy stuff in your car, or maybe you just forget one time. Do you want that one day to be the end of your motor?

 

Sold my mechanical pumps

Thanks guys

 

Maybe I'm just ignorant, but the engine runs because it is getting a mixture of air, fuel, and heat (spark). If it ceased to squirt ALL fuel on deceleration the the motor would cut off, would it not? The throttle regulates the air charge and fuel is added based on the map sensor readings, engine load, and rpm. Not the 'gas' pedal (air pedal?)

 

My PFC Commander reads zero injector duty-cycle during off-throttle decel. When I lift my foot, it goes to zero. Not a tuner, but there maybe a way to play with that with a datalogger..I'm not sure. Regardless, very little or no fuel, very little or no lubrication...and frequently at relatively high rpm and for relatively long periods with just pre-mix.

 

Most times when you are decelerating in gear, the stock ECU will stop injecting fuel. By lifting to 0% throttle, you have essentially told the ECU you don't want the engine to make any power so it will turn the injectors off to conserve fuel. This also tends to result in an engine note that is quieter and smoother than if fuel was injected. There are a few geeky science-type methods to confirm this by measuring the electrical signal to the fuel injectors, but the easiest way to feel it for yourself is let the engine coast all the way down to idle RPM in 2nd gear. It takes some discipline to avoid pressing the clutch when you know the engine is about to bog, but you should be able to feel when the ECU turns the injectors back on and the engine makes enough power to continue coasting without any throttle... I don't remember the exact RPM but it is probably between 1000-1400 RPM.


If you have entirely too much time, get an ECU that will cut fuel or spark when the engine runs too lean, then configure it in such a way that will trigger that fuel cut without hurting the engine (for instance, set the target fuel ratio to something unrealistically rich). When the ECU decides the mixture is not rich enough, it will cut fuel or turn on a low-RPM rev limit to protect the engine, and you'll end up with the fuel injectors turned off when the throttle is fully open. The engine will still coast down to a stop, but the sound will be even quieter and it will not decelerate as quickly without the vacuum that would have been present with a closed throttle. Probably best not to do this often, but it's entertaining and a good way to double-check that the failsafe functions as intended.

 

Many EFI systems cut fuel on deceleration. Assuming a manual transmission in gear with the clutch out, the car remains running because the momentum of the vehicle spins the engine.

Edit: scotty beat me to it.

 

Regarding the OMP, if you're making much more power than the stock ECU could support, you might be running more fuel than the maximum output of the OMP... I measured it once and saw maximum of ~4.3 volts at 11psi with stock a nearly-stock engine: aftermarket downpipe but stock exhaust and intake. My take on that is there's not much headroom, unless they were injecting more oil than needed for stock power levels.

Pouring 2-stroke premix is a mess but seems unavoidable if you're running E85 even near stock power levels. I've been looking for some sort of large plastic syringe to suck premix out of the container and push it into the fuel tank. I'm told large syringes exist for farm use, but haven't yet found a clear one that will hold as much fluid as I'd like.

 

4.3 volts is only a vague appreciation of where the position sender has sat on a s5 or FD engine
and is not in any way an output to the pump

the number you see is also subject to a ground offset when you measure without earthing to the ecu earth point
and the oil output from one engine to another when returning 4.3 volts can be different
as the body of the position sensor is fine tuned at the factory by displacing it back with small shims


the EOMP itself works by action of a 5/6 wire stepper motor ( 4 channels and two power )
which variably depresses a plunger,, which in effect is the inlet valve to the mechanical pump that is turning with engine speed

removing the ECU control will just "park" the plunger at one setting,, and the OMP part will still work with engine speed but at a fixed inlet flow

it is a simple matter to displace with a spacer between the stepper output rod and the plunger for more flow everywhere

or to take the shims out ( or add them in ) and make the pump move either less everywhere,, or more


by this design,, there is more left in the pump than many of you can achieve
and there is scope for the user to add a physical offset trim to his need

also will point out that FC s5 ( 4 outlets ).. FD rx7 ( 2 outlets ) and 20 B ( three outlets )
all use exactly the same pump .. with only the final tapping of the holes for banjos makes them any different from each other

note that a 20b and an FD engine has significantly more stock HP than the FC

and from that then you should see what the pump is capable of keeping up with

but yes., once you go through to silly HP.. it pays to add something extra to the tank . to be sure

and if you have custom mapping for your OMP..
to push it to max flow ( 5 V return ) once you have gone beyond stock boost ( or earlier for aftermarket seals )
and dont pull any out unless you have an octane related knock

to be sure, to be sure

edit .. note that the rx8 changes things a little,, and only seems to use the position sensor for a switch at either limits,, and instead "counts" the number of full winds it orders the stepper plunger to
it also only seems to do the self check immediately after startup

and so mazda made moves to improve the redundancy of the pump ,, where silly flags before caused warrantee issues
( EG ..engine code and limp )
for what may have been fleeting errors or a bad wipe of the return sensor rheostat

as such,, have seen the "jason dixon eomp controller" operating just fine ( in rx8 mode )
on s5 eomps that had previously produced codes and limps from bad wiper when on stock vehicles

 

Thanks for all this info bumpstart!

 

Yeah, to build on what scotty305 said: if I let off the gas at 5000rpm in 2nd gear with clutch engaged, the engine is now spinning, but it's not firing. No fuel is injected, no spark is fired. So in that sense, yes it did "cut off." The friction in the engine from the rotating assembly creates engine braking. The braking is transferred to the wheels through the clutch, transmission, diff, etc.

Once engine speed falls low enough, the fuel will inject again and the spark will fire again, so combustion resumes and the engine generates torque to overcome friction and propel the vehicle forward.

 

Thank you for the great info, this right here is a great post with arguments that people don't think about!

 

This thread is now in the FAQ

 

Mazda has had a tough time keeping rotaries emissions compliant. Couldn't that have a lot to do with the changes in the OMP system? Perhaps it had something to do with everything bumpstart said, or perhaps it has to do almost entirely with pandering to ignorant customers and strict emissions laws and Mazda had to design a system that would appease both. I imagine that in that attempt they would be creating an oiling system that used the minimum amount of oil needed to get by, still maintain a lengthy engine life, be easy for customers to use.

 

This forum is so great! I've been thinking of this after reading Howard's write-up awhile back on this subject. I was going to remove the pump and go straight to premix, but I am interested in this route now. After reading through, I searched the googles to see if a kit existed, and (of course) the first links were from this forum!

 

Engine oil is not dirty. It is the oil that is lubing all the moving parts in the engine. If it were so dirty all the bearings would be chewed up.

 

I removed the OMP a couple years ago and do not regret it.

My FD is race only though, and premixing is no big deal.

If it were a street car I would have just fixed all the leaky stuff.

As it is a race car, and every winter something new leaks, I just blocked them off and premix.

The OMP not working properly was a bit of a worry, so less things to leak, one less thing to break my car.

 

Thanks for chiming in guys.

I ended up buying new lines and washers.

Call up Ray at Mazda Malloy, he knew exactly the part I needed, cheaper than atkins, and I got my pkg in 2 days vs 5 days.

 

don't you just love that feeling when you receive a package from Ray filled with new Mazda goodies?

 

The 0% duty cycle on decel was enough to convince me to keep mine. I had a PFC and you can watch the injectors go to 0% when in decel, then once you get down to an rpm where you are no longer compression braking, the injectors turn back on. I kept mine, but I also have an Adaptronic ECU which allows control of the OMP. So I dialed back the amount of oil injected and use premix.

 

I'm pretty sure you can turn off the fuel cut on decel...

 

I'd be interested to hear more about this, fendamonky. I've only spent a little time running without decel cut because I was told it helps assist tuning the very low-throttle sections of the map. With the injectors off (decel cut active), the car feels and sounds smooth when coasting down... with the injectors on (decel cut disabled) the car bucks, burbles, and generally feels & sounds rough.

As soon as I was happy with the car's transition from decel cut to light-load fueling I re-enabled decel cut and never looked back. I'd be interested to hear if others found some combination of AFR, timing, and (whatever else is a factor... trailing split? injection angle? idle position?) that would help.

 

I'm no tuner, so I can't really go into the "how" of it. I just recall that mine didn't cut fuel, nor did it have noticeable issues with driveability.

That was 2 years ago, running a PFC.

 

Yep you can still spray a little fuel on decel with a PFC

For those interested I have an OMP (approx 62k miles taken off of a mostly stock 94 touring) in good shape with SS lines (the good ones with rubber coating on the outside)

$125 shipped

 

Hi everyone,

I'll chime in. I have been reading the forums and replying for some time. I modified my car with some of the knowledge I have gained through this forum and some from my experience and knowledge as an engineer, and I am not a design type engineer.

I went with an external tank and OMP with some premix. I think Mazda engineers knew what they were doing and strategically located the OMP injectors in that location for a reason and I run 2-cycle oil through the OMP. I also pre-mix a little due to running more WHP and ensuring that enough oil gets injected into the engine. Now ensuring how much and exact amounts is a debate, but I do .5 to 1oz premix with a working OMP. I am at 380-400WHP.

So I think lubricant is very important and I spent a lot of time thinking about the options and weighing them against each other.

Then on to what can possibly kill an engine. Most engines need rebuilds due to coolant seals, fuel delivery problems, overboost, or carbon'd up.

Coolant seals are damaged from heat cycling out or age. Ensure water temps and oil temps are in check and replace with viton seals. done.

Fuel delivery problems, keep the fuel filter clean, use the car on a regular basis, use stock parts were can (hardlines, etc), replace with a stock denso supra pump for reliability. Check system on a regular basis.

Overboost can happen from a line cracking going to the wastegate or something with a boost controller failing. Best option would be to go off spring pressure on a wastegate. If something fails like a vacuum line, ensure you have enough fuel to run the engine in an overboost state. But now you need to worry about detonation.

Carbon. probably from running rich. most speculated on that here. I run a healthy idle at 12.6-12.7 AFR to catch the idle from decel. This is needed because the engine does cut fuel when cruising off throttle. The powerFC adds fuel back in depending on when the tuner says to add it back in. Most tunes I have seen add fuel back in around 1100-1250 rpms. otherwise fuel is cut.

Water injection/methanol - This helps remove carbon from the engine/seals/etc. It also removes heat from the combustion chamber and increases the octane (when using meth). If tuned to say 14PSI where the car can run without water meth (safe tune), and you add a water rich, slight meth mix, it removes the carbon from the engine, prevent engine detonation, can save you on a fuel delivery problem (maybe), and protects against a possible overboost scenario.

I do everything above on mine. I would also run stock seals for the best housing to seal interface with lots of design R&D behind them with predictable manufacturing processes/quality control. My car does have super seals in it from the previous owner, and will run till I need a rebuild and replace with stock seals.

And just by observation on these forums (I know a little off topic). Those who venture the furtherst from stock seem to have the most problems. A lot of people have blown engines from E85 even though that was supposed to protect them. Lots of very low mileage engines having to be rebuilt using aftermarket seals, Chattering marks and destroyed housings. Unknown causes but most with aftermarket seals. Stock seals can handle the power, they just don't handle detonation well, so we try to find seals that can at the expense of reliability. Why not handle the detonation first and use the most reliable seal?

 

You can I think I mentioned it . BUT! you MUST get it tuned and set up for it ..

Because I turned on the fuel on off throtle set it at 8k ... and lets JUST say.. the flames comming out of the FD were a bit much . and the MPG definitely suffered ..

if you do remove the OMP . THen You should raise the fuel cut . and lean it out to a point where its not turning black gold into fireworks all the time ..


I have been thinking about doing JUST this .. BUT I dont know what AFR to tune the car to during decell I mean