Zero throttle, rolling in gear: what happens?
 

As far as I know, all modern cars shut off the fuel injectors when you let off the gas but stay in gear (i.e. on the overrun), until the RPMs get below a certain point (e.g. 1500 RPM).

What does the S2 RX-8 do? Does it shut off the fuel injectors, too? If it's not burning fuel, what happens to the oil that gets injected? Does it just accumulate and/or get blown out the exhaust? If that's the case, does that mean I should keep engine braking to a minimum for the sake of the catalytic converter?

I never downshift for the sole purpose of slowing down, but I will sometimes let off the gas way early and engine brake if I know I'm going to have to slow down ahead, especially while going down a hill. Just wondering if I should change that habit.

Fuel injection IS shut off.

So is OMP oil injection. The oil that is in there just gets spread around until the fuel/spark get going again.

Continue to keep engine braking as you wish, there is no extra harm coming to the car.

I'm sure it's fine, but it's always scared me that the OMP stops when one is not on the gas...

Thanks for the responses!

The OMP shutoff does scare me, too. Then again, there's quite a bit about this car that's superficially scary, so....

I originally had the same worry. The OMP shutoff doesn't mean that there isn't any lubrication any longer though, there is still a layer of oil getting drawn through the lines from the last time the OMP motor stepped. No harm being done.

Well you have an SII so I'm not sure how that oil metering system works in comparison to the S1's system. I'm not sure I have ever seen anything that confirms the info stated here.

I looked up the OMP map for an S2, and it doesn't 'shut off' presumably, since there are still stepper values at zero load.

This is from Paimon's S2
https://www.rx8club.com/attachments/...daedit-omp-png

Thanks for digging that up, RIWWP!

One of my main concerns was what happens when you lift off at 8k+. Interesting that the OMP gives about as much at 0% load near redline as it does at ~80% load between 4k and 5k...

Has anyone made one of these maps for a Series 1?

Yes S1 maps are all over.

same thread, 1 post later: https://www.rx8club.com/series-i-eng...239275/page13/

https://www.rx8club.com/attachments/...daedit-omp-jpg

Not that it aids the conversation in any way, but just incase anyone sees my map and is wondering why it doesn't match their (stock) map, it is because mine has been adjusted with a 30% rate increase

Across the board?

Mine also has a 30% across the board, but from 0-20 pct load i have raised my oiling quite a bit to cool seals and help relube anything that may be washed away by water meth under high loads.

9000-60setps
8500-55
8000-50
7500-45
7000-40
6500-35
6000-30
Im in my phone but will post my map when i get a chance.

Also i believe is continues to inject oil while engine braking since the proper steps appear on my logs.

Maybe you are confused

even under engine braking engine load and rpm never goes to zero, the OMP never shuts off if the engine is running/turning over

Lifting at high RPMs (> 6,000 rpms) decreases the % load I'm seeing to a minimum of ~10% (idle on a fully warmed up engine is around 29% load). As to how these numbers from the ScanGauge correlate to actual load and the OMPs' injection rates I have yet to be able to discern.

edit: The load-based S2 OMP rate map is posted above, you can see there, the stepper values are different than the S1 maps, but then it's an entirely differentOMP setup with two OMPs and a third oil injector so there's no real correlation between the two

I don't have an S2, but on the S1 anyone with a Cobb AP or MazdaEdit can verify by logging the OMP position that it never goes to zero unless the engine stops, as long as the engine is rotating you would never want it to have zero output regardless


.

A bit of a thread revival, but I couldn't find anything in my search.

On an S1...... Does the OMP shut off while on the overrun or is there still oil injected into the housings?

On the other end of the scale - If I adapt my driving style to avoid overrun as much as possible, will this cause carbon buildup? (running premix and decat)

From what I'm reading, there's always some oil being injected. The only thing that changes is how much.

Not sure whether minimizing overrun would increase or decrease carbon build-up. The alternative to overrun is disengaging the clutch or dropping into neutral, which means the engine drops down to idle, which is bad. Then again, overrun means unburned oil whipping around. My instincts say overrun is better, but that's just shooting from the hip.

Why would idle be bad?

Well "bad" was a bit of an overstatement. Rotaries just don't like low revs. They'll tolerate idling but can build up gunk until you rev them out.

Most of the carbon is from gasoline, not oil.

Well yeah.

Just saying, if you have unburned oil washing around and not being burned, that's going to be a source of carbon deposits as well.