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RX7 FD - part throttle transition lean out issue around 4-5000rpm.

Practical Standalone Tuning

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I'm experiencing a cruising issue around the primary and secondary injector staging area.

in 4th or 5th gear as I approach 4000 rpm....there is suddenly a lean spot which can be felt as the secondary injector comes online. Is there a way this can be dialled out or made into a smoother transition.

I also noticed this during track driving at SPA. if i held onto an gear partial throttle around 4-5krpm.....there would be a lean spot as the secondaries started staging. Really frustrating issue. Even if i increase the accel fuel from 30-50 and time from 25-50 it doesnt seem to make any difference to the lean out. Never had this issue with the pfc. What am i overlooking for the partial throttle map? I am looking to get rid of the lean spot during light and partial throttle tip ins.

primaries are 850cc

secondaries are 1500cc

Any help appreciated.


Seems to happen at throttle tip in...or very light throttle sub 30% tp. Anything above that...the afr's are tracking well.

I tend to look at 3 things no matter the ECU:

1. Fuel pressure drops on changeover (looks otay though I don't know the sampling rate in your screenshot)

2. Secondary dead times and potentially using a pulsewidth adder if the ECU has the ability and they're actually correct. May create a rich spot but its easier to tune out.

3. Injection angle of the secondaries vs primares. Some ECUs can split them up, others can't.

Most of what I build are rotaries, and only rarely do I come across setups that don't 'Just work' out of the box but those are all things to fiddle with and check. Every build is different else I'd give you specifics.


When you say this "Even if i increase the accel fuel from 30-50 and time from 25-50 it doesnt seem to make any difference to the lean out."

Can you clarify where? In accel fuel for staging I'm used to single digit values, so yours sound quite large.

Link handles the transition to secondaries on rotaries and other engines really nicely in my experience, so at least you have an ECU that can do it once we help you sort out what's going on.

As David mentioned, having your injectors accurately characterized is key. I use Injector Dynamics injectors which makes that bit easy.

You can use the Sec PW Lockout at say 2.0 ms to avoid many injectors from being in their low slope non linear region, but you still need accurate flow and dead time data. When I mention flow data, make sure it's at the reference pressure you enter in software.

Also, did you tune the VE table as far as you could go with primaries only, then enable secondaries down in an area long before primaries run out? This helps confirm the VE table is at least set up well for the primaries, and then if bringing secondaries in causes large lambda error, the issue is likely with the secondaries themselves or their data.

Not sure if the link has a way to split primary and secondary injection timing. Perhaps a Link engineer or expert can confirm or deny?

Mike - see attached. I believe this is what controls the primary injection as the secondaries stage.

Thanks, Mike i really hope there is a simple tweak on the link which can smooth out the lean spot during throttle tip in for track driving. The Main fuel table is fully tuned....on 100% throttle runs, there's literally zero issues....but part throttle and and throttle off and reapplication as you come out of corners...i'm having issues.

The primaries are the stock 850cc mazda fd injectors.

The secondaries are ASNU 1500cc injectors and i've input the injector data from the ASNU data sheet.

I was running 2.0ms sec pw lockout but i was having issues with 100% wot runs between gear changes where the primaries would go over 100% duty cycle before reaching equilibirum and settling at 60% duty cycle.

Adam from link advised to change the staging to RPM instead of loading the staging by MAP which has resolved the primaries maxxing out WOT 100-200 draggy runs....but something is def wrong in the partial throttle area with staging. I'm not certain what the issue is.

Accel fuel doesnt seem to be kicking in during these lean outs....leading me to think its likely a secondary injector staging issue. However, as a test even making or asking the primaries to inject double the fuel for twice the time still doesnt seem to make a difference.

Attached Files

Ah I'm guessing G4+ then. I had looked at my last G4x tune and it's a bit different.

I pulled up one of my G4+ rotaries and it looks like your screenshot with the accel time value.

I suggest using a higher Sec PW Lockout value first though, to get yourself out of the low IPW non linear area of the injector. Perhaps 2.0 ms.

There's no scenario where you should be using 100% of 850cc injectors before reaching 2.0 ms on the secondaries so that would be a staging table adjustment and it sounds like you've already resolved that.

For what it's worth I'm using a lot less staging accel fuel, but for longer duration (staging accel time). Depending on the behavior you're seeing that may or may not be a step in the right direction for you, but getting out of the area of the injector that's likely not characterized perfectly should be a much bigger benefit.

Sounds good Mike, I'll change it back to 2.0ms and pull the accel fuel out which i nearly doubled and report back.

Sounds good. I look forward to hearing how it goes.

Hi Mike,

Problem solved...purring like a kitten now. Got brilliant throttle modulation again inline with my bone stock E92 M3. The smallest issues can create the biggest problems.

Thanks again.



Fantastic! Thank you for reporting back.

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