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Accel Enrich - Gear Change

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Good Afternoon, I hope everyone is safe and well in these strange times.

I have a kitcar powered by a fully forged CA18DET engine with a GTX2867r gen2 turbo and the engine management is maxxecu. (Swedish based)

I've had the car mapped on a dyno dynamics rolling road but a local tuner and 'in gear' the car drives perfectly but the accel-enrich is all over the shop.

The tuner says it needs to be setup on the road but he "doesn't do road tuning".

I've finished one of the webinars relating to this, and will be watching the other two with the hope of improving this as best I can whilst being stuck on my drive (UK is in lockdown) but my issue is primarily in relation to high-rpm gear-changes.

On reviewing logs I'm seeing HUGE afr spikes of 20+ on high-rpm gear changes (7k 2nd to 3rd, 3rd to 4th etc). The car noticeable lags before coming back on-song.

As I said, I'm only one video in so still have some to go but my understanding so far is that accel-enrich is typically not needed at higher rpms so I'm a bit confused as to the results I'm seeing in my logs.

I'm happy to post some screenshots from my log files and settings if that would help.

You need to log data in the ECU to see what is happening at your high RPM shifts.

I don't know how the logging setup works in the Maxxecu, but you should be able to specify channels that will help you debug -- of course the basic conditions (Engine Speed, Throttle Position, Manifold Pressure, Lambda, Fuel Pulse, Ignition Timing), but be sure sure the add any channels related to acceleration enrichment (or perhaps decel enleanment which sounds like what is happening), channels that are used as axis for any accel/decel tables would be good to know, as well as what the resulting trim values are. Once you find the correlation with what you are currently seeing, you will understand what to change.

Do you have a Deceleration Fuel Cut Off (aka DFCO)? Sometimes that offers a delay setting to avoid cutting all fuel when you lift the throttle for a shift, check if that can be increased.

As David mentioned, posting a log will be a big bonus and help us understand what is going on.

Another thing I would suggest looking at is injector timing. You can find that running a later end of injection point will generally give a power gain although can also cause hesitations.

Thanks for the replies. Two webinars done 1 more to go.

I fully intend to start from scratch with the accel-enrich but as above, this will really only help me on idle and cruising not a high-rpm shifts.

I've attached some screenshots from the maxxecu software. The logging is second to none (as long as you know what you're looking at!!)

1 - revving at idle

2 - accelerate with no gear change (no issues with fuelling at high rpm)

3 - accelerating through the gears. Huge lean spots once I get back on the throttle.

@chris.wall - I add the fuel primary after reading your comment (but unfortunately after saving the logs above) and note that the injector timing doesn't seem to be 'quick' enough to get enough fuel in ready for me being on the throttle again. Does that imply an issue with the injector timing or is that exactly what accel-enrich is meant to solve?

I've also added a screenshot of the accel-enrich settings from with the software itself.

My injectors are DENSO 1000cc if it helps.

Attached Files

Yes, you might try a little more acceleration enrichment, but because the lean spike is short, it can be difficult to tune out completely. Realize that the AFR readings are delayed somewhat from the operating conditions of the engine. For example when you close the throttle to shift, note the time before the mixture starts to indicate rich -- that is the delay time before the AFR reading represents the change in operating conditions. So, that lean spike is mainly occurring just as you go to the throttle and the enrichment brings it right back to the target pretty quickly.

I would say that your AFR is not the issue with the "lag feeling" you are experiencing. I believe that is caused by the drop in Boost Pressure (indicated by the Manifold Pressure reading). The mixture returns to normal very quickly, but the long delay is the time it takes for the boost to build up to pre-shift levels. I don't have a lot of forced induction experience so others will probably chime in with tuning methods to address this.

You probably see this same behavior if you just lift the throttle for a few tenths of a second and return to wide open.

In this Webinar, they discuss how to setup the ECU for flat shifting using a clutch switch instead of closing the throttle. This is specifically to keep the boost up on turbo charged engines.


Might be something for you to consider...

I would be interested to see your injector timing, can you post a screen shot. Under Fuel Inj General, or have a play with this in the higher rpm.

Note that changing the injector timing can (usually does) have an effect on the overall AFR for that specific rpm and might need to be fixed in the main fuel table.

When you say "lag" do you mean a hesitation/stumble for a split second, or like boost lag?

As David mentioned it can be near impossible to remove that lean spike in a log, but you should not feel it as a driver. The amount of accel enrichment at that rpm seems reasonable, so does the decay values. However that isn't to say it needs more.

If it was me and there was a noticeable hesitation when jumping on the throttle, I would try some more enrichment and also moving the injector timing.

Thanks all for the replies.

I am looking at fitting flat-shift but still want to fix whatever issue I have.

@Chris.wall - I've just found out that the original tuner used the wrong injector choice on my map. My injectors actually have a LOWER 'dead-time' than the options that have been used in my map. Would that difference in setting give the problems I'm having?

No, I wouldn't expect incorrect dead times to cause issues with hesitation like you're describing. Since the dead time is essentially the time the injector takes to open (and close) if you have the settings wrong, you will end up compensating for it in your main fuel table.

Incorrect dead times are most noticeable at low PW (idle/light throttle) and if wrong will generally cause a big step in fuel table values in these areas.