Idle catch RX7 13B-REW - Haltech Nexus S2

Hi HPA!

I have an issue with idle catch where clutch in results in hot stalls.

I have been chasing this issue for 1 few months now and cant seem to wrap my head around the issue.

BAC seems to be doing its thing, ignition correction seem to be doing its thing.

I think the issue started when tuner did fuel film pooling changes due to lean spike on quick throttle change (not 100% sure though).

Tuner says it should work and blames a mechanical issue.

I already did pressure and smoke test to rule out any vac leak.

The stalling seems to be a bit better when o2 control disabled below 2000 rpm, so i guess a fueling issue of some sort?

RX7 FD 13B-REW

Single turbo

Pump gas RON99

ID injectors 1050/1700CC

Haltech Nexus S2

Attached map and log (with catch and stall)

There's a few issues here that could be contributing. The closed loop idle control doesn't appear to have been properly configured. It has values of '0' in the base table at a vehicle speed of 0. That being said, the minimum output has been set to around 60% at the idle range so it kind of over rides the base table. Irrespective, this isn't the correct approach. In your log file at the point the engine stalls, the AFR is a little lean at around lambda 1.0-1.2 as you're getting down to the target idle speed. This may be due to the decel fuel cut off parameters and at minimum I'd tend to raise these so they're at least 600-800 rpm the idle target to allow sufficient time for the fuelling to recover.

At the point you're down around 5-600 rpm and the engine is about to stall, the lambda is too lean at 1.15 which definitely won't be helping. The main issue I see is that the BAC is at 100% so there's nothing more it can do. My gut feel is you're operating too close to the max opening of the BAC. At one point in the log where it is idling around 1000-1100 rpm the BAC output is about 80%. I'd probably address this by adjusting the throttle stop to open the thorttle a little more so that you can achieve a hot idle with around 20-30% BAC. That will give a lot more headroom to control idle speed in the evnt the engine speed dips too low.

Lastly, while I don't think this is a major contributor, your idle ignition control is a touch aggressive. Your base idle timing is 18 deg which is in the ballpark (I'm usually more like 16), but when the engine stalls it's adding up to 15.9 deg for a total of 33.9 deg which will be well beyond MBT so not really achieving the aim. I'd be using a range of 0 deg as the minimum allowable and around 26 as the max for that range at idle. Ideally you want to tune the BAC base so that it's normally idling around 16 deg to give the idle ignition scope to move in both directions.

Hi Andre,

Appreciate the feedback!

TB has been mechanically adjusted to idle at 800-900 rpm, and that requires a bac duty og 70ish% in hot idle. I remember the bac didn’t seem to do much below 60% duty, but I will take a look and see if I can give bac more headroom.

Could the leaning out before stall be due to bac opening too aggressively?

I agree ignition correction is aggressive. It is also VERY active at idle. I found the rpm derivative is bouncing a lot with swings of thousands rpm (rpm/sec). I added derivative filter of 30 ms which helped a bit but still a bit erratic.

i use FFE trigger kit, not sure if the better resolution makes it worse.

What split do you normally run in idle?

EDIT: base table for idle control is 0 and 25 rpm and not speed. I suppose the idea is to not have the bac buzz with key on only?

Mike