Hard starting and hunting at idle
 

I have my car running pretty well now, but the starting and warmup still need lots of work. I have to crank and crank to get it started and I have to play with the throttle to get it to start. Once it starts cold it goes into a terrible hunting with it almost dying and then catching until it gets to about 120 degrees then it settles down and idles fine. On a hot start it is a little easier but it still takes some cranking and working the throttle, then the RPM flares up for a couple of seconds then settles down to idle. It could be that this engine has low cranking compression, it took a good bit of cranking with the old GSL-SE ECU and I had all the idle control stuff taken off of the old system and about a 1200 idle speed.

I have a S5 intake and a S5 BAC. Looking at the logs it looks like the BAC is working at least the PWM signal is going to it. One thing that could be causing problems is my electric VDI actuation, I have it set up to be open at below 2000 RPM so it isn’t activated when it is idling then close between 2000 and 4500 then open back up again, the idle when it is in cold start is over 2000 which seems like a problem in itself since the table has cold idle set at 1500. Once it is really hot I can’t get the idle below about 1200-1500.

This is a race car so I could take the BAC off and not use it, but I would rather have it if I can make it work correctly. I have attached a log that clearly shows what happens on a cold start, and my current .msq file.

Thanks for any insight.

I disabled the BAC and it is immediately 100% better, great idle and much easier to start. Ever since I started running the car with the old SE ECU I removed the BAC so we are used to running without closed loop idle. So far I have only tried hot starts without the BAC but that is OK since this is an endurance racing car hot starts are important to me. This evening I will see how it is on a cold start but having to baby it with the throttle for 5 minutes once per race day is not really a problem at all. It could be that my valve is bad, or maybe I just haven’t hit on the exact settings that will make it run right, I may revisit this in the future but for now it is running much better with the valve disabled

Yes, until the engine is tuned and can idle on it's own, the BAC is not going to be of a help and will just cause frustration if you try to tune around the BAC trying to compensate for an unturned idle map.

Until the map is fully tuned you should be working with the minimal number of options necessary to run the engine.

Looking at your map it is not ready for a BAC yet. Still needs a lot of smoothing. If you have autotune available then that can make quick work of getting a map correct as far as AFRs go, which will save a lot of time.

Remember to make the idle are of the map like a little valley, both in timing and fuel. Idle should sit in a bowl surrounded by bins with just a little more fuel/timing. This will naturally help stabilise it.

It idles really well with the BAC disabled. I have been using autotune to work on dialing in the map but it is a race car and I am a little limited in how I can run it, I can only run circles around the parking lot at the shop I work on the car. I have been spending plenty of time trying to vary speed as much as possible, and tonight we took it to the dyno where everyone was pretty surprised at how much power it made…

Since it's a race car you probably don't need close loop idle regulation. You can switch the valve to warmup only with just a fixed PWM curve. Then all you get is a temperature vs. PWM graph that the ECU follows as the engine warms. A lot more convenient for cold starting but easier to dial in than full closed loop PWM idle.

PWM closed loop idle can't really be enabled anyway until the VE table is very close to perfect anyway otherwise the BAC is just chasing the instability.

I discovered my main starting problem was a dying starter, it had been going bad slowly enough that I didn't really realize that it was cranking way slower than it should have. Put a spare starter on and now it spins like crazy.

So far I am pretty happy, went to the dyno Wednesday and made 200hp then we ran our first time today and won, beating the second place car in our class by 8 laps.