350Z - Supercharged/E85 cold start

[Timboj]

Hi guys, I'm struggling with my cold start after playing around with a lot of settings of many months. This is about as close as I've been able to get it.

I've tried playing around with startup offset, hold time, fuel etc. 

Can anyone advise on what I'm missing here? I'm hoping it's obvious to some and just hasn't clicked for me yet. Should startup hold time be longer but with a higher startup offset?

Warm/hot start is pretty much perfect (from about >60C).

 

 

[castillaricardo]

It seems you need more throttle opening for this temperature, because your idle stabilized around 5.5%TPS, but your cranking was around 5.1%TPS. Is your idle ignition control kicking in while cranking? Try a longer hold time, more cold start TPS offset, and ~15 idle ignition target.

[Timboj]

Thanks @castillaricardo. I've tried a couple of things but something is still missing on getting this to play nice..

I raised the idle base position to where the ECU wanted it, lowered the idle ignition target and extended the startup hold/decay (admittedly too long). Total 'startup' time marked in red.

 

All that's really changed is that the same rpm undulations go for longer now (obviously the overly long startup hold time). What's it going to take to prevent that first dip down to 500rpm?

Tune and log attached this time:

https://drive.google.com/file/d/1FSWBUUmnv4oldYTVPb7ZrL1og04n_zRb/view?usp=sharing, https://drive.google.com/file/d/1MnxwbTUHz82Fb5drquz0V5QFy2D8cCRK/view?usp=sharing

[castillaricardo]

The pre-crank prime is HUGE. It is set to 150, which means 150ms of injector opening time not percentage of VE.

Your idle settings also have a max clamp of 5.5%, so your throttle is not being allowed to open much more, and this could be one reason for the undulation. 5.5% base + 0.7% offset should have been 6.2% throttle, but you were getting 5.5-5.7%.

Try these changes: https://drive.google.com/file/d/1JZV8eXtzYR4wsUmJgkBBYEjBZmvj62yp/view?usp=sharing

On a side note: Your crank enrichment is very low for non-e85 fuel. Have you tuned that area yet? At least in my case, anything under 150% enrichment causes failed start at 20C on 91 octane.

[Timboj]

Ahhh, I was wondering why the base + offset wasn't higher... max clamp, of course.

Re crank enrichment for pure 98 (that's my alternative) was a bit of a guestimate. Short answer is no, it hasn't been tuned yet. I think I've only had it down as low as 15% multi fuel blend, so it was tuned roughly around there but since then there have been some other changes.

I've just taken a look at your changes. I'll give them a shot and report back. Many thanks for taking the time.

[castillaricardo]

You’re welcome. I hope it helps.

Around here our 91 is E10. I think you could make your 0% row 40% of your 100% row, and interpolate in between for a closer guesstimate; of course trial and error is the only way to tune crank enrichment.

[Timboj]

@castillaricardo Getting there:

I've probably tried half a dozen configurations since your map. It's iterative but the thing that appears to be making the most difference is pulling fuel from the post-start enrichment. I'm experimenting with taking crank enrichment out because there's clearly an issue with too much fuel, but I believe I've hit the point where ignition is taking longer now.

Work in progress...

[castillaricardo]

That’s better than the previous screenshot! What was the temperature there? The cursor seems to have been elsewhere.

I’ve found post start enrichment to be very tricky, and currently have it set very low for -20 to 20c, like 10-20%, and yet need it a bit high for about a minute when the engine is heat soaked to combat the injectors being hot. I have no clue how this might be in a VQ, so would like to hear what you end up with. These injectors I have seem to be finicky to temperature, so it may not be indicative of “normal”?

You could play with first crank enrichment, which is a percent added to the crank enrichment for the first revolution. It could help with the initial catch while having lower enrichment overall. I played with large increments of 50%, then 20% up/down. If you can force your lambda controller to stay on while cranking that would also help you understand if you have too much or too little fuel. 

[AbbeyMS]

VQ doesnt need to have a lot of fuel after cranking/firing I have found. What injector firing angles have you got in the map? main thing it to make sure the throttle is open enough to allow the motor to breath enough to mix with the fuel.

[Timboj]

Thanks @AbbeyMS . When I get some time I've got some adjustments to try with less fuel, more throttle.

Injector timing is untouched from the Link base map, using end of injection and Single zone/360 BTDC. Would you suggest a different setting/table?

If so, would something like this be a reasonable starting point to start tuning? I picked up on a couple of forum posts that suggested VVT cam angle/rpm would the way to go...