Cold Start - Strange PW Dip During After Start

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NigeT
Master MS/Extra'er
Posts: 419
Joined: Wed Apr 08, 2015 1:14 pm

Cold Start - Strange PW Dip During After Start

Post by NigeT »

Hi,

Can anyone give me a clue what is happening here (attached log). I see there is quite a lag in PW changing, you can see a delay before PW goes from 0 to cranking PW after the starter motor has started (dip in battery voltage right at the beginning of the log) and then quite a delay after ASE takes effect (indicator) for the PW to drop from cranking level to the initial VE * (WUE + ASE) setting, but the PW seems low at that point and then drops slowly before going up, which I find confusing. Its not like the WUE is going to increase as time passes, or the ASE, so why do I get a step up at 5.169s? Probably a good thing it did step up because I think the engine was going to stall otherwise.

My car has never started well in cooler weather so I'm using the current cold snap in the UK to try to fix it.

Thanks in advance.

Nigel.
Attachments
ColdishStartup.msl
(109.71 KiB) Downloaded 26 times
CurrentTunePointlesslyRenamed.msq
(283.91 KiB) Downloaded 23 times
NigeT
Master MS/Extra'er
Posts: 419
Joined: Wed Apr 08, 2015 1:14 pm

Re: Cold Start - Strange PW Dip During After Start

Post by NigeT »

Another start, another PW oddity.
About 0.492s after the starter is engaged (voltage) RPM tarts being logged. About 0.539s after that the cranking PW starts being logged. On a good start I see this PW being logged until some time after ASE is logged as being in effect, when the PW generally drops a bit, and then slowly changes based on VE, ASE taper, WUE curve and dead-time / dead-time voltage curve, but in this case there is a big step up in PW at 255.809s, dropping back to what I would have expected based on VE, at 255.957. Then another drop at 256.039 which would appear to be my actual run PW, but I cannot see where the 10.31 PW would come from given the logged VE, Total Correction and Battery Voltage.

I'm finding these unexplainable variations in PW are making it very hard for me to dial in the cold start.

If anyone can help me understand what is logged I'd appreciate it,
Thanks.
Attachments
2018-03-03_19.12.17.msq
(284.16 KiB) Downloaded 21 times
2018-03-03_11.50_56_oddPWspike.msl
(320.46 KiB) Downloaded 18 times
NigeT
Master MS/Extra'er
Posts: 419
Joined: Wed Apr 08, 2015 1:14 pm

Re: Cold Start - Strange PW Dip During After Start

Post by NigeT »

I've just noticed that there is also an odd MAP pulse (maybe enough exhaust pressure to get the GT2560R to spin?). Would this effect cranking PW?
NigeT
Master MS/Extra'er
Posts: 419
Joined: Wed Apr 08, 2015 1:14 pm

Re: Cold Start - Strange PW Dip During After Start

Post by NigeT »

Was using flood clear to clear any fuel vapour from the engine for the next start attempt (after failure to start), but there was enough fuel left to fire the engine up so it started. Is this telling me to reduce my cranking PW?
Attachments
2018-03-07_22_start_flood_clear.msl
(35.72 KiB) Downloaded 15 times
Alex94TAGT
MS/Extra Newbie
Posts: 16
Joined: Wed Feb 08, 2012 1:41 am

Re: Cold Start - Strange PW Dip During After Start

Post by Alex94TAGT »

Few thoughts in regard to your second log:

1) As you mentioned, there appears to to be a 112 kPa spike on the MAP sensor as the engine fires up -- perhaps due to too much cranking advance, or something else. Note that this MAP spike is shifting your target AFR from 14.5 down to 11.8 due to your target AFR table layout, which I suspect is at least partially responsible for the wonky PW variations at 255.809 and 255.957 (particularly the latter). This will presumably impact PW because "include AFRtarget" is selected under General Settings.

2) Ignition timing is decreasing immediately upon startup, after the 325 RPM cranking threshold is met -- from 8 degrees (cranking) down to 4.2 degrees (base) + 2 degrees of cold advance. The slight dip in timing is perhaps contributing to the engine RPM hiccup and MAP increasing -- the engine RPM actually stalls low enough in your second log to re-enter cranking mode (<325 RPM), where timing jumps back up to 8 degrees and then the engine recovers. I'd try blending the cranking advance (under Ignition Options) into the main spark table a little more and see if that helps the engine start up more smoothly.

I have a few other thoughts, but I'm going to leave it there for now. Perhaps others can step in and offer better ideas.
MS3Pro • FlexFuel • CAN-EGT • (Pi-4)Dash || 1994 Trans Am GT - Procharged 383ci LT1
NigeT
Master MS/Extra'er
Posts: 419
Joined: Wed Apr 08, 2015 1:14 pm

Re: Cold Start - Strange PW Dip During After Start

Post by NigeT »

Thank you for replying Alex. So would you suggest reducing cranking advance further? I've already reduced it from the original setting. Actually looking at the ignition table the values in the cranking / after start cells are a fair bit lower. Will AFR will be taking effect even though EGO is delayed till 10s after start? The MAP spike will definitely impact the VE element of the fuel calculation even if the AFR does not.

I am very unclear about when the various timers and counters get started and reset, e.g. the EGO delay, the cranking and ASE tapers... I get some very odd behaviours if the start stalls out and I try a second start without fully recycling the ignition.

I was wondering what would cause the MAP spike. Could it be too much fuel vapour, i.e. too rich? If I take much cranking PW out I find it takes somewhat longer to fire and then dies between ASE being logged and the VE based PW being logged, somewhere around 0.06s later.

Here's another log of the MAP spike stalling the start, but I kept cranking a little bit longer and got the engine past it, then it seemed to start reasonably well.

Thanks again.
Attachments
map_stalling_engine_start.msl
(102.32 KiB) Downloaded 15 times
NigeT
Master MS/Extra'er
Posts: 419
Joined: Wed Apr 08, 2015 1:14 pm

Re: Cold Start - Strange PW Dip During After Start

Post by NigeT »

As an experiment I dropped the cranking advance to 4. I only got one go at starting today due to other things consuming all the time, but it did seem to speed up the cranking, so much so that I dropped the cranking PW. I suspect I also need to drop the ASE, but one thing at a time.
Again it took extended cranking with the starter to get it to start, but I suspect the stalling was again caused by the timing advance, assisted by the increase in fuel from cranking PW to (ASE + WUE) * VE.

I'm struggling to see how the base timing map can be right both for the transition from cranking to engine running during start, and at the same time for recovering an rpm dip from idle RPM on a thoroughly warmed up, running engine. Should I use cold advance to reduce the base timing figure instead of the current configuration which increases it?

My engine map originates from a professional tune. It has never cold started at all well. This is one of the issues with it that I have been trying to work on (others being frequent boost cut on full throttle transients and transient leanness on acceleration).

Thanks in advance for any advice you can give.
Attachments
2018-03-11_12_almost_stalled_start.msl
(84.82 KiB) Downloaded 16 times
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