ignition advance's effect on idle speed?

matt_fulghum · Post by **matt_fulghum** » Mon Jun 19, 2006 3:13 pm

My car idles at a stable 14.4 AFR or so now, with great vacuum (28 kPa on brand new rings!) but it runs at about 1470 rpm. I noticed that the spark advance at that point in the spark map I'm using is around 20 degrees!

I figure I could help keep the speed in check if I drop down the advance to something more like 14 BTDC or so, but I was looking for advice on this?

I'm running I think the latest v2.5 MSII code, with an MSD 6A box, if it helps at all.

Bernard Fife · Post by **Bernard Fife** » Mon Jun 19, 2006 3:21 pm

Matt,

I run around 20 degrees BTDC at idle in my car, and it works fine (anything from 16 to 20 seems to work well on mine).

To drop the idle speed, it's always better to reduce the amount of airflow rather than decrease the ignition timing or fuelling from the optimal amounts (except in emissions controlled applications). Reducing the air reduces the wear and heat (and increased fuel consumption) that come from messing with the air or timing.

Usually, the throttle body has a stop on it (though it may be hidden behind a cap on OEM TBs), or it may have a bendable 'tab' that can be adjusted. If the throttle stop is all the way out, the idle control device may be partially opened, or you may have a vacuum leak somewhere.

Lance.

matt_fulghum · Post by **matt_fulghum** » Mon Jun 19, 2006 3:33 pm

yeah, I cranked it way open to see if it would help the car start, now that I think about it. I'll close it up a little later.

Another thing, although I don't know if it should go in this topic... The car idled stably for around 12 seconds, and then just died. The afterstart enrichment had long since gone and all, it didn't seem to have any good reason for why it croaked. Any ideas? I could post up the log if you'd like.

Bernard Fife · Post by **Bernard Fife** » Mon Jun 19, 2006 3:36 pm

Matt,

Yeah, post a log. The first thing that occurs to me is the warm-up enrichments may have become insufficient, but it could be a lot of things.

Lance.

matt_fulghum · Post by **matt_fulghum** » Mon Jun 19, 2006 3:40 pm

well given that it's 91 degrees out atm, I figured that the warmup enrichment would be pretty minimal by this point. Also, the AFRs seemed pretty stable throughout the time it idled. Whatev. I'll post up the log. Gimme a second.

Although, on the note of temperature sensors, I can't seem to get the sensors to read exactly the right temp... I don't know if that's because I'm inputting the wrong resistance values, or because the engine bay is getting steamy in this weather. Well, I'll let you guys toss suggestions my way when I post the log up.

matt_fulghum · Post by **matt_fulghum** » Mon Jun 19, 2006 3:42 pm

Here you go... The idling period is right at the end, I turned off the MS right after it died.

Bernard Fife · Post by **Bernard Fife** » Mon Jun 19, 2006 3:59 pm

Matt,

There's nothing obviously wrong in the log. You show the afterstart enrichment finishing, and the rpm actually rises a bit on 100% warm-up enrichment before stalling, so I doubt that's a cause of any problems.

There's also no reset.

The AFR is droping towards the stall point, but only from 14.6 to 14.3, so this wouldn't be a problem.

The only odd thing is that the dwell rises quite a bit, from ~10 to around 25 just before the stall. Do you have the dwell compensation turned on? It should probably be 'off' (dwell voltage compensation values set to zero) for the MSD.

If this was mine, I'd do three things:

- make sure te voltage compensations for the dwell are all zero,

- upgrade to the latest 2.6 beta code (you might want to wait a day or so to see what Al might announce), it has more fixes etc. than the 2.5 code,

- make a datalog with the battery voltage included (the new beta code will have battery voltage in the datalog by default, or you can see this: http://www.msefi.com/viewtopic.php?p=10 ... att#106943)

Lance.

matt_fulghum · Post by **matt_fulghum** » Mon Jun 19, 2006 4:08 pm

ah... I was looking for the battery voltage log and I couldn't find it. No wonder

If you think I should go to the 2.6 code versus the 2.5 code I'll pop over, no problem. Is it stable enough do you think?

Alright, lemme get that stuff done, and I'll get right back to you.

matt_fulghum · Post by **matt_fulghum** » Mon Jun 19, 2006 4:29 pm

heh, I found another potential factor... when I unplugged the Megasquirt, it knocked out the crimp on the spade terminal I have running from the VB921 to the MSD box... maybe the wire was loose before? I'll recrimp it and see if it and the latest code help at all.

Bernard Fife · Post by **Bernard Fife** » Mon Jun 19, 2006 4:33 pm

If you think I should go to the 2.6 code versus the 2.5 code I'll pop over, no problem. Is it stable enough do you think?

Matt,

I ran the 2.672 code for a few weeks on my car with significant issues. I beleive Al will release a newer version very shortly though (in the next day or so) and this will be the 'public release candidate', so you might want to wait for that.

Probably a good idea to reconnect the spade terminal too!

Lance.