cold (not) starting issue

[wizrod]

Hi All...

I have a home-brew EFI set up on my Bug (T1 engine) which I'm trying to tweak to run reliably. It runs starts & runs reasonably well when the ambient temperature is above 14 or 15 deg C, but below that its extremely difficult/impossible to start.

For example, yesterday afternoon - around 8degC - it'll initially fired on random cylinders while cranking. As it got a little warmer, it'll fired on more, eventually firing on all four, but stalling as soon as I stopped cranking. Once it actually began starting and stalling, it ran a little longer each try, before stalling. Eventually it started & stayed running. In effect, this process was just warming the engine up to the point where it was happy to start normally.

I tried again this morning - around 0degC - and I couildn't get it to do more than fire on odd cylinders.

The above behaviour happens with the cranking ignition at 10degBTDC and the injectors delivering 4ms pulses (these are the best I've found by trial and error, so far). I've got all the various compensation controls switched off to simplify things. Once the engine starts reliably I'll look at bringing them into the picture.

I've tried increasing the fuelling (up to 25ms pulses), but I've had most - albeit limited - success with just 4ms should I explore more?.

I've tried ignition timing between 0 & 35deg BTDC. 10degBTDC has so far been least worst. is it worth adjusting further - a few degreesd ATDC..?

If/when the engine actually starts, its quite happy idling with the ignition at 0deg BTDC and around 4-5ms injector pulses.

Given that an EFI system really just manages when to spark & how much fuel to deliver...what sort of settings should I be exploring to make cold starting easy/earier?

The motor is 2186cc with a small turbo. The injectors are 300cc/min. Compression is even across all 4 cylinders. Single TB with no idle control facility. ECU is a Wolf3Dv4 (old, I know, but working).

To summarise...Given an EFI ACVW engine which starts and runs except in cold weather, what advice would you give to improve cold weather starting?

Many thanks for your suggestions

[Paul H]

For a quick test to see whether it just needs more fuel I use prime pulse but your ecu may not have this feature.

[wizrod]

Thanks, Paul,

It does - what duration pulse would you suggest? The default is 1.5ms. I assume (much?) higher...20ms?30ms..?

cheers

Paul

[Paul H]

You'll just have to play around but keep it as low as possible as it puts fuel in regardless of whether the engine is turning you want just enough to get it fired up and there should also be some cranking fuel enrichments to play with

[wizrod]

Thx - I've been doing just that, but with no success.

TBH, I seems to be going backwards...it doesn't even try to fire at all now...

[Paul H]

Well maybe too much fuel I'd check the spark plugs

[Bruce.m]

Prime pulse is a little squirt on power-up to wet the intake manifold/ port. Handy if the injectors are mounted in the throttle body and if its a bit slow to start from cranking. 1-2msec is typical

Cranking fuel is whats added while the starter motor is turning. 10BTDC is typically fine. You want the minimum for a quick start but not enough to flood.

After start enrichment gives you a few extra seconds of rich mix to get some heat into the combustion chamber. Certainly less than 30sec if any at all.

Then you are onto the normal running fueling modifier based on temperature. Plus the extra idle air flow to bump up the idle to a stable level, until the intake & heads are hot.

Depending on when the engine dies, you should be able to see which setting needs a tweak.

[wizrod]

Posting an update -I seem to be making progress.

I was programming a far too long priming pulse. Bringing it down to 3ms seemed to be the sweet spot. Also limiting post start enrichment helped.

It did start up but ran rough - 675rpm idle and the exhaust smelled really rich. As a quick fix & applied a -20% fuel trim, which immedialtely lifted the idle to 950rpm and cut down the exhause smoke. (I'll remove the blanket trim adjustment and apply to the relavant parts of the map properly)

Seems this engine like very little fuel to run but wants a little more but not by much to start...a small amount too little or too much & it doesn't want to play ball.

Many thanks to all who have posted suggestions - much appreciated!

[ps2375]

My experience was to add more air and have that taper off as it warmed up. Not sure is your system can control an aux air valve on pwm, most likely not a stepper aux air valve.

[Bruce.m]

If you have a map based VE table and dialled in injector settings, the base value for the idle zone is 50%. Then adjust from that starting point.

If your idle advance at say 800-900 rpm is set to 7.5 BTDC, then add an extra cell at 600rpm and set that to 15 BTDC. This is a basic anti-stall. If the revs dip advance is added rapidly which produces more torque.

[Piledriver]

Sounds like you are on the right track.

Air cooled motors with port injection don't need much additional fuel, they tend to want to idle at ~12.5-13:1 AFR anyway, and they warm up very fast compared to a Chevy V8, and usually have far better fuel distribution.

I'm currently running MS3, but ~14 years ago when I first fired up a ms2 setup the hardest thing was getting cold startup/warmup mix right, as the default settings were for the developers 350 SBC in his 'Vette.

Finally pulled all the extra fuel out, gave it a short prime pulse and slowly added fuel until it worked.
Also cut the effective warm up time to somewhere around 45 seconds. Actually set by CLT or ignition cycles, but I found the intake ports heated up very quickly on ACVW, and the injectors spray largely on the valves.

The antistall setup Bruce describes works great, esp if your cranking fuel setting is sane.