2.4 with EFI hard cold starts

[belling]

Hello. I have a '70 911 with a newly rebuilt 2.4L engine and a PMO EFI setup and Electromotive computer. Long story short it runs great when warmed up, but getting it started when cold is very hard. For what it's worth this engine used to have Webers and it has always been hard to start when cold. It'll kick when cranked, and if I give it tons of gas and really rev it I can get it to start but usually only when it's really rich and with lots of coughing and backfiring and will die at idle. Once it revs up to 4k or so a couple of times it smooths out and idle's ok.

Here are some things I've tried:

* I've tried a bunch of different mixtures, seems to need to be really rich to start, but I think it's fouling the plugs because it misses a lot and idles rough until it revs up and cleans itself out. If I add just a little of mixture on cold start it won't idle at all.

* I have Bosch WR-5-DC+ plugs now, I'm going to try some PLX R5671-A7 to try to move the spark in some.

* I've made various timing adjustments, from 0 to 10 deg BTDC and doesn't seem to change much.

If anyone has any advice I'd appreciate it.

Jeff

[jpnovak]

Do you have a cranking pulsewidth multiplier? This parameter squirts extra fuel only during the cranking phase (usually below 300 rpm running on the starter). I typically need 400X or so fuel multiplier for quick starts.

Also pay attention to your battery voltage during cranking. If the voltage drops, so will your injector PW and you will not deliver enough fuel. This can be corrected with your voltage offset or with cranking PW above.

Consider these similar to a few stabs of the pedal on carbs or the cold start enrichment on MFI. They basically dump raw fuel into the cylinder. It takes a lot of fuel to light off a cold engine and to get these going since there is relatively low compression compared to modern cars.

[T77911S]

don't mess with the plugs, that aint the issue.
how do the plugs look, if black go a heat range hotter.

[Porsche 935]

Go in the enrichment menu and bump up the cold start and after start until your happy or add fuel in temp based warm up cycle.

[pampadori]

Do you have a IACV on it or do you rely on cracking the throttles slightly until it can idle on its own?
What JP said is good advice. All of these "starting" and "idle" tables should be configured in order to get a good cold start.
You need to be pig rich when cranking and cold idling.

[belling]

No IACV, just the hand throttle lever to keep it cracked.

I can set additional pulse width for 1 second and 20 seconds after cranking starts, so I'll try to dump a bunch of fuel for the 1 second and more for the 20 and see if that helps. Good to know that it has to be rich, that's what I was seeing.

When it had carbs I used to pump the pedal to the floor 4 or 5 times to get it to start, but then it would blow all kinds of gas smoke and I'd have to rev it a ton to keep it running, I'm sure my neighbors loved that in the morning!

[jpnovak]

In most EFI systems there are 3 phases to cold start.

1. Cranking Pulse. This is extra fuel at the very beginning while the starter is running. This is like pumping the pedal right before you start.
2. After Start. This is extra fuel to keep the engine going as soon as it catches. This is like pumping, feathering the throttle to keep it started.
3. Warm-up enrichment. This keeps the engine rich when cold to help it run smooth.

Even better if all of these functions are based on your CLT (engine) temperature and also incoming (intake IAT) temperature.

[pampadori]

I don't have experience with the Electromotive setups but they have some tips on their website that might be helpful:

Hard starting in the morning

If your engine is hard starting in the morning or when cold, look under Fuel Enrichments, Starting Enrichments the value for PWO. We often see this value at 0. This setting provides a fixed amount of fuel at cranking for the programmed time. Normally 4-6ms. It is also important to set CLT0 to a temperature about 15 degrees above your average morning starting temperature.

Stalling at idle or when cold

When an engine drops below its normal idle speed, the manifold pressure rises quickly. In this case engines whose fuel mixture is controlled by MAP will go rich. If not corrected, the engine will get richer as engine speed goes down, causing the engine to stall. To remedy this condition we program a column in our tables at approximately 300 RPM below our idle speed. Each cell in this column is set with the injector pulse at idle. This technique keeps the amount of fuel at idle correct for the engine idle speed, eliminating a stall due to an overly rich fuel mixture.

[wreckah]

only experience here with MS, so FWIW:

cold engine needs lots of fuel and lots of air. Lots of air = hand throttle.

i can set 3 params for cold start fuel:
- priming pulse: the system dumps raw fuel in the engine when you turn the key to ON (no cranking yet!)
- during cranking, i can tune the extra fuel for absolute minimum temp and absolute maximum temp...so a lot of fuel for when it's cold, much less for when it's hot and linear function in between
- once it catches, there is an afterstart enrichment, for x amount of engine cycles (couple of seconds), and you can specify how much % extra fuel

after that, it simply runs on the warm up schedule.

In my experience, the aircooleds love a lot of fuel to start, but once it's running, it can lean out quite quickly.

Don't adjust mixture tables, especially not when it's running great when it's warm.

good luck.