cruisin

iTrader: (1)

Hey Braineak, what is it about raising the cranking rpm from 300-400 that helps it start better when cold?

cruisin

iTrader: (1)

[QUOTE=Braineack;769435]If the cranking RPM value is too low, you'll have trouble starting...mostly in cold weather or on a sub par battery. Say you lower it to 200RPM and you get it to crank to 250RPM, the MS with kick into normal running mode, but it could be too early. Mine is set to 400RPM. I had an issue on winter where my cranking RPM value got kicked down to 200 due to a firmware change. I had trouble getting the car to start and stay running...it would catch and stumble out. As soon as I changed the value back to 400RPM I never had the issue again.

Hey Braineak, what is it about raising the cranking rpm from 300-400 that helps it start better when cold?

rwyatt365

Let's say that your Cranking RPM is set to 250 and your car turns over during cranking at, or around 250 RPM. As soon as the MS detects that the RPM's are greater than 250, it changes from "crank mode", to "run mode". At that point all of your cranking settings (cranking advance, crank PW, cranking dwell) get changed over to your regular "run mode" settings (i.e. whatever your spark table, fuel table, idle valve PW, dwell correction, afterstart % and warmup % settings are). If everything is good and the engine is happy with those runtime settings at 250 RPM (most likely not) then it will run just fine. More than likely, your engine will stumble and stall out.

The point of the Cranking RPM is to give the engine a chance to start and stabilize before going into "run mode". That's why you should set it to slightly above what your car normally cranks at. My car, with a dodgy battery on a cold morning will crank at about 170-180 RPM, but in the summer with a full charge it'll spin at 250-260 RPM. So My Cranking RPM value is set to 400 just to be sure the engine is running good enough to "survive" the "run mode" settings.

cruisin

iTrader: (1)

Ok, yes i understand the cranking rpm is the crossover point between cranking settings and run mode settings. My current cranking rpm is 300 and i find when colder then 15c it fires but stumbles no matter how much i adjust my pw so ill give this a try and raise to 400. Will the cranking be longer as a result, or need more or less cranking pw? For example at 71c i have 2.3ms pw working well, will this change with 400rpm?

Another question related to cranking in case you may know. Some times my voltage drops as low as 6-7V when cranking and the starter gets hung up as a result. What should i check for this issue? I know the battery is good, and cables right at battery are good but still need to check ppf ground. Anything else?

Thanks for your response!

rwyatt365

If your engine cranks, fires, then stumbles at colder temps you probably should take a look at your after-start enrichment (ASE) and warmup enrichment (WUE) tables. ASE tells the MS how much PW to add (as a percentage) immediately after the engine enters "run mode", and is variable by coolant temp. The WUE is another percentage multiplier to the PW as the engine warms up. Note that ASE and WUE are additive so be careful that you're not drowning the engine in fuel right after you enter "run mode". Don't mess with your cranking PW right off the bat because what you change there happens regardless of the temp - so fixing it for 15c might just screw up your 71c condition. You shouldn't have to (necessarily) change the cranking PW just because you've increased the cranking RPM, let ASE and WUE do that for you.

There's another "player" in this scenario, and that's the ASE Taper. That tells the MS how long the ASE adder remains in effect, and it tapers the added PW over a set number of engine cycles, or seconds (I have a lowly MS2, so I'm stuck with setting the number of engine cycles - which can be translated into seconds relatively easily). ASE, ASE Taper and WUE all work together to modify what happens to the PW after the engine is in "run mode".

As far as your voltage dropping to 6 or 7V when cranking? I don't have a good answer for that aside from a weak battery, excessive drag, or a poor ground. My battery is suspect (I have to put it on a trickle charger every night) and I rarely drop below 9.5V during cranking even in the dead of winter. But then you say that your measured RPM during cranking is around 300 RPM, which is pretty stout (my measured RPM barely tops 180 RPM). Me and electricity don't get along, so you're on your own there.

cruisin

iTrader: (1)

I have MS1 so even more poverty. I am tuning the cranking pw since i put in new injectors. I think i have enough WUE, AFR is in the low 14's once things get going. So ASE should be ok as well but i am keeping an eye on it, i cant see what it is right away due to wideband delay. My cranking rpm as set in the ecu is 300rpm, but what i actually crank at is around 200-250 depending on temp. I assume the battery is fine, i use it in my winter beater as well and not one issue all winter; starts first crank down to -25c. Probably a dirty ground, ppf i suspect. I will have to sort out the voltage drop first, then move on the tune.

Thanks for your reply's, lots of good info!