MicroSquirt.com read only forum (Jan.15,2018)

Hi,

So the car will crank..fire a few times, then die.
I'm guessing I need to work on the ASE.
I've been slowly increasing the ASE and it seems to be helping... but I'm already up to 90%. A bit jump from the default value of 35%.

I'm curious as to what other people are running for ASE. Particularly you V8 guys with a healthy cam.

Is it normal to have ASE's up over 100% or should I start looking at some other reason for my starting problems.

BottleFed70,

On my 406 Chev small block with a 224°/234°@0.050" cam, I need 29% or more, for 200 cycles or more. Hovever, the afterstart enrichment needed depends a lot on having the warm-up enrichment tuned, so 'wacky' vallues aren't unusual at first.

Has the engine ran successfully to warm-up, or are you just trying to get it running at this stage? If it hasn't run much, then things to check are:

- if you have low impedance injectors, your PWM% might be too low, and you might try increasing it. If you have high-impedance injectors, check that you have 100% and 25.4 in the PWM settings (I beleive the defaults are 75% and 25.4).

- do you have a fuel pressure gauge? This would be somethig to check as well.

- can you do a datalog of a starting attempt? it might help us see something odd. Just do Alt-L + enter before cranking. Then post it here.

There are a bunch more tips here: http://www.megasquirt.info/v22manual/mtune.htm#howto

Lance.

Thanks Lance.

The car seems to run great once started and at temperature. I've been reving it in neutral to tune parts of the VE table..and everything appears to work great once the car is up to temperature.

Although starting is still a little rough...even with a hot engine.


Is there any general rules of thumb in regards to cranking PW vs idle pulsewidth? Currently my idle pulsewidth once warm is approx 5ms. My cranking PW is set to 4ms at 170* and 18ms at -40*. Does that look like it's in the ballpark?

BottleFed70 wrote:Is there any general rules of thumb in regards to cranking PW vs idle pulsewidth? Currently my idle pulsewidth once warm is approx 5ms. My cranking PW is set to 4ms at 170* and 18ms at -40*. Does that look like it's in the ballpark?

That hot PW sounds a little high, remember that the cranking pulses occur at every ignition event, not at the "running pattern," so cranking can deliver a ton of fuel very quickly. The easiest way to get the hot one is to warm the motor up fully, turn it off, set the hot PW down very low, around opening time (1.0-1.2), then try to start. Keep increasing it by 0.2 or so until the engine starts without touching the throttle. Done. Verify it a couple times and you should be good. (Cold is similar, but lots harder because that initial crank saturates the manifold walls and thus you need several tries to creep up on it.)

Eric

BottleFed70,

On my engine, with a 16.7 req_fuel and a 4.1 millisecond idle pulse width, I have the cranking pulse widths at 3.3 @ 170°F and 14.5 @ -40°F. More than 10% away from either of these numbers gives starting problems.

Generally, I set the cranking pulsewidths to:

- 20% of the 'upper' req_fuel for 170°F
- 85 to 90% of the 'upper' req_fuel for the -40°F

(The 'upper' req_fuel is in the top box on MegaTune, it is not affected by the number of squirts, etc.)

The you need to tune them to optimal values. One trap not to fall into is setting the hot pulse width in the driveway with the hood up, etc. This will almost ceratinly not be the pulse width you need when you come flyoineg in off the highway to stop for gas, and want to restart 2 minutes later. If yuou do tune the hot start in the driveway, try toi get it on the 'low side' of acceptable.

The idle pulse width is not a good basis to calculate the cranking pulse widths, because it is affected by ignition timing, rpm, cam timing, compression, etc., etc.

Lance.

Excellent information! Thanks guys!

I'll give this all a try in the next couple of days and let you know how I make out.