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While chasing a no-start issue this weekend, a novel idea came up. Check the plugs! I pulled them & they were coated in black soot. I'm guessing there is a settting or some additional tuning that needs tweaked & is somehow causing things to be too rich on start-up. I'm still wet behind the ears with tuning & will be calling on the assistance of my trusty buddy Mike H. for assistance with this. After the car fired up & hovered around 14.7 afr while idling. With maybe 3000 miles tops on these plugs I wouldn't think they've gone bad.

Sooo.... 2 questions for those that can offer up some advice:

What settings in MS should I be looking at that would cause an over-rich cold start?

How often do you change your plugs?

After start enrichment and priming pulse would be where I'd start.

I know that this probably is not related, but after installing my stage one kit with stock engine management, the idle and low speed/throttle was lean. So I tuned the FMU to richen up at atmospheric, and after doing that, noticed smoke upon startup when the motor is cold.

This is probably due to higher fuel pressure at idle pushing through the startup enrichener. My plan is to simply D/C that startup enrichener and be done with it.

If you have a priming pulse, you should zero it out. It should not be used.

I don't think you can really take anything out if the engine is starting easily and the AFR doesn't remain below around 12:1 for more than a second or two afterward. If you're reading 10:1 or richer for several seconds, which should be in conjunction with black smoke, you can lean out your cranking pulsewidth and reduce afterstart enrichment. What kind of ASE are you running now if any?

turbodan wrote:If you have a priming pulse, you should zero it out. It should not be used.

So I should set this all to zero? Will this affect cold start when temps dip into the 30-40 degree mark?

turbodan wrote:

I don't think you can really take anything out if the engine is starting easily and the AFR doesn't remain below around 12:1 for more than a second or two afterward. If you're reading 10:1 or richer for several seconds, which should be in conjunction with black smoke, you can lean out your cranking pulsewidth and reduce afterstart enrichment. What kind of ASE are you running now if any?

What do you think here?

if priming pulse should not be used what is it there for?

Just did a little searching & found this below. For our application is this generally not needed, or just a little bit in colder weather? I'll try zeroing things out to see how the car starts.

http://www.msextra.com/doc/ms2extra/MS2 ... ersion.htm

Priming Pulse
The Priming Pulse is the amount of fuel added when the ignition is first switched on. It is to help the engine start a little quicker during cranking. I tend to leave this at zero when messing about with the install, etc, as flooding can soon occur if your switching the ignition on and off a lot. So this is best set after the engine is running.

Shadow wrote:if priming pulse should not be used what is it there for?

It was intended for systems that need to purge air from the rail before cranking. Its not necessary in conjunction with all of the other enrichments. It will dump x amount of fuel into the motor every time the key is turned to the on position, which is obviously undesirable.

The only one of those maps that looks odd to me is the ASE. You should be able to run significantly less on the warm end of the plot. Taper it down to ~5% as you reach operating temp. You may need to add a little fuel to compensate for the zero'd out priming pulse, but see how it behaves first.

I went ahead & zeroed out the priming pulse across the board. Today I'll be able to do a 'true' cold start (though temps will be in the 80's) to test how it works out. I'll also tweak the ase & see how that pans out. Thanks for the tips.

I'd disable priming pulse anyway. I find that I need to key-on to check things fairly often, and gas in the oil makes me a sad panda.

Will it still prime the pump and not inject fuel if set to 0?

I don't believe so, but you really shouldn't need it to if your check valve is functioning properly.

pump will still prime.
Just set it to 0. Starts the same.

Shadow wrote:pump will still prime.
Just set it to 0. Starts the same.

True it will prime, but I'm reasonably certain it will not run until the engine turns. Which is fine, as long as the check valve works (and indeed how motronic works).

Just for clarification.

"Fuel pump prime" and "injector pulse prime" are separate and not interconnected.

Jeremy wrote:"Fuel pump prime" and "injector pulse prime" are separate and not interconnected.

In megasquirt setting a priming pulse also runs the fuel pump at every key-on. Megasquirt does not run the fuel pump until either the engine is turning or the priming pulse is set (which also fires the injectors), unless I missed a setting somewhere, which is possible. But I do appreciate that the pump will prime when it gets a tach signal and the fuel pump runs.
This mimics the behavior of motronic and I've never had an issue with it.

5/4 update

I turned all priming pulse points to 0 & this seemed to help things a bit at start-up. Initially I did notice the motor may take an extra revolution or 2 prior to starting but it didnt seem to mind the change to much. The fuel pump no longer cycles on when I key the ignition on. (i wish it did) As a test I set the PP to .01 for all points & tried starting the car. It seemed to cough when starting as though even this was throwing too much fuel at it. Turned everything back off again & things seemed normal. Fast foward to a few days later... Again on startup the plugs seemed to foul out due to a rich start. Yesterday I pulled all plugs (with maybe 3k miles on them) cleaned them & changed the gap from .028 to generous .036 So far, the startup, idle, & idle while in drive seems much improved. We'll see how this holds up. I told one guy I work with that I was running .028 at 10psi & he couldnt believe it. In the past he said he ran a blown v8 at 20psi with plugs gapped around .040 & never had a problem with spark blowout.

Leave it to my projects to always throw the abnormal curveballs.