CZSteve

I just installed a MS PNP2 the other day; overall went well & runs good - however, starting requires a little throttle feathering and when cold there's a slight back-fire.

The car runs fine once; just 'slower' to start and requires a little throttle feathering as if it's carbureted; when cold there's also a slight back-fire.

Sounds like a timing issue?
Screenshots below of current settings.
RE Ignition options I have tried 13 degrees for Cranking Advance as opposed to the default 10-degree; didn't notice an improvement and currently moved back to 10-degrees.

NOTE: I'm just looking for generally decent operation for the time being as I'll be installing a Track Dog Rotrex Super-Charger in a 6-weeks'ish and at that point plan on a full-day professional tune.

Thoughts?

Thanks, Steve

Stoffl

https://www.miataturbo.net/megasquir...9-05-a-108062/ this maybe ?

nolig2278

Check the startup enrichment as it might be a tad too high. the blipping throttle helps to balance it out. the backfire is the excess fuel igniting - i think. I had this issue for while and tweaked the ASE.

SimBa

Fair warning, I'm not the most experienced tuner, but I'm pretty comfortable playing around with my car.
Generally, if you're backfiring out the exhaust you've got too much fuel. If it's sneezing out the intake you've got too much air.
I usually find myself needing to add fuel to my cranking enrichment, it sounds like you might need to take some out. Engine's usually like a good amount of fuel for cold starts.
If the car is starting up well, but struggles to maintain idle immediately afterward, look at your warmup enrichment and see where your AFR's are at. Play with that and see what the car likes.

HPA has some videos on the topic that will probably be useful to you if you plan to tune/adjust your tune in the future.

The values in your VE table's lowest RPM value, around 90 KPA will be the base fuel amount during cranking. It can also be helpful to make all those cells the same value so your base fuel value is more stable during cranking.

CZSteve

Regarding drop fuel values to combat starting back-fire (moderate back-fire at most): Drop the three cells in red-circle?
How much begin with? 5 points? 10 points?

SimBa

I'd probably try setting them all to 60 or 65. Using the same value in all of those will give you more consistent results as the MAP is changing during cranking. Another tip I've heard a lot is to set your base cranking fuel to 1.5x your idle fuel. It looks like you're idling around 40ish? Maybe a bit higher? 40 * 1.5 = 60, so give that a shot.

This is going to affect how much your cranking enrichment adds, as that's a multiplier of the values you are modifying in the VE table. For now, just change one thing (the VE table) and see what happens.

Rrrracer

OP, have you tried putting your cranking timing back to around -2 deg to see what effect it has? It should be the same or better than what is happening at 10*.