Cold start tuning/refinment

[Tianss]

Should be simple, but........
First megasquirt project, been a few small issues but nothing I haven't been able to overcome with existing documentation, and common sense,

basic stats MS2/extra 3.57
83 Chevy 4x4 pickup
97ish vortec Bottom end, world products steel heads, Lt4 hot cam, HEI8 distributor, aftermarket dual plane intake, Ebay Big block TBI , all GM sensors, added the air temp to the inlet sleeve above the throttle body.
700r4 tranny
overall I got this, runs great, very responsive, transitions thru the warm up stage, and slips into normal warm run mode just fine..... just one small nagging issue, cold start is not quite what it should be, I have the priming pulse maxed out which helpped, and added to the cranking pulse as much as I feel like I can without going way rich after the run mode is established....the problem is it acts like an old carb with not enough accelerator pumps prior to truning it over, or not enough choke closure , it will always start, but will when dead cold 35-55 degrees F. it will on first key turn require several cycles , probably 5-10 secounds crank time (seems like 30) it will flair up, sound as though its' good, and then just die, secound attempt, will fire sooner, and die again, this can be repeated 3-5 times and genrally it will catch and run with no major deficiency at all.....

if some small throttle is applied it will start first time usually.
restarts are fine, and tunable. hot or cold its all good. I have tried increasing the IAC opening, and while it does raise the idle speed has little if any effect to the first time cold start issue.

All my old skool experiance tells me it need a heavier pre cranking priming pulse, but that appears to be limited .

Ideas? Thanks in advance for any advice.

[DaveEFI]

Assuming your fast idle is correct for a cold start, if opening the throttle further helps things, it suggests you have too much fuel.

But is your fuel rail up to full pressure when you attempt a start? My car does need some churning to start which I'd like to get better. It seems to be the rail emptying when you stop the engine hot. If I start the engine from cold one evening, then stop it before it's hot, it starts quickly the next morning from cold.

So I'm interested in any solutions too.

[Tianss]

Assuming your fast idle is correct for a cold start, if opening the throttle further helps things, it suggests you have too much fuel.

But is your fuel rail up to full pressure when you attempt a start? My car does need some churning to start which I'd like to get better. It seems to be the rail emptying when you stop the engine hot. If I start the engine from cold one evening, then stop it before it's hot, it starts quickly the next morning from cold.

So I'm interested in any solutions too.

I've got a TBI unit on an Intake, no fuel rails, just the body of the unit, and the injectors.

I've had the air increased using the cranking duty cycles, and currently have it where the engine is happy when it does fire.

Its about 40 degrees today, and after 4 start/die cycles without touching the throttle is lit, and acted very good.... I am of the belief I add fuel with air and am utilizing the warm up fuel modification table, as oppose d to just adding air with the cranking duty cycles. It always starts, and will always die 2-3,maybe 4 times if no throttle is used, when it does start and run more than that 2-3 seconds it is good to go.

The physical orientation of the TBI unit as a carb would be, and needing to get that empty space saturated with a suitable A/F charge seems to be the issue. It runs way to good , and otherwise preforms very consistently, and reliably.

Sent from my XT1650 using Tapatalk

[Tianss]

Assuming your fast idle is correct for a cold start, if opening the throttle further helps things, it suggests you have too much fuel.

But is your fuel rail up to full pressure when you attempt a start? My car does need some churning to start which I'd like to get better. It seems to be the rail emptying when you stop the engine hot. If I start the engine from cold one evening, then stop it before it's hot, it starts quickly the next morning from cold.

So I'm interested in any solutions too.

I've got a TBI unit on an Intake, no fuel rails, just the body of the unit, and the injectors.

I've had the air increased using the cranking duty cycles, and currently have it where the engine is happy when it does fire.

Its about 40 degrees today, and after 4 start/die cycles without touching the throttle is lit, and acted very good.... I am of the belief I add fuel with air and am utilizing the warm up fuel modification table, as oppose d to just adding air with the cranking duty cycles. It always starts, and will always die 2-3,maybe 4 times if no throttle is used, when it does start and run more than that 2-3 seconds it is good to go.

The physical orientation of the TBI unit as a carb would be, and needing to get that empty space saturated with a suitable A/F charge seems to be the issue. It runs way to good , and otherwise preforms very consistently, and reliably.

Sent from my XT1650 using Tapatalk

Ok here's the deal... If the default graphs/tables being what they are, don't seem to be cuttin' it... Chances are. they aren't..... If your gut tells ya you need more fuel, or more time, don't hesitate to try to change the rules... Being a rookie , I didn't realize things such as the. X or Y axis of the graphs in question could be expanded as far as they can.
Basically I expanded the "after start enrichment" about 5 times the default , as well as 3 times the default "cranking pulse" adder and How about that..... It starts, much better, now I can work with that!

Sent from my XT1650 using Tapatalk

[Tassuperkart]

More fuel more fuel
However, OP says it fires up fine with some throttle.The engine has cam and head, so inlet gas velocity will be slower and fuel condensation on the cold manifold and port walls will be a bitch due to being a TB setup which tends to retain a lot of old carby cold running issues. The higher gasflow with some throttle is helping move the fuel into the heads.
I gathering the engine lights up straight away but dies so the initial priming pulse is plenty.

What the symptoms are telling me is not enough air and not enough afterstart enrichment to keep the "relatively" agricultural TB setup alive when cold.

What form of IAC valve do you have fitted and how much authority does that valve actually have on the engine, Ie how much air does it admit at 100% effort?

E

[ChevelleFan]