Tuning startup on $EE

[johnny_b]

1995 LT1 M6 firebird formula

it’s really anemic during cranking/startup it kinda hesitates. Every other lt1 car I’ve had starts up healthy.

what tables can I tweak to try make this better?

[kur4o]

Post a list of modifications if any.

[johnny_b]

Car is pretty much bone stock to my knowledge. I noticed that it has an airfoil. I've installed full length headers and egr block offs.

I've made some tuning changes here is a summary :

Disabled egr & air pump
Turned down idle spark correction
Bumped idle timing 4*
O2 int delay increased
O2 swing voltage bumped up
Cat protection disabled
Changed blm cell boundaries
Disabled stall saver

Its definitely flowing more air based off maf readings I'm currently working on getting those tables right along, with the ve table

[kur4o]

None of these should affect startups. It will be either weak spark, too much or too less fuel, or not good enough opti spark signals to pcm.

Is it making long cranks with no signs of starting, or is it trying to start during crank but can`t engage all cylinders in a timely manner.


If you are having delay in high res signal the pcm will dump fuel only when it gets the signal or an error is set.

Revise the ignition system.

Check fuel pressure during cranking.

Check opti signal.

[johnny_b]

the problem isnt long cranking times. it fires right up everytime as soon as you hit the key no problem.

my issue is that when it does fire up the first time it struggles like a slight hesitation in that initial startup but it idles fine. its always done this even before i changed anything on the bin. I was just hoping theres some tables that i could tweak to alleviate and sort of bandaid this issue.

overall the car runs great. my blms are great from the couple of logs ive taken so i dont suspect theres a vaccuum leak.

a hardware issue was my first thought but im not sure what it could be. distrbutor cap is brand new. fuel filter and fuel pump are brand new. injectors were swapped from a known running engine (the ones on the car were locked up).

I guess it could be an injector issue.

[sherlock9c1]

Replace the ignition coil. Every LT1 I've had with a weak startup has had a failing ignition coil. In fact, you ought to consider replacing the coil and ICM just as maintenance. They both wear out.

You could always try putting a stock tune back in the car...

[johnny_b]

it does the same thing with the stock tune. I will look into the ignition coil and icm.

[steveo]

never ever ever tune a stock car because it's not running well! 100% of the time, you are band-aiding something that's broken or worn, and it's 25 years old so definitely something is worn. and 50% of the time if you just installed headers, you torched a plug wire.

[sherlock9c1]

Not to mention stock LT1 fuel injectors are JUNK. They were never designed to handle ethanol. Buh-bye!

[steveo]

yeah, that's very true, the biggest input change is that when these engines were built and calibrated, fuel was a bit consistent, now you have some corn liquor mixed in there.

a percentage of initial enrichment to handle that is a good idea.

the stock injectors are pretty stout to say the least, though, don't see why 10% or less ethanol would hurt them much.

[sherlock9c1]

It's the fact that the windings are immersed in fuel. Yes, they were stout, until ethanol started eating them.
https://www.underhoodservice.com/tech-feature-cooler-heads-prevail-pouring-over-gm-s-lt1-engine-and-reverse-flow-technology/


Some LT1 injectors have had failure problems due to internal corrosion, which some have blamed on gasoline mixtures that contain 10% ethanol. The injector coils short out internally and cause a lean fuel condition and/or misfires in one or more cylinders. On 1996 and later OBD II models with misfire detection, this should set one or more P030X cylinder misfire codes depending on how many injectors are misbehaving.

Injector resistance can be tested with an ohmmeter, and should read 11.8 to 12.6 ohms. If the injector reads out of specs, it should be replaced.