H/C LT1 stalls when coming to a stop.

[itsonlyanlt1]

Hey guys. Ive been tuning my car for a few months, and cant figure out this issue. My afr is alittle rich for crusing, but spark looks normal.

Afr is 13.6 crusing, and spark is 35-36. The car wants to die and stall when coming to a stop. What idle table can I look at?

[steveo]

what year of LT1 is it? auto or manual?

[steveo]

also, you have a wideband? 13.6 AFR should be near impossible to achieve while cruising if closed loop is functioning correctly

[itsonlyanlt1]

Its a 1996. Th350 4000 stall.

My old tuner royally jacked up my tune. He set it to run SD, and eliminated my 02s altogether. I assume its running open loop all the time, thats some of the issue.

[steveo]

is it running an OBD-II ecm, though? if it is, i cant help you, if it has been OBD-I converted, i can give you a baseline tune to work with that'll 'run' no problem

[itsonlyanlt1]

Yes it is.

[steveo]

does it even have a VSS?

[itsonlyanlt1]

No. I don't street drive often though. Just to keep the car in shape for the track.

[steveo]

well without a VSS, your car is probably stuck in CL idle which behaves as it should when the car isnt' moving. you have no idle speed follower and idle logic isn't designed for a moving vehicle.

you could add a VSS to make all this stuff behave a bit better, or.. you might just have to jack up your idle speed a bit, strengthen the timing corrections for idle underspeed errors, just get it the best you can.

fixing your cruising AFR shouldn't even really be important for a track car where it's driven hard and fuel economy isn't a concern. 13.6:1 is perfectly fine and isn't very rich, in fact lots of people would prefer it, since it will keep your combustion temperatures down. but you can always just fix that in your VE table. it could definitely handle a bit more spark crusing, but again, for a track car... dont see the point.

[itsonlyanlt1]

The car idles at 14.2 , cruises at 13.6 and wot is 12.8. Spark is 33 idle, cruising is 36, and wot is 38-39. Does this sound good, or could I refine it more. The car went 11.75 @ 116 1.55 60` last time out. I think there is alot more there.

[steveo]

that sounds fine. you can lean the crusing out a bit in VE if you want. try leaning WOT out to 13.2 but dont give it any more timing at WOT, i might even try a degree or two less.

[RobertISaar]

that still seems like a lot of advance for a fairly modern OHV combustion chamber..... ?

[steveo]

while LT1s do tolerate a ton of timing advance, they're a 'fast burn' type head, but they dont run hot. same with a lot of aluminum heads, they want to be run cold with lots of timing. a modified LT1 usually seems to make peak power closer to 34-35 degrees of advance, and anything over that is usually just waste, but does depend a lot on what heads this guy is using.

LT1s are a very knock resistant engine, but that means they have a big grey area between peak power and knock. so lots of the 'add advance till it knocks then back it off' guys end up with those kind of numbers and totally botch the tune.

most engines, i've read, have a couple degrees between peak power and knock, the last LT1 i helped dyno tune had SEVEN DEGREES between peak power and knock (peak power on that one came on at 34 degrees total advance)