having issues tuning for hot start issues

[magius231]

Hi everyone, I am just getting into tuning and HP Tuners, and I'm working on getting my new build tuned and having some issues with it not wanting to start (at all) when it gets hot. I've been pouring over posts and forums and tutorials for the past few weeks or so and just can't seem to find anything that corrects this issue. It's preventing me from VE tuning because if it dies, I'm stuck on the side of the road somewhere for a few hours until it cools off...

so some details about what I'm working with:

1999 Trans Am, Stock bottom end/heads/intake LS1 with a Sloppy Stage 2 cam (228/230 duration @ .050? with .585?/.585? lift and 112 LSA)
SEP 1000 Injectors (i have the injector data from SEP already in the tune)
3 bar MAP and OS
GT45 turbo
IAT sensor in open air (haven't drilled the hole for it yet)
Innovative SCG-1 wideband with output going to the AC Pressure sensor for scanning
4l80e tranny, need to tune for that at some point...

if I start it up dead cold (well...in 90* weather lately) it starts and idles fine, once it gets hot it starts stumbling a little here and there but no major surges so far. I can drive it, even come to a stop and it just stumbles a bit (if it gets too out of whack it tries to die when coming to a stop)
if I shut it down hot then immediately restart, sometimes it will fire OK...rough but it will start. Sometimes it won't...
if I wait for any amount of time, it won't fire no matter what I do. It may catch and spin up to ~350rpm or so for a second but it will die, it will not stay running

what I've done so far:
enabled OL SD/killed MAF, turned off STFT and LTFT, idle @900rpm
basic "get it running in SD mode with a cam" VE and spark changes, bumped up idle spark
drilled larger hole in the TB
turned down the idle over and underspeed spark
set cranking spark to 12* above 122*
bumped up my idle startup initial airflow to 12g/s abov 122*
turned off idle proportional (not sure if this was a good idea...)
set my min fuel MG down to .008 under transient at the recommendation of some folks
bumped up Friction airflow, halved decay and bumped up delay
bumped up idle airflow initial, halved decay and bumped up delay
adjusted cranking VE down to try to somewhat match where my non-tuned VE tables are
tuned my BRAF with Russk's sheet (even though VE isn't right...)
even messed with the FA Multiplier tables...

nothing has helped. it still won't start when its hot no matter what I do, even pushing AFR and timing changes in bi-directional it refuses to start. I'm lost at this point, has anyone run into something like this before, or do I just have things too far out of whack to make it happy at high temps?

I've attached my tune as well as my cold and hot startup logs in hopes someone may be able to steer me in the right direction...thanks for anyone that can help!!


Gary

[kevin87turbot]

Hi everyone, I am just getting into tuning and HP Tuners, and I'm working on getting my new build tuned and having some issues with it not wanting to start (at all) when it gets hot. I've been pouring over posts and forums and tutorials for the past few weeks or so and just can't seem to find anything that corrects this issue. It's preventing me from VE tuning because if it dies, I'm stuck on the side of the road somewhere for a few hours until it cools off...

so some details about what I'm working with:

1999 Trans Am, Stock bottom end/heads/intake LS1 with a Sloppy Stage 2 cam (228/230 duration @ .050? with .585?/.585? lift and 112 LSA)
SEP 1000 Injectors (i have the injector data from SEP already in the tune)
3 bar MAP and OS
GT45 turbo
IAT sensor in open air (haven't drilled the hole for it yet)
Innovative SCG-1 wideband with output going to the AC Pressure sensor for scanning
4l80e tranny, need to tune for that at some point...

if I start it up dead cold (well...in 90* weather lately) it starts and idles fine, once it gets hot it starts stumbling a little here and there but no major surges so far. I can drive it, even come to a stop and it just stumbles a bit (if it gets too out of whack it tries to die when coming to a stop)
if I shut it down hot then immediately restart, sometimes it will fire OK...rough but it will start. Sometimes it won't...
if I wait for any amount of time, it won't fire no matter what I do. It may catch and spin up to ~350rpm or so for a second but it will die, it will not stay running

what I've done so far:
enabled OL SD/killed MAF, turned off STFT and LTFT, idle @900rpm
basic "get it running in SD mode with a cam" VE and spark changes, bumped up idle spark
drilled larger hole in the TB
turned down the idle over and underspeed spark
set cranking spark to 12* above 122*
bumped up my idle startup initial airflow to 12g/s abov 122*
turned off idle proportional (not sure if this was a good idea...)
set my min fuel MG down to .008 under transient at the recommendation of some folks
bumped up Friction airflow, halved decay and bumped up delay
bumped up idle airflow initial, halved decay and bumped up delay
adjusted cranking VE down to try to somewhat match where my non-tuned VE tables are
tuned my BRAF with Russk's sheet (even though VE isn't right...)
even messed with the FA Multiplier tables...

nothing has helped. it still won't start when its hot no matter what I do, even pushing AFR and timing changes in bi-directional it refuses to start. I'm lost at this point, has anyone run into something like this before, or do I just have things too far out of whack to make it happy at high temps?

I've attached my tune as well as my cold and hot startup logs in hopes someone may be able to steer me in the right direction...thanks for anyone that can help!!


Gary

Will it start up when it's hot if you spray a little starter fluid or fuel into the TB? It could simply be the fuel lines are overheating?

[magius231]

Good question, haven't tried that one yet. Will get back to you!

[Alvin]

I agree, I'd put a fuel pressure gauge on it and just see what is happening when you try to restart hot. I've had several cars that would vapor lock when the engine was hot. Above around 90 psi most injectors won't open.

I'm sure you've tried cracking the throttle body while trying to restart it right? That would eliminate it being a airflow issue.

[magius231]

i have cracked the throttle body trying to get it to start, no deal.

so I don' think its a vapor lock issue although honestly that sounded pretty damn plausible to me. what I did was let it get hot, turn it off, ice the fuel lines down, didnt help. I dont have a fuel pressure gauge that I can on this but might have to get one...
sprayed starter fluid in the intake, and it starts! but it won't stay running at all...i can keep it running for as long as I want with throttle but as soon as I let off it dies. took some logs of all these events too...

BTW nice to see you Alvin! You tuned my first cammed 02 TA a long time ago (https://ls1tech.com/forums/dynamomet...cmforless.html)

[Alvin]

I'd get a fuel pressure gauge on it.

Also log injector PW in case they are being shut down for some reason.

[magius231]

Ok finally got a fuel pressure gauge on it (been down with the Rona for a bit now) and it was reading ~100psi, which I didn?t think was even possible?so I started looking around and realized I never removed the stock FPR when I put my c5 filter in. So now that ls fixed and it?s dead at 58psi, time to go try again lol!

[Alvin]

Good.. yeah injectors will not open after about 90 psi most of the time.