Tuning "hot start with defroster on"

[Slade]

I have a strange issue where if the car is not cold but not at operating temp, it dies within seconds if turned on with the defroster.

Situation: I drive 20 mins to pick up my gf from work, 2 min warm up, 5 mins normal in city, 12 mins on highway, 3 min idle, shut off then start up again after 15-20 mins. Defroster is on, fan is on min, temp is at the start of the guage (working 98) I'd say still 140-150F range.

If cold start with defroster on, the car starts fine.

If cold with defroster off, the car starts fine.

If warm start with the defroster on, car dies within seconds.

If warm with defroster off, car starts fine.

Did a datalog of that moment, I had an IAT of 88F and ECT of 150F and it died within seconds of a start. Tried again and same deal. Third time I gave it a bit of throttle to keep it up and it was idling fine within 7-8 seconds.

I played with the Startup Friction Decay Rate for 140F and 176F and reduced them to 0.060 and 0.050 a reduction of 0.01 each and it made no difference. Cold or hot it has that moment as it falls to idle where it will fall past idle and then struggle and die.

[99LS1SS]

Does it do the same thing with the AC on?

[MMGT1]

During the scan, do you see a difference in timing when you compare those modes?

[vette_c6]

if your car is stock car,,
download a file from the website hptuners.com
upload and start ,, see how it works ,,

[Slade]

I've checked timing, both are the same. I'm not sure if AC would do the same thing, but haven't really had the opportunity to try considering the winter weather. I will test next chance out.

Car is not stock. So testing a stock tune is out of the question.

[MMGT1]

Have you tuned start up and idle tables already? There is a really good idle tuning topic here if you haven't. Not sure why I am thinking this, but what is your climate control over ride set to?

[gn2beatu]

Dont rule out something mechanical, not always tune related. Check for voltage drop when you turn the defroster on. If you have body/engine grounds that are borderline, and you turn that on, that may the thing that uses everything to go whacky. Do a scan with voltage as a PID and have the scanner going before startup, then you will be able to see whats going on, and or if that is the culprit. If thats it, get a wiring schematic for your vehicle and clean ALL the grounds. Wouldnt hurt to clean the positive wires at the alt, and battery too. If they are on the small side, you can even upgrade to larger wires, or add an extra ground or two from battery to body or frame. G/L

[Slade]

Grounds are good, I had an issue with alt and battery a month ago that had me hunting all wires and such.

The idle tune itself is bang on, smooth. As stated, only under the stated conditions where car is warm, its been sitting 15 mins - 1 hour, and is still 130-150F in temp with defroster on do I have it die on me.

IF the car has been left overnight and it is COLD but with the defroster on, it will start fine. You wouldn't even know that the defroster was on. It's only when its warm which says something. It's there when the defroster is off, but the engine is able to bring itself back up and idle fine without the defroster load. I looked for any voltage dips and none were obvious on my voltmeter.

[MMGT1]

if clymate control is set to disable, **as it should be by the way**, then try raising the underspeed table a little and see if it is enough for the engine to catch its' self before dying. After that, try raising idle RPM a little to see if that would be enough to keep her going. Id really like to know if its leaning out and dying or going rich and dying. Im thinking one of the two has to be happening. Afterstart enrichment tables may fix this too. Its a strange one man, but we'll find it...lol

[edcmat-l1]

What car and what OS? Sounds like a heat soak problem. Do you have a san log of it? Do you know what the A/F is when it happens? The STITs?

Some OSs have a heatsoaker enrichment table that I've used to cure some heatsoak startup issues.

[Slade]

I'll mess with it today, the only issue is trying to catch that moment. If you shut it off then start it within a minute, it's fine. It's when the IAT temp gets a chance to soak in some heat off the rad.

I'll look into the stuff mentioned here and on other forums, one if which was to bump up the air in the Idle Startup Friction Ariflow Initial vs ECT.

From a driving perspective, its been great, I have it smooth at all rpm ranges, cruises the engine purrs, as I slow down it drops to idle nicely and even holds a perfect idle in the last few moments before you come to a stop. There's no hunting at any time. It's just this tiny thing that's driving me nuts.

[edcmat-l1]

Still didn't say what car or OS. No tune posted, or data log. Keepin secrets for a reason?

[Slade]

98Z28 98 PCM
Mods
Comp Cams Spec 230/230 115+2 LSA 0.613 0.605 Lift
L92/LS3 6.2L Aluminum Block
Wiseco k398 Alloy Forged Pistons -3.2cc 4.070"
MLS Head Gasket 0.040
K1 6.125" 4340 Forged Connecting Rods w/ ARP Bolts
Siemen 60lb/hr Injectors
Patriot Performance 5.3L Stage 2.5 Heads 65cc
SLP Lid w/ K & N Air Filter
LS6 Intake
Ported Throttle Body
EGR Obstruction Removed
Ceramic coater QTP Longtube Headers 1 3/4 to true duals 2.5
NGK TR55 spark plugs
MSD 8.5 Inch Spark Plug Wires

I've done some quick logs of the startup to illustrate the issue. On one of the logs I logged while I shut it off, think its the cold defrost on log.

I played with the Idle Startup Friction Ariflow Initial vs ECT and raised the 140 and 176 F values to 4.5 and 3 and it has had an effect of keeping the car running. Ie I start it, it dips, it recovers. On the logs you see below only the defrost on and hot had it dip and die while the defrost off started nearly normally. Also I was able to discover that it doesn't even take long for it to have an issue, within 90 seconds of shutting off, ie the time it took for me to turn on laptop and reconnect cable to log, the hot defrost on issue showed up.

[MMGT1]

If I was to guess there man, looks to me like you are starting with too much fuel, car is pulling timing and shutting down. You drop to 7* right after start there, should be seeing around 22* to 24* I bet with that set up. Pull a bit of fuel from start up and set timing to 24* and see how it does.

[Slade]

When warmed up those same tables during SD logging show to be fine and hitting 22 degrees of timing. Which table should I be going after which affects only the startup? From what I see, my timing is set in every place I can think of to be 23-24 degrees. I'll try dropping off some fuel in that range.

When playing around with the air, timing and friction values for that hot start with defrost, I came across a P0335 crank sensor a code. I was in the middle of the road and quickly tried to restart and finally got it in a spot and reflashed to the tune above and its fine again. It's fine now, but was this just a fluke thing?