Tuning the start with the defroster on...
Thread Starter
TECH Addict
Joined: Nov 2005
Posts: 2,379
Likes: 2
Tuning the start with the defroster on... 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 110-130F 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.
So since we're within the realm where I have no real sensor readings, ie open loop, which parameters do I look at with regards to "warm start, defroster on"
So far I've adjusted the rpm to be 50rpm more than the non defroster mode, but it seems that's not enough when warm.
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 110-130F 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.
So since we're within the realm where I have no real sensor readings, ie open loop, which parameters do I look at with regards to "warm start, defroster on"
So far I've adjusted the rpm to be 50rpm more than the non defroster mode, but it seems that's not enough when warm.
Compressor load adds drag torque that the idle airflow
maybe can't support. When hot you're asking for min
air, and you probably have some IAT heat soak worsening
things.
The model for compressor torque depends on your (bogus?)
IAT reading as a proxy for head pressure, and your model
of engine torque vs air mass which sets the air-mass bump
for compressor engaged is not really tweakable but gets
bent by motor mods.
I'd try pulling the IAT out of the engine bay as a simple
start.
maybe can't support. When hot you're asking for min
air, and you probably have some IAT heat soak worsening
things.
The model for compressor torque depends on your (bogus?)
IAT reading as a proxy for head pressure, and your model
of engine torque vs air mass which sets the air-mass bump
for compressor engaged is not really tweakable but gets
bent by motor mods.
I'd try pulling the IAT out of the engine bay as a simple
start.
Thread Starter
TECH Addict
Joined: Nov 2005
Posts: 2,379
Likes: 2
I think you are bang on with the IAT being the culprit. I have the space cut open under the lid which tends to heat soaked specifically in these situations, its funny though how with the defroster being off, it has enough to keep it running where the defroster will die during that same hesitation moment.
I just tested and found there's a "hesitation" moment where the rpm drops when started heat soaked but defroster off, BUT the car doesn't stall. I wonder what that event is in terms of settings where maybe it cuts into closed loop at that point?
I just tested and found there's a "hesitation" moment where the rpm drops when started heat soaked but defroster off, BUT the car doesn't stall. I wonder what that event is in terms of settings where maybe it cuts into closed loop at that point?
How soon after starting is the dip or hesitation in RPM occuring? If it is pretty quickly (within a few seconds) after it starts, you may need to work on the startup friction airflow decay table - make it decay at a lower amount so it isn't taking the startup added air away so quickly... some cases with big cams, they don't like that added air pulled away so quickly.
Thread Starter
TECH Addict
Joined: Nov 2005
Posts: 2,379
Likes: 2
Ok I'll take a look in that setting to see what's going on.
It's dying within 1-2 seconds of starting it, ie it catches, starts and then the rpm plummets and if the defroster is on it dies.
If not on, its able to recover fine.
It's dying within 1-2 seconds of starting it, ie it catches, starts and then the rpm plummets and if the defroster is on it dies.
If not on, its able to recover fine.
Thread Starter
TECH Addict
Joined: Nov 2005
Posts: 2,379
Likes: 2
I've reduced the friction decay rate and it made a noticable difference in the start where that "hit" when it settles down doesn't drop it as hard as it used to. With the defroster on, I was able to start it on the 2nd shot now instead of being forced to shut off the defroster but the hit is there when the defroster is on. I'll play around with dropping it 0.005 further across the board and see if that helps.
I also noticed my Power Enrich (Cold) was altered compared to a stock tune, mind you I'm not stock but does this have any bearing on that cold start?
I also noticed my Power Enrich (Cold) was altered compared to a stock tune, mind you I'm not stock but does this have any bearing on that cold start?
You may want to add some to the startup friction airflow correction in the colder ECT areas.
What is the table number for the power enrich cold you are talking about?
What is the table number for the power enrich cold you are talking about?
Trending Topics
LS1 Tech Stories
The Best V8 Stories One Small Block at Time
6 Common C5 Corvette Failures and What's Involved In Repairing Them
Pouria Savadkouei
Retro Modern Bandit Pontiac Trans AM Comes With Burt Reynolds' Autograph
Verdad Gallardo
Top 10 Greatest Cadillac V Series Performance Models Ever, Ranked
Pouria Savadkouei
Top 10 Most Powerful Chevy Trucks Ever Made!
Hennessey's New Supercharged Silverado ZR2 Has 700 HP
Verdad Gallardo
Coachbuilt N2A Anteros Is an LS2-Powered C6 Corvette In Italian Clothes
Verdad Gallardo
Awesome K5 Blazer Restomod Comes With C7 Corvette Power
Verdad Gallardo
10 Camaros You Should Never Buy
10 LS Engine Myths That Refuse to Die
Verdad Gallardo Thread Starter
TECH Addict
Joined: Nov 2005
Posts: 2,379
Likes: 2
So I datalogged the hot start and found my IAT temps at 88F high but not blazing. ECT was at 150F. I've reduced the Startup Friction Airflow decay to 0.045 originals had 140F-> 0.060 and 176F->0.050. Need to understand just how much load the defroster puts on the car when starting hot and what the car does. It dies very quickly when the rpm comes down and its trying to idle. Target idle is 950 where a/c off idle is 900.
Is there another table that comes into play here or am I just stuck sticking the idle to like 1000 or 1050 with the ac on? It seems like friction airflow decay is having no effect.
Is there another table that comes into play here or am I just stuck sticking the idle to like 1000 or 1050 with the ac on? It seems like friction airflow decay is having no effect.
Did you add any air to the startup friction airflow correction (B4343) in the colder ECT areas? That table adds air at startup - this is the air that the other table is controlling the decay of after startup...
You may also try adding to table B4357 - this table adds air to compensate for the A/C clutch based on IAT.
You may also try adding to table B4357 - this table adds air to compensate for the A/C clutch based on IAT.
Thread Starter
TECH Addict
Joined: Nov 2005
Posts: 2,379
Likes: 2
I didn't add any air for startup. I only removed the decay part. I'm trying to get a handle on which tables do what at startup.
Is Idle Startup Friction Ariflow Initial vs ECT, the table you are referring to? Should I add air there for the 140 and 176 cells?
Is Idle Startup Friction Ariflow Initial vs ECT, the table you are referring to? Should I add air there for the 140 and 176 cells?
I use EFILive, so the titles are slightly different than HPTuners - yes, that is the one. Add air in the ECT range where you are having the issue. One thing to note, this is going to add air to the startup at all times, not only with the defrost on - so, add only a little bit at a time. It will cause the engine to idle up a little higher when you first start it and then it will settle in...
Thread Starter
TECH Addict
Joined: Nov 2005
Posts: 2,379
Likes: 2
Ok so after modifying the value, the one that got affected the most is the hot with defrost on start. Every other start felt the same.
The current effect is now just as it is about to die, it recovers!~ It's dramatic but it recovers and it seems like this is the table which hits it on the nail. The question is, why is the start with defrost on hot the one that is most affected by this. Contrast the start with defrost off hot which starts and doesn't have a dramatic a time.
I posted on HPTuners my tune along with the logs and some suggested that I have too much fuel for idle yet during SD logging the idle itself is tuned and running fine.
The current effect is now just as it is about to die, it recovers!~ It's dramatic but it recovers and it seems like this is the table which hits it on the nail. The question is, why is the start with defrost on hot the one that is most affected by this. Contrast the start with defrost off hot which starts and doesn't have a dramatic a time.
I posted on HPTuners my tune along with the logs and some suggested that I have too much fuel for idle yet during SD logging the idle itself is tuned and running fine.
Thread Starter
TECH Addict
Joined: Nov 2005
Posts: 2,379
Likes: 2
Anyone with this issue, my fix for this was switching to a 85mm maf with built in IAT sensor. The relocation of about 6 inches back away from the lid dropped the IAT temps significantly that I can now warm/hot start it with the a/c or defroster on.
I noticed the condition got worse in the crazy summer heat we had this year, IAT's were cooking 120's.
I noticed the condition got worse in the crazy summer heat we had this year, IAT's were cooking 120's.
