Maybe, just maybe an end to SD issues?

[WS6FirebirdTA00]

Well, go with me for a little, and if you can help and test some things out please do. Just read this and try it yourself lol

This has to do with lean hot restarts, I dont think this is going to fix cold starts but those arent bad with the help of the OLFA.

I left my IAT sensor out of my car, and measured the resistance on it at ambient temp (2.30, no Idea what it was really lol I just used the same setting on the multimeter when checking my resistors). I let the car sit after running it for about the time it normally takes to lean out on me (although I am not 100% sure if it was but I am about to try again with the heat soaked IAT sensor).

Ambient temp here today is 83*, I was using resistors that commanded 79*. I started the car up and it was no leaner than about a 15.0:1 and showed no signs of leaning out when on the throttle like it did before. With all the startup enrichment I have in the car right now, it acutally had a hard time starting, which is good becuase it is way too much fuel.

I just put a bunch of resistors in series until I got the right resistance. If you guys can try this, please do and get back. Make sure you plug the resisotrs into the IAT connector BEFORE starting. Last time I tried this with a cooled off IAT I did it after I started the car. I am going to see if the car starts lean with the heat soaded IAT plugged up. If this helps out, I am going to just put a resistor in there at the temp I tune the car at and leave it. It will go rich on hot days now instead of lean hopefully. Hopefully this is a temporary fix and can be taken care of correctly once we get an IAT VE modifier.

Please post up your results if you try this. This is the first trial at this so I am not 100% sure it will work.

[WS6FirebirdTA00]

Yep, thats her. Started up and a 16.0:1 AFR, constant throttle around 1600 about an 18:1 AFR, put in the resistors and 14.5-15.0 idle and 14.7 at 1600 rpm. Now the test will be to see how much the fueling changes day to day. I did the calcualtions one time and it was a small percentage if tuned from a median point. I figure the best thing to do is tune it for the night time temp and in the day time will be a tad rich.

What made me think about this more is my WOT airflow reading based on IAT at 5000 rpm was around 315 g/sec when cool (60*F) out, and 290 when hot (85-90*F). I then put the MAF sensor on there and it was still reading around 310 g/sec WOT at 5000 rpm when it was 88*F out. I still want to try some more things out and see what the real deal is, and also get feedback from you all on this.

[WS6FirebirdTA00]

Also, the cold start lean issue is caused (based on what Chris and I talked about) by tuning the VE with a hot motor. The charge coming in is actually cooler in the morning and the IAT sensor is reading correctly. The cooler air with a correct IAT reading will cause the car to lean out due to the air which is more dense.

[MeentSS02]

Hmmmmmmmm...interesting. One thing I've noted this week (still running open loop SD) is that in the afternoons, when I'm starting my car up to go home, it runs much leaner than it does in the mornings when I start it up to go to work. It definitely relates to this in that the IAT readings (although not verified through the scanner) have to be much hotter - after all, my car sits outside baking in the now 90* Florida heat all day. Between morning and afternoon "cold" starts, there is a full point difference in AFR at the very least (leaner in the hotter, afternoon "cold" start).

I wonder if this relates at all to the complex temperature model that our cars can (and usually do) employ. Since it seems to affect your car more than mine, I wonder if there is much of a difference in how that model is calculated between 2000 and 2002 Operating Systems...that is, if you are still running your 2000 operating system (and if my memory serves me, you updated to a 2002 OS).

[WS6FirebirdTA00]

Exactly another think I was going to say. It alsmot seems liek the car makes a VE correction based on start up IAT. If I tune the car for cool morning temps it runs right where I want it. In the afternoon it is hot and leans out. This makes me think IAT correction is wrong. But today, I started the car cold, same ambient temp and it was decent. Then shut the car down, changed the idle airflow for colder ECT after logging and then went for another ride. The car was then a LOT leaner than before. This is why I want to try to start the car, see how the fueling is, let it sit after getting hot and then try again. This would be the true test to see what is going on really. The car shoudl really run rich on hot starts I would think, so this definately has to do somehting with IAT whether this is the fix or not.

[WS6FirebirdTA00]

and for what its worth, the 2002 OS was no help to me, the fueling does the same EXACT thing. Maybe something to do with the way the fueling needs to be for the cam I have, you have the stock cam right?

[MeentSS02]

Yeah...completely stock internals on my car.

[MeentSS02]

Ttt

[WS6FirebirdTA00]

I am going to try to find a resistor at work today, otherwise, when I get home I am going to solder up the one I have now and tape it off. I will do an idle log, then drive it and do the same after letting the car sit 10-15 min.

[S2H]

I am going to try to find a resistor at work today, otherwise, when I get home I am going to solder up the one I have now and tape it off. I will do an idle log, then drive it and do the same after letting the car sit 10-15 min.

my next consideration is to try just relocating it to the outside of the engine bay...seeing if just being in real ambient air temp is more accurate than heatsoak temps

Just gotta have time to do it

[MeentSS02]

In the meantime, I'll be over here crying, and waiting for my burrito warmer.

[WS6FirebirdTA00]

yeah I was going to relocate it but I wanted to find a good spot where it would not get road or engine heat.

[WS6FirebirdTA00]

OK, well the car is a TOUCH lean on start up. After running a min or so idle is back to normal. This may be due to exhaust flow, maybe, since its such a small amount. The car was lean on a hot drive in some spots, and not in others. Maybe there is some calculation done and the car thinks on a hot start everything is hotter (this would maybe have to do with the bias) so it ends up leaning it out too mcuh. Either way, this is MUCH better. I put a 2.3 k-ohm resistor in the IAT connector. It is reading about 82*F now.

I did notice after driving the car a while when the oil temps came up on the cold start, that it was fairly close with a warm start. Main thing I want to see now is transient conditions. Before the car woudl go 25% lean, and would do this at low rev at stand still. It went a little lean, about 15.0-15.4 for a split second on the rev warm this time, I will have to try it cold and see what happens, but before the car would shoot to 18.0+.

Next test is to see what the car does in cooler temps and make sure this warm start stuff is really fixed. I am sure the computer is still making some changes, we will see.

[WS6FirebirdTA00]

What about a potentiometer, wire it up in the car to a dial and you can adjsut the air fuel as you drive, no more worries lol

[BLOWNZO6]

I have no issues with this on my ZO6.. 2002 with TT setup.

I know a few that are having similar issues.. they have 2001 and older setups.

[WS6FirebirdTA00]

Yeah that seems to be the problem, its all the older OS's. Odd thing is though, a 2002 didnt help me out. I wonder what the difference is in the vette to fbody OS's?

[ninobrn99]

time to start testing Mike

[WS6FirebirdTA00]

I am going to try and find a 0-100k ohm potentiometer here at work and it can be my in car fuel correction. I will wire it up to the IAT connector, then if the car is rich, I just lower the resistance lol

[MeentSS02]

Why oh why can't we find a resolution to this?

[ninobrn99]

because its something simple thats being overlooked