I've got an 89 383 Corvette that is 99% tuned. I mean EVERYTHING is near perfectly dead-on....except.

If the car is stopped or going 10 mph or so, you stab the gas, then come to a stop (like at a left hand turn), it has about a 20% chance of stalling. Based on advice on this forum, I've removed all of the stall saver settings (set them to 0 rpm), and that greatly improved things, and this is an issue that doesn't EVER happen with the HVAC turned off. I suspect the load from the A/C compressor isn't adequately handled and the car stalls before the ECU can catch it. With it being a 'smart' HVAC, it turns the compressor on and off as it sees fit...I think that's why it's been so hard to run this problem down, it MAY only happen if it requests the A/C clutch engagement during a maneuver.

The RPM add for A/C is 50 rpm, I could raise that, but that means I'll be sitting in traffic, with the motor running at 1100 rpm, and it's normally not necessary.

relevant info: Moates EEPROM and burner, TunerPro RT, $6E, 3200 Stall 9/11 TC, 3.54 gears, 700r4, Lingenfelter SuperRam, forged 383, 13mpg

 

These kinds of things can be tough to control. When the stall occurs, by any chance is the steering wheel being turned at all? The reason is that $6E appears to support a P/S pressure switch. Which is normally used to turn off the A/C at low speeds when the steering is being used.

The switch will need to be added to the P/S high pressure hose. But stock f-body parts are available from V6 & V8 TBI vehicles.

Another tip that may help is to add SA to the main table. This would be in the area the RPM dips too prior to stalling. The additional SA will increase the engine torque, helping to prevent a stall.

RBob.

 

I had a similar problem for a while. Adding a little SA and then maybe a little fuel if needed in that area might help. It is probably at a very light load that you would want to add the timing, as when you let off the gas sharply the load drops significantly. I see you said your A/C rpm adder is at 50rpms. I wouldn't be afraid to set it higher than that, it might not add as much as you think. It is trying to add that much but it doesn't always add exactly as many rpms as it says it does. Is there a setting for what speed it adds the rpms to or something like that? Working from memory here, not at my tuning laptop right now. Also, you might want to add in some on the setting for rpm adder or IAC step adder when in drive. That helped me quite a bit

Also, your IAC valve may be sticking. Easiest way to tell is to sit in your driveway idling in park with the A/C off. Turn it on, you should hear the motor lug down just a little, then rev back up to an rpm a little higher than normal idle.

Also, your A/C compressor should not be kicking in unless either the A/C or the defroster is on. If it is, or if it is kicking in and out alot, you are likely low on refridgerant.

 

It does seem to happen when I'm turning, yes. I've had the p/s apart recently and don't recall seeing anything electrical involved...Obviously, I'd _prefer_ a software fix to running another wire to the ECU.

Poking around here, I FINALLY found a description of how SA functions, I'll see if I can re-enable it with more useful values.

I'm using an Ed Wright base program and have mostly been futzing with non fuel/ignition stuff (TC timing, RPM threshholds, etc). I'm not too comfortable playing with the things that could hurt the motor.

Dan: this is on a Vette with a computer controlled HVAC, so it chooses to cycle the A/C whenever it wants to. Convenient when it works, hard to troubleshoot when it doesn't.

 

I also have a '89 vette. Running the '165 stock computer. I have the digital climate control, if that is what you mean by computer controlled HVAC. Unless you have something I don't know about, I think the only options were manual hvac controls or digital hvac controls. I can assure you that when the A/C is off and the defroster is off, the compressor will not kick in. When the A/C is on, it will run, the IAC steps up to kick the idle up to compensate for the load on the motor, and the coolant temps begin to climb! (I acutally cut every 3rd row of fins out of my A/C condenser to let more air through to the radiator so it doesn't get so hot so fast with the A/C on!)

 

Yeah, I've got what you've got. With the HVAC on 'auto' it'll cycle the compressor as it sees fit. Your overheating with the compressor on ALSO jives with what I'm seeing. I've got an oil cooler and a tranny cooler mounted in front of the A/C condenser and I just assumed there was too much heat in the stack to dump to a hot engine compartment with a single fan (the pusher couldn't be reinstalled with the other coolers in place)

So, HVAC off = no stalling, everything stays cool, HVAC = auto, stalls once or twice a week, and you've gotta keep the car above 20 mph or so for it to keep cool....it's amazing how good at hitting neutral and turning the key can get...it's not even stressful anymore. Course, it means the wife'll never drive the car, but I'd just as soon get it stable.

 

For what it's worth, I just noticed that there's nothing in the SA vs. coolant temp table, I can't say I've ever correlated if it's a coldstart only problem.

 

You are correct, if it is set to auto, it will cycle the A/C when it needs to to try and reach the temperature you have set. Nice feature actually. I don't use mine much, although when it is really hot I put the top down and run the A/C at the same time. I actually put manual shutoff valves on my heater core lines because my wife's feet were getting too hot!

Yeah, I also have a tranny cooler out front of the condenser too. My underhood temps were getting so hot (alot from uncoated LT headers) that I kept melting brake boosters and I actually vapor locked. I was only seeing about 200 tops coolant temp, and usually 180 or so, but the underhood temps were sweltering. 'Vettes just don't move much air under the hood. Cutting every 3rd row of fins out of the condenser helped alot. Fuel cooler helped alot. Metal brake booster this time, still alive.

I just posted my timing table in another thread if you want to look at it, maybe you can adapt the very light load timing to your .bin file and see if it helps cure the issue you are having. IAC setting changes may help but I'm betting you need a little more timing and possibly a little more fueling in the very light load low rpm areas.

 

I'll look for it, and throw my bin on the internets for general interest.

I guess I dodged a bullet with the ceramic coated Hooker Supercomps. I DID have a point where I was melting things, but that was due to the base timing being set to 4 ATDC instead of 6 BTDC (I mistook a valve phasing mark as the timing mark). Sure was nice when I finally got the timing dialed in.