Stalling with air conditioning

[GTamas]

Inread in another post about TFI and heat topics, I am just wondering if my problem might be also TFI-related? Or is it a oroblem at all and might be just normal behaviour with these cars?
For starters, my car is a '94 GT manual, stock everything.
Car starts and runs well when cold. It never gets too hot, cooling is working well. It runs also well when hot. Air conditioning is working well, too.

What I noticed is, when I shut down the car from normal operating temperatures and restart it while still hot AND the air conditioning turned on, it won't idle and it stalls. If I start it with ac off, it has a normal idle. Maybe a tad weaker idle than from cold start.
After a minute or so idling or driving the idle stays stable even if I turn on the ac.

I can live with this by turning off the ac before starting the car... I was just wondering if it is normal or not. And if it might be pointing at some other issue I didn't notice yet. What do you think?

 

[RAU03MACH]

from the experiences i have had with TFI
they're very touchy and delicate in extreme weather
their resistance is not what it used to be
built very cheap

 

[RAU03MACH]

in fact when you needed one
it cost almost 200 for it back then
now 30 40 bucks

 

[cobrajeff96]

Well that's at least 50 Amps you're demanding from the hi speed fan being activated right at start up, for one. Gotta remember that Ford from the factory equipped our cars with just enough amps to get the job done. Add the fact that heat in general increases the resistance of any electric circuit, so in reality you're going above the normal amperage of the cooling fan. How much exactly is a matter of testing/troubleshooting with real equipment, but let's just say the car is not advantaged by this type of habit. You could probably get away with it cold, but obviously not hot. The alternator probably just can't keep up due to engine speed being low and thus amperage output also low. If you're looking to maintain this habit and forget about A/C being switched on in any scenario, you need to get an alternator from J2 Fabrication. Other outfits like PA Performance are junk. I've heard good things about Nations alternators, but my only recommendation is J2 Fab.

 

[dsrtjeeper]

Inread in another post about TFI and heat topics, I am just wondering if my problem might be also TFI-related? Or is it a oroblem at all and might be just normal behaviour with these cars?
For starters, my car is a '94 GT manual, stock everything.
Car starts and runs well when cold. It never gets too hot, cooling is working well. It runs also well when hot. Air conditioning is working well, too.

What I noticed is, when I shut down the car from normal operating temperatures and restart it while still hot AND the air conditioning turned on, it won't idle and it stalls. If I start it with ac off, it has a normal idle. Maybe a tad weaker idle than from cold start.
After a minute or so idling or driving the idle stays stable even if I turn on the ac.

I can live with this by turning off the ac before starting the car... I was just wondering if it is normal or not. And if it might be pointing at some other issue I didn't notice yet. What do you think?

This could be an IAC issue. The engine may not be getting enough air at idle with a/c engaged. Stock ECU?

 

[RAU03MACH]

So with ac on what is the idle

 

[GTamas]

This could be an IAC issue. The engine may not be getting enough air at idle with a/c engaged. Stock ECU?

Yes, ECU is stock. Air filter and MAF are clean. Distributor cap and rotor replaced 20 years ago to MSD (stock type), spark plugs and wires, noise filter, 2 years ago. Fresh battery. I cleaned the IAC 2 years ago.
Everything else ignition and air & fuel related are 32 years old.
Could be that this behaviour was given since longer. I took over the car from my mother 4 years ago and I only noticed it now.

 

[GTamas]

Well that's at least 50 Amps you're demanding from the hi speed fan being activated right at start up, for one. Gotta remember that Ford from the factory equipped our cars with just enough amps to get the job done. Add the fact that heat in general increases the resistance of any electric circuit, so in reality you're going above the normal amperage of the cooling fan. How much exactly is a matter of testing/troubleshooting with real equipment, but let's just say the car is not advantaged by this type of habit. You could probably get away with it cold, but obviously not hot. The alternator probably just can't keep up due to engine speed being low and thus amperage output also low. If you're looking to maintain this habit and forget about A/C being switched on in any scenario, you need to get an alternator from J2 Fabrication. Other outfits like PA Performance are junk. I've heard good things about Nations alternators, but my only recommendation is J2 Fab.

Sounds logical. But then why is it not a problem when AC is turned on while idling after driving around? This problem only occurs when restarting the engine.

 

[GTamas]

So with ac on what is the idle

I will check the next time I am driving the car. Maybe I will try to shoot a video too.

 

[cobrajeff96]

Sounds logical. But then why is it not a problem when AC is turned on while idling after driving around? This problem only occurs when restarting the engine.

Part of it is definitely heat related. A hotter engine is harder to restart all on its own (more heat built up in every cable within the engine compartment). My own car experiences this some times, not as much as yours it sounds like, but it still happens. The portion of the fuel lines inside the engine compartment also gets a little cooked, and I have noticed it will take about 5 - 10 seconds for throttle response to be snappy after restarting hot just because of this. This is one way a vented hood will help.

Turning over a motor consumes a lot of amps, so it's a bit of a battery drain. If the motor is only idling for a while, the alternator hasn't had enough time to put those amps back in to the system to replenish the ampacity of the battery. If you're asking a 110 or 160 amp alternator to do all the work then I think you have your answer right there, as the alternator must supply the 13 - 15 volts to also power the fuel pump, ignition, lamps, ECU, etc.

These stock alternators don't put out enough at idle for you to just leave the A/C on at all times, especially in hotter months with an already hot motor from driving around. You have to at least get some rpms going for a little while.

 

[RAU03MACH]

i notice my idle at 789 796 almost 8 with a/c on
but the temp here is wicked hot 108

im thinking if yours is low bump your idle up so its not killing the car

 

[GTamas]

My idle after cold start is ca. 850. When the engine is warmed up it is ca. 600. With AC on it is ca. 750.

Today it stalled when I turned the AC on while idling. Then tried restarting it with AC on and it stalled immediately. Then restarted it with AC off and it idled well. I made a video:

So what do you think? Is something wrong or my warm idle speed is just too low?

 

[RAU03MACH]

On the throttle body bump up a bit
That thing is starving

 

[RAU03MACH]

At cold start it will raise
But after it worms up that's the problem

 

[RAU03MACH]

Closer to 800 with ac