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03 Buick Century Stalling w/ A/C on

07-22-2009, 01:44 PM
2003 Buick Century 3.1lL.

Stalls mostly when idling w/ the Air Conditioning on but will always start right up, i replaced the Fuel Pressure regulator - it was leaking into the vacuum hose and it's still stalling. No Codes are present. my Snap-On Solus Pro scanner shows some known causes are:
1) Leaking fuel Pressure Regulator.
2) Bad Battery - overloading the alternator: amperage drop. which would result in battery overheating.

1) Replaced the Fuel Pressure Regulator. still problem exist.
2) started the car and disconnected the battery - still stalls when you turn on the A/C.

The car stalls only when you turn the A/C on, but has happened a couple times when restarted after initial stalling b/c of A/C. I thought I might have got it figured out but I was wrong, I swapped relays (a/c-horn, same relay) and the problem was gone when I turn the A/C on it didn't stall. Well i swapped them back and it still didn't stall, I swapped them back again and took it for a test drive when I turn the A/C on it stutter/stalls but as soon as I turn it off it picks up again, so I went back to the shop swapped relays again and still doing it, I did this with the HEAT on and it doesn't do it, so it has to be something within the A/C clutch wiring.
I removed the fuse box, expecting to see a bad wire, but didn't see anything wrong anywhere under there, I am at a loss.
Any help is greatly appreciated.


07-22-2009, 04:17 PM
First, you should never disconnect a battery cable while any computerized vehicle (especially OBD-II vehicles like this one) is running. You're running a very high probability chance of short circuiting some very expensive components.

It sounds as though the problem may be the compressor itself is going bad, and drawing the engine down when engaged.

07-22-2009, 08:55 PM
Well vehicles these days don't use the battery for anything except for starting the car and running accessories while the engine is off, once the vehicle is started all power comes from the alternator so the chance of damaging anything is very unlikely.

I can understand the A/C Compressor causing the issue but I don't see how. When this happens it does not change the voltage reading from the alternator or battery, it just shuts off like you turned the key off. I have been a mechanic for 6 years and have never seen anything like this before.

07-23-2009, 06:01 AM
silly idea but. If the bat is bad replace it
second 2003 buick? you say that when you start the car it stalls. You also say that when you turn on the a/c it stalls. HMMM. OBD3, when you turn on the a/c you senda a/c request signal to the PCM. the PCM opens the air bypass valve and within a few seconds (giving the motor time to move) it sends a signol to the compressor via the high and low pressure, and steering rack.

are you sure that your air bypass motor is not stuck in a place that works just fine in the summer and the car is warmed up? or that the motor is moving just slow enough not to generate a code but not respond fast enough to compensate for the faster a/c pump?

any who I believe that you need to check other stuff

07-23-2009, 06:51 AM
well i don't think the IAC (Idle Air control) valve is the problem if that was the case when the A/C turned on it would idle real low and may or may not stall but this just stall like you turned the key off.

07-23-2009, 02:38 PM
The problem was the ground wire on the trans-engine mounting bolt, the top set of ground wire (2 wires connected to 1 eyeloop) the nut was actually off about 1/4". I figured this out by testing for power at the wire going from the A/C Clutch relay to the compressor with the relay removed. it stalled a few times without the A/C being on and I tested for voltage here and had about .65v, well the couple times it stalled today when it did stall it would jump up to about 2.0v then back down to .65, there shouldn't be any voltage here so i knew I had to be getting voltage (residual or bare wires crossing) from somewhere, so I started wiggling wires around and found the intersection of wires in front of the transmission under the Accumulator/drier would give me a voltage fluctuation when I would move them around, so I removed the electric tape - expecting a couple bad wires, but nothing then I grabbed the lower ground wires and nothing but when i bumped the upper ground wires accidently it would fluctuated and then noticed the bolt was backed off about 1/4", tightened it up and the voltage went away and no more fluctuation when I move the wires around. Put everything back together and "wa-la" no more stalling.

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