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Problem with brief hesitation while A/C is on

nytebyte

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On the wife's 2002 Mustang GT:

If the A/C is on (at least that's when the problem seems to occur), once in a while when accelerating from a stop, there is a brief, but very noticeable hesitation. It's almost as if the throttle is being violently cut for a split second and then it's fine.

Also, wife reported that yesterday when she was backing out of the garage with the A/C on, the car just died completely. It started right back up normally though.

When driving down the road, it's fine.

I checked / cleaned the air sensor and throttle body, both of which really weren't dirty. Didn't seem to have an effect.

Anyone have any ideas on what to check next?
 

willizm

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Spark Plugs/Wires? Maybe you're not getting a good enough burn at low rpm and that added load of the AC is making that more apparent.
 

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Nah, it's just the compressor turning on/off. IDK about it shutting the car off though, that's weird. I can feel the compressor kick on with both of my Fords.
 

bikrboy128

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do you have a way to check the low/high side ac pressures? is the condenser fan on with the ac on?
usually this is caused by the high side pressure being way too high, from either an internal restriction or condenser fan not turning on.

PT cruisers are notorious for this. the fan fails and the car runs like shit at idle/accelerating from a stop with the ac on because the compressor is slowing the engine down so much.
 

nytebyte

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Battery is fairly new, about 2 years old. It starts the car fine and seemingly at the normal speed you'd expect.

Have not checked the pressures on the A/C, but it blows as cold as the day it was new. Should I still check the pressures? The radiator fan does turn on like it's supposed to when the A/C is on.

My first thought was that it might be plugs / coil packs, but the car only has about 40K miles.
 

nytebyte

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Well, yesterday the SES light came on, which finally gave me something to go on.

The code was P0340 - Camshaft Position Sensor Bank 1.

After doing some research, I found out that it's fairly common that this code gets triggered by a bad alternator.

So, I tested the alternator and it does indeed seem bad. When cold, it starts out at 14.2v but after about 2 minutes after it warms up, it drops to 13.7v and this is with no accessories on. If you turn on the A/C and other accessories, it drops to 13.4v. There also seems to be a scraping / hissing sound coming from it after it warms up.

I ordered a new one and will install it to see if that fixes the problem.
 

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That sounds like it's working to me :dunno: I would investigate that sensor.
 

P40E

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Alts usually push out more at initial start . Then reduce output as battery is charging for a little bit The 13.4 is there because you now put another load on it .

Could be bad internally not being regulated correctly . Or not putting out the correct amperage. You also said it's making noise.

I would definitely check that cam sensor though. Clear codes and see if it comes back first.
 

nytebyte

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Update on this issue:

Looks like it was the alternator. I got a new 130A unit from AmericanMuscle.com and installed it Saturday morning.

The voltage now reads a steady 14.2 volts no matter what load I put on it. I had the A/C on which included the radiator fan, headlights and radio. The voltage never budged.

Also:
- No more hesitation / misfiring.
- No more rough idle.
- The engine was noticeably more responsive and had more power.
-Engine started right up each time, even after sitting for 30 minutes while hot.
- Strangely, the engine seemed quieter.
- No more SES codes.
- We’ll have to see if the gas mileage improves, but I’m guessing it will.

The wife says it drives like a new car. It's crazy how many problems a bad alternator can cause.
 

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That's super strange, but I'm glad you got it all sorted out! :bigthumb:
 

nytebyte

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So the wife calls me from 80 miles away and says the battery light is on. Right away, I'm thinking the new alt is bad. She tries to drive home and makes it and says that the battery light went off after a few minutes.

When she gets home, I check the alt and it's fine. Then I wiggle the power terminal on the alt and can get the power to cut in and out as I wiggle it.

Fuck.

Checked the wire and bolt on connection from the car and all is fine. It looks like there is a loose connection somewhere in the alternator terminal itself. I didn't have time to pull it and take a closer look, but is that terminal bolted down to the alt somewhere that I can check? Or should I just get another new one.
 

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I would just get a new one, if you fiddle with it to see if you can fix it and try to get it warrantied after that, they might not take it.
 

nytebyte

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I just called the place where I got it and they agreed it was bad. They're going to take it back and even sent me a pre-paid UPS label.

I decided to have them send me an upgraded alt for a few bucks more. I don't want to screw around with this issue anymore. I just want the best thing in there that's gonna work and continue to work.
 

boostedguy05

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change the battery as well.

a bad alt can kill a battery, and a bad battery can kill an alt.
 

Sprayin

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Very very common problems on modular Mustangs. Glad to see you figured it out.
 

nytebyte

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The battery still seems to work OK and has the correct voltage. I have an actual battery tester and will give it a test later to be sure.

The battery is practically new, so I really don't want to buy another one unless this one is actually bad.
 

boostedguy05

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if its newer and has gone bad, sounds like a waranty swap to me.

batteries and alts work hand in hand. If 1 goes out, and its not caught, it can make the other go out by over working itslef.
 

nytebyte

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Update on this issue:

I didn't want to post the place I bought these alternators from until the entire transaction was complete, just in case.

The place I got them from was AmericanMuscle.com. They were extremely helpful and have great customer service. They sent me out a new alt and refunded the cost of the old one very promptly.

I highly recommend them.

Oh, and so far the new higher quality alt is working fine.
 

boostedguy05

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you said you got tehm from ther in post #12. :rofl:
 

nytebyte

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Did I? Well fuck, I'm losing it.
I blame old age.

Can't remember shit..

What are we talking about again?
 

boostedguy05

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how you were going to post nudes of the wife.
 

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