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Problem with brief hesitation while A/C is on

nytebyte

Not Politically Correct
Mar 2, 2004
13,627
20,958
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?
 

bikrboy128

Some say.....
TCG Premium
Jul 15, 2007
12,878
11,502
Wheaton
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

Not Politically Correct
Mar 2, 2004
13,627
20,958
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

Not Politically Correct
Mar 2, 2004
13,627
20,958
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.
 

P40E

TCG Elite Member
Nov 4, 2012
9,150
4,466
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

Not Politically Correct
Mar 2, 2004
13,627
20,958
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.
 

nytebyte

Not Politically Correct
Mar 2, 2004
13,627
20,958
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.
 

nytebyte

Not Politically Correct
Mar 2, 2004
13,627
20,958
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.
 

nytebyte

Not Politically Correct
Mar 2, 2004
13,627
20,958
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.
 
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