So, here's a new chapter in the ongoing saga known as my 2002 Mustang GT.

To recap for those that are new to the site.

Dec '06 - After a speedy jaunt down an access road testing out my new gears, something snaps and the engine starts to sputter and lose a bit of power and develops a severe idling problem.

I do the usual self maintenance checks, change plugs, clean IAC, MAF, TB/Plenum, change fuel filter and flush the fuel lines. Car still runs like ***. Out of frustration, I park it for a little while.

I get a new set of heads and have them installed and find a shredded timing chain tensioner arm:


Replace timing chain parts on both sides. The car sputters less but still sluggish and misfires quite a bit and doesn't settle to a steady idle. Only now, I have white smoke pouring out the exhaust and can hear gas boiling in the cats when I turn the car off. The cylinder rings are trashed at this point and the engine is wrecked.

Install new forged short block, heads and bullitt intake. Also suspect a PCM problem, so off to Ford to get it checked. The injector files were corrupted and they found a failed TPS. Replaced the sensor and reflashed the PCM.

I get the car back after its been in the shop for 2 months and it runs great. But living in Central Texas it gets hotter than hell and this year is no exception. I crank up the a/c and after a couple of days, the idling problem starts to crop up again. At this point, I'm freaking out and getting pissed. I just spent a few thousand dollars getting a new engine and one of the original problems is still there. I'm really worried about trashing my new engine, so I called my mechanic to see what he thought. He said to turn off the a/c and let him know what happens. With that done, all the idling issue dissappeared like magic and the car once again runs great. Well, the a/c compressor is the only part left from the orginal engine.

Anyone care to venture an opinion as to why my a/c compressor was causing my car to idle so horribly and possibly corrupt my PCM?

I'll give ya'll the answer in a lil bit, just curious for now what ya'll think.

 

i have no clue....

a/c compressor causing PCM problems. sounds like your flux compacitor is out of adjustment

 

Sounds like you may have not been getting enough voltage to power everything up. Poor ground cable or not tightly tied down, power cable corroded or not tightly secured,AC clutch short. One of the engine harness wires touching ground or open. Thats my guess.

 

Thats actually pretty close. The problem was from the a/c clutch selonoid. There's a timing sensor cable that runs below the a/c compressor to the PCM that controls the ignition sequence of the engine. When the a/c is on, the a/c clutch selonoid spins and generates RFI or Radio Frequency Interferance. This isn't a problem most of the time because the unit is shielded. In my case, the shielding is worn (not sure how) and throwing RFI waves that were being picked up by the ignition sensor cable and feeding the PCM false data and causing the engine to misfire and idle like crap.

Whether or not this false data stream contributed to corrupting the computer files, I don't know. I'm not a computer expert and I'll leave that open for debate. The data stream was definitely causing the engine to misfire or not fire and thats one of the reasons so much unburnt fuel was going throw the cylinders.

Moral of the story: If you have a mysterious idle problem that won't go away after you've cleaned and checked everything, it may be your a/c clutch selonoid. Its certainly not a common problem and one of the last things ppl think of when trying to solve this problem.

 

damn dude that really sucks, but glad ya got it all figured out!

 

Lol, thanks, we'll just have to see if this is the end of the problem or not. I'm running out of parts to replace. Too often I've thought that the issues have been resolved only to have them pop up again. Tomorrow the a/c compressor, clutch and clutch selonoid gets replaced.

 

Off topic but i was wondering what type of hood you have on your yellow stang. It doesnt look stock to me but i like it.

 

Its a '04 Mach 1 stock hood and shaker:



I had the hood painted:

 

haha, rockin' tha smiley on the antenna! nice.

 

Well glad to see the problem is fixed. A lot of times that kind of stuff pops up and when it comes time for someone to look at it, it disappears until its back in the owners hand.

And since your timing chain tensioner was shredded, it was only a matter of time before your engine went anyways. Forged is stronger but it doesnt mean indestructible like some people thing. Good to see that you parked it and fixed that problem.

 

Thanks, I'm hoping this is the end of the problem, I've been dissappointed before these last few months. I've certainly learned quite a bit about the workings of a mod motor, if nothing else, its been very educational. When I get it supercharged, I'm planning on a conservative, pump gas tune. I'm wanting a fun car to drive, not a street monster and I've learned nothing is indestructable lol.