The Engineer

2005 Mustang GT Premium
4.6L Manual Transmission
75,000 miles

Allow me to give some background first:

I purchased this Mustang in February 2011 in stock condition except for 20" wheels & mufflers. It has been garage-kept but has been parked in the rain occasionally. Used as daily driver. The car has always been reliable and ran well.

The car has occasionally exhibited intermittent bizarre electrical behavior such as A/C turning itself on and radio shutdown / restart.

I have had issues with vibration coming from the front-end, most likely due to the 20" wheels or possibly some sort of suspension issue. I have not been able to sort this out despite new tires.

I drag raced it in November 2011 (roughly a dozen passes). Did not notice any issues with it afterward despite running it very hard.

In December 2011 started to notice a little bit of misfiring, so I decided to do some maintenance which included replacing the original spark plugs. I learned the hard way about the trouble with the factory plugs seizing in the 3V engine, and I snapped of 4 of them in the engine. Working very carefully, I used the Lisle kit to remove the old spark plugs. I cleaned everything very thoroughly. I used a borescope to check that the cylinders were clean and compressed air to blow out the little white pieces of broken ceramic. I chased the threads with a tap and then I replaced the old plugs with new Champion plugs and the old factory coils with Accel super-coils. The car ran fine afterward with absolutely no indication that there was ever a problem. The old plugs looked very worn, so I assumed that was the problem and it was fixed.

In March 2012 the car passed GA emissions with no problem.

In late March 2012 I decided to replace the existing Flowmaster mufflers with a set of Corsa Extreme mufflers.

Okay, so here is where things start to get weird:

About a week later, in early April 2012, the automatic-up feature on the passenger window stops working. Auto-down still works and the driver window still has full-function. Around the same time, the outermost-left taillight goes out as if the bulb is blown. Then the engine light comes on and stays on.

Then the car starts to stall at red lights. This happens about three times over two days, but the car restarts immediately each time it happens. Then the next day, it stalls at red light but wouldn't restart for ~1 minute. When it restarts it is running rough.

I took it to a local shop and they discovered trouble code PO600. There were a few other codes which did not seem relevant such as an evaporator code, ABS wheel speed sensor, etc. They instructed me to take the car to the Ford dealership to have the PCM replaced for $900 and flashed for $300.

A few days later, the auto-up feature on the passenger window inexplicably starts working again and so does the supposedly blown taillight bulb.

Where I am at now:

Now the car starts normally and idles okay, but the exhaust smells of unburnt gasoline. It has a significant misfire if the engine is revved and upon acceleration, however the overall power is still good. I had no trouble smoking the rear tires and taking off like a bat out of Hell. It just misfires while doing so. The car is surprisingly drivable, but appears to randomly misfire quite a lot.

I have parked the Mustang in my garage and will be driving my truck instead for the next 6-10 months, as I am currently working on an out-of-state project. I am trying to figure out what my next course of action should be. I am very open to suggestions. Help!

1. Does anyone have any idea what is going on here?
2. Can the PCM be tested to see if it is bad?
3. Can the current PCM just be flashed?
4. Is there a less-expensive alternative to the Ford dealership?
5. What is the root cause for the PCM to go bad?
6. Does this sound like an SJB water-leak issue?

I am desperate to get this thing fixed to so I can go play in my pony again. Many thanks to you all!
-Andy

wayne613

1. After clearing the codes does the P0600 come back? Any additional codes? Very well might be having issues. Tried pulling it looking for corroded pins, damage, or the seal not being good on it anymore?

Offhand, I know aftermarket coil-packs = misfire problems down the road. May wish to get OEM ones once you figure out what you plan to do about the PCM.
Reset the keep alive memory while you're at it:
http://iihs.net/fsm/?dir=8&viewfile=Resetting%20The%20Keep%20Alive%20M emory%20(KAM).pdf
2. Not without the VCM tool I think. It's unlikely this is false considering the evidence that the PCM is responsible if that code still comes back after clearing.

3. If it isn't something simple like harness pins corroded or the like, I would not trust it to just be re-flashed again. Better to just spend the money. Although I'd probably ask for a price from multiple stealerships.

4. You'd have to have it flashed with the proper information and settings. So you could get a wrecked/salvage/re-furb compatible PCM, but the programming would still need to be done by one unless you want to buy the tool/software. I'd ask if it would cost more to re-flash the existing one along with a new one, at least you could have a potential (working) spare for free. No harm in asking, since you'll be getting reamed anyhow they might feel generous.

5. In this case my guess would be moisture got into the case. It's flash-able, EEPROM data can and does corrupt without any real external factor(s) though, even though it's pretty rare. So you'd have to investigate on you're own to find out with any certainty.

6. The windows have no CAN-BUS functionality tied to the PCM, so that should be solely SJB related. Frankly, IMO the 05-07's should only be sold to someone with this TSB attached to the dang title in any state besides Nevada if you ever drive it outside of sunny conditions.

You're likely not going to find much moisture unless it's rained hard in the past day or so and you drove it, but if you take the SJB out you will likely find signs of corrosion, which means this is the likely cause of your internal electrical non-PCM tied into woes.

Just clean it up best you can, I've seen many where this was all that was needed to remedy the situation they were having. But since yours is now back to how it should be, you're already a step ahead. The given of course being to track down and then sealing/clearing the cause(s).

Jessescc

ECM malfunction

Jessescc

ECM malfunction powertrain/engine control module has failed

Jessescc

if you take the car to the dealer, they guarantee that work anything goes wrong you hold them accountable