2006 4th Bad PCM?!?!? - Taurus Car Club of America : Ford Taurus Forum
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post #1 of 29 (permalink) Old 06-18-2019, 08:10 PM Thread Starter
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2006 4th Bad PCM?!?!?

Now that I got your attention, I have been troubleshooting my 2006 Taurus with the 12V Vulcan for a while. I have done a few posts on here and I was trying to avoid this one but I'm officially at the end of the road... all signs are pointing to a bad PCM. The car came with a clean CARFAX but I know it was in a wreck because it's got different fenders, over spray on the headlight wiring, cheap paint, and a cracked engine fuse box. For what I've done, here's the history for those who don't know (and all parts replaced are Motorcraft parts).


Purchased car with a cyl. 6 misfire and bank 2 catalyst fail. (P0306 and P0430)
Replaced all 6 spark plugs, wires, ignition coil pack and both catalytic converters w/new O2 sensors. P0430 went away but P0306 remained.
Reflashed PCM and it still failed but it added a start up misfire code (P0316).
Performed a compression check and failed. Pulled the heads and both were bad.
Replaced both heads, all gaskets associated with a head kit, water pump, thermostat, and fuel injectors. Code changed to a P0301 (cyl 1 misfire) and P0316.


Ran another compression check and all cylinders are now reading around 180 psi. Checked for vacuum leaks with carb fluid and had no change to idle.
Replaced fuel filter, all 6 plugs and wires (again), Ignition coil pack (again), Idler Air Controller, PCV, Throttle positioning sensor, and Camshaft position sensor, and I cleaned the MAF sensor and Throttle body... Still have P0301 and P0316. Reason why I replaced the IAC, TPS, and fuel filter is that the car has a problem where it won't always let off the gas when I take my foot off the gas pedal. Occasionally it holds an extra second or two which has cause numerous close calls. I also have an idle issue where it likes to idle between 800 and 1200 RPM.
The car does not leak or eat oil. The car DOES drink anti-freeze but that is due to a leaking coolant line from the thermostat to the reserve tank at the reserve tank connection (I am replacing that this weekend). Leak is obvious and you can see standing fluid on the top of the reserve constantly. No fluid has been found in the cylinders.


Currently, the car starts ruff but smooths out after about 2 minutes and then runs almost perfect (or so it seems except the fuel economy). If the engine is warm then it starts with no issues. I have had problems where the car wouldn't start (it would crank but no start) for up to 45 minutes but the moment I reset the computer, the car will fire up instantly.
I've done everything I can think of before going after a PCM. I swung through a Ford dealership today and they pulled the VIN only to find that a Ford dealership replaced the PCM and Harness in 2011. I also have a sticker under my hood from a non-Ford mechanic shop that says it replaced the PCM in 2016.
Oh, also... If I reset the computer before I go on a long drive, I averaged 32 mpg (manual calculation, not computer) on the way there with the cruise set at 65 mph. Once I restart the car 1-2 times, I drove it back and it averaged 27 mpg with the cruise set at 65 mph. Same road, no differences. Then after I got back, I will average 23-25 mpg. Once I reset it again, it goes up until I restart the car a few times and then it drops again.


Today I tried an experiment and I put 2 gallons of gas in it. The fuel gauge didn't budge and the electronic miles to empty did not change. I drove 5 miles and shut the car off for 6 hours. I came out and it still read the same. Took off down the road and about 10 miles down the road the fuel gauge increased and the miles to empty jumped up 50 miles.
Today I also experienced 3 times where I lost throttle response during a turn. I was exiting the interstate on a cloverleaf and halfway through it, the gas pedal went limp and dropped to the floor, the throttle and RPMs dropped for a moment, I picked my foot off the pedal and pushed it back down twice and then it came back. This happened twice on the way to work and once on the way home.
I've check my fuel pressure and it's on par to Ford's requirements.

Things that concern me now though is that this will be the 4th PCM in 13 years. Is there something that is causing the PCMs to fail? Is there anything I can check myself? Is buying a $590 PCM from Ford directly worth it or can I just use a PCM from the junk yard WITH MATCHING NUMBERS and have Ford reflash that one? Is there anything else that you guys think I should do or check first? Thank you for reading this extremely long post and I look forward to any assistance.

Here are my previous Forums for those who wish to know more:
https://www.taurusclub.com/forum/82-...fire-help.html
https://www.taurusclub.com/forum/82-...ay-taurus.html
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post #2 of 29 (permalink) Old 06-18-2019, 08:14 PM Thread Starter
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Join Date: Jan 2019
Location: St. Louis, MO
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Year: 2006
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Engine: 3.0L 12v Vulcan V6
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I should also point out that I'm working hard on this car because it only has 90k miles. When I got it, it has 65k miles on it... that was 8 months ago.
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post #3 of 29 (permalink) Old 06-21-2019, 01:56 PM
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I'm a new owner of a 2005 with the DOHC motor, and am having the same intermittent cyl #6 misfire. Did much the same as you, new plugs, coil packs, PCV valve, yet I still have the intermittent misfire. It took weeks for the PCM to set a code P0306 to give me an idea where to start.
I removed the PCM and opened it up as I know just enough about electronics to get myself into trouble. The driver IGBT's that operate the coil packs (B8202N) all seemed to check within the makers specs (ON Semiconductor).
While the PCM was open I decided to simply change out all 6 IGBT's. The originals are now obsolete and no longer made by ON Semiconductors so the replacement is an updated version from Littlefuse.(NGB8202AN)
Should be here in a day or 2 so I'll let you know if that cured it.
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post #4 of 29 (permalink) Old 06-21-2019, 02:26 PM
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Checking for vac leaks with carb cleaner, propane, etc doesnt work well on modern engines and will only show significant vac leaks, and that is if you can get get to the leaking area with the testing fluid.

Did you check fuel trims at idle and under load? Higher + trims at idle that drop closer to 0 when under load = vac leak. Checked for any pending codes like 171/174? A vac leak can easily cause a missfire. Tecs are known for leaking UIM to LIM gaskets. An air leak into 1 cyl can be enough to cause occasional missfire but not set lean codes as the 02 sensors basically average the A/F over all 3 cyls in the bank.

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post #5 of 29 (permalink) Old 06-21-2019, 04:22 PM
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I would start with cleaning and fixing every ground under the hood. Pic of one you might miss and it is critical for the PCM and sensor "return = body ground" signal. This one causing erratic idle speed and TPS signal variations. Ford bolts this PCM ground on painted metal and it rusts. I pulled this one off and sanded the metal and coated with anti corrosion electric compound. Issue fixed.


Imagine, your PCM wants to be grounded to the car body.


-chart-
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post #6 of 29 (permalink) Old 06-22-2019, 08:07 PM
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Yep for above. Grounds are problematic in this car and everything is sensitive to it. You sure have been around the block with this car. I hope it's worth it.

You might try a new MAF. That commonly causes slow starts first start of the day even when it checks good. WalMart $25 for Motorcraft. Worth a shot. I wouldn't even bother with ebay junk.
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post #7 of 29 (permalink) Old 06-23-2019, 10:15 AM
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Quote:
Originally Posted by 46davis View Post
Yep for above. Grounds are problematic in this car and everything is sensitive to it. You sure have been around the block with this car. I hope it's worth it.

You might try a new MAF. That commonly causes slow starts first start of the day even when it checks good. WalMart $25 for Motorcraft. Worth a shot. I wouldn't even bother with ebay junk.
Could you provide a link for a MC MAF sensor from Walmart for $25?

To the OP if you do go for an MAF sensor it is advisable to get a Motorcraft one.
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post #8 of 29 (permalink) Old 06-24-2019, 09:41 AM Thread Starter
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Quote:
Originally Posted by Jeff K View Post
Checking for vac leaks with carb cleaner, propane, etc doesnt work well on modern engines and will only show significant vac leaks, and that is if you can get get to the leaking area with the testing fluid.

Did you check fuel trims at idle and under load? Higher + trims at idle that drop closer to 0 when under load = vac leak. Checked for any pending codes like 171/174? A vac leak can easily cause a missfire. Tecs are known for leaking UIM to LIM gaskets. An air leak into 1 cyl can be enough to cause occasional missfire but not set lean codes as the 02 sensors basically average the A/F over all 3 cyls in the bank.

Both my dad and I have both searched high and low for a vacuum leak and found nothing multiple times. I've probably gone through a few cans over the past few months rechecking for leaks. As for fuel trims, both are within Ford specs so I've ruled that out. No pending 171 or 174.
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post #9 of 29 (permalink) Old 06-24-2019, 09:43 AM Thread Starter
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Join Date: Jan 2019
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Quote:
Originally Posted by 46davis View Post
Yep for above. Grounds are problematic in this car and everything is sensitive to it. You sure have been around the block with this car. I hope it's worth it.

You might try a new MAF. That commonly causes slow starts first start of the day even when it checks good. WalMart $25 for Motorcraft. Worth a shot. I wouldn't even bother with ebay junk.

I'll scope out the ground that was previous called out but when I looked at it earlier in my troubleshoot process, they all looked clean and checked good with less than .4 ohms to a secondary ground. I have not tried a new MAF, just cleaned the one that has been in it with the MAF cleaner spray.
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post #10 of 29 (permalink) Old 06-24-2019, 10:10 AM Thread Starter
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Join Date: Jan 2019
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Also, I was talking to a Ford service rep this weekend and he said something that seemed strange to me so if anyone has info on this, let me know. I was talking to him about my problem and one of the 3 Ford service shops I talked to said that it's common for the 12V Vulcan engine to fry PCMs if their spark plugs haven't been changed regularly and that if the gap gets too big, it causes the plug to receive to large of a power draw and then it back feeds into the ignition coil and has been known to back feed to the PCM and fry something inside of it that controls the ignition sequence... Has anyone heard of that? This guy was extremely confident on his response and said that his car is on it's 3rd PCM also for that issue. Sounded fishy but then again, this is a Ford and so far almost nothing about this car has troubleshot per my knowledge...
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