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Discussion Starter #1
Hello everyone,


To give you a brief background of myself, intermediate mechanic on cars, expert mechanic on aircraft. This is my first Taurus I have owned and they say that you get what you paid for and this car is no exception. I knew it had problems when I bought it but I thought I could figure it out. Now I've invested $3k into it and I'm at the point where I'm out of ideas. Here are the facts. The car is a 2006 Ford Taurus with the 3.0L V6 DOHV and only 75k miles (which is why I bought it). The previous owner was the child of an elderly man who had passed away and never drove it. The CARFAX report showed on average, 5k miles a year for the past 10 years. There were a few years where it only had 2k miles put on it. I drive an hour to work every day so I put on roughly 100 miles per day and needed something that could get better fuel economy than my diesel. When I bought it, the seller disclosed it had a P0306 (cyl 6 misfire) and p0430 (Bank 2 failure for Catalytic Converter) which is why it had a CEL on. I took the car to AutoZone and had them verify the codes were still accurate which they were. It also had a few other issues (warn rack and pinon and worn tires) but for the price, I decided to go with it. Sadly, $3k later and many parts later, myself and my mechanic shop are stumped to figure out what is the problem. Right now, if the car sits for hours on end (over night or for longer than roughly 3 hours) and cools down, I have a misfire on startup. HOWEVER... once the engine is running for a minute and warms up, it runs perfectly fine. Take it for a test drive and it populates no codes. After the 3rd or 4th startup after resetting the codes, it pops the P0306 instantly with the CEL on.



This is the rough timeline of the issues.
Purchased Car with P0306 code indicating misfire cyl 6 and P0430 indicating Bank 2 failure for Catalytic Converter
Replaced all 6 Spark Plugs and Wires and intake gaskets
Replaced ignition coil
Took to a mechanic shop to do the following: (since I have limited tools)
Replaced Catalytic Converter and O2 sensors
(Replaced warn serpentine belt, head lights, power steering pump and rack & pinion due to warn out and perform alignment)
Smoked engine to verify no vacuum leaks
Replaced ignition coil again
Re-flashed computer and now codes ready P0306 and P0316 (Misfire on startup)
Changed cyl 6 injector and intake gaskets and start up misfire code went away leaving P0306.
I then:
Performed oil change and added Lucas Oil Stabilizer (in case it was a lifter)

Checked resistance in cyl 4, 5, & 6 injectors and all read similar resistance.
Checked for voltage at cyl 4, 5, & 6 injectors and all ready 11.4 volts.


As of right now, the car runs the same. Driving down the road it runs smooth. At stops, it runs smooth. At start ups if it is WARM, it runs smooth. At start ups if it is cold, it runs rough for a minute and then runs fine. Fuel economy has been holding around 23 mpg which is mostly interstate. I need the car to run right because I have to pass emissions for the state of Missouri and I don't want to kill the new Cat. Any assistance is requested. If there is any more information you need, please feel free to ask and I'll get you what I can. Thank you again.
 

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I thought that 2006 models only had a OHV 12 valve Vulcan engine. Sounds like a bad intake gasket. I had a similar issue on my 2001 and it ended up being a bad upper intake gasket. Same start up issues with misfire only during the first minute.


What brand coils did you install, many aftermarkets are known to fail out of the box.
 

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Is it just me, or does it sound like a faulty MAT sensor, which I believe is part of the MAF?
 

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I think Automender is on the right track for driveability. Those plenum gaskets and intake runner motor o-ring were the cure for me.

Although, that doesn't account for the cylinder 6 problem, unless that plenum gasket is in really rough shape.
 

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I think Automender is on the right track for driveability. Those plenum gaskets and intake runner motor o-ring were the cure for me.

Although, that doesn't account for the cylinder 6 problem, unless that plenum gasket is in really rough shape.

He said he performed a smoke test for vac. leaks. I asked about a compression test / leak down because I've seen Vulcans with leaky valves. These 3 tests should be performed before you start throwing parts at it.
 

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He said he performed a smoke test for vac. leaks. I asked about a compression test / leak down because I've seen Vulcans with leaky valves. These 3 tests should be performed before you start throwing parts at it.

The gasket leak on the intake was so small I doubt a smoke test would show it and a smoke test is only as good as the person doing it. It is intermittent because the plastic expands and the area was soaked with oil. A compression test is appropriate and easy to do on #6 cylinder. I never had a valve issue on my fleet with four having over 200k miles and one at 120k.
 

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Youtube has some videos of a guy that had a hard to fix miss on a Vulcan. Leading to head removal and valve repair/replacement. The guy at South main Auto has some great videos on how to use a smoke machine to locate hard to find vacuum leaks.
 

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Thread stater does need to clean up the discrepancy in his OP about the engine... In his signature he indicates it is the 12V but in the body he references the DOHC which is the 24V. The 12V as i was schooled is also very plug picky...Double platinums only and many will limit what brands should be used..also one must take great care if adjusting the gaps as your double platinum may quickly become a single platinum or worse...and then there is the coil pack question that has already been asked...
 

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It is worth mentioning that the OP did not state whether or not he replaced the IMRC motor o-ring when he changed the UIM gaskets.

Was the smoke and leak-down test done on a cold engine that had not yet been started?

If not, then your mechanic missed the window for finding a leak. (My upper intake leak went away in less time than it would take to move the car 30 feet, but exhibited the same rough running on the first start of the day, as described by the OP.)

To the P0306 misfire:

It is rare, but not unheard of, for an engine computer to incorrectly assign a misfire to the wrong cylinder. Sometimes, it turns out that a cylinder adjacent to the reported cylinder in the firing order that is the real problem.

Have the new spark plug wires been resistance tested to make sure that none are defective?
Have the new spark plugs been double checked to make sure that they are not defective?
Have the signal wires from the computer to the fuel injectors been checked to verify that they are not making intermittent contact?

Also, it wouldn't hurt to verify that all the grounds are in good condition. I'm really reaching here, but it is remotely possible that a sketchy ground could be interfering with the injector/spark signals.

It might help to look at ignition and fuel injector wave forms on a scope to see if there are any clues to help pinpoint the issue.
 

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problem with coil pack

check your coil pack. no need to remove intake manifold. My problem on 2001 DOHC was this part - replaced with Delphi. if you remove the coil pack you will see a small crack on the bottom. good luck
 

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Discussion Starter #16
Confused still...

I thought that 2006 models only had a OHV 12 valve Vulcan engine. Sounds like a bad intake gasket. I had a similar issue on my 2001 and it ended up being a bad upper intake gasket. Same start up issues with misfire only during the first minute.


What brand coils did you install, many aftermarkets are known to fail out of the box.

To resolve the OHV/DOHV, I will be honest, I'm not 100%. I know the car front fenders have the DOHV 24V stickers on them which is why I believed it was a DOHV engine but you aren't the first to question that so I don't know. I know my 8th digit in my VIN is "U" which previous forums have stated is a Vulcan motor so maybe aftermarket fenders? When I bought the car, it had a clean CARFAX so to my knowledge all panels are original but doesn't mean someone didn't replace them on their own or have a back woods auto shop do repair damage. From researching the two engines, I'm sure I have a OHV not DOHV.
With that being said tho, I do have reason to believe that this car has had body repairs done to it because there is overspray on the headlight wiring and all over the car, the paint has blemishes that look like it isn't stock. The fuse box in the front of the engine also has cracks in it but that's all small things that I noticed over time working on this car. Personal opinion tho.


As for the coil pack, I replaced the one that was in it (Motorcraft) with another Motorcraft one from O'Reilly's and then the mechanic shop said it was reading multiple misfires so they replaced that one with one from NAPA (not a fan of their parts but what do you do) and they said it now only flags cylinder 6 again.


Is it just me, or does it sound like a faulty MAT sensor, which I believe is part of the MAF?

I have cleaned the MAF sensor with the appropriate MAF sensor spray, not sure if it needs to be replaced tho.


It is worth mentioning that the OP did not state whether or not he replaced the IMRC motor o-ring when he changed the UIM gaskets.

Was the smoke and leak-down test done on a cold engine that had not yet been started?

...


To the P0306 misfire:

It is rare, but not unheard of, for an engine computer to incorrectly assign a misfire to the wrong cylinder. Sometimes, it turns out that a cylinder adjacent to the reported cylinder in the firing order that is the real problem.

Have the new spark plug wires been resistance tested to make sure that none are defective?
Have the new spark plugs been double checked to make sure that they are not defective?
Have the signal wires from the computer to the fuel injectors been checked to verify that they are not making intermittent contact?

Also, it wouldn't hurt to verify that all the grounds are in good condition. I'm really reaching here, but it is remotely possible that a sketchy ground could be interfering with the injector/spark signals.

It might help to look at ignition and fuel injector wave forms on a scope to see if there are any clues to help pinpoint the issue.

To be honest, I don't know if it was done when it was cold or hot, a very good point there. I saw a video online about just smoking a cigar and blowing it into the tubes and see if it leaks. Good excuse to light up right? I was thinking about trying that this weekend. The UIM gaskets were replaced by a local mechanic shop since I was in the middle of a move and didn't have my tools yet. They were the ones who replaced the plugs, wires, and UIM gaskets. I don't know if they replace any others.
As for the misfire code other cylinders, ready my next post because I'm going to post an update next. My thoughts were that it would end up resulting with wiring but I know how bad of a rabbit hole that can become.


check your coil pack. no need to remove intake manifold. My problem on 2001 DOHC was this part - replaced with Delphi. if you remove the coil pack you will see a small crack on the bottom. good luck

Coil pack has been replaced 2 times already. Current one on there looks to be in good shape with no issues.
 

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... I saw a video online about just smoking a cigar and blowing it into the tubes and see if it leaks. Good excuse to light up right? I was thinking about trying that this weekend.
I don't think you'll get enough pressurized smoke in the system to do any good using the cigar method. I think you are going to need to use a real forced air smoke machine to do it. I've seen you tube videos of how to make your own smoke machine, but it looks like a lot of fiddling around. I'd prefer to take it to a shop that has a real machine, and knows how to use it properly.

... The UIM gaskets were replaced by a local mechanic shop since I was in the middle of a move and didn't have my tools yet. They were the ones who replaced the plugs, wires, and UIM gaskets. I don't know if they replace any others.
The IMRC motor o-ring is an easy one to miss when doing the UIM. It is not an obvious place to put an important seal. The o-ring and gaskets are inexpensive, and fairly easy to change out.
 

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Discussion Starter #18 (Edited)
Update

Alright, I'm at a complete lost. Last night I replaced the number 4 cylinder injector since the number 4 plug showed buildup on it even though it is new. Remember that the CEL still is on and shows a failure for a misfire in cylinder 6 (P0306) and a startup misfire code (P0316). Because of the problems I have been having and some of the comments on here, I also removed the IAC and sprayed it down with carb cleaner along with following a youtube video on how to clean the thottle body with the car running. Now here's the catch. I have attached a picture of the injectors. I understand that OEM are the prefered ones to go with but with a tight budget and already investing a ton of money into this car, I got the BWD ones from O'Reilly's. Number 6 was originally changed from the auto shop it was at and they also replaced it with a BWD. The issue I have, since I'm new to replacing injectors, is does the top hole size matter as long as the bottom spray holes are accurate? Original ones have a small hole on top and the aftermarket ones have a large hole in the top but both still have the same spay nozzle design. None the less, since replacing both injectors and cleaning the IAC and Throttle Body, today I still had the miss fire and this time it miss fired like crazy between 40 and 50 mph right after shifting into overdrive. If I would peg it or keep it in Drive then it wouldn't miss fire but if I let it go into Overdrive then it would misfire. I looked around the engine bay and couldn't see anything disconnected for air lines or electrical.


Now here is the next issue I have. On my way home, I stopped and picked up an Intake Manifold Gasket kit and a Motorcraft FL-400s Oil Filter for the O-ring on the IMRC since it was recommended to replace as well. This time while I was looking around the engine bay, I noticed a sticker I had overlooked before and got curious. "ECM/PCM Modification" with the mechanic shop, the ID number, and the date (Aug 10, 2016). Intreged, I called them and they pulled up their old records which showed the car was in for a P0430 (Bank 2 Failure - Catalytic Converter) and emission fail. Their notes were limited but said they replaced the Catalytic Converter, PCM, Serpentine Belt, IAC Motor, Speed Sensor, and rebuilt the Speedometer. None of this was reported on the CARFAX report I had but it does show on Aug 13, 2016 it passed emissions at a Texas station with 60,xxx miles on the car. I bought it in Nov, 2018 with 72,xxx miles. Like I said in the OP, it had the P0306 and P0430 codes which if the car had a misfire for that long would explain another Cat going bad that fast. With that being said tho, I had to replace the Serpentine belt also due to a rib being missing on it. Now I am worried at what kind of mess I am dealing with.


Please review the previous posts and give some advice on how to move forward. Below are the plugs and the injectors. Again I have the UIM gaskets so that is my next step unless someone can offer some better advice. Pics go as follows. First 2 is the injectors (Order: original-aftermarket-original) then spark plug 4 (light build up), spark plug 5 (clean), and then spark plug 6 (heavier build up). Some oil around the plug is from when I install the plugs, I put a drop or 2 of oil on the treads. Also want to point out that this car does not eat oil.
 

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Discussion Starter #20
You should make sure your wires are connected to the coil properly and in the right order. It has been an issue more than once on the forum causing a misfire. #5 and #6 are easy to mess up on the coil.
Yes I have verified that #5 and #6 are hooked up correctly multiple times just because I doubt myself more times then not. Lol.
 
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