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Engine hesitation at highway speed

6K views 6 replies 3 participants last post by  fishx65 
#1 ·
My 2008 Taurus with 65K miles has developed an odd hesitation. It usually occurs at highway speed (around 70 mph), under light acceleration (1500 rpm) and usually when going uphill. It will appear at other times, but that scenario is the most predictable. I have also tried to see if the condition would worsen under hard acceleration at highway speeds, but have no problems. I have cleaned the mass air flow sensor with no improvement. I also do not have any check engine lights, and the Autozone scan showed no codes. Has anybody dealt with this situation?
 
#2 · (Edited)
Exact same thing happened to my 2008 around the same mileage. I thought for sure it was the transmission sensors but it's the spark plugs and/or COPs. Believe it or not a simple spark plug change will probably fix it but I changed both the plugs and COPs. Motorcraft has a cheap kit that comes with everything you need. Comes with 6 plugs, 6 COPs and upper intake gaskets. Price has gone up a little but still an awesome deal.

https://www.ebay.com/itm/Genuine-Ford-Kit-BA5Z-12259-A/273285147965

Since ya gotta pull the upper intake to change the rear plugs it's nice to just replace the COPs while ya got it apart. There's a few good youtube videos if your gonna do it yourself.
 
#6 ·
Exact same thing happened to my 2008 around the same mileage. I thought for sure it was the transmission sensors but it's the spark plugs and/or COPs. Believe it or not a simple spark plug change will probably fix it but I changed both the plugs and COPs. Motorcraft has a cheap kit that comes with everything you need. Comes with 6 plugs, 6 COPs and upper intake gaskets. Price has gone up a little but still an awesome deal.

https://www.ebay.com/itm/Genuine-Ford-Kit-BA5Z-12259-A/273285147965

Since ya gotta pull the upper intake to change the rear plugs it's nice to just replace the COPs while ya got it apart. There's a few good youtube videos if your gonna do it yourself.
Your suggestion makes perfect sense, but I went a little cheap and just changed the plugs. The plugs that were removed had almost twice the gap and I'm probably lucky that no coils were ruined. The good news is the new plugs cured my misfire issue!
 
#5 ·
I took my vehicle to a local mechanic I trust. I explained my symptoms, even mentioned the video you posted, but unlike the guy in the video, his mode 6 scan showed no misfires. The misfires for me seem to happen in a very narrow range, 1200-1400 rpms, always going slightly uphill with light acceleration. It's possible he may have accelerated too heavily on his test drive. Despite the occasional misfire, the car drives very well.
 
#4 ·
I drove mine a looong time with this problem before replacing everything. It eventually started going into limp mode and throwing COP codes. I had to pull over every time and cycle the ignition a few times to get it out of limp mode. I've read that bad COPs can eventually take out the main computer so ya probably wanna get it repaired pretty quick.
 
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