Incompatibility issue with Iridium spark plugs on a flex fuel vehicle?

[BrooklynBay]

I replaced 6 Motorcraft Platinum spark plugs, and cables on a 2004 Taurus 3.0L with flex fuel (Vin code 2) yesterday with Autolite Iridium spark plugs, and Motorcraft cables. It was OK until it warmed up, then it started to sputter, and run rough. I disconnected the battery to clear the memory in the PCM, but it was still rough. The Autolite plugs were removed, and replaced with Motorcraft Platinum spark plugs. It was rough at first, but after driving for a few minutes, it suddenly went back to normal. The vehicle was driven with Iridium plugs for a similar amount of time, but there was no change. It appears that there might be an incompatibility with Iridium spark plugs being used on a flex fuel vehicle. Did anybody else have a similar experience?

 

[dogfriend]

I don't have any experience with the Flex Fuel vehicles, but I have read enough bad reports about people trying Bosch and other aftermarket brands of plugs to believe that you are better off staying with the Motorcraft Platinum plugs on Fords that originally came with them.

Along those same lines, I think my dad installed Champion plugs in a Toyota pickup once with similar bad results. The Toyotas seem to like Nippondenso (Denso) which are OEM or NGK which is a very similar plug. The late model Toyotas use Iridium plugs which are supposed to have a 100k lifetime.

 

[Joe Dirt]

I know that one of my friends had the same exact problem with Iridiums installed in a 4.0L Flex Fuel Ranger... Swapped back to Motorcraft and all was well... No idea why...

 

[BrooklynBay]

Dogfriend, what kind of plugs does your Prius come with?

 

[dogfriend]

Dogfriend, what kind of plugs does your Prius come with?

Iridium. They are supposed to be good for 100k, I will probably remove and check at 60k or so to make sure they don't get seized in the head. My GF's Avalon also has Iridium plugs, its got about 75k on it. The rear plugs are a ***** to get at, I may get her to take it to someone to change those plugs.

Back to the original subject, I would speculate that the impedance of the iridium plugs may be different than the platinum plugs, but I don't have any way to prove it. If you had a automotive oscilloscope, you might be able to see the difference in how it fires...

 

[BrooklynBay]

I read that the flex fuel systems detect the resistance of the fuel being used with a sensor, and adjust the program in the PCM accordingly. Sometimes the mixture could get thrown off (different spark plugs, vacuum leak, etc), and the PCM might think that a different fuel is being used (E85 being detected instead of regular gasoline) even though regular gasoline is used the whole time. The PCM will change its program accordingly, and create issues similar to what the Taurus experienced (rough idle, pinging, back firing, sputtering, etc).