Bad Ignition Coil?

[Ruley73]

Hello all....

I am working on my sister-in-law's 2002 Ford Taurus with the Vulcan 3.0L (Flex Fuel). It has about 130K miles on it. I've recently replaced the OEM plugs and wires with double platinum Motorcraft plugs and Autolite plug wires. The fuel filter was also replaced with a Luberfiner/AutoZone replacement as well as the air filter with a Fram. No vacuum leaks that I can see.

It still hesitates a little when accelerating from a stop or if it is floored while idling in park. She had it scanned and came back with codes P0301, P0303, and P0316.

I recently pulled the plug wires off one at a time while the engine was running and noticed that the spark arc (when holding the plug wire on/near the respective terminal on the coil) was much weaker on cylinders 1 and 3. Based on this I believe the ignition coil is bad, but was wondering if there was anything else I could check before replacing the coil?

[shorod]

Ahhh, a fellow Cedar Rapidian!

Did you happen to notice if cylinders 1 and 3 happen to share a coil? If you have an inductive probe for plug wires you could measure the voltage on the plug wires to see if in fact the spark is weaker to those two cylinders. You also could check those two plugs to see if they look like they've been firing.

Before buying a new coil you could also swap the plugs with some other cylinders to see if the misfire code follows the plugs, swap around wires to see if the codes follow the wires, and maybe even swap coils to see if the weak spark follows the coil.

-Rod

[Ruley73]

Originally Posted by shorod

Ahhh, a fellow Cedar Rapidian!

Did you happen to notice if cylinders 1 and 3 happen to share a coil? If you have an inductive probe for plug wires you could measure the voltage on the plug wires to see if in fact the spark is weaker to those two cylinders. You also could check those two plugs to see if they look like they've been firing.

Before buying a new coil you could also swap the plugs with some other cylinders to see if the misfire code follows the plugs, swap around wires to see if the codes follow the wires, and maybe even swap coils to see if the weak spark follows the coil.

-Rod

Yes, fellow Cedar Rapidian here .

No, 1 & 3 don't share a coil. I was reluctant to replace it because I haven't seen a coil fail like that before. It appears that 1 & 5, 2 & 6, and 3 & 4 share coils like I've illustrated below.

|1 2 3|
|5 6 4|

(Front of car on this side)

I really didn't want to mess with removing the plugs & wires since the two in question are somewhat difficult to access being they are on the firewall side and I didn't have much time since she is still driving it.

What I did do though was temporarily switch the wires around on the shared coils. When I did that the same weak spark persisted when I held the #5 wire over the #1 coil tower and also when I held the #4 wire over the # 3 coil tower. Like I said before, there is still spark there but it is night and day much weaker than the other four terminals on the coil.

[shorod]

Next question then is did it have this problem (including the diagnostic codes) before replacing the plugs and wires? I ran in to something like this on a 1997 Chevy Malibu. Instead of jumping a spark I was using an inline spark tester and on the misfiring cylinder the spark tester was not as bright as on other cylinders. I swapped wires, still showed up on cylinder #5. Swapped the coil, still #5, swapped the plug and the issue followed the plug. Upon close inspection we could see a fine crack in the ceramic of the plug. We replaced the plugs and the issue went away.

-Rod

[shorod]

If you want to borrow an inline spark tester let me know. I also have a handheld scope and inductive probes to measure spark voltage on the wires. I won't loan these out, but could hook them up and make a few measurements some evening.

-Rod

[Ruley73]

Originally Posted by shorod

Next question then is did it have this problem (including the diagnostic codes) before replacing the plugs and wires? I ran in to something like this on a 1997 Chevy Malibu. Instead of jumping a spark I was using an inline spark tester and on the misfiring cylinder the spark tester was not as bright as on other cylinders. I swapped wires, still showed up on cylinder #5. Swapped the coil, still #5, swapped the plug and the issue followed the plug. Upon close inspection we could see a fine crack in the ceramic of the plug. We replaced the plugs and the issue went away.

-Rod

Before the tune up it was running so bad she said it would even stall at stoplights once in a while. She had the codes scanned a while before the tune-up and it came back with P0300 and P0440; so she changed the gas cap as advised by me and we decided to put off the tune-up for a couple more weeks until it was convenient.

I reset the computer (by removing the PCM fuse) after performing the tune-up so the codes only reflect the recent issue. As far as I know the car ran fine up until about a month ago. It's now been about 3 months since the tune-up.

The coils are all integrated into one serviceable part so I can't swap them around. The other thing is that I have limited access to the car because she's so busy, so I don't get much opportunity to mess with it. She's going on a trip to DSM this weekend so I was hoping to have it fixed before then.