I thought I would pass along so things learned from my recent secondary tensioner and coil pack exploits. I found some of this info on some old threads so am embellishing with what I learned. My car is a 2000 XKR that has the AJ27 engine that just turned over 66K miles. I think 99 or 00 was change over year from AJ26 to AJ27 but it is important to know which you have.

My problem started with a miss on cylinder A1 which generates code P0301 along with some other more general codes. The relevant codes are P0301-P0304 for the A1-4 bank, which is passenger side with 1 forward, and P0305-P0308, which is the B1-4 bank, or driver's side with 5 forward. If you get one of these codes along with other associated coil codes, the problem is most likely a failing coil pack. These codes can also be associated with injector and fuel related codes, which would push thinking toward the fuel side of things. I had no fuel related codes.

I am currently using a PLX Bluetooth OBD adapter paired to Torque that runs on my Android phone. This seems to do a good job of reading codes although it lacks some advanced features you get with the devices that are oriented toward the mechanic. The XK8/R has two diagnostic networks, the standard OBD CAN net, plus the proprietary Ford network. Both are connected to different pins on the OBD port. This reader seems to get both.

Coil problems usually present as an occasional misfire, particularly under load or at idle. I know of one instance where the car only missed when pulling a hill. In my case, initially the misfire would stop and start, resulting in the "Reduced Performance" message on the speedo. I checked the code and got P0301, so pulled the cover and found that there was a leak in the plug cavity. Since this meant replacing the valve cover gasket (not trivial) I decided to turn this over to a mechanic and get the 2nd tensioners replaced at the same time. After he got through the car was still missing so I took on the Coil Pack issue rather than cough up another $5-600 to the mechanic. BTW, his price for the tensioner change was in the $600 range with my parts.

I bought the Lincoln LS V8 version of tensioner for significantly less than the Jaguar equivalent. I also bought the bolt set that is supposedly required. These bolts turned out to be the wrong length as reported by others. The problem is that Lincoln only used the AJ26 engine and mine is the AJ27. Therefore I think when doing this job it is necessary to buy the Ford tensioners and the Jag bolts for a later model year (2003 ?) that had the latest version tensioner as a standard install. The advantage being that the Ford parts are much less expensive. I think any MY up to 2006 would be the same.

I tried to apply the same thinking toward coil packs but soon learned that the AJ26 and AJ27 use a different configuration. The AJ26 has ignition modules between the ECU and coils and the Coil Pack is just a coil with a 2 wire connection. The AJ27 incorporated the ignition module components into the Coil Pack, resulting in a 4 wire connection.

After some research I found at least 3 unique sources for Coil Packs, and a wide variety of prices. The OEM Coil Pack (with Denso marking) lists for $147 but is available for less. I paid $112 but with extras the cost was in the $130 range delivered. I was able to buy a NAPA version in the $130 range, but it has none of the original part number marking. Then I found a Prenco coil (made in China, see Prenco Progress & Engineering Inc.), at an online place called Partsgeek, for $56 including shipping. I tried all three versions in the car and found that they all worked well. All the above also have the 2 wire version available. My choice going forward is the Prenco part because it works and costs less than half of anything else.

I ended up replacing A1 and A3 coil packs (A3 apparently failed after my initial code check) and the XKR is back to life. I noted that both had extensive rust on the coil core and other deposits along the boot. This leads me to think that both plug tubes were leaking and this somehow resulted in the coil failure. The other 2 coils on A bank do not show corrosion and have not failed.

Also of interest, my mechanic's code reader showed P0301 and P0308 while mine showed P0301 and P0303. Mine turned out to be correct so not sure what that means. I also did an ohm grid on the Denso and Prenco versions and found them to be quite different. This created some doubts but they went away when A3 came back to life with the Prenco. At this price point I could easily justify replacing all coil packs just to have it out of the way.

 

good read.