I just had my xk8 in for flush and fill on coolant. I drove the car about 25 miles and got a reduced performance, along with rough idle at stop. This happened to me in the past and I traced it to a rotting snorkle. The corrugated portion between the throttle body and the MAF had rotted and was full of holes due to exhaust heat. So I cut out the bellows and replaced this with a Chrome plastic tube from an aftermarket intake kit and a couple of silicone couplers, $25.00. This worked, cheaper than a new snorkel. Rought idle was cured. So this was the first thing I checked and sure enought the chrome tube had a heat crack on the bottom. I wnet out and bought another tube and some heat dispersing tape and replaced the cracked tube. Drove the car about five miles and stopped to pick up a passenger, no issues. Started out again and another five miles down the road got the restricted performance and check engine. After several traffic lights and rough idle's stopped car, ate dinner, 1.5 hour car sitting. Left to return home car ran great not issues smooth idle no screen prompts. All appeared normal. Took car to the dealer for help. They did not get codes so they went old school and traced the problem to the coil pack on the #6 cylinder. I needed a new coil pack in #6. They told me that its is not unusual for these to start acting up once you get to 70K and higher. My question is should I go ahead and replace the other seven when I get the car back and do the plugs as well. This car, Murphy's law, and full moons, usually get me. Suggestions!

 

on my previous cars i usualy treated coils packs, fuel injectors , and spark cables the same as sparkplugs. replace 1 replace them all.

theoretically replacing just 1 of those items will equal less efficiency and poor performance.

 

I went ahead and ordered the remaining 7 coil packs today. I showed the dealer's parts manager the best price I found on line and asked if he could match or come close to that price. He not only came close but reduced the original price I was billed on the initial repair to the same price. The best price I found on line for the four pin coil pack was $144.00 ea. the dealer got down to $148.00. So he got the order and the business stayed local.

Now does anyone know the torque numbers for the two bolts that hold these in place? Also should I go ahead and change the plugs, and what is the torque numbers for the plugs? Lastly do you need to use dielectric grease on the plug connections, spark plug boot dressing, and any antiseize on the plugs?

 

Spark plug torque is 27 nm (18 FT LB)

Coil Cover Bolts 4-6 nm

This info is from alldata.com. I can't find any info for coil bolts, so I'm not sure if the cover bolts are what they call the bolts that hold the coil on or not. I wouldn't torque them very much. I have not removed one from a spark plug myself but from what I've read on this forum they break pretty easy.

I'd dress the plugs with antiseize and I'd also use a dielectric grease on the plug connections.

I took a 400 mile trip yesterday and we're having a hot spell here in OrEgone.. it was 107. The engine bay was really hot, there doesn't seem to be a lot of air flow to the engine other than the radiator fans which were on constant low speed and high speed kicking on and off while stopped.

Good work getting the dealer to lower his price! Part prices for our cars are like gold!

Here's a bit more info from JITS. The "coil cover bolts" ARE different than the "coil on plug bolts" but they are the same 4-6 nm torque. JTIS shows the plug torque to be 25 to 29 nm. Looks like alldata.com picked a happy medium. Plug gap is listed as 0.039 to 0.043 in for NA engines and 0.047 to 0.051 for supercharged engines.

 

Thank you for all of the information. It will get put to use this weekend after the IRL race Saturday. I guess at 107F it would be HOT CHOCOLATE. Liquid delite.