Agreed. It's very frustrating. If I take the car back to them, we'll have a conversation about it.

The shop is well respected as being the top (or one of) Porsche indy shops in Phoenix and the owner has been nothing but gracious. I do think they're trying but perhaps overwhelmed.

In their defense, they road-tested the car for five days after swapping the plugs and the CEL did not return for them. The owner even took the car home with him one night to try to replicate a dead-cold start... No problems. They thought it was sorted... Until the light came back on at my house two days later.

 

With all due respect, have you tried a Porsche approved plug? There is more to it than just a brand. Was the Beru a 14 FGR-6 KQU?

 

Hal, I appreciate your persistence. I double checked my notes.

The plugs that were installed initially were actually Bosch FGR5KQE-0. Purchased from FCP by the P.O: https://www.fcpeuro.com/products/por...kt#description

Pelican Parts does list this as the correct Bosch plug for my car?

This does appear slightly different than your note above though. As far as the plugs that were used in replacement, I don't know the exact model. I can find out.

I certainly am not willing to rule out anything but... Just thinking about probabilities here; even if the plugs were to blame, what are the odds that the exact same three cylinders have issues on two completely different sets of plugs? I'd love to be proven wrong, genuinely curious how this might work.

Also just one additional note, this car does have an X51 package so I'm not sure how that might affect a plug recommendation.

 

X51 is a great motor, but I don't think it is a direct factor. It seems to me that you have an impedance issue. The system is expecting X and it is getting Y. That is why you need to research the correct, Porsche Approved plug for your motor. Not just brand, but exact model of the plug.

Do you have the correct Owners Manual? The correct plug should be listed there. Otherwise, somewhere, someplace is a listing for the Porsche approved plug.

Before you throw more money at other problems, make sure it is not something as simple as the plugs.

 

Hal, thank you. I do have the owner manual and unfortunately nothing is listed for plugs. The websites I've checked show the Bosch plug that I had/have, but I will continue to research.

I do have some additional data points from further testing with my Durametric

- On a dead cold start, I couldn't get my Durametric hooked up fast enough but when I finally did it captured the following misses:

Cyl 1 - 10x
Cyl 2 - 1x
Cyl 3 - 1x
Cyl 4 - 1x
Cyl 5 - 8x
Cyl 6 - 1x

- Once the car is warmed up driving around, all six cylinders are about 99% perfect. However, Durametric will show random misfires on all six, maybe once every 8-10 minutes for each. Perhaps this is normal operation?

----

So as we discussed, Plugs (replaced twice) and Coils (Beru) are new and while I'm certainly not willing to completely rule them out, wondering what else might cause this?

- Can a Vacuum leak cause misses on cylinders on opposite banks when cold only, but no further symptoms?
- Does the fact that this happens badly to two cylinders when cold, but all six cylinders slightly, point to anything?
- Doesn't this rule out any grounding issues since it's clearly temperature related?

 

You must be doing something wrong.😜

Hope some of the forum folks with experience chime in with suggestions for you. It has got to be frustrating.

 

Suggest checking and cleaning your harness round connectors. Use some CRC followed by dielectric grease. Disconnect the battery neg cable first, to be ECU safe. Probably not the problem, but easy, quick and free to do. Also, as mentioned, the engine ground wire behind the pass wheel. On another vehicle i had a gremlin that turned out to be a corroded ground strap that looked fine but it wasn't.

 

These engines are not that sensitive when it comes to spark plugs. I use regular copper core Champions and don't have any misfire issues. They won't last as long as the exotic tipped ones but since I do all my repairs, I don't care. For lack of better terms, a plug is a plug as long as it's in the same heat range and same physical dimensions.