Engine stumbling/misfiring/check engine light!

[itzbob46]

My 2001 Boxster was stored for the winter and before I took it out of storage I put in a set of original type Beru spark plugs. The job went OK except that reconnecting the wiring harness to the coils was somewhat troublesome on several cylinders. This was the first plug change at 36K.

I drove the car over 3 days and it ran as good, or better, than ever. All mild driving. All of a sudden the engine started to shudder and the check engine light came on. After a quick roadside exam I was fairly convinced that I had a misfire condition as a result of one of the coil wiring connections slipping off. My logic says that this has something to do with my spark plug change. No damp or rainy weather involved.

The car will run at an idle but somewhat unsteady. It definitely stumbled and shuttered when accelerating but would cruise at 3000 rpm fairly well so I drove it the 3-4 miles home. No smoke of any kind. Once home I got under there and rechecked the wiring boots on the coils…….to my disappointment they were solidly in place.

Now I’m worried. I don’t have a OBD11 meter. I don’t know if an ordinary meter would tell me which cylinder was misfiring, so perhaps I need an expensive Porsche specific one to tell me that.

I can pull all of the coils and spark plugs and look for a problem, but unless the problem is visual, I don’t know how to diagnose it.

Any advice would be appreciated.

Thanks,

Bob

Ps Oh….and get this. While it was in storage, I bought a 3 yr extended warrantee WHICH HAS A 1000 MILE WAITING PERIOD. What I dope I was to be honest with them about the miles!!!

[RFM]

It's difficult to diagnose the problem without a reader, but most of the errors after a spark plug replacement are not well checked spark plug gaps (one of the 3 mass electrodes too close or against the central electrode), not well checked coils (fine cracks) and coil connectors (bad contact).

[Steve Tinker]

itzbob, I guess you could replace the new plugs with your originals & see if the misfire is still present. At the same time you can inspect the coilsfor cracking. I know its a pain, but at least you are isolating the fault.

[itzbob46]

Seems odd that the car was perfect for parhaps 50 miles and then failed instantly. What happens if coils have cracks? Where are these cracks? Rechecking the plugs is a time consuming step, but I may have to do this. However, if the flaw of one plug is not visually obvious, I dont want to change them all as then I have no knowledge which one it was. Then what?

[Glyn]

This would point to a connection not being fully engaged on the wiring.

The clips on the coil connection are a real pain, disconnect the coils electrical connections and re do it, push until you hear a faint click.

I think the connections were made and so normal running but one or two have become detached through not being properly locked in.

It is possible one of the new plugs are faulty and breaking down under load though not very likely

[itzbob46]

This would point to a connection not being fully engaged on the wiring.

The clips on the coil connection are a real pain, disconnect the coils electrical connections and re do it, push until you hear a faint click.

I think the connections were made and so normal running but one or two have become detached through not being properly locked in.

It is possible one of the new plugs are faulty and breaking down under load though not very likely

As I said when I started the thread, I did check the wiring connections and they were firmly attached. However, as you said they are a PITA, so I did not disconnect and reconnect them. I guess I have to. And maybe get a look at those coils while I'm at it. I really doube that the plugs "gave out" at 50 miles.

Thanks.

Does anyone have a coil checking method for me??????

[wvicary]

I will echo the comments about rechecking the coil connections.

[itzbob46]

Borrowed an OBDII meter and it said misfire on #4. Sure enough, even though I checked each wire-coil connection before, it actually was loose. # 4 is the hardest plug to reach due to location and obstructions. It took me a half hour to get that thing to click into place, but it's done and I'm now enjoying a La Fin Du Monde ale (our Canadian readers will know about that....9% alc.) in celebration.

Thanks, guys for your advice and logical approach. I really felt that was it, but after checking each connection the day that it occured, I thought I ruled out the wiring connections. The OBDII allowed me to be certain it was a misfire and where it was, so I didn't have to screw around with each connection.

Nice meter for $139. I'd buy one if it did ALL Porsche stuff and my daily driver wasn't a 1995 (pre-OBDII)!

Bob