[dave968]

Last time I drove my 968 at Roebling Road, my E class stock 968 was missing intermittently. During a 20 minute session, I could run at speed but intermittently the tach needle would bounce to near 0 then back to a normal engine RPM and the car hesitated for only a few secs. But on 2 cool down laps, the engine missed and stuttered badly, almost shutting down. Then next session ok with only the tach needle bouncing a few times and a few sec hesitation. I replaced the fuel DME relay, but it didn't help. The car starts fine, idles fine, I loaded it in the trailer and off the trailer at the end of the day without any missing.

Any ideas or suggestions.



Dave

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[flash]

wow - a missing engine? witchcraft? i've never seen an engine disappear before, and certainly never reappear afterward



seriously, check the coil wire - also, check the main ground on the battery

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[Cloud9...68]

Unfortunately, there are dozens of things that could cause this. Is your problem strongly temperature related? I had a similar problem several years ago, and it was very strongly correlated to temperature - on a hot day, after the engine had warmed up, it missed very badly, but on a cooler day, especially during the first fifteen minutes or so of running, it was fine. In my case, it turned out to be a bad set of spark plug wires. Good luck.

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[craigawoodman]

No steam? THen it is most likely not the water pump leaking onto the rotor, etc. Had this happen at a track day where the car did not run well (bu it didn't go to zero rpm). Did the tacho in the car go to zero rpm while the engine was still turning over?



Interesting if the tacho needle went to zero and the engine was still rotating as this would be different to the leads/plugs issue (more a position sensor or ECU/harness issue)?



Regards,



Craig

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[chudson]

Yo Dave968 - Craig is correct. As soon as the spark leaves the coil that is considered the "secondary" side of the ignition system and cannot affect the tachometer. Your hunt needs to be in the primary side of the ignition system which is everything except distributor cap, rotor, wires, and ignition (coil and spark plug) wires. Note: The ignition coil itself has both primary and secondary windings and could fail in such a manner as to cause this but VERY unlikely.

.....and in my secondary list I forgot to mention spark plugs - sorry

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[flash]

the tach dropping is exactly what led me to the coil - i was looking at either a dead short, or the hot lead being loose



more likely though a main ground

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[Eric_K]

I'd also would check the flywheel sensor and make sure the plug for it is tightly connected. The plug is on the back side of the intake manifold.

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[chudson]

Yeah, 968gene had an almost identical symptom on the track (his 944 track car) that we could never duplicate in the shop. The flywheel sensor cured his.

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[flash]

i've had my intake manifold off, and i sure don't remember any such plug

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[Eric_K]

Directly below the O2 sensor plug.



   

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[flash]

ah - ok - yeah - the bracket that holds it is connected to the manifold - got it

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[dave968]

yes, tach dropped quickly to zero and car lost power briefly while at speed on the track, lasted ?1-2 sec.

I talked to my mechanic, he will check the grounds and speed reference sensor.

Since Paragon sells an alternative Bosch non-Porsche speed reference sensor for $66 vs $169 for the Porsche Bosch speed reference sensor, I am going to have him replace the sensor.

Will let you know what he finds and when I get back on the track if the problem is resolved.

Thanks for all the comments.



Dave

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