drb007

So I just spent a ton of $$$ and a weekend putting on new caps, rotors, wire, plugs, adjusting the valves, new coils, fuel, air and oil filters, new DME, to try to solve two problems. First, I was overdue on some of the maintenance things.
Second, it had been running poorly for a while. At cruising speed in any gear (ie, not under acceleration) it would stumble or miss. After all the work I just did, it still does it. What gives!?! What else could it be?
Any ideas?
Dave

C4Russ

Is the distributor belt in place? Are you getting spark in all twelve plug cables? Both coil cables? If you don't have one, go get a spark check device, I picked one up at Napa for $5. It's just an inductive pick up that is simply a small plate with an LED, much like a timing light.

How did the plugs look? Were they even in color and wear? Was any particular cylinder darker, more worn? How many miles on the engine? Any major work done, ever?

I forgot to ask: Last time fuel filter was changed? This sounds more like fuel starvation then lack of spark.

Indycam

Ground wires ?
Funny battery ?
Funny alternator ?

America

I had the same problem. My mechanic replaced everything and there was still a hesitation. After 4 months of the car being in his shop, I took it to a Porsche specialist. He found a cable that was reversed going to the distributor cap. It was going to a senor and it got fried. He replaced it and the car is runing fine 4 years later. Hope that helps.

RallyDogRacing

Does anyone have a quick, or verbose synopsis of all the vehicle main grounding points? Were this an Audi that's the first place I'd start, by finding all the majors and taking them apart, cleaning & de-oxidizing, and them re-assembling. I'm thinking allong the same lines as Indycam.

Can you take it for a ride and get it to do the stumble - then return home and pull the codes before shutting the engine down? Can this even be done sans-HAMMER?

dutchcrunch

just a tip, i had changed my cap and rotors with 17000 miles on them, on 1 cap the sparkplug connctor for #1 had a strange color to it. i ohmed all the wires but that particular on failed. removed cable end and found corroision. orderd new end and ohmed out perfect.

this failure was due to the clear coating that bosch sprays on the caps, i think its not supposed to be applied to the contacts but it happens. i know some of you think i am crazy but i had a hard time checking continuity on these used caps, seemed that when you push the wire onto the cap it scraped the clear coat off and makes contact, probably the wire that failed did not remove the coating.

the new one had this same problem on more than half of the top sparkplug wire connectors. i cleaned them of with acetone and you can clearly see the coating com off.
pacticular inside the cap at the contact where the rotors swings by.

next time you get some caps try to do a continuity test from outside the cap to the inside for each connector and see if it is not so.

so just because its new and its Bosch this is not right and could lead to missing.