[s-cars] Reading Spark Plugs / WOT stumble, miss / dropped cylinder

Manuel Sanchez manuelsanchez at starpower.net
Mon Feb 9 05:59:36 PST 2009


Yes I was thinking the same thing (but hoping it was/is something  
else). I have 034's High Output coil system, which I had hoped would  
solve any coil & POS problems for years to come. The system only has  
about 4,000 miles on it.

In my attempt to investigate the stumble / miss under load I decided  
to inspect the plugs among other things (all plugs have the same  
deposits (at least it's consistent). I found a few images on-line for  
plugs, but my increasingly failing memory recalls that my old Toyota  
manual had about 16 or so images of different residue conditions. It  
went down into the detail level of describing if there was a little  
too much timing advance or a little too much fuel, etc...  Closest  
thing I've found on-line was some dragster discussion:


although I'm not sure if it's applicable to "non" dragster fueled  
beasts, but somehow think the principles would be the same. I was  
curious about the color as I had a few "yellow" specs on the  
grounding straps of the plug and I was curious to find out what that  
meant (still not sure). It's hard to see in the photo's(it's actually  
not visible in the photo's), so I found it curious. Maybe my car is  
producing GOLD! Mr Baloney will be happy to hear that. The ceramic  
had a "pink" color which I haven't found a reference to yet. See them  



Anyway, after I inspected and "fixed" things I went on a 40 min  
highway drive to Baltimore and I dropped a cylinder as soon as I  
parked. I love it when I "fix" things this way (from bad to worse). I  
found the dropped cylinder by unplugging the injector leads one at a  
time. Trying the easy thing first I moved the ignition cable of the  
dropped cylinder to a working one and the dropped cylinder moved with  
the cable. So seemingly I've got an easy fix (he says under his  
breath so the Audi gods don't hear).

Now I'm curious about the health of the other cables. I checked for  
resistance in all of them and this is what I found:

Multimeter set to 200k

Ignition Wire 1 - 40 ohms (wire length = 17-1/2 inches)
Ignition Wire 2 - 75 ohms / 52 ohms (wire length = 12-1/2 inches)***
Ignition Wire 3 - 84 ohms (wire length = 20 inches)
Ignition Wire 4 - 50 ohms (wire length = 7 inches)
Ignition Wire 5 - 79 ohms (wire length = 7 inches)

***Interestingly, before the cylinder dropped (when I was  
experiencing just a burp/stutter/stumble at WOT) this wire read 75  
ohms of resistance but once the cylinder dropped, this wire read 52  
ohms of resistance. I'm not sure why.

I'm not sure what the resistance measurements are supposed to be for  
these cables from 034, but I've sent them an email in hopes of  
finding out.



On Feb 9, 2009, at 1:01 AM, Robert Myers wrote:

> Manny,
> Might the failure you are calling a stumble be a miss in one  
> cylinder? Your description sounds like that to me. If so, the usual  
> cause for a miss under boost is a failing coil. What ignition  
> system are you running? OEM? Other? Either way you can identify the  
> bad coil by disconnection one injector at a a time and going for a  
> short high boost drive. If the disconnected cylinder is the one  
> with the miss then the (now full-time miss) will not get worse  
> under boost. If it does get worse under boost then go to the next  
> cylinder until you find the one which doesn't get worse at boost.  
> Replace that coil.
> Bob
> At 12:36 AM 2/9/2009, you wrote:
>>  A quick search of teh internetz shows:
>> http://www.ngksparkplugs.com/techinfo/spark_plugs/faq/faqread2.asp
>> Hope that helps ya.
>> Harold
>> > Subject: [s-cars] Reading Spark Plugs
>> > To: Scar <s-car-list at audifans.com>
>> > Message-ID: <313CDA5A-B999-4AB6-A802-6C93FBA96975 at starpower.net>
>> > Content-Type: text/plain; charset=US-ASCII; delsp=yes;  
>> format=flowed
>> >
>> > Fellow S-Heads,
>> >
>> > Anyone have a good link to color photo's that would help explain  
>> how
>> > to read the deposits on spark plugs?
>> >
>> > I used to have a nice print from an old Toyota service manual,  
>> but I
>> > can't find it. It was pretty useful in that it explained all the
>> > colors variations in color pictures.
>> >
>> > Audi content is that I've developed a stumble, burrrrp, under WOT
>> > (again- - - -sigh).
>> >
>> > Thanks.
>> >
>> > -Manny
>> >
>> > 95.5 urS6 Avant (mostly RS2'd)
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