Date:         Tue, 1 Feb 2005 23:28:03 -0500
Reply-To:     "Daniel L. Katz" <katzd54@YAHOO.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         "Daniel L. Katz" <katzd54@YAHOO.COM>
Subject:      Re: Low Compression after Spark Plug Incident

james:

after reading some of the dire replies, i would suggest taking a break,
and not jumping to hasty conclusions. make sure all four plugs are clean,
properly gapped, and torqued to about 20 ft-lb, and that all four plug
wires are good, and connected in the correct order. a bad wire will show
up most on hard acceleration, as will a fouled plug, or, for that matter,
shorting inside of a wet or dirty distributor cap.

the broken plug is suspicious, and it would definitely make sense to check
that ignition timing is correct.

sometimes plug wires test ok in a static test of DC resistance, but will
show internal breaks if flexed while observing an analog meter. also, it
might be possible to spot arcing between plug wires/boots and the engine,
or maybe a blue glow around wires. in the dark, especially under a load
(thus simulating hard acceleration).

does compression in supposidly bad cylinder improve a lot by first
squirting in a tablespoon or so of motor oil? if so, rings at issue,
valves probably ok. if not, valve(s) not sealing, but rings may be ok.
also, vacuum guage, easy and inexpensive, will confirm bad cylinder
(though not tell you which one), and tell a lot about condition of valves.

in any case, there are tons of possibilities here. i cannot recommend too
strongly using a vacuum guage to help diagnose the problem. sticking
valves, worn valve guides, overall compression, valve timing, a single bad
cylinder, and more, can be cleverly diagnosed with this tool.

dan

On Mon, 31 Jan 2005 13:22:39 -0800, James V <tornadored@EARTHLINK.NET>
wrote:

>Recently, I posted regarding a problem where my van suddenly lost power
and
>I found that one of my spark plugs (#2) had broken (topic: "Broken Spark
>Plug Electrode/Tip").  After receiving some kind advice from the list, I
>simply replaced the plug and hoped for the best.  But after replacing, the
>van was still running poorly, with low power particularly on acceleration,
>as if that cylinder was not running right (it was firing).
>
>After some obligatory useless fiddling, I ended up taking it to the shop,
>which found that compression on the #4 cylinder was very low, while it was
>good on the others, including the #2 which had the fried plug.  The van
was
>running fine before the spark plug incident.  So, strangely to me, it
seems
>that the spark plug incident on the #2 cylinder caused the problem I'm now
>having w/ the #4.
>
>Is this possible?  Any ideas?
>
>Thanks,
>
>James V
>90 Carat