Listers -
Since the big fires here in San Diego I had a little time off and could
devote some time to figure out what my intermittent miss/backfire was. I
figured, since we werent in any immediate danger (the fires were basically
burning all around us) I might as well do something to take my mind off of
all the destruction etc. This was on my daily driver V6 Spitfire (throttle
body FI) that I was going to take to Triumphest in Laughlin, but due to
this several month long, on-going problem, I had to resort to the 1970
Spitfire backup vehicle.
The problem as it were, was that the car would miss/jerk at random times
while driving around. One would never know when this would happen, but
usually once a day on some occasions, several times, it would
misfire/backfire. Usually at speed, more often than not when just
accelerating, but I could never just get it to do it on demand so to speak.
It would do this then drive for many miles before it would happen again.
After going through the entire electrical system, systematically replacing
every component (fuel pump, sensors, injectors, coil, plugs, wires, dist,
modules not necessary in that order, but you name it I replaced it etc),
and after cleaning the air filter, replacing the fuel filter checking the
pump pressure fuel lines blah blah blah, and still having no luck I was at
my wits end. Then, just after I had replaced the throttle body and was
watching the idle spray I got a misfire (this was the first time I had
actually SEEN it happen, not just felt it). This got me thinking about the
number three plug that looked just a little different than all the rest,
since it was on the intake log of that bank, and I decided to check the
valves - Sure enough, the exhaust valve had basically no clearance, and the
intake was minimal, probably around .006-8 thou. EUEKA!!! Problem solved!
It didnt show up in the compression check because there was just enough
valve closure so that at cranking speed I still had compression (a little
low, but not out of the ordinary) and apparently would have to bounce just
enough, and at the right time, to ignite the incoming mixture and shoot the
flame back up the intake track which is what I saw.
As usual, I figured it was electrical because it was so random, but it just
goes to show you, not all random problems are electrical or fuel related -
they CAN be mechanical! Frustrating to say the least, but sure nice to
have the problem fixed.
So now I have my Spitfire back (I ran in to the house, after I discovered
the problem, and did the little victory dance that my wife found most
amusing).
The fires are becoming more under control, and most people are getting back
to their homes, at least those that have homes to return to and things
are slowly returning to normal!
So I had my victory brew (a Carl Strauss Amber Lager) whilst cleaning the
car of ash and soot, (yeah, it even gets inside the garage) and am now
able to install the new molded carpeting I had purchased but was not ready,
or felt like installing, and can start doing the fun stuff for the
vehicles!!
Barry Schwartz
San Diego (La Mesa) CA
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