new 240 queston

New problem with my '91 240. At first I thought this was a water in
the gas problem but now that I've run a couple of tanks of "good " gas
and 4 bottles of "drier" through the car I'm beginning to think it's
something else. Yesterday I did a 50 mile drive and for the last 20
or so ran the AC. As I was going down an exit ramp off the highway
the car started missing and backfiring. I made it to a store and let
it sit there for a half hour or so. When I tried to restart it it ran
great but I took it to a garage nearby. The mechanic did a cursory
check and said he couldn't determine anything wrong. The engine was
fine. Drove back home (another 50 or so) with no further problems.
Today I've run several short errands and then later in the day did sit
(while waiting on someone) with the car running and the AC on for
maybe 15 minutes. When I went to leave it ran fine for a couple of
minutes and then starting bogging down and missing again. Died in
traffic but I coasted into a lot where I sat with the engine off for a
couple of minutes then it restarted and ran great the rest of the way
home. (10 minutes)

I don't know if this is related to the extra pull on the engine while
running the AC or it's something unrelated. Any ideas?

Thanks.

 

When was the fuel filter last replaced? I just had mine done (as far as
I know, the first time in the car's lifetime of 20 years) and it runs
astonishingly better.

 

Try removing the gas cap after you've driven for a while, if there's a
WHOOSH of air entering the tank you may have a plugged vent.

Is the Check Engine light on? Your car has onboard diagnostics for both
the fuel and ignition systems that should store fault codes in the event
of something like this.