Re: mechanics stumped

[paul rogers <perogers@ix.netcom.com>]

KSMITH1@mailgw.sanders.lmco.com wrote:

> Greg Woodard <gwoodard@ndsuext.nodak.edu> requested:
>
>      I really need help with this one.
>
>      1987 1.8 4cyl.
>
>      My son can start the car in the morning and drive it to school
> (15
>      miles)- no problem.  Start it after school and and drive it to
> work
>      (15 miles)- no problem.  Start it 2 hours later and drive it
> home- no
>      problem.
>
>      But if he drives around town, stop and go driving, lets it idle
> for a
>      few minutes.  It will start to miss.  He can limp it home, but it
>
>      takes over 1/8 of a tank of gas (14miles).   You can smell raw
> gas
>      almost running out of the exhaust.  The plugs will be completely
>      black.  If we clean the plugs and leave it sit overnight, he can
>      drive to school- no problem.
>
>      We have replaced nearly everything with known good (ie borrowed
> from
>      my 1.8).  I'm stumped, my sons stumped and several mechanics are
>      stumped.  The car is getting really close to the crusher, would
> be
>      now except that my son really likes the car.
>
>      HELP
>
> OK, since I have never seen this engine, I feel eminently qualified to
>
> guess at your problem.  I'm assuming it has a Motronic injection
> system that controls the duty cycle of the injectors.  I also assume
> that the distinguishing difference between "normal" driving and idling
>
> about town is the decreased natural air flow through the radiator and
> engine compartment.  This is usually mitigated by the radiator fan.
> Are you sure the fan works when the coolant temperature rises?  If so,
>
> perhaps the engine compartment temperature rises anyway, and causes
> some electronic part (a transistor comes to mind) to have high
> leakage, stay on, and cause 100% injector duty cycle.  An oscilloscope
>
> on the injector drive would be revealing, perhaps.  Ignore this if
> anyone who seems to know responds.
>
> ***                 ...Kirby    (Kirby A. Smith)                 ***
> ***                      2 X 1988 90q                            ***
> ***              ksmith1@mailgw.sanders.lmco.com                 ***
> ***              [=]   kirby.a.smith@lmco.com                    ***
> ***  Opinions expressed herein are entirely those of the author. ***

   Greg,
     My feelings are that you probably should look into the water
temperature sensor
for the F.I control system. A two prong electrical sensor located in the
upper water
neck on the side of the head, if the sensor is in open cycle, the engine
will continue as
if trying to choke the engine during the warm-up, thus fouling the plugs
and flooding the
engine.