Date: Sun, 23 Jul 2000 14:29:33 -0500
Reply-To: Tim Wise <wise@hyperformix.com>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Tim Wise <wise@hyperformix.com>
Subject: Re: High altitude power loss
In-Reply-To: <003701bff4d8$559f9be0$664f0a3f@pavilion>
Content-Type: text/plain; charset="iso-8859-1"
Thanks, Joel!
I just did my basic tune up (oil change and filter, plugs, rotor, cap,
belts, air filter). Didn't smell any gas in the the oil. So I don't
think #4 is the problem.
I've had this happen one other time on a trip. Ran downhill first thing
in the morning for a long way. As soon as we flattened out and I had to
use the engine, it started spewing black smoke out the back and runnning
rough, like it was too rich. I pulled off the road and let it settle
down (maybe turned off the engine, I can't remember) and the problem
went away.
I like #1 because (it's easy to fix ;) it doesn't happen all the time
and I probably have my foot on the pedal running downhill, both resting
and giving it a little gas on the flat sections.
#3 is a possiblity. After the tune up, I fired up the engine and heard a
sucking sound. It's not real loud and I can't locate the source (I need
to find out where the air flow meter is). I nudged all the air cleaner
and inject stuff and was able to change the idle speed of the engine,
but nothing definitive. We did, however, run many miles on bumpy dirt
forest roads on the trip and never had a problem, so maybe #3 is not the
problem.
Thanks again. Heading out to the FL Keys this week which will be very
flat so we probably won't encounter this problem, but others... ;)
> -----Original Message-----
> From: Joel Walker [mailto:jwalker17@earthlink.net]
> Sent: Sunday, July 23, 2000 2:01 PM
> To: Tim Wise
> Subject: Re: High altitude power loss
>
>
> > After driving a long downhill, where the engine was not really doing
> > much but idling, then starting up a climb, then engine would have a
> > serious power loss, to where I had to pull over to the side of the
> road.
> > Revving the engine, it sounded like it was missing, not running on
> all
> > cylinders, or just not getting the right fuel/air mixture.
> > In both cases, turning off the engine and restarting it cured the
> > problem. Seems like the ECU got out of wack and restarting it caused
> it
> > to reset and function correctly.
>
> there are a few suspects ...
> 1. your foot. if you did NOT take your foot completely off the pedal,
> then the computer is trying like crazy to make sense of the rpm, your
> throttle setting, and the temperature sensors, and all the while
> trying to figure out what the oxygen sensor is telling it. trouble is,
> going downhill, doesn't require much fuel ... BUT! with the pedal
> slightly pressed, the injectors ARE still squirting. and probably a
> lot of that fuel isn't getting burned, but going out the tailpipe
> ...which confuses the oxygen sensor, who confuses the ECU. what is
> supposed to happen is that when you take your foot OFF the pedal, the
> little microswitch tells the idle stabilizer to tell the computer to
> quit telling the injectors to squirt gas. so the fuel flow to the
> engine is completely shut off. this was to lower emissions going
> downhill and when coasting to a stop (like taking an exit ramp off the
> interstate, where your foot is on the brake, not on the gas).
>
> anyway, this could have 'loaded up' the engine: made the mixture way
> too rich (too much fuel for the amount of air coming in. and at
> altitude, there's less air anyway) and gotten the computer very
> confused. you said it happened only twice, so that makes me think that
> probably you just were relaxing/resting your foot on the gas pedal and
> didn't realize it. or were trying to keep up a little speed but didn't
> need to all the time, due to curves or traffic. if it has not happened
> again since you got home, this would be my guess.
>
> 2. the little microswitch on the throttle. the thing that tells the
> idle stabilizer to tell the computer that your foot is (a) completely
> off the gas pedal, so the computer can stop squirting fuel (until the
> rpm drops below 1500 ... where it assumes that you are coming to a
> stop and starts squirting again), or (b) you've mashed the pedal all
> the way to the floor and the mixture needs to be richened a bit for
> full speed. this switch could be misadjusted a bit, or wearing out.
> maybe. but if so, it should do this all the time, and even give you
> some bad running symptoms in town.
>
> 3. possibly the rubber boot on the airflow meter. might have a crackin
> it, or be loose on the airflow meter, and downhills could vibrate it
> enough to make it open up and suck some air into the system, which
> would confuse the oxygen sensor (mixture at the sensor isn't what it's
> supposed to be). maybe. long shot. cause if this was doing it on a
> downhill, it should do it at other times of high vibration, like bumpy
> roads, or city streets, and so forth.
>
> 4. leaking fuel injector. could be loading up the engine, when it's
> supposed to be shut off (by the computer). if you check the engine oil
> dipstick, and sniff it, and smell strong gasoline smell, this is a
> likely suspect. the extra fuel also gets past the piston rings and
> into the crankcase oil. it also goes out the tailpipe, confusing the
> oxygen sensor, etc., etc. but again, this should cause problems
> elsewhere and more often.
>
> so my guess would be #1. but i'd change the oil anyway, just to get
> any fuel that might be in there after the trip. if it only happened
> twice, then any fuel that got into the oil SHOULD have been evaporated
> by the time you got home. but an oil change never hurts. ;)
>
> hope it helps. good luck!
> joel
>
> s
>
| 
