Date: Thu, 13 Jan 2011 11:29:28 -0800
Reply-To: Scott Daniel - Turbovans <scottdaniel@TURBOVANS.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Scott Daniel - Turbovans <scottdaniel@TURBOVANS.COM>
Subject: Re: Strange problem in Belize
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Vaccum is used to pul fuel into the engine on carbureted engines.
In port fuel injection, which vanagons use, the fuel is sprayed into the
intake port right in front of the intake valves ....it's pressurized, and
the 'open time', in milliseconds, of the injector is controlled by the ecu.
your right ....it's always good to check compression ...'just in case.'
also ....intake leaks... Not likely intake leaks are keeping this engine
from starting ..
( btw ...
you'd be surprised how much a cracked air intake boot can look like all
kinds of other problems ! ..
the boot is perhaps all grimy .....the bottom of it is hard to see ....often
the crack doesn't 'open' until the engine moves a little under power ..can
be maddening ..unless you know to look for it. Doesn't happen very often
....I see a cracked intake boot on one out of hundred vanagons ...but you
always need to check for that. )
an engine is really an air pump.
pistons moving down draw air in through the open intake valves, through, and
past, the throttle plate.
Bascially ...it's drawing air in, and pumping it out the exhaust.
Fuel is added, and igntited by spark plugs at the right time to cause
explosions that drive the pistons down, turning the crank, and thus turning
the wheel via the transmission..
meanwhile...one one piston is doing that ..
other pistons are in other phases of the 4 stroke cycle ..so they all
overlap, smoothing things out.
It's both genious and crude. < I like to say that an airliner up in the
sky, at 30,000 feet going 560 mph is just a 'very evolved campfire'
..............and it is just burning carbon based fuel..whether from refined
crude oil or wood. >
how open the throttle plate is determines how easily air is drawn in .
here's the fun part ..
the ecu reads various things ........it reads how much air is flowing via
the flapper in the air flow meter. It knows the temp of the air and of the
coolant. It knows that the engine is turning ( from the distributor
pulses ) and how fast the engine is turnign ( rpm ). It then decides how
long to hold the injectors open to put the right amount of fuel into make
the engine go and produce power properly.
it also happens to know when the engine is at idle ......from the thottle
swithc.
It also knows when the engine is a WOT from the throttle switch .
There is a 'fine tuning' aspect from the oxygen sensor ...the ecu gets
feedback information to find tune mixture. It can run quite well without
that input if it needs to.
also ..in order for injector open time to really provide the right amount
of fuel for a given load and rpm ...the fuel pressure needs to be right (
regulated by fuel pressure regulator of course ) ..injector spray pattern
has to be fairly decent ..injectors can't leak...fuel pump, fuel filter, and
fuel pick up from the tank all have to be pretty right. And the ecu is what
controls when the fuel pump is energized and thus when the fuel pump runs.
there's more ...
but really ....a fun system, not that hard really to tell what's missing if
you ..two things..
crasp the basic nature of how it works...
AND ..most importantly ..have Some Way to tell what is missing, or what is
not right.
If you don't have those two things ....basic understanding and what to look
for ..
and how to tell what's missing ..like some basic test equipment,
without those two things ..
even professional shops that are really faking it are left with 'throwing
parts at the problem.'
that's a terribly expensive and ineffecient way to fix a car !
there are a few times where there is no easy way to test something. I like
to have say 5 reasons why I believe a given component isn't working, then
I'm pretty sure that part is needed.
the value of having known-good components to try can't be overstated.
For a no-start ...
I just love this trick ...I grab my spare distributor, I remove the
connector from the side of the dist on the engine ...I plug mine in ...turn
on the key, then turn the dist with my fingers.
the first thing that should happen is each time the dist is turned..the
fuel pump will run a few seconds.
next..if doing a basic test for igntion ....remove coil wire from center of
dist and arrange it near ground ..
watch for a fat preferribly blue spark.
if those two things work ...then hang two injectors out ( plug the coil
wire back into the distributor cap !!!! ...must be hyper careful at ALL
TIMES to never get loose fuel spraying around and loose sparks jumping
...man does gas ignite easily if it can ! ..keep two fire extinquishers
handy, and NEVER get loose fuel and loose sparks going at the same time !! )
..
ok...so then you're watching injectors spray fuel .......
if those spray ...great. Means there's fuel pressure, and the ecu is firing
the injectors.
last...
put fuel injectors back in place..( ! ! ! ! )
and pull a spark plug or two, ground them..
and watch for good sparks jumping acorss the elctrodes.
if it does all that it should with turning a known-good distributor with
your fingers and key on ..
that's fuel pump energizes,
injectors spray,
spark plugs spark across the electrodes,
it will run with your known good distributor installed, and timing set
rougly correctly ..
that is if there are no intake leaks, and there's compression.
a no-start is a lot easier to fix generally, then not running completely
correctly.
Plus it's so rewarding to go from 'dead' to 'she's alive !'
have fun, do good work..
and ..as always ..
don't think 'component' ...thing inspection and diagnosis, and smart
diagnosis starts with understanding how the thing works.
To me it's not so rewarding that it runs again becuase I swapped a few parts
..
I want to master the thing and be smarter than it is. That's rewarding to
me.
oh yeah...NOID light.
a noid light tells you in 2 seconds if the ecu is firing the injectors.
I wouldn't leave home without one, a spare igntion swithch and a remote
starter switch.
all trouble shooting on the engine should be done with a remote starter
switch connected.
and try not to think 'what component is not working' ...sometimes it IS a
compoenent. ..
I don't find that it is usually really ...it's a blockage or a leakage of
fluids or electrons . sometimes it's just a poor conennector or two, or an
adjustment or two. Typically 4 half-not right things and one pretty really
not right thing.
scott
www.turbovans.com
----- Original Message -----
From: "john" <mreid157@XPLORNET.COM>
To: <vanagon@GERRY.VANAGON.COM>
Sent: Thursday, January 13, 2011 6:17 AM
Subject: Strange problem in Belize
> Hi Ken,
>
> What comes to mind is the motor is not generating enough vacuum
> to pull the fuel in.
>
> When you pinch the return you create such a rich environment is gets
> enough
> fuel to run.
>
>
>
> As you know this has to be caused by a mechanical fault of some kind.
> Valve
> timing is the most common.
>
>
>
> Try the old rag trick in the spark plug hole and see if it blows out.
>
>
>
> Good luck and I'll be watching your results.
>
>
>
> John
