Date: Tue, 15 Feb 2005 08:32:23 -0800
Reply-To: Craig Oda <craigoda@GMAIL.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Craig Oda <craigoda@GMAIL.COM>
Subject: Re: Boston Bob Big Valve Update? Not really... (LONG)
In-Reply-To: <421212C9.9040205@adelphia.net>
Content-Type: text/plain; charset=US-ASCII
Marc,
I don't have detailed technical knowledge, but I've had an 83
waterboxer for 4 years and have had to nurse it regularly for most of
that time. I believe that many drivability problems are caused by
incorrect fuel/air mixture. There are several switches, sensors, and
hoses that affect fuel/air mixture. Many of them go bad over time and
I've swapped many of them.
Two things seem to go wrong pretty often and then cause a cascading
series of problems:
- O2 sensor goes bad
* which results in a lean signal getting sent to the ECU,
* which results in more fuel being dumped into the system,
* which causes the system to get rich, which further damages
the O2 sensor
- spring on AFM gets weakened by age
* which I THINK results in a lean engine (might cause richness)
The problem is made worse because people generally try to pop open the
AFM and adjust the spring tension themselves and it is often not set
properly. This makes things more difficult later. Prior to
isolating the problem, people often look for vacuum leaks (there might
be some, but these are usually easy to find and plug if they exist),
low fuel pressure (possible, but not as likely if the engine is
running) and various temp sensors and throttle position switches.
I finally managed to isolate my problem and set the AFM properly by
splicing a wire into the O2 sensor and connecting it to a digital
voltmeter on my dash. I can now monitor basic air/fuel conditions
while driving. I have another T connector so that I can measure the
O2 sensor output while I have my head in the engine bay. Here are
some of my thoughts:
- O2 sensor must be disconnected from the ECU
- wait for the O2 sensor to get nice and hot (at least 3 minutes)
- use a new or known good O2 sensor for the measurement (not your
suspected bad one) and AFM calibration
- voltage should hover around 0.45VDC
- use white paint or something to mark the original position of the
spring wheel inside the AFM. Make sure you do this in case you need
to set the position back.
In my case, I also took apart and cleaned my entire air intake system
and checked for leaks. I don't think you need to do this. At one
time, I suspected I had a vacuum leak. I now believe that there were
never any vacuum leaks.
Also, in my case, the fuel pressure regulator did go bad resulting in
low fuel pressure. I believe that this was an unrelated problem and
rare. My fuel pressure problem was intermittent. I believe this is
an ununsual form of regulator failure and I don't know what was
causing it. I was able to diagnose the problem by tapping an
electronic fuel pressure sender into my system and putting a pressure
gauge on my dash. I believe that if I didn't have the gauge in, I
still would have been able to isolate the problem when the regulator
would eventually fail completely.
Good luck. My van is now my daily driver every day to work. Though,
I suspect that its days are numbered with the changes CA emissions
testing and that this might be the last year I have it.
Regards,
Craig
On Tue, 15 Feb 2005 10:18:33 -0500, Marc Perdue <marcperdue@adelphia.net> wrote:
> When my van first started doing the lost power thing a couple of years
> ago, I was on my way home and couldn't make it up a hill. I pulled over
> to the side, disconnected the O2 sensor and it ran fine the rest of the
> way home. My catalytic converter went bad some time after that,
> probably a result of the old O2 sensor rusting clean off, and when I
> replaced it I replaced the O2 sensor too. I still would occasionally
> lose power and disconnecting the O2 sensor didn't seem to affect it
> anymore. Go figure.
>
> When the problem occurred down in Salem, we also tried disconnecting the
> O2 sensor, with no change.
>
> Haven't tried disconnecting the idle stabilizer valve yet, but will try
> that next time it happens.
>
> Bob D., the mileage was high at first, but now it's not. And now I not
> only get what I take to be the "normal" VW burnt rubber smell, but the
> exhaust smells rich with unburned gasoline. The engine seems to have
> most issues when running below 1200-1400 RPMs. If I can get it over
> that speed, the engine perks up and will run okay, though it still
> occasionally feels like I've turned the ignition off when I'm driving
> along, just for a second or so . . . When I turn it on first thing in
> the morning, it will idle kind of roughly at about 900 RPMs for a while
> then jump up to 1100-1200 for a few seconds, then drop back down. Oy!
>
> I've got a spare AFM (don't ask) that I'm going to swap into the van and
> I'll check the timing too. Then, well, we'll see . . . If I don't get
> this fixed by May, I might do something different. I'm going to a banjo
> camp in Groton, MA, the second week of May. I was going to fly up and
> rent a car, but I might consider driving up and spending a day in
> Boston, Bob, if you'd be up for that on the 11th or 12th . . .
>
> Thanks all,
> Marc
>
> Bob Stevens wrote:
>
> >Different engine, but very similar symptoms on mine one time on a long hiway
> >trip. I stopped, disconnected the O2 sensor, and it ran just fine from there
> >on. I reconnected it a week later and it's operated just fine since, but
> >that was the variable that made the difference when I lost power at speed,
> >and the more I pressed the accelerator, the slower it wanted to go, until
> >the O2 disconnect.
> >
> >bob
> >
> >
>
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