Intake air sensor issues!!!- '77 Campmobile

Ok, I threw a question out there a while ago regarding my '77 Campmobile.
It would start, but would soon quit again. If I pressed the gas pedal, it
would die immediately. Well, after checking, testing, & all that over &
over, I came up with nothing. Then suddenly, it occurred to me. An air
problem? Disconnect the wires from the intake air sensor!! I did that &
I'll be damned. It worked! The beast fired right up! Now, do I replace it?
Can I repair it? What happens if I cruise around with it disconnected? If I
do replace it, does anybody have a line on where I could come up with an
inexpensive one? Does anybody have one I could buy for cheap? Any help
will be greatly appreciated I assure you.

arthurp wrote:

> Ok, I threw a question out there a while ago regarding my '77 Campmobile.
> It would start, but would soon quit again. If I pressed the gas pedal, it
> would die immediately. Well, after checking, testing, & all that over &
> over, I came up with nothing. Then suddenly, it occurred to me. An air
> problem? Disconnect the wires from the intake air sensor!! I did that &
> I'll be damned. It worked! The beast fired right up! Now, do I replace it?
> Can I repair it? What happens if I cruise around with it disconnected? If I
> do replace it, does anybody have a line on where I could come up with an
> inexpensive one? Does anybody have one I could buy for cheap? Any help
> will be greatly appreciated I assure you.
>

You pulled the plug off the air-flow sensor box? That will prevent
the fuel pump from running after the starter stops cranking.
Often, the engine *will* run for a while like that on the residual
pressure in the fuel ring. But don't expect to drive it:-)

Rare for anything serious to go wrong with the air-flow sensor,
but you might pull the air cleaner box off and see if the vane
moves freely. Once in a while they will get jammed due to a backfire.

Speedy Jim
http://www.nls.net/mp/volks/

Usually when an airflow sensor starts to fail it results in a flat spot at
cruising speed, where you'll be cruising along at say, 50mph on flat road
with no headwind and the engine will just die. You give it throttle or back
off the throttle and the engine is running again. That and the "stuck vane"
from a backfire that Jim mentioned. I missed your original post
apparently... The most common things to go wrong on your bus engine (fuel
injection related) are #1 Vacuum leaks. These are USUALLY caused by the
large pre-formed hoses being brittle and actually falling off or being blown
loose by a backfire. They are hard to detect because they appear to be
attached when they in fact aren't. They also tend to break and the ones down
in the hot spots actually fall apart. Often a bus with FI will stall after
crossing railroad tracks and fail to start again. It's usually one of the
big vacuum hoses attached to the big black "S" hose between the throttle
body and the airflow sensor. There are other large vacuum hoses buried down
below all the wiring harness lying on top of the engine.
#2 is the head temp sensor circuit attached near the #3 cylinder spark plug.
It should have about 2400 ohms resistance at about 70 degrees farenheit. If
your engine is belching black smoke, this is usually the culprit. The '77
model had a throttle position switch attached to the throttle body. Those
commonly lost a screw and just hung there.
Why it ran when the airflow sensor was disconnected? Strange. As Jim said
the fuel pump should not run when the airflow meter is disconnected. Now
there is something else that goes wrong with these beasts that is very
confusing and that is the double relay. That is what actually sends power to
the fuel pump and the fuel injection system in conjunction with the resistor
pack right next to it. It is not uncommon for the plugs on the double relay
to come loose or become corroded if the bus is not driven regularly.
A description of what happened when it stopped running would be helpful to
diagnosis.
Trust me on the vacuum lines being #1 cause! A lot of these buses have been
given away or sold cheap because a vacuum line came loose!
-BaH
"arthurp" > wrote in message
lkaboutautos.com...
> Ok, I threw a question out there a while ago regarding my '77 Campmobile.
> It would start, but would soon quit again. If I pressed the gas pedal, it
> would die immediately. Well, after checking, testing, & all that over &
> over, I came up with nothing. Then suddenly, it occurred to me. An air
> problem? Disconnect the wires from the intake air sensor!! I did that &
> I'll be damned. It worked! The beast fired right up! Now, do I replace it?
> Can I repair it? What happens if I cruise around with it disconnected? If
I
> do replace it, does anybody have a line on where I could come up with an
> inexpensive one? Does anybody have one I could buy for cheap? Any help
> will be greatly appreciated I assure you.
>

"arthurp" > wrote in message
lkaboutautos.com...
> Ok, I threw a question out there a while ago regarding my '77 Campmobile.
> It would start, but would soon quit again. If I pressed the gas pedal, it
> would die immediately. Well, after checking, testing, & all that over &
> over, I came up with nothing. Then suddenly, it occurred to me. An air
> problem? Disconnect the wires from the intake air sensor!! I did that &
> I'll be damned. It worked! The beast fired right up! Now, do I replace it?
> Can I repair it? What happens if I cruise around with it disconnected? If
> I
> do replace it, does anybody have a line on where I could come up with an
> inexpensive one? Does anybody have one I could buy for cheap? Any help
> will be greatly appreciated I assure you.

My '77 acts just the opposite. When I accidentally left the air intake wires
off, it would idle ok but die when given any throttle.
Did you jumper anything out to get it to run with wires disconnected? Maybe
just bad/corroded connections at air sensor?

Jack

Found the problem. Well, I took the filter box/air sensor out, and I feel
like an idiot. I shook the whole thing and heard a rattle. If you look
inside of your sensor, from the square end, there is a flapper/valve
assembly. Part of this assembly is a little round disk, which is exactly
the size of a quarter. On mine, this has broken off. Now my only concern
is, what else broke off (because it looks like there should be more to it)
and where the hell did it go? I cringe at the thought of little metal bits
being sucked into throttle & so on. Bad news!

arthurp wrote:
> Found the problem. Well, I took the filter box/air sensor out, and I feel
> like an idiot. I shook the whole thing and heard a rattle. If you look
> inside of your sensor, from the square end, there is a flapper/valve
> assembly. Part of this assembly is a little round disk, which is exactly
> the size of a quarter. On mine, this has broken off. Now my only concern
> is, what else broke off (because it looks like there should be more to it)
> and where the hell did it go? I cringe at the thought of little metal bits
> being sucked into throttle & so on. Bad news!
>
Only late air-flow sensors had this "back pressure" valve. It was
supposed to relieve pressure during a backfire.

There was a pin and a spring around the pin holding the disc
in place. I doubt that they got tangled in the throttle.
Might be worth taking the big rubber bootie off to see if
anything is in there. (Or, maybe leave well enough alone...)

If this were *my* Bus and I needed it to drive, I would have
the tube of silicone caulk out and I would be fashioning
a new disc out of a thin plastic bottle cap, or some such.
Just glue it to the side of the flapper facing the air cleaner.

Speedy Jim
http://www.nls.net/mp/volks/

If anyone's still interested, I ended up finding the round disc inside the
air filter box, the outer half of the rectangular part in the air intake
distributor, and the now destroyed spring/pin inside of #4 cylinder. It
had started making noise as it was slammed between the head and piston
end. Luckily, it didn't make it into the rings, and the cylinder walls
weren't scored. Thank god. It was a long Saturday, but we got the engine
out, torn down, reassembled, back in and running all in one day.

arthurp wrote:
> If anyone's still interested, I ended up finding the round disc inside the
> air filter box, the outer half of the rectangular part in the air intake
> distributor, and the now destroyed spring/pin inside of #4 cylinder. It
> had started making noise as it was slammed between the head and piston
> end. Luckily, it didn't make it into the rings, and the cylinder walls
> weren't scored. Thank god. It was a long Saturday, but we got the engine
> out, torn down, reassembled, back in and running all in one day.
>

Good job!!

J.

"arthurp" > wrote in message
lkaboutautos.com...
> If anyone's still interested, I ended up finding the round disc inside the
> air filter box, the outer half of the rectangular part in the air intake
> distributor, and the now destroyed spring/pin inside of #4 cylinder. It
> had started making noise as it was slammed between the head and piston
> end. Luckily, it didn't make it into the rings, and the cylinder walls
> weren't scored. Thank god. It was a long Saturday, but we got the engine
> out, torn down, reassembled, back in and running all in one day.
>
Good for you! -BaH