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.
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arthurp wrote:

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 /
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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

I
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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
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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!
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arthurp wrote:

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 /
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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.
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arthurp wrote:

Good job!!
J.
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Good for you! -BaH
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