Help! Vapor lock? Are we pushing the bus?

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Our cross-country trip from Georgia to Monterey has been very eventful. I need to understand if what is going on now is vapor lock, and if we are pushing the bus too much.

We have a '77 Westy with stock AFC 2L fuel-injected engine. The primary symptom is after driving for a while (2 hours) on highways or interstates, when we next come to a stop, the bus stalls. Then it won't start--engine turns over, but it is as if it is getting no gas.

This happened today when driving from Monterey to Sacramento. Yes, some tremendous hills, especially going down to Muir Woods, but we did not lug the bus, and the weather was cool. We took a 2.5 hour break in Muir Woods, and as the weather heated up, took two breaks on the way to Sacramento. North of Sacramento, we pulled over at an exit to take another break, and as we stopped at the light, the bus stalled.

At no time has the engine or oil stick felt hot to the touch, unless we stop for a while and that is when it heats up.

Then it exhibited the same symptoms--turning over, but as if it was getting no gas. After sitting for 30 minutes, it would then start, beginning with a backfire, but only idle for about 30 seconds before stalling. Later, it does the same thing.

Only an overnight rest seems to solve the problem, and that only most of the time. It happened in the evening in Barstow with the same symptoms, and the tow truck driver thought it would cool down during the 20 minute drive on the wrekcer. After that, it did start, but stalled after a minute. The next morning if fiddled with some hoses and connections (which has helped sometimes) and it ran fine.

The following day, we drove north and made to Monterey. Admittedley, this was a long haul, but the air was 65F and very humid. We made it five miles outside of Monterey before coming to a traffic light, where the bus stalled. This time, the next morning it would not crank.

We spent a week in Monterey, where a mechanic did some considerable work on it: adjusted valves, points, changed condensor (he thought that was the source of the starting trouble), changed valve cover gasket, changed push-rod tube seals, replaced some hoses, oil change.

When we drove it after he was done, we got some heavy lurching, and took it back. He changed some hoses and thought that solved the problem. We were suspicious of a fuel problem, perhaps dirt from the dessert or bad gas near Barstow as someone here mentioned, but he totally discounted that.

Today, after driving for about an hour, we had one heavy lurching incident, again when in first gear after a complete stop. But then we had the same stall, this time in the afternoon.

I don't want to push this bus. But I want to understand vapor lock. It can happen even when the weather is cool and humid and at night? And is it natural to happen after so many miles a day, regardless of weather? And while others mention waiting for the bus to cool, mine seems to tack many hours before it is back up to snuff.

And once it is cool, how do I know it is safe to proceed back on the highway? If it idles for 5 minutes? Or if it starts should I proceed immediately at some high rpms to cool it further?

Thanks for any help for the stranded newbies...

[ratwell]

FI busses don't tend to vapour lock. Bosch/VW designed the fuel system to pump more fuel through than required. The excess fuel is returned to the tank via the pressure regulator and this prevents vapour lock in the lines in addition to keeping things cooler.

The problem you describe sounds just like a blocked fuel filter. Quite often the inside of the gas tanks rust on these old busses because VW didn't use terne metal, a tin/lead coated steel that resists rusting.

There is also no screen inside an FI tank and the rust comes down in flakes and powered form and clogs the filter. Even when the tank has been cleaned the rust can coat the inside of the fuel lines and flake off and make its way to the filter so new fuel lines are a must when the tank is restored.

Change the filter and tell us what improvement you see.

[Tram]

Also, the airflow meter or electric fuel pump can cause this problem. Install a grounding wire from the airflow metre to the engine as a first starting point. If the bus stalls again, check the fuel pump. Is it very hot? If so, replace it. Also replace it if it's noisy. Airflows tend to cause a bucking problem after several hours of operation when they get elderly, but this problem occurs MOSTLY in Vanagons. Something is getting hot and quitting in the fuel system. Ignition systems are usually good or they're bad. Also, the next time this happens, remove the gas cap and try to start it. Sometimes you can get a vacuum buildup in the tank.

[[email protected]]

i had this happen on my 76 fi bus. it turned out to be a loose head temp sensor. it caused it to stall when it was humid out after it had warmed up also it caused it to lurch while going up hills. brought it to a shop and they tightened the sensor and problem solved. i guess if it is loose it shorts every once in a while and caused the bus to run way too rich.

[ratwell]

If it's loose then there is no ground between the case and the temp sensor II terminal in the ECU so it reads infinity which would be very cold. Temperature based sensors don't last forever: test them and replace them. It's only a $17 part.

[[email protected]]

Everyone,

The fuel filter appears to be OK, but the Cylinder Head Temperature Sensor was bad. The engine is running much smoother now, and I really think (hope) it was the source of the main problem.

Ratwell--thanks for vapor lock explanation; that really helps dispel the most common comment of those who have seen us broken down. I appreciate the labeled hose photos on your .mac website as well. I'm a Mac user as well--just let me know if you ever need any AppleScript automation so I can return the favor.

Ray Robertson
http://www.scriptingmatters.com