1980 Vanagon backfire and stumble

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cegammel
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1980 Vanagon backfire and stumble

Post by cegammel » Thu Aug 08, 2019 1:43 pm

I came back from a month if traveling, took the Van for a spin... I encountered a stumble so hard it put my nose on the steering wheel. The van recovered and ran fine. I have continued to have a very intermittent stumble like that. I found a loose wire to the coil,and thought I had it licked. Today, we had a backfire and stumble that scared the bejeezus out me. The van still recovered and ran fine afterwards. I know that this is very little info...any preliminary ideas?

cegammel
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Re: 1980 Vanagon backfire and stumble

Post by cegammel » Fri Aug 09, 2019 6:37 pm

Follow up:. I was late picking up glass, and I pushed her hard today to beat closing time. No stumble, no nothing. Van ran like a brand new machine. Weird this is.

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Amskeptic
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Re: 1980 Vanagon backfire and stumble

Post by Amskeptic » Wed Aug 21, 2019 5:50 pm

cegammel wrote:
Fri Aug 09, 2019 6:37 pm
Follow up:. I was late picking up glass, and I pushed her hard today to beat closing time. No stumble, no nothing. Van ran like a brand new machine. Weird this is.

Electrical ... yes.
Lousy connector ... probably.

Experiment: Spade connectors can go on firmly and foll you into thinking that they are secure, but in fact, have a lousy electrical connection at full insertion depth. You can feel it, Firm slide, but at full depth the spade connector develops a little side-to-side slop. Pull them all out 25% to the definitely firm no wiggle spot and drive. If symptoms are gone, now you have to find which one is responsible.

For additional fun ... fuel injection can drop you if the parameters are exceeded. Try just a silly half turn one way on the mixture screw, test, now go one full turn (back to "0" then a half in the opposite direction) and just tease out if the symptoms worsen or improve. Do same experiment on speed screw at the throttle body. You are attempting to find agency over the symptom. Think boldly, experiment largely.
Colin
BobD - 1978 Bus . . . . . . . . . . . 111,155 miles
Chloe - 1970 bus . . . . . . . . . . . 206,820 miles
Naranja - 1977 Westfalia . . . . . 108,000 miles
Pluck - 1973 Squareback . . . . . . 55,570 miles
Alexus - 1991 Lexus LS400 . . . 78,885 miles

cegammel
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Re: 1980 Vanagon backfire and stumble

Post by cegammel » Fri Aug 23, 2019 3:25 pm

You hit it. Spot on. The causes, though are even stupider. I fiddled with the mixture to try to improve my lousy mileage. I was at 4 turns,so I reset it to 3.5...but no. I can't count...When I reset, I was actually at 4.5. I have now readjusted to 3.5 and eliminated the problem. Damn counting turns is apparently above my skill level.

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Amskeptic
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Re: 1980 Vanagon backfire and stumble

Post by Amskeptic » Sat Aug 24, 2019 10:09 am

cegammel wrote:
Fri Aug 23, 2019 3:25 pm
You hit it. Damn counting turns is apparently above my skill level.
Exactly right, I hit it. It fell over. Again.
Keeping a Diet Coke can vertical is way past my skill level ...
Colin
BobD - 1978 Bus . . . . . . . . . . . 111,155 miles
Chloe - 1970 bus . . . . . . . . . . . 206,820 miles
Naranja - 1977 Westfalia . . . . . 108,000 miles
Pluck - 1973 Squareback . . . . . . 55,570 miles
Alexus - 1991 Lexus LS400 . . . 78,885 miles

cegammel
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Re: 1980 Vanagon backfire and stumble

Post by cegammel » Sun Sep 08, 2019 12:23 pm

The same problem occurred again today...as I was crossing four lanes...the van backfired, lost power, struggled every time I pushed the gas, then died in the middle of the road. I coasted off, it started back up and ran fine home.

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Amskeptic
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Re: 1980 Vanagon backfire and stumble

Post by Amskeptic » Tue Sep 10, 2019 6:12 am

cegammel wrote:
Sun Sep 08, 2019 12:23 pm
The same problem occurred again today...as I was crossing four lanes...the van backfired, lost power, struggled every time I pushed the gas, then died in the middle of the road. I coasted off, it started back up and ran fine home.

Do you use dielectric grease on connections? It has been damp on the east coast all summer, yes?
Colin
BobD - 1978 Bus . . . . . . . . . . . 111,155 miles
Chloe - 1970 bus . . . . . . . . . . . 206,820 miles
Naranja - 1977 Westfalia . . . . . 108,000 miles
Pluck - 1973 Squareback . . . . . . 55,570 miles
Alexus - 1991 Lexus LS400 . . . 78,885 miles

cegammel
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Location: Thomasville Georgia
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Re: 1980 Vanagon backfire and stumble

Post by cegammel » Wed Sep 11, 2019 5:43 pm

Not yet. I think a thorough goin' over is in order.

Another thing: after a short stop while hot, the starter will just barely turn the motor. It only takes a partial revolution to start it, luckily, but it acts like it isn't going to turn at all at times. The starter is relatively new and works great most of the time, and always on a coldish motor. Any thoughts?

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Amskeptic
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Re: 1980 Vanagon backfire and stumble

Post by Amskeptic » Wed Sep 11, 2019 5:53 pm

cegammel wrote:
Wed Sep 11, 2019 5:43 pm
Not yet. I think a thorough goin' over is in order.

Another thing: after a short stop while hot, the starter will just barely turn the motor. It only takes a partial revolution to start it, luckily, but it acts like it isn't going to turn at all at times. The starter is relatively new and works great most of the time, and always on a coldish motor. Any thoughts?

A) rebuilt or new? windings can lose strength when hot if the shellac is melting off the coiled wires

B) is engine physically more difficult to rotate when hot?

C) what is idle timing? Actual timing at idle?

C) if "B" is a no and "C" is less than 7* BTDC (i.e. any idle timing from 7*BTDC down to 5* ATDC is fine) and all grounds and wires are good, make sure your battery is fully fully charged and go try to start it when hot. If slow, replace the starter
Colin
BobD - 1978 Bus . . . . . . . . . . . 111,155 miles
Chloe - 1970 bus . . . . . . . . . . . 206,820 miles
Naranja - 1977 Westfalia . . . . . 108,000 miles
Pluck - 1973 Squareback . . . . . . 55,570 miles
Alexus - 1991 Lexus LS400 . . . 78,885 miles

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