Bucking, lurching leads to no camping and bummed out kids

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SlowLane
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Re: Bucking, lurching leads to no camping and bummed out kid

Post by SlowLane » Thu Jul 26, 2012 9:31 am

My personal strategy is to eliminate ignition gremlins first, then move on to vacuum and fuel-related gremlins. With that in mind:
1) Replace cap, rotor and wires (just plug and play?)
Pretty much. It's easy to get the wires mixed up going into the top of the cap, but if you transfer them one at a time from the old cap to the new cap and put them in the same order you should be fine. Make a note of where the indexing tab is under the rim of the cap (it mates with the notch in the rim of the distributor) and hold the new cap in the same orientation as you transfer the wires one-by one.
When you replace the rotor, put a drop or two of engine oil on the little felt disc you will find in the shaft under the rotor. This keeps the advance mechanism happy. Make sure the new rotor is fully seated.
Don't replace the wires and cap all at once, unless you're certain you can replicate the firing order from scratch. Do the cap first, as described above, then replace the wires one at a time, matching the lengths and the plug ends of old wires to new.

2) Check plugs
If you've never had the plugs out, then plan to replace the plugs as well as check them. Use Bosch copper plugs. Avoid the fancy platinum ones. Keep track of which plugs came out of which cylinders (I mark mine with a Sharpie). Analyze the plug conditions using information available on-line. Keep the old plugs around for when Colin comes to visit.

3) Test vacuum with a vacuum gauge (once I get one, where/how to I hook it up?)
In retrospect, I'll recommend getting a MityVac hand pump instead of just a gauge. It comes with a vacuum gauge attached to it, so it can be used just as a gauge, but it also enables you to test vacuum pots (like the ignition advance pot and decel valve) by applying vacuum to them. It will cost just a little more than a standalone gauge, but gives you so much extra flexibility.
You would hook up a vacuum gauge to the tiny spigot off of the central plenum that feeds the decel valve and fuel pressure regulator. Use a tee fitting so that these two important parts are still getting their vacuum signal as you are doing your tests.

4) Remove S boot and inspect for cracks (what else do I have to remove to get this out? I do not want to damage this NLA part, could not find Bentley procedure for removal)
I find it easiest to keep the S-boot attached to the AFM and remove them together, unclipping the top half of the air cleaner and just loosening the band clamp at the throttle body.. The breather hoses should come off easily. Vanagons and Bay Windows may differ in the level of difficulty for this task, however.

5) Distributor vacuum can/diaphragm?
Use your MityVac for this. Or use the old-school method: with the distributor cap off, and with a good view of the distributor internals, apply mouth suction to the hose coming from the distributor vacuum can. You should see the actuator rod from the vacuum can retract and the point plate rotate with it. Hold your tongue on the hose end for a few seconds and make sure the vacuum holds. That's it. The MityVac gives you the ability to measure how much vacuum is needed to move the actuator, but the mouth suction method is perfectly valid for a functional test.

6) brake booster/hose
The MityVac again, although it may take a lot of pumps.

7) Check valve cover gaskets for leaks
Plan to do a valve adjustment instead and do the gasket check or replacement then. Have replacement gaskets on hand, because you don't know the condition of your existing ones. If replacing, clean the valve covers scrupulously and use a thin layer of Hylomar or Curil on the valve cover gasket mating surface. It helps to keep them in place.

8) Switch back to points and condenser (not sure how to do this, yet)
Probably best done with Colin on hand. Adjusting points can be fussy and frustrating on Bosch distributors.
'81 Canadian Westfalia (2.0L, manual), now Californiated

"They say a little knowledge is a dangerous thing, but it is not one half so bad as a lot of ignorance."
- Terry Pratchett

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Amskeptic
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Re: Bucking, lurching leads to no camping and bummed out kid

Post by Amskeptic » Fri Jul 27, 2012 12:21 am

SlowLane wrote: Adjusting points can be fussy and frustrating on Bosch distributors.
If you barely snug the breaker point adjustment hold down screw and use a screw driver between the two little nubs and the slot in the point set, it is tolerably easy enough.
Colin
BobD - 1978 Bus . . . . . . . . . . . 111,155 miles
Chloe - 1970 bus . . . . . . . . . . . 206,820 miles
Naranja - 1977 Westfalia . . . . . 111,075 miles
Pluck - 1973 Squareback . . . . . . 55,570 miles
Alexus - 1991 Lexus LS400 . . . 78,885 miles

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SlowLane
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Re: Bucking, lurching leads to no camping and bummed out kid

Post by SlowLane » Fri Jul 27, 2012 8:07 am

Amskeptic wrote:
SlowLane wrote: Adjusting points can be fussy and frustrating on Bosch distributors.
If you barely snug the breaker point adjustment hold down screw and use a screw driver between the two little nubs and the slot in the point set, it is tolerably easy enough.
Colin
Yes, and then the frustrating part comes in when, having adjusted them to perfection, you further snug the hold-down screw to keep the points in place, and they shift on you as you snug.

Iknowiknowiknow, an unabused distributor point plate, screw and washer shouldn't do that. How many of those have you encountered on your travels?

I was trying to point out that points installation and adjustment is something that can be confusing and frustrating to someone who has never done it before and has no knowledgable guide available.

On the other had, I learned how to do it wth little more than Muir's Idiot Book many years ago, but that was back in the day whan practically all cars used points, so the care and feeding of points-and-condenser systems was part of the common lore, pretty much the first thing you picked up after learning which end of a screwdriver was which. It's somewhat sobering, not to mention depressing, to realize that it no longer is, but that's progress.
'81 Canadian Westfalia (2.0L, manual), now Californiated

"They say a little knowledge is a dangerous thing, but it is not one half so bad as a lot of ignorance."
- Terry Pratchett

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Amskeptic
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Re: Bucking, lurching leads to no camping and bummed out kid

Post by Amskeptic » Fri Jul 27, 2012 8:45 am

SlowLane wrote:having adjusted them to perfection, you further snug the hold-down screw to keep the points in place, and they shift on you as you snug.
How many of those have you encountered on your travels?
Many. My default with those devilish occasions is to bend the stationary point into proper dwell.
ColinItDoesNotAppreciablyChangeContactAreaSaysI
BobD - 1978 Bus . . . . . . . . . . . 111,155 miles
Chloe - 1970 bus . . . . . . . . . . . 206,820 miles
Naranja - 1977 Westfalia . . . . . 111,075 miles
Pluck - 1973 Squareback . . . . . . 55,570 miles
Alexus - 1991 Lexus LS400 . . . 78,885 miles

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aopisa
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Re: Bucking, lurching leads to no camping and bummed out kid

Post by aopisa » Fri Jul 27, 2012 9:19 am

I had a friend help me out last night. We discovered that spark plug wire 2 was arcing. Replaced them. No real change.

Vacuum gauge shows pressure of about 17 psi. Rechecked all hoses again.

S boot appears to be OK. It is actually still somewhat pliable.

Distributor cap shows some carbon deposits. Rotor looks a little worn. Cleaned with sand paper. I will order a new cap and rotor, but it appears that I need to know what distributor I actually have. It looks like the original SVDA. Do I have to remove the distributor to find out? Can I remove the rotor in place (how)?

The bus was idling low and after adjusting mixture screw 1/2 turn CCW, it seemed to idle slightly better.

I have to check the valve cover gaskets, but need to review the valve adjustment procedure before hand. And I still need to get a timing light and some kind of tach to adjust the timing afterward.

I want to point out again that this problem while now almost constant, is still intermittent in nature. The bus will drive along fine for a while and then lurch, buck and even lose all power for several seconds and then return to running fine under full power, rinse and repeat. It appears to be more prevalent as the engine heats up and only does it under acceleration. Should I be looking at the fuel pump too?
1977 Westy 2.0L F.I.

Flow with whatever may happen and let your mind be free. Stay centered by accepting whatever you are doing. This is the ultimate. - Chuang Tzu

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Westy78
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Re: Bucking, lurching leads to no camping and bummed out kid

Post by Westy78 » Fri Jul 27, 2012 10:15 am

I'm going to chime in here with the same advice I always give in an intermittent buck and lurch situation when all other parts check out. Have you checked the resistance of the pins on the afm for spec as per Bentley? I chased a similar problem for a year before I found high resistance on one set of pins on my afm. The last thing I suspected as it was a newer rebuilt unit from Fuel Injection Corp.
Bought a good used one and haven't had a problem since.
Chorizo, it's what's for breakfast.

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SlowLane
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Re: Bucking, lurching leads to no camping and bummed out kid

Post by SlowLane » Fri Jul 27, 2012 10:20 am

Distributor cap shows some carbon deposits. Rotor looks a little worn. Cleaned with sand paper. I will order a new cap and rotor, but it appears that I need to know what distributor I actually have. It looks like the original SVDA. Do I have to remove the distributor to find out? Can I remove the rotor in place (how)?
Caps and rotors didn't change much over the years. This distributor cap should work for you, as should this rotor.

The rotor should come out with a firm tug upwards. Should be no need to remove the distributor.
I want to point out again that this problem while now almost constant, is still intermittent in nature. The bus will drive along fine for a while and then lurch, buck and even lose all power for several seconds and then return to running fine under full power, rinse and repeat.
I had very similar symptoms with my van several years ago, and it turned out to be a split AAR elbow, which is the chief reason I cry "AAR elbow" whenever someone reports lurching. I'm thinking of changing my username to "Mr. AAR Elbow". :geek:
'81 Canadian Westfalia (2.0L, manual), now Californiated

"They say a little knowledge is a dangerous thing, but it is not one half so bad as a lot of ignorance."
- Terry Pratchett

vdubyah73
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Re: Bucking, lurching leads to no camping and bummed out kid

Post by vdubyah73 » Fri Jul 27, 2012 12:35 pm

do the points first. why? the last paragragh of your last post point to high electrical resistance for spark. the more gas in the cylinder the higher the resistance across the spark plug gap. the rising engine operating temp, as engine warms, up can also increase resistance in coil going bad, same can be said for hall effect points replacements, any brand.
1/20/2013 end of an error
never owned a gun. have fired a few.

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56ovalbug
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Re: Bucking, lurching leads to no camping and bummed out kid

Post by 56ovalbug » Fri Jul 27, 2012 12:45 pm

Try bypassing the double relay. I had a wonky one a few years back that gave me grief. Run a length of wire from the positive side of the fuel pump to the positive side of the coil.

Make sure all of the push on connectors that are going to your coil and elsewhere are in good shape and none are just hanging on by a few strands of wire - especially the one that comes from the FI harness and goes to the negative side of the coil.

Check the FI wire harness for places where it may be worn through and shorting on something.

I once had a distributor that the shaft would jump out of the drive gear which made the engine lurch & buck. The fiber shims between the drive dog and the distributor disintegrated. Remove the distributor cap and rotor and pull up on the shaft while trying to rotate it... it shouldn't turn.... it's a long shot but who knows.
Joey

'56 Beetle|'65 Beetle|'74 Bus|'79 Panel

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aopisa
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Re: Bucking, lurching leads to no camping and bummed out kid

Post by aopisa » Sat Jul 28, 2012 10:37 am

Ok, with all these new posts, I still have a bunch of stuff to check out.

I did remove the rotor and put a few drops of oil on the felt in the shaft. I am ordering a new rotor and cap. I also did the mouth suction test on the distributor vacuum can. The arm does move when suction is applied and will stay in place when I plug the hose with my tongue.

I just wanted to add some new information in case it helps to point to something more specific.

I bought a timing light and multi-meter that shows RPM and dwell.

When I start the bus it idles at about 950. After running a few minutes the idle drops to 650 and sounds like it is on the verge of stalling. After revving the engine to 3500 while doing the timing it settles down to about 800. Hooked up the timing light. With the distributor can hose off it idles at around 15 BTDC. At 3500 RPM it at about 35 BTDC. The engine fought me by "cutting out" while I was trying to get it up past 2500 or so. I just kept even pressure on the throttle until the episode passed and was able to get it up to 3500 at that point.
1977 Westy 2.0L F.I.

Flow with whatever may happen and let your mind be free. Stay centered by accepting whatever you are doing. This is the ultimate. - Chuang Tzu

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Re: Bucking, lurching leads to no camping and bummed out kid

Post by 56ovalbug » Sat Jul 28, 2012 1:36 pm

You're timing is a bit too far advanced. Did you check the dwell?
Joey

'56 Beetle|'65 Beetle|'74 Bus|'79 Panel

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SlowLane
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Re: Bucking, lurching leads to no camping and bummed out kid

Post by SlowLane » Sat Jul 28, 2012 3:26 pm

aopisa wrote:I did remove the rotor and put a few drops of oil on the felt in the shaft. I am ordering a new rotor and cap. I also did the mouth suction test on the distributor vacuum can. The arm does move when suction is applied and will stay in place when I plug the hose with my tongue.
Good! That not only checks the vacuum diaphragm, but also the integrity of the hose. While you have the cap off and with the rotor fully seated on the shaft, gently turn the rotor and shaft a little bit clockwise. You should feel a springy resistance as the centrifugal advance springs resist your efforts. The motion of the shaft should be smooth with no sticking points or hitches, and the rotor should return to the same resting position when you relax the pressure.
aopisa wrote:When I start the bus it idles at about 950. After running a few minutes the idle drops to 650 and sounds like it is on the verge of stalling. After revving the engine to 3500 while doing the timing it settles down to about 800. Hooked up the timing light. With the distributor can hose off it idles at around 15 BTDC. At 3500 RPM it at about 35 BTDC. The engine fought me by "cutting out" while I was trying to get it up past 2500 or so. I just kept even pressure on the throttle until the episode passed and was able to get it up to 3500 at that point.
15 degrees BTDC is twice as much initial advance as you should have at idle. Set it back to 7.5, no hoses connected. The high-speed advance should then reduce by the same amount to about 28 degrees.

Be sure to plug the hose coming from the throttle body when you are doing your timing adjustments.

You will need to adjust the idle speed screw after you adjust the timing. Adjust for 850-950 RPM when warm (or whatever your engine compartment sticker says). Cold idle should be between 1000 and 1200 RPM.
56ovalbug wrote:You're timing is a bit too far advanced. Did you check the dwell?
Yup, what he said. Note that you can't really adjust the dwell with points-replacement systems, nor should you have to (well, Pertronix is an egregious exception. See Ratwell's Pertronix Adjustment write-up), but it is worth checking to see if it is in spec. Plus, it gives you an opportunity to get familiar with your new testing equipment.
'81 Canadian Westfalia (2.0L, manual), now Californiated

"They say a little knowledge is a dangerous thing, but it is not one half so bad as a lot of ignorance."
- Terry Pratchett

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Re: Bucking, lurching leads to no camping and bummed out kid

Post by 56ovalbug » Sun Jul 29, 2012 7:07 am

SlowLane wrote:
56ovalbug wrote:You're timing is a bit too far advanced. Did you check the dwell?
Yup, what he said. Note that you can't really adjust the dwell with points-replacement systems, nor should you have to (well, Pertronix is an egregious exception. See Ratwell's Pertronix Adjustment write-up), but it is worth checking to see if it is in spec. Plus, it gives you an opportunity to get familiar with your new testing equipment.
Oh yea... forgot he had no points. #-o
Joey

'56 Beetle|'65 Beetle|'74 Bus|'79 Panel

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Amskeptic
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Re: Bucking, lurching leads to no camping and bummed out kid

Post by Amskeptic » Sun Jul 29, 2012 1:05 pm

SlowLane wrote:
aopisa wrote:I did remove the rotor and put a few drops of oil on the felt in the shaft. I am ordering a new rotor and cap. I also did the mouth suction test on the distributor vacuum can. The arm does move when suction is applied and will stay in place when I plug the hose with my tongue.
Good! That not only checks the vacuum diaphragm, but also the integrity of the hose. While you have the cap off and with the rotor fully seated on the shaft, gently turn the rotor and shaft a little bit clockwise. You should feel a springy resistance as the centrifugal advance springs resist your efforts. The motion of the shaft should be smooth with no sticking points or hitches, and the rotor should return to the same resting position when you relax the pressure.
aopisa wrote:When I start the bus it idles at about 950. After running a few minutes the idle drops to 650 and sounds like it is on the verge of stalling. After revving the engine to 3500 while doing the timing it settles down to about 800.
At 3500 RPM it at about 35 BTDC.
We all must be careful to build a process of elimination here. If we chime in indiscriminately, he will have a pile of exploding variables.

The highlights above suggest that the engine was timed with a possibly sticky centrifugal advance and the idle speed was set with the slightly sticky centrifugal advance unit stuck at wherever it happened to be.

We need your actual current dwell number. I did a lousy point adjustment in Saint Helena, CA, and it ran like crap, would not rev worth a damn and it was just at a stupid 34*
Dwell when it calls for 45*-50*. Get it right!
Low dwell? Too monster a gap.
High dwell? Point gap is too closed.

Ever do a quicky centrifugal advance lubrication? Remove distributor, pry out the little metal "window", lubricate the pivots as you rotate them past the window and twist the rotor in relation to the drive dogs back and forth and back and forth, I think you already did the felt wick.

Reinstall distributor. Manually insure the rotor and shaft is fully counter-clockwise in relation to the now engaged distributor drive dogs. Start engine at whatever idle it is, and set timing to 4* BTDC exactly at idle !!! without revving the engine!!! ever!! we are trying to keep weights fully in. If you accidentally do rev engine, merely shut it off and turn rotor counter-clockwise, start engine again no revving, time it at 4* BTDC. Set idle speed to a warm egine 950 minimum rpm. There! No variables! Now rev to 3,400 rpm and see what your high speed timing is. Hopefully I did compensate for your worn distributor and you found 28*. Let engine return to idle. Is it 4*? Good. Is it 12 with a fast idle? Need to disassemble distributor.
Colin
BobD - 1978 Bus . . . . . . . . . . . 111,155 miles
Chloe - 1970 bus . . . . . . . . . . . 206,820 miles
Naranja - 1977 Westfalia . . . . . 111,075 miles
Pluck - 1973 Squareback . . . . . . 55,570 miles
Alexus - 1991 Lexus LS400 . . . 78,885 miles

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aopisa
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Re: Bucking, lurching leads to no camping and bummed out kid

Post by aopisa » Sun Jul 29, 2012 1:24 pm

Amskeptic wrote:
SlowLane wrote:
aopisa wrote:I did remove the rotor and put a few drops of oil on the felt in the shaft. I am ordering a new rotor and cap. I also did the mouth suction test on the distributor vacuum can. The arm does move when suction is applied and will stay in place when I plug the hose with my tongue.
Good! That not only checks the vacuum diaphragm, but also the integrity of the hose. While you have the cap off and with the rotor fully seated on the shaft, gently turn the rotor and shaft a little bit clockwise. You should feel a springy resistance as the centrifugal advance springs resist your efforts. The motion of the shaft should be smooth with no sticking points or hitches, and the rotor should return to the same resting position when you relax the pressure.
aopisa wrote:When I start the bus it idles at about 950. After running a few minutes the idle drops to 650 and sounds like it is on the verge of stalling. After revving the engine to 3500 while doing the timing it settles down to about 800.
At 3500 RPM it at about 35 BTDC.
We all must be careful to build a process of elimination here. If we chime in indiscriminately, he will have a pile of exploding variables.

The highlights above suggest that the engine was timed with a possibly sticky centrifugal advance and the idle speed was set with the slightly sticky centrifugal advance unit stuck at wherever it happened to be.

We need your actual current dwell number. I did a lousy point adjustment in Saint Helena, CA, and it ran like crap, would not rev worth a damn and it was just at a stupid 34*
Dwell when it calls for 45*-50*. Get it right!
Low dwell? Too monster a gap.
High dwell? Point gap is too closed.

Ever do a quicky centrifugal advance lubrication? Remove distributor, pry out the little metal "window", lubricate the pivots as you rotate them past the window and twist the rotor in relation to the drive dogs back and forth and back and forth, I think you already did the felt wick.

Reinstall distributor. Manually insure the rotor and shaft is fully counter-clockwise in relation to the now engaged distributor drive dogs. Start engine at whatever idle it is, and set timing to 4* BTDC exactly at idle !!! without revving the engine!!! ever!! we are trying to keep weights fully in. If you accidentally do rev engine, merely shut it off and turn rotor counter-clockwise, start engine again no revving, time it at 4* BTDC. Set idle speed to a warm egine 950 minimum rpm. There! No variables! Now rev to 3,400 rpm and see what your high speed timing is. Hopefully I did compensate for your worn distributor and you found 28*. Let engine return to idle. Is it 4*? Good. Is it 12 with a fast idle? Need to disassemble distributor.
Colin
I have some questions, but have to run to the airport right now. Just wanted to say, no points, no dwell. Running with electronic points replacement.

I did time the engine earlier today before these instructions and reset the idle. At 3500 RPMs = 28 degrees. At idle about 900 RPM = 12 degrees. Vacuum hose removed.

Questions to come later before I embark on this procedure.
1977 Westy 2.0L F.I.

Flow with whatever may happen and let your mind be free. Stay centered by accepting whatever you are doing. This is the ultimate. - Chuang Tzu

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