2-for-1 and possibly related: Bucking and unstable/nonidle

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Ronin10
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Re: 2-for-1 and possibly related: Bucking and unstable/nonid

Post by Ronin10 » Tue Dec 16, 2014 12:10 pm

To be clear, I can grab the wiper below 1500 rpm and fix it into a given position. Offhand, I'm not sure how low of an RPM I could achieve with foot off the gas and manually fixing the position of the wiper arm. I'll try and get some help to do that test tonight.

When the engine is left to try and idle on it's own the wiper are doesn't settle into a relatively fixed position. It's so active as the engine is on the verge of dying, sweeping out large arc quickly, that I can't discern what a "natural" idle position would be. The engine does a lot of rapidly dying (wiper goes to almost closed) and resuscitating (wiper pops open) until it finally dies. The wiper's very still then. :|

Last compression was done sometime this summer. I can't find it in my records so I'm going off of memory. It was a solid 120-125 across all cylinders. I adjusted my valves just last week and didn't detect any changes in the point of contact of the adjuster screws with the valve stems.

Swapping out my AFM remains on my list, but that's a full re-tune of the other AFM. Not that it's the end of the world or a massive time commitment, just that I'd be introducing other variables if I get different, but still anomalous behavior. In theory, I should be able to pinpoint the issue with this current setup.

In further news...I'm spending the week experimenting with the mixture screw on drives to and from work to take advantage of the commute for a little testing. Started with the mixture screw at 4 1/2 turns out (what all the previously described symptoms are based off of) and backed it out 1/2 turn further for the drive in. Result: still had a bit of a bucking issue (didn't expect a change here) and no real change in idle, but it ran more or less the same, maybe a bit better, but nothing crystal clear. I arrived at work and adjusted it another 1/2 turn out and will see how that affects things on the way home. It's about a 16-17 mile drive (about 35 minutes w/traffic) and I'm judging differences upon arrival at whichever destination. I'm doing this based on the vague recollection that my mixture screw was previously way the heck out...much further than I would expect.

Lots of good suggestions and questions coming in. I hope I covered them all. My plan going forward at this point is:
  • Continue trying to find the best (of the worst?) mixture screw setting on commutes to/from work and in the evenings if the opportunity presents itself.
  • Over the course of the week, try and make up my mind about how best to address replacing my harness
  • Perform a manually fixed position wiper-arm-nudging test at "idle"
  • At the weekend, swap AFM, tune w/LM-2, and pray to whatever gods will listen.
Thanks folks.
Oscar: 1976 Sage Green Bus, Stock Motor, Solid Lifters, Manual Transaxle

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energyturtle
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Re: 2-for-1 and possibly related: Bucking and unstable/nonid

Post by energyturtle » Tue Dec 16, 2014 1:22 pm

Have you changed the fuel filter? I saw you had a good fuel pressure reading, but maybe, by coincidence the reading was when you had full flow and something is intermittently blocking the flow and producing the symptoms your describing. Just my 2 cents, as I have had the same problem twice now. Fuel filter both times. Also, the ground that is bolted to the 3rd case through bolt, on top, under the plenum could cause these issues as well. Good Luck.

Scottie

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Ronin10
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Re: 2-for-1 and possibly related: Bucking and unstable/nonid

Post by Ronin10 » Tue Dec 16, 2014 6:01 pm

Changed the fuel filter. So I'm confident we can rule that out. I'm going to give harness a one over tonight and see if I can make one of my spare 77 harnesses useful. Bucking is getting worse.
Oscar: 1976 Sage Green Bus, Stock Motor, Solid Lifters, Manual Transaxle

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Ronin10
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Re: 2-for-1 and possibly related: Bucking and unstable/nonid

Post by Ronin10 » Wed Dec 17, 2014 7:16 pm

Hopefully this is not premature, but I think we can set aside the bucking issue. Last night, I repaired the one of the spare harnesses I had, adding the clipped off cold start valve. Despite my poor soldering skills, it was electrically viable and robust enough to last me until I can get a proper one made (or make myself). I swapped it out this evening, took my bus for a 6 mile drive and nary a buck. Time will tell if it indeed works, but it looks very promising. Only drawback at this point is that I lost my full throttle enrichment as this was a 77 harness and my bus is a late 76 bus with the full throttle microswitch on the throttle body.

On the idle front, I seem to have found a "rich" limit to adjusting the mixture screw. This week, I've been adjusting the mixture screw a half a turn at a time. Driving it into work and adjusting it another 1/2 turn upon arrival. Well, this morning, I left with it set to 4 turns out. It was actually a very nice drive in. I turned it in another 1/2 turn and when I came out to leave in the afternoon, it was tough to start and simply wouldn't stay running once I did get it started. I'm now exploring the other limit. Sitting ready at 6 turns out for tomorrow.
Oscar: 1976 Sage Green Bus, Stock Motor, Solid Lifters, Manual Transaxle

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satchmo
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Re: 2-for-1 and possibly related: Bucking and unstable/nonid

Post by satchmo » Wed Dec 17, 2014 8:08 pm

Allllllrighty then!

We are going to call this Satchmo's Law:

"Bucking and/or wild movement of the AFM wiper is ALWAYS an electrical continuity problem, either at the wiring connectors, or in the wiring harness itself." (unless it is found to be due to some other problem, of course)

Tim
By three methods we may learn wisdom:
First, by reflection, which is noblest;
second, by immitation, which is easiest;
and third, by experience, which is bitterest. -Confucius

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Amskeptic
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Re: 2-for-1 and possibly related: Bucking and unstable/nonid

Post by Amskeptic » Thu Dec 18, 2014 8:58 am

satchmo wrote:Allllllrighty then!

We are going to call this Satchmo's Law:

"Bucking and/or wild movement of the AFM wiper is ALWAYS an electrical continuity problem, either at the wiring connectors, or in the wiring harness itself." (unless it is found to be due to some other problem, of course)

Tim
I'll give you bucking as a subset of Satchmo's Law, but "wild movement of the wiper" can also be airflow interruptions like dropped valve seats, worn cam lobes leaky guides, over-pumped/under-pumped hydraulic lifters. I have fooled with injector plugs on running engines, and I do not recall the wiper getting all upset because I pulled off an injector plug. Some of the dancing wipers I have come across have been so violent that you can hear the flap banging.

How's it going out there? Sodden?
Colin
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

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Ronin10
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Re: 2-for-1 and possibly related: Bucking and unstable/nonid

Post by Ronin10 » Thu Dec 18, 2014 9:45 am

Law seems a bit strong...maybe Satchmo's Postulate or Satchmo's Theorem. ;-)
How's it going out there? Sodden?
Not sure if this was directed at me or Satchmo, but given the PNW's reputation and Clairemont being in lovely San Diego area, I'm assuming so. Rain hasn't been too bad here, for what it's worth. About a week ago, we actually had a couple of fluke, 60* afternoons.

Back on topic...drove around a bit more last night, experimenting with the mixture screw and still no bucking although I may have detected an occasional miss. I drove into work today with the mixture screw 7 turns out. Not sure yet if this is the real deal, but I seem to be heading in the right direction...the "collapse" in the 1000-1500 rpm range seemed less severe. Going home with 7 1/2 turns out. We'll see if that improves things further.
Oscar: 1976 Sage Green Bus, Stock Motor, Solid Lifters, Manual Transaxle

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satchmo
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Re: 2-for-1 and possibly related: Bucking and unstable/nonid

Post by satchmo » Thu Dec 18, 2014 9:49 am

Hey, I'd settle for Satchmo's Conjecture.
By three methods we may learn wisdom:
First, by reflection, which is noblest;
second, by immitation, which is easiest;
and third, by experience, which is bitterest. -Confucius

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Ronin10
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Re: 2-for-1 and possibly related: Bucking and unstable/nonid

Post by Ronin10 » Thu Dec 18, 2014 8:10 pm

The bucking %$#@! returned. No idea why I got a reprieve during my drives last night and this morning, but my temperamental bus will not be subdued so easily. The only changes between last night's blissful cruising about and tonight's mayhem was two half turns of the mixture screw. Reset back to 6 1/2 turns (where I was last night after the harness swap), but my test drive still bucked. None of it was as bad as I had been experiencing before the swap, but it's still intermittent with no discernible pattern causing it.

One of the things I did notice was that I could use the throttle to stabilize the "idle" around 1,000 rpms. I think the mixture screw is actually close to where it should be and that the problem lies elsewhere. I'm leaving it for the moment.

Upon getting home from work, I took out the LM-2 and tried to see where this 1,000 rpm forced idle was getting me. Turns out the numbers would still blow up, but at 1500 rpm, I was getting slightly lean, around 15.2 or so. The higher rpms matched what I had before, so nothing went awry with my AFM settings.

While I was doing this testing, I happened to have the garage door only halfway up (rain) and I think this helped me hear something significant. Around 2500 and definitely at 3000 rpms, I could hear a bit of a bass note come from the engine. I wasn't quite every 1-4-3-2 firing of the engine, but pretty frequent. I first noticed it around 2500 rpm, but it was very persistent at 3000 rpms and continued through to the higher rpms. I checked spark on cylinders at 3,000 rpms, both by pulling plugs and with my timing light, moving it from wire to wire. I didn't notice any missed sparks at all, let alone when the bass notes came. So I think we're down to fuel supply, right? I already did a fuel pressure test and the pump was able to keep up with the demands of normal driving, so that seems okay. I guess that means it's likely an injector. I've previously tested these, but that was before the bucking, I guess one or more is on it's last leg. Any differing views?
Oscar: 1976 Sage Green Bus, Stock Motor, Solid Lifters, Manual Transaxle

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Amskeptic
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Re: 2-for-1 and possibly related: Bucking and unstable/nonid

Post by Amskeptic » Thu Dec 18, 2014 9:14 pm

Ronin10 wrote:The bucking %$#@! returned.
at 1500 rpm, I was 15.2
higher rpms matched what I had before, so nothing went awry with my AFM settings.

at 3000 rpms, I could hear a bit of a bass note come from the engine.
I didn't notice any missed sparks at all,
I think we're down to fuel supply, right?
Any differing views?
At 3,000 rpm, can you change the bass note with nudges on wiper?
Check dwell, looking for 45-48* even if you just did the points (see below)

Get the engine to hold that speed with mechanical means only, like a paint stick with a notch "tenting" the accelerator cable.
a) Pull each injector plug one at a time and note the rpm drop for each cylinder on your tach/dwell meter.
b) Pull each spark plug wire from cap briefly at same rpm and note rpm drop for each cylinder.
*note - pertronix does not like open fire, points don't care

This will give us some diagnostic focus. I ran into a high rpm engine breakdown on Kleinevw's bus, and we found both a faulty brand new condensor (white dust and burn marks on new points) and lack of lubrication on point rubbing block that reduced his point gap by half in a day.
Colin
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

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Amskeptic
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Re: 2-for-1 and possibly related: Bucking and unstable/nonid

Post by Amskeptic » Thu Dec 18, 2014 9:16 pm

Ronin10 wrote:
How's it going out there? Sodden?
Not sure if this was directed at me or Satchmo,
That was directed at Satchmo . . . I am following the drought in California very closely.

You folks in Renton Washington, I do not worry about, no sirree, I have never stood in Washington and thought to myself, "these people need more RAIN."
Colin
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

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Ronin10
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Re: 2-for-1 and possibly related: Bucking and unstable/nonid

Post by Ronin10 » Fri Dec 19, 2014 8:57 am

Will try to get some assistance tonight to conduct the rpm drop of spark vs. injectors or perhaps on Saturday morning, but much going on in the household this weekend. It could be Sunday before I find the time and assistance.

Quick aside on fuel injectors...I was delaying doing some actual work to investigate purchasing fuel injectors. I'm trying to look ahead at budget should it come to that. German Supply has brand new Bosch for about $160 each. Aircooled.net has rebuilt units which it goes on at length about, highly recommending by them, for $60 each. And then I visit GoWesty Auto Parts and their site says they have brand new Bosch injectors for $50, plus free shipping. They use the cost + 10% model, but that still seems remarkably low. I intend to give them a call to verify the part number and country of manufacture to see if those trip a red flag, but I know Bosch has let it's build quality slip in certain areas. Anyone know if this is the case for their injectors and are there any other questions I should ask before I order, if it comes to that.

EDIT: Links to injectors...
German Supply injectors
Aircooled.net injectors
GoWesty Auto Parts Injectors
Oscar: 1976 Sage Green Bus, Stock Motor, Solid Lifters, Manual Transaxle

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Amskeptic
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Re: 2-for-1 and possibly related: Bucking and unstable/nonid

Post by Amskeptic » Fri Dec 19, 2014 12:44 pm

Ronin10 wrote:Will try to get some assistance tonight to conduct the rpm drop of spark vs. injectors or perhaps on Saturday morning, but much going on in the household this weekend. It could be Sunday before I find the time and assistance.

I know Bosch has let it's build quality slip
Yeah, let's not throw money away needlessly. I have dealt with too many defective injectors (mostly those cleaned by professionals with flow charts and stuff and everything) this summer, and always the return of the crusty old ones restored the engine to happiness. If you have continuity through injector plug terminals and they spray in a nice cone and have intact screens, use them.
Colin
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

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Ronin10
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Re: 2-for-1 and possibly related: Bucking and unstable/nonid

Post by Ronin10 » Sun Dec 21, 2014 8:31 pm

Not planning on buying injectors until we're confident they're the issue, but I do have to do the "what if" scenarios for next month's budget.

I just did the comparison test with pulling the plugs and injectors. Here's the results:
  • #1 - plugs in: 3000, plugs out: 2680, delta: 320 rpms
  • #1 - injectors connected: 3000, injectors disconnected: 2700, delta: 300 rpms
  • #2 - plugs in: 3000, plugs out: 2680, delta: 320 rpms
  • #2 - injectors connected: 3000, injectors disconnected: 2630, delta: 370 rpms
  • #3 - plugs in: 3300, plugs out: 2800, delta: 500 rpms
  • #3 - injectors connected: 3300, injectors disconnected: 2790, delta: 510 rpms
  • #4 - plugs in: 3000, plugs out: 2700, delta: 500 rpms
  • #4 - injectors connected: 3000, injectors disconnected: 2700, delta: 500 rpms
I couldn't come up with a good rig to mechanically hold the throttle in a fixed position so I had my wife sit in the driver's seat and coached her to a steady idle. She was a little high on the 3/4 side, but stable.

#2 stands out with the injector disconnected.
Oscar: 1976 Sage Green Bus, Stock Motor, Solid Lifters, Manual Transaxle

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Amskeptic
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Re: 2-for-1 and possibly related: Bucking and unstable/nonid

Post by Amskeptic » Mon Dec 22, 2014 11:30 am

Ronin10 wrote:Not planning on buying injectors until we're confident they're the issue, but I do have to do the "what if" scenarios for next month's budget.

Cyl . . . . rpm drop
#1 plug 320
injector 300

#2 plug 320
injector 370

#3 plug 500
injector 510

#4 - plug 500
injector 500

#2 stands out with the injector disconnected.
Which means that we may have an ignition issue.
It would be helpful to have steady rpms throughout the test, but loosely speaking, your cylinders are all behaving, your injectors are all spraying, your spark plugs are all sparking.

The injector plug pull did a more comprehensive kill than the plug pull test on #2. If you pulled the #2 wire from the distributor cap, you may have been getting some cross firing through the wires from other cylinders. If they are all properly separated with plastic clips, then this particular speculation is for naught.
Colin
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

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