AFM Trauma

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drober23
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AFM Trauma

Post by drober23 » Wed Jan 30, 2013 12:16 pm

It was really nice here in Michigan for a few days, so I broke the bus out of the barn and drove it around a bit.

My estimates told me I had another 10 miles to drive before I would run out of gas (gotta fix that gas gauge!), as I headed the last half-mile to the gas station. Then came the first cough. It didn't immediately occur to me that I could possibly be out of gas, so I drove a little further. Then there was cough-cough-cough. Blerg, I was out of gas and had probably driven a bit further than I should have coughing and sputtering.

No worries! I walked the remaining few blocks to the gas station, got a gallon of gas in a non-approved container, and walked back to the bus. Put the gas in, and went to start it. Cranked, but no fire. Hmmm.... Waited a minute and tried again, and the same thing - maybe the slightest hint of a flutter, but no real fire. Went to the back and looked everything over to make sure a hose hadn't fallen off, or something silly like that. Tried one more time and "BANG!" a big backfire! NOW a couple hoses were off. The whole S-Boot had been blown off on both ends, and the decel valve and breather tubes had been blown out of the S-Boot as well.

I walked the 2 miles back to my house and loaded the bus tow bar into my dad's truck (he keeps it at my house lately). Went back and retrieved the bus. Picked up a bit more gas in a can and added it to the bus just to be sure I had plenty for later. I let the bus sit a couple days and looked it over again. Made sure plug wires and coil were engaged properly, re-installed the vacuum hosing that had blown off, and looked at anything else I could think of. Everything seemed to be in order, so I tried to start it one more time (cause that big bang must have been some sort of fluke...). Of course, it goes BANG! again, and blows the vacuum hoses off again, and I am feeling like not the sharpest knife in the drawer.

I sulk back in the house to gather my thoughts, and eventually decided to check a few things. In the course of this, I popped the air filter off to push the AFM "door" to test the fuel pump. Hmmm, the door only moves 1/8" then stops. This can't be good. I took the cover off the AFM to see what was going on in there and saw the "silver wiper arm" had come fully clockwise and was being physically stopped by the edge of the AFM housing. Further inspection showed the screw holding the afm wiper arm adjustment had failed, allowing the wiper arm to shift as it had.

I re-positioned the wiper arm to where I recall it having been (glad I made a few marks). Re-tightened the screw, and attempted to start the bus. It started, but only ran a few seconds. By this time it was dark, and snowing so this is where I left it.

Next Steps:
Replace the adjustment screw - it is looking like it's been adjusted a few too many times with the wrong size screwdriver
Troubleshoot the fuel pump behavior - verify it is pumping with the ignition on, and the AFM door propped open

Questions:
Did the AFM being out of position cause it to backfire, or did the backfire force the AFM out of position?
How big of a deal is it to run an FI bus out of gas?

Any comments, complaints, or outbursts are welcome as well.
DJ

'75 Westfalia, '79 Deluxe
(plus more busses than sense)

In a time of chimpanzees I was a monkey

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satchmo
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Re: AFM Trauma

Post by satchmo » Wed Jan 30, 2013 12:51 pm

drober23 wrote: Questions:
Did the AFM being out of position cause it to backfire, or did the backfire force the AFM out of position?
How big of a deal is it to run an FI bus out of gas?

Any comments, complaints, or outbursts are welcome as well.
It isn't good to run completely out of gas on a fuel injection system. At least that is what I've been told. However, I'm not sure what one should do differently than you did if they run out. Perhaps just run the fuel pump a while to get pressure in the fuel rail before you apply electricity to the starter and the coil.

Although I have never experienced it myself, I do know that a backfire bad enough to blow your S-boot off can do significant damage to the AFM. The backfire blows the flapper/door the wrong way and carries the poor wiper who-knows-where. Don't attempt to run it unless you are sure the AFM is back to spec (maybe replace it with a good used one instead).

Good luck, 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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drober23
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Re: AFM Trauma

Post by drober23 » Wed Jan 30, 2013 1:40 pm

I do know that a backfire bad enough to blow your S-boot off can do significant damage to the AFM. The backfire blows the flapper/door the wrong way and carries the poor wiper who-knows-where.
That's exactly what happened. It blew the wiper arm PAST the little copper contact strip. I had to force it back, then reshape the copper strip to get it set up close to how it had been.

So if the backfire is what caused the AFM mis-adjustment, what caused the backfire? Hmmmmm....

I had done some AFM tinkering, and left some marks where it had been running well. I'm sure I didn't get it "exactly" where it had been, but it started right up. I should not have a problem adjusting it back to where it is running well if the only damage done was blowing the adjustment. I am not afraid of this bit, and I also have at least one backup AFM I can use if things don't go well.
DJ

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(plus more busses than sense)

In a time of chimpanzees I was a monkey

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satchmo
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Re: AFM Trauma

Post by satchmo » Wed Jan 30, 2013 2:03 pm

drober23 wrote:
So if the backfire is what caused the AFM mis-adjustment, what caused the backfire? Hmmmmm....
Backfire through the plenum is due to ignition of unburned fuel in the intakes (just to state the obvious.). Your next question, of course, will be why there was a spark and unburned fuel that got into the intakes. This may have to do with running out of fuel and the gas might be dribbling out of the injectors rather than spraying like they do when the fuel pressure is better. Not sure.

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: AFM Trauma

Post by Amskeptic » Wed Jan 30, 2013 5:28 pm

drober23 wrote:what caused the backfire? Hmmmmm....
Damp Michigan air on lousy spark plug wires? Condensation in distributor cap? Two wires cross-talking?
Valves stuck in varnished guides from sitting around too much? Really serious backfires that blow up the S-boot and damage the AFM are not your simple ignition backfires. I think you had an intake valve yawning open when a fresh big combustion event was unleashed. The cure is to drive it fully warmed up and an oil change with good detergent oil, and perhaps a fuel system cleaner that also promises varnish removal.

The slow test for valves not closing is to get each cylinder to TDC, slip the correct feeler gauge on (or with a Raby engine "0" lash) then open the valve manually using the valve adjustment locknut with a socket and long ratchet. Go towards tighten and push in at the same time. Recheck valve adjustment. If it is looser, the valve is hanging in the guide. I had this happen once to the Road Warrior right after rebuild #1 when the machine shop gave me way too little stem clearance, I had a carburetor fire with my little big backfire.
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
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drober23
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Re: AFM Trauma

Post by drober23 » Thu Jan 31, 2013 9:58 am

The slow test for valves not closing is to get each cylinder to TDC, slip the correct feeler gauge on (or with a Raby engine "0" lash) then open the valve manually using the valve adjustment locknut with a socket and long ratchet. Go towards tighten and push in at the same time. Recheck valve adjustment. If it is looser, the valve is hanging in the guide.
Let me try to understand this clearly. the valve adjustment locknut is the jam nut you loosen so you can adjust the screw. I should tigthen the locknut while pushing in on the socket at the same time? I don't need to mess with the adjustment screw during this? I would not expect the locknut to tighten any more unless I exceed the tightening torque. Am I missing something here?

For what it is worth, the engine was fully warm when it ran out of gas. It had been driven about 2 hours total since being taken out of the barn and 45 minutes continuously before it ran out. It is due for an oil change though, so I'll get that done too before driving it more in the spring.
DJ

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(plus more busses than sense)

In a time of chimpanzees I was a monkey

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Amskeptic
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Re: AFM Trauma

Post by Amskeptic » Thu Jan 31, 2013 3:05 pm

drober23 wrote:
The slow test for valves not closing is to get each cylinder to TDC, slip the correct feeler gauge on (or with a Raby engine "0" lash) then open the valve manually using the valve adjustment locknut with a socket and long ratchet. Go towards tighten and push in at the same time. Recheck valve adjustment. If it is looser, the valve is hanging in the guide.
Let me try to understand this clearly. the valve adjustment locknut is the jam nut you loosen so you can adjust the screw. I should tigthen the locknut while pushing in on the socket at the same time? I don't need to mess with the adjustment screw during this? I would not expect the locknut to tighten any more unless I exceed the tightening torque. Am I missing something here?

For what it is worth, the engine was fully warm when it ran out of gas. It had been driven about 2 hours total since being taken out of the barn and 45 minutes continuously before it ran out. It is due for an oil change though, so I'll get that done too before driving it more in the spring.
There is no attempt to actually move the locknut or anything, it just allows you to "brace" as you push open the valve. You may have the experience (particularly with Type 1 engines) of opening a valve as you try to loosen the locknut. Now then, two hours of driving before this backfiring? Might . . . be cooked varnish. Got vacuum gauge? It will have intermittent dives of the needle. I think this might be a better less-involved test.
Check those clearances anyway . . . and mop the kitchen floor. . . BECAUSE I SAID SO, THAT'S WHY.
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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satchmo
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Re: AFM Trauma

Post by satchmo » Thu Jan 31, 2013 3:23 pm

Shouldn't one be able to look at the valves as a helper rotates the engine by hand to see if a valve is sticking?

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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Re: AFM Trauma

Post by Amskeptic » Thu Jan 31, 2013 9:29 pm

satchmo wrote:Shouldn't one be able to look at the valves as a helper rotates the engine by hand to see if a valve is sticking?

Tim
The spasmodic push and release shows actual sticking, you can feel it. Sort of a delayed katank. A creeping wrench turn of the engine will show a badly varnished stuck valve. Have you ever tried to loosen a valve adjustment locknut and felt the valve push in?
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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drober23
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Re: AFM Trauma

Post by drober23 » Fri Feb 01, 2013 6:32 am

Check those clearances anyway . . . and mop the kitchen floor. . . BECAUSE I SAID SO, THAT'S WHY.
I always do a valve adjustment when I do an oil change, so the bus is due for one of those too. I'll do the push-in check while I am adjusting them.

I still think the backfire is related to me running out of gas, and cranking more than normal during the restart. I see how a stuck valve would allow that to happen though.

Headed to California for work on Sunday, so I won't get to it until I get back though. Work has me travelling a LOT this year. A return trip for Thief River Falls MN seems to be in the cards for later this month to get things rolling.
DJ

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(plus more busses than sense)

In a time of chimpanzees I was a monkey

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Re: AFM Trauma

Post by Amskeptic » Fri Feb 01, 2013 2:14 pm

drober23 wrote: I still think the backfire is related to me running out of gas, and cranking more than normal during the restart. I see how a stuck valve would allow that to happen though.
IF the engine was cold enough to trigger the cold start valve that left a pile of nice gas vapor in the intake manifold, perhaps, but what was the ignition source? How many of us have had endless cranking, hard starts, running out of gas, and we did not blow all the hoses off the intake plenum and damage our AFMs. Be alert, you may have an issue, and it involves explosive combinations of fuel and sparks.
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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Bleyseng
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Re: AFM Trauma

Post by Bleyseng » Sat Feb 02, 2013 4:02 am

crappy ignition can cause this too. Check the ignition system for proper operation including cleaning the dizzy spotless along with its wiring connections.
Geoff
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drober23
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Re: AFM Trauma

Post by drober23 » Thu Feb 07, 2013 9:24 am

but what was the ignition source?
I see. Hadn't thought it all the way through to that point yet.
Now that you put it that way, I will be more diligent in the "push test" looking for sticky valve seats.

Got about a foot of snow on the ground here still, so it will probably wait another month before I get after it.
DJ

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In a time of chimpanzees I was a monkey

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drober23
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Re: AFM Trauma

Post by drober23 » Thu Mar 07, 2013 2:54 pm

As I mentioned in my Fuel Gauge post, I got the bus running (and the fuel gauge working). I returned the AFM settings to where I had last marked them, and she started right up once I sorted out the fuel pump contact in the AFM.

It wasn't running well, or idling smoothly though. When I went looking for clues, I found one more, hopefully last, bit of trauma from the big backfire.

Image

Should be able to change the oil and do a valve adjustment this weekend. When I do, I will do the test Colin recommended and report back.
DJ

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In a time of chimpanzees I was a monkey

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drober23
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Re: AFM Trauma

Post by drober23 » Mon Apr 22, 2013 5:37 pm

I adjusted the valves today. When I did so, I did the "push-test" that Colin had mentioned above. I did not see any signs of the valve sticking. A couple valves were a little tight though. Since my engine is set to zero lash, I am not sure exactly how tight. From the screws point of view, two were "5-minutes" tight. As in, the screw was pointing at 5-o'clock before the adjustment, and 4-o'clock after. I was able to wedge my finger in there and spin the push rod though!

I have a vacuum gauge, and will poke around with that once I get an alternator that wants to charge.

Failing that, Colin can help me with it when he visits :-)
DJ

'75 Westfalia, '79 Deluxe
(plus more busses than sense)

In a time of chimpanzees I was a monkey

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