Engine cutting out

[satchmo]

I'm one hour north of San Francisco and need some advice. 78 Westy has been running pretty good but has had increasing episodes of cutting out or bucking behavior. Last time I had this happen, cleaning the AFM wiper board helped a lot. This time, not so much. The tracks on the wiper board are worn through in a few places, so I moved the wiper board a bit, and the engine still cuts out, mostly on acceleration. I moved the board again, and the bucking is worse. No trouble starting and no trouble at idle. I really can't get the engine to reproduce the bucking in the driveway either.

I checked the distributor, the points, the Plug wires, the AFM connector and, to placate my co-pilot,put in a new fuel pump and filter. Is there something else I should check?

Thanks in advance for your help. I need to head back home on Sunday; a nine hour drive. However, there are many places much worse than the Point Reyes National Seashore to be stranded. I'll tell you all about it, ONCE I GET HOME.

Happy New Year, Tim

[SlowLane]

Hate to sound like a broken record, but have you checked the AAR elbow for cracks/splits? That one has caught me a couple of times with lurching/bucking behavior.

Feel free to swing by Livermore on your way home if I can be of any help. I have a few spare parts, including some AAR elbows. PM me for address/directions.

Lyle

[Amskeptic]

increasing episodes of cutting out
checked the distributor,
the points,
the plug wires,
the AFM connector,
put in a new fuel pump and filter.
Is there something else I should check?

Smoothly increasing rate of episodes might suggest a vacuum hose split that opens up a little more after the engine does a major shake. As SlowLane mentioned, start with a comprehensive check of vacuum integrity. Did you glue your valve cover gaskets to the valve covers? If not, check them for proper positioning.

If this symptom is temperature related (like it never screws up when engine is still cool), consider things like ignition coil resistance, temp sensor 2 resistance. If everything checks out, lean the mixture at the black cog 4-6 clicks, we want to either inflame or ameliorate symptom. If inflamed, go rich a bit and see if that helps. If it improves (my guess), you have a choice.
A) lean it by means of wiper?
B) lean by means of black cog?

Use A if idle is saying it is a little rich at full operating temp.
Use B if idle is already close to too lean.
Colin

[satchmo]

OK, thanks, I'll give it a go. My tool box is pretty limited (ie, no vacuum gauge) and I'm on a steep driveway, plus it looks like rain for the next two days. Slowlane, you may hear from me!

Tim

[SlowLane]

My tool box is pretty limited (ie, no vacuum gauge) and I'm on a steep driveway, plus it looks like rain for the next two days. Slowlane, you may hear from me!

I'll be here, I expect. Don't know what the wife has planned for my day off. Looks like rain here, too.
Vacuum gauge may not be of much help diagnosing a split AAR elbow on a warm engine (when the AAR is closed), as the leak would show up on the upstream side of the throttle plate, but after the AFM. End result is a lean condition caused by "false air" introduced into the engine that the AFM doesn't get a chance to measure.

[Amskeptic]

Looking forward to the successful resolution report. When you see the dashboard on his Vanagon, satchmo . . . . . you'll see how serious fun can be.

[SlowLane]

When you see the dashboard on his Vanagon, satchmo . . . . . you'll see how serious fun can be.

Heh. I've added more toys, er, monitoring capability, since your visit.

[satchmo]

No joy yet. I checked all the hoses including the AAR elbow. Nothing appears to be causing a vacuum leak. I always use hylomar on the valve cover gaskets.

I leaned out the AFM six clicks counter clockwise and I really don't think that helped much. Maybe a little. I don't understand how making the map leaner across the board could be helpful if there was a possibility of a vacuum leak.

For what it's worth, the cutting out happens most frequently when accelerating with rpms between 1800 and 3000. It happens when coasting at times. It never does it when I test it in the driveway. Tweaking and driving here is difficult since I'm at the end of a long drive on a hill with a hairpin turn and no road, over 35mph nearby.

I still think there is something wrong with the AFM or the signal to or from the AFM. Moving the wiper board slightly is the only adjustment that has reliably made any difference at all.

I'll ponder this some more and maybe investigate why my camper battery isn't charging and why my headlight high beam on the driver side isn't working - and yes, I put in a new bulb.

[SlowLane]

No joy yet. I checked all the hoses including the AAR elbow. Nothing appears to be causing a vacuum leak.

Checked the S-boot for cracks, too?

For what it's worth, the cutting out happens most frequently when accelerating with rpms between 1800 and 3000. It happens when coasting at times. It never does it when I test it in the driveway.

I still think there is something wrong with the AFM or the signal to or from the AFM. Moving the wiper board slightly is the only adjustment that has reliably made any difference at all.

If you're convinced that it's the AFM, and if you can limp your way over here, we can try substituting my AFM (less than a year old on the rebuild by FIC) to see if it smooths things out. Yes, it's a different part number for a Vanagon, but I bet there isn't that much difference in the AFM respone curve between an '78 and an '81. Then, if that gets rid of the hiccups, you can borrow my AFM to get you back home. My van is off the road until I can get it past the smog referee anyways, so you woudn't be depriving me of the use of my van.

why my headlight high beam on the driver side isn't working - and yes, I put in a new bulb.

Fuse?

[Amskeptic]

the cutting out happens most frequently when accelerating with rpms between 1800 and 3000.

I still think there is something wrong with the AFM or the signal to or from the AFM. Moving the wiper board slightly is the only adjustment that has reliably made any difference at all.

If you're convinced that it's the AFM, and if you can limp your way over here, we can try substituting my AFM (less than a year old on the rebuild by FIC) to see if it smooths things out. Yes, it's a different part number for a Vanagon, but I bet there isn't that much difference in the AFM resposne curve between an '78 and an '81.

Please bear with me, Tim. Leaning it out was not a prescription for a lean condition that a discovered cracked hose or shifted gasket would have pointed towards. Leaning it out would only point out a too rich condition that I have discovered sometimes results from a little too much counterclockwise on the cog (especially if you followed my intuitive AFM adjustment procedure ).

There is an insane possibility, one that has been addressed a few times, where the rear tires slowly go out of balance and rock the engine just enough to annoy the AFM. The VW dealer first pointed this out to me with my '89 Vanagon shod with oem Dunlop tires. I had gone through every conceivable fix to get rid of the irritating minor hesitation, and nothing worked. Only when I had reached apoplecty did I seek out assistance. The dealer recommended replacing the rear tires which unleashed a new fusillade of fury, but that fixed it forever. And by the way, a simple "rebalance at the tire shop" will not erase the distortion through the tread that makes the AFM dance at a sympathetic frequency. "hysteresis" the guy said.

If SlowLane's AFM does not cure it dramatically (and let's hope it does) , get another set of wheels and tires on the rears as a time-consuming and annoying experiment, especially if you can feel cupping.
Typing is exhausting.
Colin

[satchmo]

Thanks for the advice and the offers of parts and assistance. So far, everything I have tried today has resulted in worsening the problem rather than improving things. Now I get about 5-10 seconds of decent running before it bucks, sometimes just once or twice and other times I just have to let off the gas as the bucking is horrible. I thought at one point it may be temp related, but this eve it bucked right after a good cool down, and continued to buck when warm.

So far, I have checked every hose connection for vacuum leaks, checked every wire connection (but I haven't checked every wire for continuity), replaced the fuel pump and filter, replaced the Temp sensor II, examined the points, rotor, cap and plug wires, checked the ground connections, and cleaned the AFM. I was able finally to reproduce the bucking in the driveway but I have no idea what I did that caused it. The engine still starts easily every time, but now the idle can be a bit lumpy; surging and slowing in a cyclical way.

Tomorrow, I will take the S boot off and look for splits. I don't know how to check the coil and unfortunately I don't have a spare. It's raining now, of course, and if that keeps up it may force my hand a bit - no garage here.

Tim - index finger tired of typing on a tiny screen.

[SlowLane]

Sorry to hear that the solution continues to elude you, Tim.

Out of curiosity, how old is your distributor? Has it ever been rebuilt or relubed? I'm wondering if maybe you have a sticking advance mechanism (either vacuum or mechanical) that is causing your woes.

[satchmo]

Sorry to hear that the solution continues to elude you, Tim.

Out of curiosity, how old is your distributor? Has it ever been rebuilt or relubed? I'm wondering if maybe you have a sticking advance mechanism (either vacuum or mechanical) that is causing your woes.

Not sure how old it is, but I neglected to mention above that I checked the function of the advance plate. It moves well and the vacuum canister holds a vacuum. The EEC diaphragm holds vacuum too. No electrical issues seen at the dist either. Wire connections are good. No arcing noted in the cap.

I will check the s-boot and all the wiring again today, then maybe run a test with the Temp sensor grounded and one with the vacuum hose on the FPR plugged if I'm not getting anywhere. What's your schedule this weekend?

Tim with a little insomnia

[SlowLane]

Not sure how old it is, but I neglected to mention above that I checked the function of the advance plate. It moves well and the vacuum canister holds a vacuum.

I was actually thinking more along the lines of mechanical advance stickiness, rather than the vacuum advance.
If needful, I can also loan you a fairly fresh Mexican SVDA (with either poiints or XR700) which I can assert is a solid performer. Fedex is an option to get you the parts if you can't get 'er running well enough to survive Bay traffic trying to get here.

What's your schedule this weekend?

I'll be helping a young friend put his GTI back together this afternoon at his place. Aside from that (and the inevitable honey-do list), it's open.

[Amskeptic]

So far, worsening problem.

Worsening should help you find it.

Imagine, what kind of problem could have actually survived all that you have already dealt with?

Loose double relay ground? Cracked spade on the engine block ground cluster? Slightly out-of-position wire terminal in the double relay connector?
Colin
(if it gets hopeless, make it sunny and warm, and I will come out and help)