Troubleshooting 1.9L 1984 Vanagon distributor timing

[vanquick]

Hello!

So, I have a 1984 watercooled volkswagon vanagon and I have been running into some issues adjusting the distributor timing. Here is my procedure:

1. make a mark 2" to the right of the notch in the flywheel (~35 degrees).
2. Loosen 10 mm bolt to adjust dist. position
3. turn van on
4. shine timing light on mark
5. adjust van rpm to ~3000 rpm.

My problem occurs in step five. As I am increasing the throttle the mark suddenly disappears. There is almost a specific threshold of rpm where the mark just vanishes. It almost appears as if the flywheel is too unsteady to properly show the mark. I have taken a video of the phenomenon, and will attach a link here: https://www.youtube.com/shorts/vOK5drrTgV4

My apologies, the video quality is far from professional.

Some additional background information:

1. The van experiences "jerking"/"bucking"/power reduction at higher rpm's while driving.

2. I conducted timing procedure also with the vacuum lines plugged but it didn't prevent the mark from disappearing

2. I tested to make sure the hall sensor on dist. was working properly by loosening the dist. enough so that I could rotate the rotor. I disconnected the ignition coil plug and put in on the engine. Every quarter turn successfully sent a spark to the coil. and the pump was activated as well. However, in the Bentley manual there is a test in section 24.20 where you test the pins in multi-pin connector of the ECU. in the test where you check voltage across pin 1 and 7 and ground the center ignition wire of the distributor cap. In this test I read 0v but it should've read 12 v. So that is odd.

[DanHoug]

what cap and rotor are you using on the distributor? i see a brief flash of a new orange color that is like the JP Group 'Classic Line'. that alone may be your problem. try a genuine Bosch cap AND rotor if that isn't what you have.
_________________
-dan
60% of what you find on the internet is wrong, including this post.

'87 Westy & '89 Westy both 2.1 4spd

Past projects can be found at--
www.thefixitworkshop.com

[vanquick]

Hi Dan,

Thanks for responding so quickly! It is the original Bosch distributor. I was reading another post where the weights inside the distributor were not moving freely. Part of me wants to bench test the distributor. I’m curious if another component could be causing the weird disappearing mark thing. I did all of the other multi pin connector tests in the ECU and they all passed. So, I have a feeling it is something funny about the dust.

[hdenter]

The Strobe keeps flashing, so the spark plug is firing. You need to cast the light about a bit more to see where the mark jumps to as the RPM increases. If you are timing by the 10cent method with the Idle Stabilizer leads connect to the unit, then it may be trying to do it's job. Are you sure your throttle position switches are working properly and that you were not interfering with them as you were holding the throttle open? If the ECM does not know that you have come off idle, the ISU will electronically change the timing to try to bring the engine back down to 900RPM. Make sure you throttle position switches are functioning properly and that you aren't interfering with them when you hold open the throttle. Or, disconnect the leads to the ISU and plug them into each other to take it out of the picture.

Hans
_________________
'79 triple white convertible bug
'84 sunroof vanagon
'85 weekender

[DanHoug]

i'm not liking the flash tube behavior of the timing light. is it steady at idle? at what RPM do the timing marks become erratic?

i'm always one for making solid base lines when troubleshooting. so:
- new coil, cap, rotor, plug wires, and plugs. aside from the coil, which are all approaching 40 years old, this is just basic tune-up stuff.

i'm suspecting cross firing on the plug wires, coil breakdown, carbon tracking in the distributor cap, dirty coil tower, arcing of the RF shield, etc... something in the high voltage side of the ignition system. regardless, a new and true baseline is not money wasted.

additionally, test your advance and retard cans to a) make sure the diaphragms don't leak, and b) each can moves the rotor when vacuum is applied.
_________________
-dan
60% of what you find on the internet is wrong, including this post.

'87 Westy & '89 Westy both 2.1 4spd

Past projects can be found at--
www.thefixitworkshop.com

[heimlich]

Is this occurring at high or low RPM?
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[Wildthings]

I would paint the mark a color that was easier to see.

35° BTDC at high rpm is not the correct timing setting for a 1.9L engine, don't know where that came from. Best to set the timing at 28° BTDC @3800+ rpms, hoses removed and plugged and the Digital Idle Stabilizer bypassed. If the retard can will not hold vacuum, then do not reattach the hose to it, but plug it off. 28° BTDC is something like 1 5/8" to the right of the "u" mark.

[hdenter]

He's probably trying to use the "all in" 10cent method. He just tried it without th vacuum advance once to see what would happen and still had the same trouble. "All in" works, just need to test the vacuum can first.

Hans
_________________
'79 triple white convertible bug
'84 sunroof vanagon
'85 weekender

[vanquick]

Thank you everyone for the replies! So, to answer some of your questions:

1. The timing light is steady at idle and up to 2000 rpm, but as I increase from there timing mark disappears (I can not see it even when I search around on the whole flywheel).

2. This only occurs upwards of ~2400 rpm

3. The mark is a little hard to see in the video, but is very clear in person that the mark is no where to be seen on the flywheel when the timing light is firing.

4. I am using the 10cent method I believe.

Please correct me if I am wrong, but this is my knowledge of how the timing light works with the distributor:

At 0 degrees advance, the timing light flashes exactly when the first cylinder spark plug wire receives an electrical signal. At 0 degrees at advance, this signal (and flash of light) should occur when the notch of the flywheel is aligned with the case seam. When the flywheel notch aligns with the case seam, the first cylinder is at the top of the stroke.

For my mark on the flywheel to "disappear" the signal being sent to the first cylinder would have to be very out of time, or the timing would have to be inconsistent. This leads me to believe it isn't a problem with the vacuum advance not working. Because, if the advance wasn't working then as I increased the rpms the mark would just stay in the same location. It wouldn't disappear. Dan said it is likely a high voltage electrical problem. I think this is correct based on this reasoning.

Thank you for allowing me to think out loud a little bit. I'm sure everyone knows this, but I just wanted to clarify my understanding just in case.

In addition, I ended up dissecting the distributor just to get a better understanding of things. I took some photos and everything seemed to be in good condition. there wasn't much wear on the contacts. However, when I took the hall sensor out I may have found something.

The vacuum advance arm is connected the hall sensor plate, but this plate is very "sticky". its really hard to rotate this plate, and this plate is responsible for adjusting the amount of advance. Also, I checked the vacuum cup itself by sucking on either vacuum line and it held air and I could hear the vacuum adjusting.

Do y'all know if this plate is supposed to have some friction to it? Would it hurt to put some wd-40 between the plates? Furthermore, if you can think of a likely culprit for the erratic electrical signal at high rpm let me know.

Here is a link for a video of the hall plate rotor stickiness that I am talking about: https://www.youtube.com/shorts/9Yq_rDnSYMY

[heimlich]

[skills@eurocarsplus]

yea, service the sticky points plate before going any further but you're not going to build pressure or blow out the canister because of this
_________________

[heimlich]

If you have a door that is stuck closed does it take the same amount of force to open it? If you apply the same amount of force does it take longer to open the door? Vacuum canisters are just door pulls. The more vacuum you put into a canister or the longer you put vacuum into a canister the more wear that occurs. The more wear that occurs the quicker the wear will fail the part.
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[Glenn]

I'm surprised that gas shocks don't blow out after just a few miles.... if that as true.

I found that most vacuum canisters fail over time being exposed to fuel dripping down the vacuum hose and causing the diaphragm to harden and rupture.

While rebuilding vacuum/mechanical distributors, that had frozen breaker plates, I did not find a higher than average failed vacuum canister.

But then what do I know about distributors.
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74 Beetle Specs | 74 Beetle Restoration | 2180cc Engine
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[Wildthings]

[heimlich]

Gas shocks use a piston and a cylinder. The piston is pressed in and creates pressure. Ask some experts: https://camloc.com/us/help-centre/how-gas-struts-work/how-do-gas-struts-work/

Picture below of the internals of a vacuum canister. It's a diaphragm with a metal arm attached to it. The pressure of the metal arm is dispensed against that diaphragm. I wonder where it tears. I think it's where that arm has all the extra pressure on the middle of the diaphragm.

_________________
www.vwnos.com [email protected]
Classic Brands. Classic Quality.
Not all parts are made the same. NOS OE/OEM parts made mainly in West Germany, Early Germany, and Early Brazil are where VW produced the best quality parts and best fitting products.
5% Off your order with coupon code: 5%OFF
Restored Distributors Available (<--Click here)

[hdenter]

So, the OP was trying to do the 10cent method. I never said he was doing it correctly, and yes, 42deg would be closer to ideal. However, a 7deg error wouldn't explain what is being shown. When he get to the point where the mark disappears, the strobe keeps flashing. That means the sparkplug is firing (or at least the high voltage is going to ground through the sparkplug wire) and that the mark is somewhere WAY off and out of view. The only thing I can think of that could do that is the Idle Stabilizer. As was said earlier, pulling the leads from the idle stabilizer and plug them together will take it out of the picture.

Hans
_________________
'79 triple white convertible bug
'84 sunroof vanagon
'85 weekender

[wcfvw69]

[Ahwahnee]

The video is gone now but when I watched it I wondered if the OP was using the wrong timing mark. The correct one is, of course, the U-shaped mark in the rearward rim of the pulley (TDC). The V notch on the rim closest to the engine block is 5° ATDC.

FWIW, I use 40° BTDC all-in. Seems to be happy there and no issues in running with that.

[MayorMcCheese]

For reference here are the Bentley specs.

21-25° centrifugal advance at 3800RPM
12-16° max vacuum advance

25+16= 41° all in by my count?

The range is 33-41° all in, if all that's correct.

As for your sudden drifting at high RPM are you sure it's not your timing light getting a signal from a different spark plug lead? They can interfere at high RPM if they are grouped together.

[Wildthings]