Replaced AFM. Starts but stops again

[Tejo23]

Hi,

My AFM was faulty. I purchased another after a long search... ('79 Cal) 022. I'm from the Netherlands.

I replaced the AFM and started the motor. It started immidiatly but stopped after a few moments it just died on me.

I checked the fuel pump switch and it worked fine.

Before installation i checked the resistance on the pins and also checked the voltages on the different degrees of the wiper. It was the same as the original AFM. And the values corresponded with the chart given here on the Samba.

Is there a logical explaination for this symptom? Is the adjustment far of?

Thanks a lot for all your knowledge!

Regards
Frank

[Wildthings]

Sure you don't have a large vacuum leak like the brake booster hose being off? You need the white wire attached to the correct side of the coil as well.

[busdaddy]

X2 on the vacuum leak, if it ran a few minutes the system is working, but when it warms up and leans out the vacuum leak wins.

Disconnect the temp sensor #2, it will likely stay running with a stinky exhaust and possibly some black smoke, if it does then vacuum leak or low fuel pressure is to blame.
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[Tejo23]

Thanks for your replies,

The previous AFM is working but it's "on his end". The VW specialist sais it's on his limit on adjustment and the spring is too loose (?)

So the car runs fine with the original AFM. No vacuum leakes and timing is okay.

I was testing the new second hand purchased AFM.

First I hadn't connected the AFM plug accidently and the car run. When I connected the plug the motor started but died immidiatly. not minutes but seconds. I thought no power to the fuel pump but the pump switch works fine (checked by hand at the wiper).

Is it possible the adjustment is way of?

I will try the test with the temp sensor and see if it keeps running.

Thanks

[busdaddy]

There's only two reasons to adjust an AFM, extreme engine modifications, or big vacuum leaks. Sounds like your "specialist" is poking in places he shouldn't be without doing any diagnosis first.

It's so much easier to find the leaks and fix them, here's how: https://www.thesamba.com/vw/forum/viewtopic.php?t=620083&highlight=smoke+tester
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[Wildthings]

A bad vacuum leak will cause the engine to die as soon as the excess fuel from the cold start valve is used up.

Check the operation of the points in the AFM using a meter hooked up to where the plug fits in, so you are reading the complete circuit. Also make sure none of the pins have pushed back out of the plug.

I agree with BD, don't go messing with the adjustments on the AFM, on my '91 Vanagon which we bought new the AFM was never touched during the 300K miles +/- it was in service.

[SGKent]

I must agree. If the old AFM only ran way out of adjustment and with no spring resistance, there is usually only one reason, a vacuum leak somewhere. That includes the brake booster. The solution is to test all the vacuum diaphragms, brake booster, fuel pressure regulator, and do a smoke test on the engine to see where the leaks are. An FI engine needs to be tight. If for example the Oil cap is off and the PCV valve is perforated, then the manifold will suck in unmetered air and die. You have some work to do.
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[Tejo23]

Thanks guys,

I still wonder why the motor runs fine with one afm and dies after a few moments with the other...

I will go and find a way to check for vacuüm

Regards Frank

[Wildthings]

[SGKent]

the most common cause is that the contacts fail so the fuel pump stops. That said. the bodies warp too and let air leak. Another cause is that some early vanes had a spring and button in the vane to help in case of a backfire, they break sometimes and create a big hole in the vane. One of mine had the rubber seal from a connector stuck in it so the pins didn't hook up right with two of those seals - one on the connector and one stuck in the AFM. I pulled the extra one out and all was normal.
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[airschooled]

Bad TS1 air temp sensors in the AFM will cause a no-run condition. Engine will briefly fire on the CSV fuel then die.

Robbie
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[Tejo23]

So i tried the smoke test with a canister, pump, and sigarets (i had to use a lot of sigarets, they burn fast!)

I found a leak in a tiny hole in the cap of the oil breather? Should there be a hole there!?

There was also smoke at the bottum of oil filler tube and at the oil dipstick. I assume those are okay because of the pressure in stead of vacuüm?

BTW it's a 1979 Cal 2.0 injection

[SGKent]

the PCV valve is bad. That is why you see smoke out the small hole. The diaphragm is perforated. When it is bad it allows any air leak on the case, like the oil filler leak, valve covers with leaky seals etc., to pull air in there, thru the case and into the S-boot, That reduces the accuracy of the AFM vane. If the leak is big enough then the AFM is way off.

There is a page not long ago on how to adapt a later model PVC valve because the originals are NLA. I bought a couple a year ago. They are $100 each shipped insured. The work around is a lot less.

The leaks would affect how it runs but probably not keep it from running.
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[Tejo23]

[AshC]

FWIW, part of that setup for the replacement PCV using VW 06A 129 101 D means making a hose that goes from 19mm ID at the PCV to 22m ID at the S-Boot through 90 degrees. Although a bit "string and glue" I found one of these useful to make that up: https://www.carbuilder.com/uk/black-nylon-stepped-elbow-1619mm-2522mm

Obvious, but I cut the 16mm section off : )
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[Tejo23]

I installed the new PCV-valve. I Couldn't find a good grommit so I cleaned out the inside of the old valve and placed the new valve in the hose to the S-boot.

The motor runs well on idle. But with a little bit of throttle it stalls. No power at all...

I installed the old AFM and the bus runs fine! Exept th idle is a bit high even with a warm engine.

Is it normal for the idle to be higher after a vacuum fix?
Is it possible the replacement AFM's adjustment (my spare) is way of? (too rich?)

Regards frank

[busdaddy]

If you didn't plug the little hole in the cap of the old PCV it'll still leak vacuum.

Sounds like your new AFM isn't turning on the fuel pump, have you tried the continuity tests on the pins to confirm it works?
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Rust NEVER sleeps and stock never goes out of style.

Please don't PM technical questions, ask your problem in public so everyone can play along. If you think it's too stupid post it here
Stop dead photo links! Post your photos to The Samba Gallery!

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[Tejo23]

I did plug the little hole so it doesn't leak there anymore.

When i turn the rotor of the afm by hand the fuel pump starts pumping. How does the continuity test work?

Frank

[SGKent]

bad question on my part but did you plug the connector back in, is it possible you forgot it again?

If it were me, and one AFM worked fine, I would run with that one and put the other in the parts box for another day. There are a couple things that can go wrong with them, including the TS1 going out, the fuel pump points not making contact at idle, the copper where the center sweep attaches getting corroded and not making good contact, the body warping and bypassing air around the vane. Sometimes the rubber seal can come out of the plug and stick inside the connector on the AFM. If it came out of another bus and your connector plug has the rubber then there are two rubber seals on the connection and that can keep the connector from going on fully. I actually had that happen to me with a used AFM I bought once. I also had one that was unstable - I suspect the TS1 was bad in it.
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