TheSamba.com :: View topic - Air flow meter (AFM) plug

Sun Nov 15, 2009 12:28 pm

Quote: Just ran another test. The fuel pump works with the ignition in the ON position but only when the AFM flap makes contact. if I crank the engine, there is not enough contact in the AFM to activate the fuel pump. It bounced back and forth off of the contact so there is no hum or clicking from the fuel pump. Any ideas?

I have a 1977. Based on what you are saying, you can pop the black top off the AFM by cutting the silicone glue seam. At rest the contact points to the right inside the AFM should be 1 to 2 business card thicknesses apart. It is not a critical measurement. When the AFM wiper is rotated, which you can do by swinging the metal shiny part on top sort of triangular, the relay should click if the keys are on. Then when you crank the engine the air passing through the AFM should be enough to open the door and those contacts should touch. When you go to seal the black cap back up, do not use regular silicone sealer as the acid in it will get into the air and attack the electronics in the unit. Get the 3M Silcone II type at Home Depot for bathroom caulk etc, the clear kind. It doesn't have as much acid in it, or if you can find it get the MIL spec electronic safe silicone. Below is a photo from Richard Atwell.

We got our replacement AFM from Fuel Injection Corp in Livermore CA. See Robert White Jr (CEO) or Tony. I believe that German Supply and Bus Depot sell their rebuilt units also. These units are all getting old and even rebuilt ones can have minor imperfections, but they do stand behind their warranty. Or you can just pay to have yours tested and rebuilt if needed. I took in 3 - one was bad, one was marginal so we replaced it and one was good but out of adjustment so they adjusted it.

If your fuel relay clicks then the bus should start if you have spark. The coil probably gets hot because if you have points you cannot leave the keys on or it will burn the points - meaning they will get hot and glazed. I use a timing light to check for spark. If the light flashes then you have spark.

Sun Nov 15, 2009 12:41 pm

I have a huge black wire that runs from the starter into the engine bay. In the engine it is spliced together with the red wire that does to the positive terminal of the battery. Where should the alternator be grounded?!? My battery only has one grounding strap to the frame - should there be another wire from the battery going to something else?

Sun Nov 15, 2009 12:47 pm

the transmission to post on the driver side torsion tube mount.

Sun Nov 15, 2009 12:58 pm

Here is what mine looks like. I'm guessing the braded wire cable is ground?

I wil try the clicking AFM test next.

[img]http://www.thesamba.com/vw/forum/album_page.php?pic_id=619305[/img]

Sun Nov 15, 2009 1:00 pm

Sun Nov 15, 2009 1:05 pm

"Ground?"

That is the wire that supplies power from the solenoid to the starter. The ground wire is on the left front of the transmission, connecting to the torsion tube. It braided ground wire and its connections are often pretty corroded. At a minimum remove it and clean the connections. If the wire itself seems even slightly corroded just replace it.

Sun Nov 15, 2009 1:13 pm

The fuel relay clicks when I put the ignition in the second (ON) position. I'm guessing I don't have spark? There is definitely a strong spark from the coil but the spark is weak from the plug.

Sun Nov 15, 2009 1:18 pm

The ground is intact and good on the transmission.

Sun Nov 15, 2009 2:18 pm

So, from this page (http://www.nls.net/mp/volks/htm/spark.htm) I did a test using the light meter on terminal 15 at the coil while I cranked over the engine. Terminal 15 is not getting any power when it's cranking over.

"Double check that there is power at Terminal #15 while cranking the engine with the key. This is important because sometimes power will be lost while cranking due to a contact failure inside the ignition switch."

Ignition switch?

Sun Nov 15, 2009 3:46 pm

Quote: The fuel relay clicks when I put the ignition in the second (ON) position

yes but only when the AFM door is open.

Does the engine crank over?

Also, I am trying to figure how you know you have a spark if there is no voltage at the coil. If you do have a strong spark at the coil but a weak one at the plugs, check the rotor and cap for carbon tracking, then measure the resistance in the plug wires. It should be no greater than 8,000 to 15,000 ohms if resistance wires and 5 to 15 ohms if solid core wire or spiral wound. Also - sometimes if you have someone else crank it in the dark (keep your hands out of the engine bay and just observe) you will see if the jackets on the wires are breaking down and shorting to ground by sparks and glow along the wires where they pass metal.

Sun Nov 15, 2009 4:24 pm

My guess is that some wire you messed with in your "hot coil" post didn't end up going back to where it needs to be. I really think you need another vehicle to compare your wiring with.

Sun Nov 15, 2009 5:04 pm

This thread has changed a lot since last night :shock:
Can you tell us if the bus ever ran? Or if anything changed recently?
Did it suddenly stop "starting".
If it did run previously, Have you checked the coil?
here is a procedure::
Quote:
For a stock coil about 3 ohm primary (between terminals 1 and 15) and 8 kohm secondary (terminals 4 and 1).
Dont give up!! when you get er figured out you will be well versed in the workings of your rig.

Sun Nov 15, 2009 7:45 pm

Quote: Can you tell us if the bus ever ran? Or if anything changed recently?

The bus ran when we first got it but not very well. The only way to keep it running was to keep your foot on the gas. One of the valves was stuck, it had bad compression, and was squirting oil everywhere. So we did a rebuild. Bought brand new everything. We accidentally dropped the coil and broke the end so we bought a brand new coil. The only thing on the bus that hasn't been replaced is the distributor (rotor, points, and condenser are new) and starter/solenoid.

Sun Nov 15, 2009 8:16 pm

I'm sure you statically timed it after replacing the ignition components. Do you have a remote starter trigger? They can make cranking while testing much simpler. Test that your ignition system is firing properly.

Sun Nov 15, 2009 8:16 pm

Ok - so can we ask some questions. Please forgive me if I ask something you have already answered because it is late and there isn't time to re-read the whole thread.

Where are you with the fuel pressure? Have you confirmed that you have fuel pressure to the injectors?

The fuel is new, yes?

With a timing light hooked to #1 and the engine cranking what is the dwell showing and where does the light fllash (what is the timing)?

With the rotor pointing at #1 on the distributor can you confirm that both intake and exhaust valves are closed?

Sun Nov 15, 2009 8:18 pm

also - ziggybean you might consider putting where you are into your signature so if someone else is nearby who has been through this they may be able to help.

Mon Nov 16, 2009 9:14 am

We have not tested the fuel pressure, checked the timing, or looked at the valves yet. We set the timing internally when we assembled the engine as well as adjusted the valves at that point (it has hydraulic lifters). Will check these things today. The fuel is brand new.

We clamped an inductive timing light to each of the wires going to the spark plugs last night and there's a current flowing through them.

The timing was perfect when we assembled the engine - everything lined up as it should at TDC. Can the timing be off if everything internally was set correctly?

Thanks!

Mon Nov 16, 2009 9:37 am

normally an engine will start if the timing shows between 10ATDc to 25BTDC by a timing light when cranking. Once started the engine builder can adjust it. Personally I static time it and then tweak it a degree or two once it starts but you have to be quick about it because of the breakin procedure. If the light is flashing them you have spark. So if you have spark and the timing is in the ballpark, and you have compression, there is only one thing left - air to fuel mixture. Use a trouble light to verify that each injector is firing.

Mon Nov 16, 2009 9:01 pm

One of the valves on cylinder #1 (closet to the flywheel) is not moving when we manually crank the engine (intake?). The valve spring doesn't compress. Is this a problem with that lifter or something else? We have hydraulic lifters. I bled all of the lifters prior to installation. It makes a hissing noise but nothing moves.

Mon Nov 16, 2009 9:19 pm

The valves closest to the flywheel on #3 and #4 are closing (spring fully released) at the same time.