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Wed Aug 24, 2011 12:08 pm

I just got my 1975 bug running after spending a year going through restoration. It starts right up and has a decent idle. When I open the throttle slightly, the engine will begin to rev up and then die. I have been going through the fuel injection components, and I have come across something with the air flow meter that certainly does not look right. Looking at the schematic, there is a variable resistor connected to the air flap. The wiper goes to pin 7, and the two ends of the resistor go to pins 6 and 8. Therefore, if I connect an ohmmeter across pins 7 and 6 OR across pins 7 and 8, I would expect to see the resistance vary smoothly as the air flap is moved through its range. What I get is resistance readings that jump all over the place. For example between 6 and 7 the resistance starts out around 800 ohms, then it quickly jumps into the 300 range, then it jumps up and down between 100 and 300 until it gets near the end of travel, where it settles down to about 40 ohms. I cannot imagine how a signal like that can be useful to the ECU, and I am guessing the variable resistor is bad. Does anyone know what the resistance readings are supposed to be on a good unit? These things are not cheap so before I buy another one I would like to confirm that the one I have is really bad. :?

Thu Aug 25, 2011 1:52 am

If there is an Mass Airflow Sensor (it's a small metallic thing), it is very sensitive so don't touch it but spray it with electronic parts cleaner and maybe a Q-tip, gently, let it dry and then try running it again. I found that my sensor on my MPV was covered with 8 years of dirt. I cleaned it once and I couldn't believe the pick up on the van. It was like a new car.

Just a shot in the dark. I have a '66 and know nothing of VW FI. I just read your post and the MAF sensor popped into my head. Good luck.

Thu Aug 25, 2011 4:23 am

Bosch L-Jetronic did not use a mass airflow sensor like modern vehicles. This is an airflow meter, Bosch part number 0 280 200 006. It is nothing more than a variable resistor tied to an air flap. Airflow through the intake pushes the flap open which in turn moves the wiper arm on the resistor. What I need to know is: What is the normal range of resistance readings between pins 7 and 6, and between pins 7 and 8, as the flap travels through its range of motion. Pins 38 and 39 connect to switch that simply switches the fuel pump on and off, this part I know is good. Does anyone have a specification for the variable resistance range? Or, does anyone have a known good unit who would be willing to clip an ohmmeter on it and measure the resistance values? I would be most grateful.

Thu Aug 25, 2011 6:49 am

Been here?

http://www.thesamba.com/vw/forum/viewtopic.php?t=369815&highlight=afm+testing

Thu Aug 25, 2011 9:07 am

Randy in Maine, Thank You for the pointer! That AFM is for a Vanagon but it is exactly the same concept, only the pin numbers are different. This confirms my AFM is defective. Now I just need to find a new one...

Thu Aug 25, 2011 11:57 am

madwelder wrote: Randy in Maine, Thank You for the pointer! That AFM is for a Vanagon but it is exactly the same concept, only the pin numbers are different. This confirms my AFM is defective. Now I just need to find a new one...

Did you try cleaning it first?

Thu Aug 25, 2011 1:23 pm

Yes, I cleaned the resistor with alcohol. There is so much wear on the resistor it looks like the contacts wore completely through in one spot. I even tried moving the board around slightly so the contacts are touching a different area, but the grooves are so wide I had no luck. The cover had been stuck on with silicone, so it appears that someone had worked on it once before.

Thu Aug 25, 2011 4:22 pm

Well if it all goes bad, we usually send them off to these guys to have them rebuilt.....

http://www.fuelinjectioncorp.com/about.php

Thu Aug 25, 2011 8:27 pm

I hade to do the same with my 75.
Rock Auto has new (refubished I think.) from BOSH

Thu Sep 01, 2011 1:08 pm

I ordered a remanufactured air flow meter from a place called auto-parts-online because they had it listed at the amazing price of $76. It turned out to be too good to be true; after 5 days they sent me an email saying they had nothing to ship to me.
I then ordered a Standard Motor Parts remanufactured unit from Rock Auto. It showed up in two days. I put it on and I could barely even keep the engine started. Pulled it off again and noticed it looked a bit different from the original. I flipped it over to check the part number, and found that someone had ground off the last three digits! I do not even think it is the right part. Needless to say this one is going back.
Rock auto lists brand new genuine Bosch units but they are expensive! I am not sure what other alternatives I have. It is either try for another rebuilt unit or try some old used one, either way it is a crap shoot. I will probably just bite the bullet and get the new Bosch. The car has already gone way over budget so I guess it really does not mater anymore.

Thu Sep 01, 2011 5:04 pm

Send the original one to these guys....

http://www.fuelinjectioncorp.com/about.php

Fri Sep 02, 2011 8:02 am

I looked into ordering a brand new Bosch air flow meter from Rock Auto, a message came up saying it is no longer available from Bosch and it was removed from my cart. I called up Fuel Injection Corp, I asked if the remanufactured units use new resistor boards and was told no, they are good used parts. The guy I spoke to, Bob, seemed like a real nice guy and talked to me for a while, he convinced me that he really knows his stuff. He said they guarantee the unit for 18 months, so I deceided to take a chance with them. Hopefully this one works out better than the last one.

Tue Sep 13, 2011 4:58 pm

I bought a remanufactured air flow meter from Fuel Injection Corp. I installed it, the car started right up, then stalled a second after I let go of the key. I suspected the fuel pump was shutting off. I pushed the air flap open with the key turned on and did not hear the fuel pump. I hooked an ohmmeter across terminals 38 and 39 and pushed the air flap open, sure enough there was no continuity. It looks like they remanufactured the thing with a broken switch. Nice work. This is two junk remanufactured units I have received from two different companies. I ran out of time on this project weeks ago and need the car out of my shop now. I did not want to take my chances with some old used unit, but at this point I am thinking I would probably have better luck. I now understand why people rip the L-Jetronic system out and install carburetors.

Tue Sep 13, 2011 6:41 pm

Call them. See what they say.

Thu Sep 22, 2011 12:57 pm

I am a little late getting back to this, but anyhow I calld Fuel Injection Corp as soon as I realized I had a problem. The guy was trying to tell me I have a vacuum problem even though I told him there was no continuity across the fuel pump switch. I asked him to send another unit out but he said he had no more cores so he needed to get the one he sent me back so he could fix it. I told him not to bother, issue a call tag, and refund my money. Fortunately some nice person recently posted a NOS air flow meter in the classifieds and I bought it.

Wed Dec 21, 2016 11:48 am

Yeah an old thread but for anyone needing to know you can probably just bend the connector a bit to make the pump contact work, It is really easy. There are two brass armatures inside the potentiometer, and if they don't meet fully when the flap opens there is no fuel pump.