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Posted by: jd74914 Jan 24 2007, 10:12 AM

My brain seems to be toast, and I'm looking at buying a spare known good one to swap in to test out this theory. I have a 74 1.8L with L-Jet; can I use a '75 brain? Are there any important differences between the 2 years?

Thanks.

Posted by: SLITS Jan 24 2007, 02:10 PM

According to Bosch, the brain is the same from 11/73 - 07/75 on the 1.8L
Bosch Part # 0 280 000 103 VW Part # 022 906 021 G

Posted by: Jeff Bowlsby Jan 24 2007, 02:19 PM

I don't have access to my references here at work, but I can say with certainty that there are two different L-Jet ECUs for the 914, a 1974 and a 1975 version. I dont not know what the internal differences are, but one has a 6-pin connector the other has a 7-pin. Contact Jim Hoyland, he may know the specifics.

Posted by: ClayPerrine Jan 24 2007, 04:14 PM

The differences in the L-Jet systems were all in the air flow meter and the wiring harness. The "brains" are identical.

In 74, they used a common wire for both the AFM and Air Temp sensor that is co-located in the AFM assembly. In 75, they split out the wiring, separating the AFM and Temp sensor. Seems there was some feedback issues with the common wire.


I have never seen one of these "brains" fail, its usually something else causing it.

Posted by: Brando Jan 24 2007, 04:19 PM

Usually it's the heating element inside the Air Flow Sensor. The only reason you would need a new ECU is if the one in question has been opened (exposed to the elements and is corroded or broken) or has been physically damaged due to impact or some other trauma.

1.8L L-Jet ECUs are interchangeable.

Posted by: ClayPerrine Jan 24 2007, 04:23 PM

Heating element?? What heating element? This is a vane air meter, not a mass airflow sensor.

Posted by: SLITS Jan 24 2007, 04:26 PM

Ok, I had included in the post but erased it that there were different air flow sensors (VAF) but didn't think it was germain to what was asked ..... silly me

To 07/74 - 0 280 200 001 Porsche & VW Part Number 022 906 301
From 08/74 - 0 280 201 002 Porsche & VW Part Number 473 906 301

Posted by: Brando Jan 24 2007, 04:28 PM

MY MISTAKE, was confused for a moment. There's no heating element, there is a temperature sensor though.

Posted by: jd74914 Jan 24 2007, 06:00 PM

I know my box has been opened by the PO, and had extra wires soldered into it . . . I cut a bunch out, but I would just like to put in a new unopened box.



My real problem is that I went of vacation. The car was running before I left. Then I came back to start it, and it wasn't getting any fuel (i think) or spark. The coil was so hot I burned myself, and I have yet to replace that, and know I definately need to. I found a brain locally that I figured I might swap in as to be garanteed an untampered with box.

Anyone have any ideas what could be the problem preventing the car from getting fuel? I think I can hear the coldstart valve shooting gas, but I'm not sure.

The injectors definately aren't starting? Are the injector pulses times off of the coil?

Thanks for any help.

Posted by: Dave_Darling Jan 24 2007, 08:08 PM

The injector pulses come off the coil--the same connection as the ignition points. Without that one white wire connected, the injectors will never open.

Are they opening?

--DD

Posted by: jim_hoyland Jan 24 2007, 08:26 PM

Don't know the answer; but I do have spare 6 and 7 pin AFMs and a spare brain that came out of one of Joe Sharp's late 1.8L L-Jet cars. They say the brain is the last thing to go.