[T3] Diagnosis help for a badly running 1971 VW 411 (Jim Adney)

Doug Brashear dougbrashear at yahoo.com
Mon Aug 12 06:45:29 PDT 2019

I have both a '73 FGI Fastback and a '75 FI Bus and can tell you that the FI systems are definitely different...L-Jet vs. D-Jet if I remember correctly. The one in the Type 3 is based on manifold pressure measurement and the Bus' is based on volume of air intake (likely akin to what we have in modern cars). 
You'll definitely find a LOT of good Type 4 FI advice in the "Bay Window" forums over at TheSamba.com. There are entire sticky topics focused on trouble-shooting the FI system. Right Off the bat I'd say that your engine is exhibiting symptoms from likely several different causes. You'll definitely want to baseline your understanding of the situation by beginning to rectify and set to factory standard one component of the system at a time, and in the process perhaps replace some of the lower cost yet super important items like points, condenser, plugs, etc.
If it were me, I'd probably:
- Install new points (with the correct gap) and condenser and set the ignition timing, and at first statically set the timing as well as you can.- Install new spark plugs and check your plug wires for resistance (and if too much, replace them).- Check the air filter and if there's too much dust on the intake side of the element, replace that.- Find your fuel filter and replace that. While you're under there, check the condition of all hoses...nothing torches an FI Type 4 engine faster than 40 year old hoses that break and spray gas all over a hot engine. The Bus crowd tends to recommend Gates Barricade FI hose, replaced every 5 years.- Check the coil for appropriate resistance at the primary and secondary windings and that, when the ignition is on, you're getting 12V to the coil +. - Check all FI connections...make sure all the terminal plugs are installed into the FI components like the 5th injector, each cylinder's injector, the auxiliary air regulator, the air flow sensor, and the throttle position sensor.- Look for disconnected vacuum hoses...unregulated air will be an issue in any FI engine, and the Type 4 is no exception. 
Then, if it were still running badly at all speeds, I'd look for an issue in the air flow meter like a sticky flap, would check the fuel pump for appropriate flow, and If it were just idling low but then running fine once warmed up then I;'d look to adjust the auxiliary air regulator.
But yes, head over to the Bay Window forum on TheSamba.com for a ton of Type 4 engine FI resources. I haven't checked the 411/412 forums there but given the level of knowledge in the other foums you'll likely find something useful.
Good luck and keep posting on your progress!
- Doug'73 Fastback'75 WestyFalls Church, VA
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