[T3] 1971 fuel injected fastback

[Jim Adney]

This could be either too much or too little fuel. For a '71 here are seveal 
common possibilities to check:

Verify that when you turn the key ON, you hear a relay click and then a 
second click about 1 second later. If someone has worked on the starter and 
miswired it, you will not get the second click and the FI will be in cold 
weather "choke" (rich!) mode.

Check the system voltage. It should be above 14 V measured at the battery, 
at medium rpm, with the engine warmed up. If it gets below 13.5 V the FI 
starts to run too rich. If below 13.5 V replace the voltage regulator with a 
Bosch 30 019. I have these in stock. While you're at it, make sure the fluid in 
your battery is covering the plates. If necessary, top up with distilled water. 
[Important: "Topped up" means fluid up to the bottom of the fill ports, which 
will be about 1" BELOW the top of the cell opening.]

Check that the vacuum hose from the pressure sensor is still connected on 
BOTH ends. Also, using a spare piece of hose, connect one end of that hose 
to the pressure sensor and suck on the other end. You should be able to 
develop a decent vacuum in the pressure sensor. If it's leaking it will be 
obvious and it will need to be replaced. I have good used replacements. You 
can also send it to me to be cleaned and to have a new O-ring installed if 
there's a very small leak there.

As others have mentioned, it could be fuel pressure which should be 
constant at ~30 psi.. If it runs okay for 20-25 minutes the pump and filter are 
probably okay, but the fuel pump relay could be getting resistive. If this car 
has either of my fuel primer switches installed, switching the primer switch 
ON will bypass the relay and that would tell you where the problem is. If it's 
the relay, you can take it apart and clean the contacts or get a better relay 
from me. A gauge and long hose is the only sure way to eliminate fuel 
pressure as the problem.  

It could be the FI trigger points in the distributor. You can try to find a 
replacement or I can readjust yours. The best option would be to send me 
your distributor to be rebuilt; I would adjust the trigger points in that process, 
as well as go thru everything else.

It could be the cylinder head temp sensor, although this is not as common as 
some people seem to think. Make sure the wire has been allowed to come 
straight out of the sensor and has not been bent severely where it exits the 
sensor. The only way to check it would be to disconnect it from the harness 
once the engine is hot and has died. Measure the resistance of the sensor. It 
should be neither zero or infinity. There's no magic number here, but it's 
likely to measure 200-2000 Ohms. The resistance comes down as the temp 
goes up.

Long shot: Try a different rotor and cap.

Good luck, and keep us posted on your progress,

Jim

On 26 May 2020 at 13:15, Arthur Sterrett wrote:

> My 1971 fuel injected fasttback is giving me problems!  Everything looks good and seems to checkout good, valve adjustment is ok, idle when started is ok, belt is not slipping, plugs and points are good.
> 
> Here is the problem, car starts right up and runs great for 20 to 25 minutes at different speeds.  After that it will die when slowing down for a stop sign or traffic light.  When this happens it is real hard to get started again and acts almost like it is starving for fuel.
> 
> My thoughts have been that it is overheating, an ignition problem or fuel problem (filter or pump).  I have pretty much ruled out overheating.
> 
> I am not sure where to go next, looking for some help!  Thank you.
> The Bentley hasn´t been a lot of help.
> 
> 
> 
> Arthur Sterrett
> asterrett38 at gmail.com
> 
> 
> 
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Jim Adney, jadney at vwtype3.org
Madison, Wisconsin, USA
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