[T3] Bad day at the (FI) office

Jim Adney jadney at VWType3.org
Tue Mar 15 10:00:10 PDT 2016


Daniel,

Sorry to hear that you're having what appears to me to be new 
problems. It's certainly POSSIBLE that the "new" B brain which I sent 
you is responsible. I'll get on some of the ones you've sent me, and 
send some, including another "new" one, back to you ASAP. The only 
testing I've done on any of my "tested" versions is to make sure they 
would start and run a car.

My B brain tests were done on Gary Forsmo's '69 with Gary's help in 
the driver's seat. Each test ran for only about 1 minute, just enough 
to make sure the FI would start and run the engine smoothly, so there 
was no long term testing.

It's quite likely that the hiss you're hearing is just the sound of 
air slipping by the throttle plate at the front of the IAD. That's 
normal. It's loudest at idle, when the vacuum is max and the throttle 
opening is min. I'm hoping that you just forgot that it was always 
there at idle. If that's not it, check the hoses to the pressure 
sensor and pressure switch to make sure they are both connected at 
each end. If either of those hoses was disconnected or broken, the FI 
would run rich and cause engine bucking. This is like running a 
carbed car with the choke on. (Don't ask how I know that....)  

Make sure the hose from the AAR to the IAD is correct. It can be hard 
to install and it's possible to skive off some of the ID of the hose 
while trying to force that hose into position. It should also not be 
too long, as that puts it under stress and forces it to squirm 
sideways and get into other things. (hint, hint)

With the engine running grab the air runners and shake them. If this 
changes the hissing, something's loose, and you can find and tighten 
it. Make sure the back (actually front) cover of the IAD is tight.

I don't think this is a simple vacuum leak. If it's a leak at all, 
it's a leak that confuses the FI. A simple leak into the intake air 
system would have different symptoms: the "loping" you're familiar 
with.

On an original '69, the only ground wire at the center of the case 
would be #11, which is the ground for the brain. Without that, the FI 
is dead, as that's the ground side of the power for the logic side of 
the brain. In your case you have a modified FI wiring harness which 
also brings the 4 injector ground wires to the center of the case, 
which is a good thing. Wire #31 is only for cars which have the very 
complicated early cold start valve circuit, which was optional in 
'68-9. My impression is that you don't have that, so your harness 
does not have wire 31.

Note that it's always important to be careful with your wires. Watch 
how they are routed and what's routed around them. Never pull on the 
WIRE to unplug a connector; always grab the connector itself.

If your pedal travel seems small, remove the air cleaner and look 
down the throat of the IAD and watch while someone else depresses the 
pedal. The throttle valve should go from fully closed to fully open. 
If it does not, you may need to adjust the position of the rear cable 
end in the clamp or rearrange the carpet. Both problems are common. 
You should also make sure the Bowden tube around the throttle cable 
from the pan to the engine breast plate is installed correctly.

I encourage you to disconnect wire 18, to the starter solenoid, the 
TVS plug, and the pressure switch plug. That just takes those items 
out of the picture, simplifying it. Leave those disconnected until 
you have this sorted out, or until it becomes clear that 
disconnecting them fixed the problem. If one of them caused the 
problem, reconnect them, one at a time, one per week, until you find 
the culprit.  

Our weather has been improving. Wish you were here....

-- 
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Jim Adney, jadney at vwtype3.org
Madison, Wisconsin, USA
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