[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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