[T3] Diagnosis help for a badly running 1971 VW 411

[Keith Park]

cracked diaphragm in pressure sensor?  Does it hold vacuum?

Keith


-----Original Message-----
From: type3-vwtype3.org [mailto:type3-vwtype3.org-bounces at lists.vwtype3.org]
On Behalf Of Jens Vagelpohl
Sent: Sunday, August 11, 2019 1:25 PM
To: org type3 at vwtype3.org
Subject: [T3] Diagnosis help for a badly running 1971 VW 411

Hi all, hi Jim,

Not directly Type 3 but closely related in this case.

I'm currently looking at a very low mileage all original 1971 VW 411.
Original engine, original fuel injection. The car itself is in beautiful
shape otherwise and I took at 2.5 hour flight yesterday with money in hand,
my plan was to complete the purchase and drive back to Fort Worth where I
currently live. Unfortunately, the seller had not fully explained how badly
it runs right now and I had no choice but to leave and fly back. The seller
wants to do more diagnostic work, he has been working off some Bosch guides
and the Harold Glenn guide to test individual components, but there's
obviously something he hasn't hit yet.

I am hoping for some input about likely causes and troubleshooting
strategies for the following:

- starts up pretty willingly, but idle too low and stumbling
- constant backfiring into the intake when I push down on the accellerator
- no power when driving, I think I got it up to 50
- backfiring doesn't change much as the engine gets warmer
- keeping the accellerator in one position, inclucing all the way down,
causes more backfiring than actual speed increase
- the only way to get accelleration for split seconds is to "pump" the
acellerator, by backing up and pushing down carefully, at that moment the
engine runs well and accellerates for a sub-second period, and then returns
to the no-power situation.

These issues apparently developed over the last year or so, the owner told
me when he had the car first it would cruise at 75 on the freeway without
issue. He has already replaced the fuel pump and verified with a pressure
gauge that there is no fuel pressure issue. He also replaced the injectors
and all fuel lines. On the ignition side he did the points, plugs, plug
wires and coil. Oil is changed and valves are adjusted.

Any help is highly appreciated. If the car wasn't located just over 4 hours
from Jim I would already try to bribe him into going there to look at it ;-)

jens




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