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

[Jens Vagelpohl]

Thanks Keith and Phil,

The fact that the situation is uniformly bad across all RPM levels does make me think it’s an issue with a component that influences the whole operating range, such as the MPS - or, as Phil says, a vacuum leak on the way to the MPS.

Since I am about 900 miles away I’ll take all the help I get here and my own reading of the FI guides and write up a set troubleshooting steps for the current owner. He’s proficient with working on cars so I am confident he can use it.

Any and all ideas appreciated!

jens



> On 11. Aug 2019, at 20:53 , Keith Park <topnotch at nycap.rr.com> wrote:
> 
> 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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