That may be the case Stuart, pricey but might be the culprit.
Any way to know if it is for sure the culprit?

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*GIL NGAI* • *I TELL GOOD STORIES*
*cinematographer • **chief storyteller • instructor*
* www.dayonemedia.ca <http://www.dayone-media.com/> *

On Mon, May 17, 2021 at 3:35 PM <stuartmacm@gmail.com> wrote:

> It seems to me swapping the ECU with a known good one would be a good idea
> at this point.
>
> -----Original Message-----
> From: Vanagon Mailing List <vanagon@gerry.vanagon.com> On Behalf Of Gil
> Ngai
> Sent: Monday, May 17, 2021 10:45 AM
> To: vanagon@GERRY.VANAGON.COM
> Subject: Re: Crummy Vanagon performance
>
> Neil here is a response form my mechanical friend Ron to your comments:
>
> Caveat: I didn't read your entire post.
>
> Yes.
>
>
> If a tach is present, a tach needle dropping when engine issue happens
> might indicate that the issue is electrical in nature.
>
> No.  Not observed.
> (FROM GIL) I do have a tach.
>
>
> The inner lead on green shielded O2 cable on vehicle harness may be
> shorting to cable shield.
>
> No.  O2 sensor signal observed to be oscillating as expected.
>
>
> A failed and clogged cat might cause what you see.
>
> Catalytic Converter? (From Gil)
>
>
> If vacuum hose to fuel pressure regulator is leak free, while it's
> attached to FPR, if you can blow (gently) air into it, the diaphragm in FPR
> is broken.
>
> No.  All Fuel Pressure Regulator vacuum lines replaced at fuel line
> replacement and two new FPRs.
>
>
> Try to recreate the issue(s). Note if they *only* happen once the engine
> is warmed up.
>
>
> A PDF of the Digijet pro training manual can still be found online AFAIK.
>
> What's the best place to find this?Is this the right manual?
> http://cabby-info.com/Files/DigifantProTrainingManual.pdf  (From Gil)
>
> I doubt Vanagon syndrome is the issue but to me, the VW TSB on VS
> indicates that VS can also happen in Digijet.
>
> Can you please email Technical Service Bulletin? Thanks!
> •••••••••••••••••••••••••••••••••••••••••••••••
> *GIL NGAI* • *I TELL GOOD STORIES*
> *cinematographer • **chief storyteller • instructor*
> * www.dayonemedia.ca <http://www.dayone-media.com/> *
>
>
> On Mon, May 17, 2021 at 11:32 AM Gil Ngai <eyebawlgil@gmail.com> wrote:
>
> > Hi Everyone,
> >
> > Thanks for all your input! I think I am getting the emails but who
> > knows for sure.
> > I do see your comments Neil, thanks!
> > To confirm I do have a new fuel tank, fuel lines, square fuel filter.
> >
> > Dennis, here are responses to your comments from my mechanical friend
> Ron:
> > ----------------------------------------------------------------------
> > -----
> >
> > *From Dennis:*
> >
> > Since it starts and runs OK cold most things are close enough to run.
> >
> > Yes.  Otherwise the effort to undertake repair would not have been
> > attempted and a recommendation to proceed directly to replace engine
> > would have been made.
> >
> > So part of the diagnose is to look at tings that change after warm up.
> > If truly going rich after warm up the next steps
> >
> > Yes.  This was observed after starting issue was corrected.
> >
> > I take are to look at the temp 2 circuit
> >
> > Yes.  Verified signal as expected at both cold and hot engine
> > temperature and observed at both sensor output terminal and Electronic
> > Control Unit (ECU).
> >
> > and O2 Sensor circuit.
> >
> > Yes.  Verified signal as observed at both sensor output terminal and
> > Electronic Control Unit (ECU).
> >
> > On the 1.9L the O2 sensor is not as reactive as the 2.1L but still it
> > can cause some grief.
> >
> > The observed signal varied as expected for an O2 sensor.
> >
> > The temps 2 and O2 sensor inputs relay heavily on proper ground
> reference.
> >
> > Yes.  O2 and Temp 1 and 2 are low level signals that are transmitted
> > over single conductors, which is extremely prone to reference (ground
> > in this
> > case) instability.
> >
> > Check for stray voltages on the O2 sensor wire outer sheath
> >
> > Yes.  None observed.
> >
> > and the ground side of the temp 2 sensor.
> >
> > Yes.  None observed.
> >
> > Also make sure the inner signal wire for the O2 sensor is not grounded.
> >
> > Yes.  Verified signal wire intact and isolated from ground.
> >
> > Be prepared that you can have broken wires inside the insulation and
> > defects in the harness.
> >
> > Yes.  This would be an intermittent.  But as it does not present when
> > engine is cold lessens this possibility.
> >
> > Resist the temptation to just clean all the grounds.
> >
> > Yes.  All grounds were carefully cleaned.  Very carefully!
> >
> > The more you blindly touch the more broken wires and failed
> > connections you can have.
> >
> > Yes.  A prime reason the Bostig option is superior.
> >
> > Diagnose as much as possible in place.
> >
> > Yes.  Done before attempting electrical wiring work.
> >
> > For aggressive cleaning
> >
> > Yes.  Removal of corrosion does NOT require aggressive mechanical
> removal.
> >
> > or sanding terminals
> >
> > Yes.  Very fine grit and used abrasive applied.
> >
> > consider that all quality terminals have a surface finish
> >
> > Yes.  Abrasive action applied to only remove corrosion - with some
> > surface finish remaining.  If no finish remains, then terminal would be
> replaced.
> >
> > to maximize contact
> >
> > Yes.  Ensure electrical contact surfaces are clean.
> >
> > and some type of coating or plating to control corrosion.
> >
> > Yes.  See previous comment.
> >
> > They also were not designed for 4 decades of service.
> >
> > Yes.
> >
> > If needed carefully replace with quality stuff, sealed connections to
> > stop further corrosion of the wire and good crimping tools.
> >
> > Yes.  If replacement is needed, then quality parts and correct tools
> > are used.
> >
> >
> > While probably not the cause of shut down situations the poor engine
> > health can be a contributing factor.
> >
> > Yes.  What testing beyond compression test, as specified in the
> > Bentley manual, is useful?
> >
> > The fuel management relies on a number of assumptions.
> >
> > Yes.  This was discovered.  The ECU is not much of a control system.
> > It merely accepts available inputs, uses inputs to look up values in a
> > stored table, and outputs the look up values to fuel system mechanical
> > components.  It is apparent that there is no validation of inputs nor
> > compensation for when inputs may be suspect which results in outputs
> > that cause poor performance.
> >
> > Bad intake valves and worn guides present the same problems as vacuum
> > leaks with the addition of burning combustion gasses.
> >
> > Yes.  How would this manifest in a compression test?  Hot/cold engine?
> >
> > Think of stuck EGR valves on other vehicles. This combination can give
> > faulty reading to the O2 sensor and cause it to way out either rich or
> > lean.
> >
> > Clarify.  Not clear on what the combination is nor how such might
> > affect the exhaust gas composition at the O2 sensor.
> >
> > Same for leaking valve covers.
> >
> > Yes.  No leaks observed.  Would this manifest so strongly between cold
> > and hot engine?
> >
> > Also make sure the exhaust is tight. If exhaust is getting out then
> > outside air is getting in. Fresh air in the exhaust, drive the engine
> > richer.
> >
> > No.  The exhaust is pressurized, which would prevent fresh air from
> > entering the exhaust stream.  Unless there is a gross exhaust piping
> > wall failure upstream of the O2 sensor - none observed.
> >
> > Back firing, the fuel is igniting in the exhaust, not the cylinders.
> >
> > Yes.  BANG!!!  Good thing for PPE!  Backfiring was greatly reduced,
> > almost eliminated, after rebuilding the Air Flow Meter (AFM).
> >
> >
> > Some of the parts choices are also questionable.
> >
> > No.  Assumption that the domestic parts used are of lower quality is
> > not the case.  Parts were selected, inspected, and found to be of
> > excellent quality - low price was NOT used as a positive selection
> > criterion.  Low price parts are disqualified from consideration.
> >
> > For spark plugs you want to only use plugs that are nickel plated.
> >
> > Yes.  ACDelco spark plugs used are plated for corrosion protection and
> > cylinder head thread protection.  Further, spark plug threads,
> > regardless of brand, are inspected for damage and corrected as necessary.
> >
> > The black oxide ones will at some point take the threads out of the
> heads.
> >
> >
> > Yes.  Corrosion protection plugs used with light application of
> > quality anti-seize, and correct use of torque wrench to apply
> > specified torque - cylinder head threads are safe!
> >
> > Distributor cap and rotor, Bosch only.
> >
> > The distributor cap and rotor were acquired while on a trip.  Thus,
> > selection was based primarily upon availability.  Regardless, the
> > Champion cap is of good quality:  Finish, electrodes, and terminals;
> > and the rotor is of good quality:  Finish, electrodes, terminals, and
> > integrated resistor within specification.
> >
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> > •••••••••••••••••••••••••••••••••••••••••••••••
> > *GIL NGAI* • *I TELL GOOD STORIES*
> > *cinematographer • **chief storyteller • instructor*
> > * www.dayonemedia.ca <http://www.dayone-media.com/> *
> >
> >>
> >>
>
>