RE: [T3] Dead Injectors Puzzler

["Fuhriman, Mark" <mfuhriman@fugro.com>]

> -----Original Message-----
> From: Jim Adney [mailto:jadney@vwtype3.org]
>
> > Oh! Oh!  I remember that now.  So tonight I ran out, started the car
> > (started right up on all 4), drove around a while, and then
> let it sit
> > on the driveway and idle.  Within a half hour, it was
> running on just
> > 2 and 4.  Unplugged one at a time 1 and 3 to find them both not
> > firing.  Verified spark on all 4.
>
> Try checking the TIMING of the spark for all 4 next time. 1 & 3
> should look alike, timed to the timing marks, while 2 & 4 should
> light up the wide molded spot on the pulley that is 180 deg from the

I did that, and there is no cross firing.  Everything is "spot on".

> > signal.  Reconnected everything, started the car, and it was still
> > running on just 2 and 4.  No 1 and 3.  So it seems the 1 and 3
> > injectors don't get their signal to fire when at temp??
>
> Just for clarification: #1 is the RF cyl, #3 is the LF. Right?

Right.  The distributor contacts *do* fire the #1 and #3 together and #2/#4
together, right??

> Here's a thought: What if the 1 & 3 injectors ARE firing, but there
> just isn't enough gas to support combustion? As the engine warms
> up, the FI leans out the mixture, if there were some problem with
> those 2 injectors (flow rate too low) these cylinders would
> eventually stop firing. You could have partially clogged

But why would 1 and 3 both go out together?  I have been checking carefully,
and I never see just #1 or #3 by themselves out.  They always go out
together.  And it seems like only when warmed up or nearly warmed.  When
cold, the car starts right up and drives with all 4 working.  Seems like
only when warmed or nearly warmed up that #1 and #3 quit firing.  I'll try
to look at the spray patterns and measure rates sometime soon.

> Do all 4 of your injectors LOOK alike?

Yes, they are all the same yellow color.
>
> Have you replaced your fuel overflow hose? What are the chances
> that there has been water in your tank which could have rusted
> some of the injectors?

Replaced that hose soon after I got the car last spring.  It was broken in
half.  The gas tank has a very small amount of surface rust inside, but the
in-tank screen is (and was when I first looked) clean.  I drove the car
every day for 8+ months before my problems began.

I think it's a long shot, but I'll do as Tom suggests and switch locations
of the 1/2 and 3/4 injectors to see if the problem follows the injectors.

I don't *think* it has anything to do with possible loose injector
connectors either, Jim.  On one of the questionable injectors (#3), the
plastic holder is gone, and the wires plug into the pins without the holder.
So I can see and feel a solid connection there.  And the two ends are not
shorting together.  Wiggling the connectors does not smooth out the rpm, as
I would expect if the connectors were just loose.  But I'll check anyway.
And again, the #1 and #3 injectors stop firing *together*.  And when they do
quit, the engine is close to or at temp.

Maybe I can measure the voltages in turn at each injector connector and see
if there are any differences... hmm..  Anyone know what voltage I should
measure?  Should be the same voltage at all 4, right?

> > Recall that all of this is with a replacement ECU.  Is it possible
> > that something in the old ECU couldn't handle 1 and 3 going out, so
> > the engine just quit completely?  Seems like the
> replacement ECU keeps
> > the car running on 2 and 4 at times when the old ECU would make the
> > car quit and not start.  ???
>
> Hmmm.... Yes, puzzling. Check the 10 digit Bosch number on the
> brains; are they the same? Sometimes more than 1 OE number

Same Bosch part numbers.  And they both have stickers on them indicating
that they are Bosch-rebuilt units.  Maybe the brain swap just introduced
another variable that I don't want.  I think I have access to one more spare
B brain I can try (I'll call if I need it Greg.  Thanks!).

And at both temp sensors I measure appropriate resistances hot and cold.


Quick recap of the whole mess:

With the old brain, car would intermittently miss/stall/no start.  Seemed to
be happening with increasing frequency to the point I quit driving it to
work.  Seemed to start up again after it cooled down.  Sometimes after 20
min, sometimes after 12 hours.

Tried many things, finally swapped brains.  Now, instead of stalling, the
car will start running on just #2 and #4, leaving #1 and #3 dead until it
cools.  When this is happening, it restarts on 2 and 4.  1 and 3 stay dead
until it cools down a while.  When cold, it always starts and runs on all 4.
And sometimes when fully warm, too!  Trigger contacts are opening/closing -
checked with ohmmeter with wife cranking starter.

Thanks to all so far!

-Mark Fuhriman
 '69 Fastback

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