[tech] Help diagnosing an 8V?

[soltwede@privateI.com (Night Shadow)]

On Wed, 14 Aug 2002, Michael Carlson wrote:

> Sorry for the late reply; it's been a busy day...
> 
> Well, I performed the OXS control unit tests per the Bentley today.
> According to those tests, everything checks out.  (I feel like a certified
> Scirocco owner now that I've actually made and used my very on fuel pump
> relay switch.)  I also performed the oxygen sensor test, and it checked out,
> too.
> 
> Beyond the tests, I watched the frequency valve duty cycle as the engine
> warmed up.  Just out of curiosity, please verify that the following behavior
> is correct (or at least reasonable):
> 
> 1)  While the engine was cold, the duty cycle was solid at 50% (even when
> the engine ran rough and stumbled).
> 2)  Once the engine warmed up a bit, the duty cycle fluctuated between 40%
> and 58%.
> 3)  A little later, the duty cycle fluctuated between 45% and 56%.

OK, definately not *mixture* control related if I remember correctly from
the bentley, those duty cycles are just fine, and your mixture control
system all checks out.

> I believe my thermo-time switch is broken.  I didn't get any resistance from
> it when the engine was cold, which means it's probably never turning on the
> cold start valve.  I didn't have enough time to pull out the cold start
> valve and verify this, but I trust my meter.  That would explain the hard
> starting when cold, but I doubt that's causing my rough-running issue.

Hmm..now this is odd, I thought that the thermo-time was also responsible
for telling the Jetronic to run in open loop mode (that solid 50% you were
seeing) till the motor warms up....

But I agree, we are seeing NO correlation between your duty cycle readings
and the rough running.

So we are left with: An injector not firing properly, or a spark issue.
And from what I am seeing, this is not enough to affect the OXY readings,
so it must be a single cylinder mis-firing.  I'd concentrate on the #2
cyl, the one that you found the ugly plug.  Test the spark plug, the wire,
etc.  Also check out that injectors spray pattern, look for
leaks/dribbles.

> I suspect this is my next step.  Argh.  Now I need to get an injector puller
> and some new O-ring seals (been meaning to replace those for awhile now)...

Orings are good, no need for the puller, I use a small set of vice grips
clamped onto the injector and a screw driver under it for leaverage.

> There's no shame in that.  At least you gave me a direction to start
> marching in.  There's just as much value in verifying what the problem
> *isn't* as figuring out what the problem *is*.  (Can you tell I'm a software
> engineer?)

:-)  And I am a tech support geek, I fully understand this importance :-)

> Oh yeah, one more thing.  While I was scrutinizing stuff today, I discovered
> that the rubber sheath on the line between the fuel filter and the fuel
> distributor had some visible cracks in it.  Could that be letting unwanted
> air in the system, or is that rubber sheath just a protective layer for the
> fuel line?  Either way, I plan to replace it--should I go ahead and replace
> the fuel filter while I'm at it?

Fuel filter is a good idea, since you don't know its age, cheap insurance.
As for that line..it is just a protection, don't worry about it.  All mine
have had those cracks...

--
Eric
Northglenn, CO

76 Honda CB400F Super Sport (400cc, 4 cyl, OHC 8v, 10k RPM redline *grin*)
80 Scirocco (FOR SALE $500) 
81 Scirocco S (2.0 16v swap and complete restoration in holding pattern)
81 Rabbit Truck LX Diesel (Waiting for BAE Turbo Install) 
87 Suzuki Samurai JX Hardtop (Soon to be VW Turbo Diesel Powered)
91 Cabriolet (2.0 Crossflow 8v swap and mechanical rebuild in progress) 

"For Aquarians, the physics of loopholes is a perfectly valid science."
-Kelli Fox