Date:         Tue, 16 Nov 1999 08:46:18 -0800
Reply-To:     "T.P. Stephens" <doktortim@ROCKISLAND.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         "T.P. Stephens" <doktortim@ROCKISLAND.COM>
Subject:      DM: F.I. diagnosis, was: vanagon Digest
Content-Type: text/plain; charset="us-ascii"

To: Lance LeBaron <lebarle@HOTMAIL.COM>
From: "T.P. Stephens" <doktortim@rockisland.com>
Subject: DM: F.I. diagnosis, was: vanagon Digest

At 06:58 AM 11/16/1999 PST, you wrote:
>One member explained his Vanagon was running rich at idle but OK at speed
>based on his failed smog test.  Another member suggested this could be
>caused by leaking injector seals.
>
>My 1.9L Digijet Vangon is running rich also.  My injector seals look like
>crap.  How could bad seals cause the van to run rich?  This would be an easy
>fix.
>
If you know the're bad or marginal, replace them. They are an obvious
weakness and can contrubute to a psycedelic CPU.

If false air is causing a lean condition, the OXY sensor will tell the
computerto go RICH to compensate. Theoretically, it should be adjusting to
a correct mixture. But if the OXY sensor is slow or inaccurate from age it
could be the synergy of false air/weak OXY tricking the CPU to say, "****
IT, I'll guess." Rich or lean can result. Measure the fluctuation of the
voltage at the OXY sensor when hooked up. No fluctuation??? Either bad OXY
or non spec. mixture adjustment.
Slow/sluggish fluctuation??? OXY is weak, replace it.

If the OXY has ever had to contend with a rich or lean condition for some
time, it can be weakened or killed prematurely no less than a CAT converter
that can convert that CAT to a dog.

If the OXY cannot be documented as to use interval, replace it out of
prudence if you can't measure the actual signal. It may or may not resolve
you issue. Right down when you replaced it so you will know next time it's
history. If you do this, you can just pull out the bulb from the OXY dash
indicator. Your history will allow at a future point to quickly identify
the most likely culprits the next time something goes "**** IT!!!"

Very rarely, the CPU can be damaged and not sending the proper reference
voltage to the OXY. This will result in the same abscence of fluctuation at
a good OXY. Maybe a 1:100 probability that can spoil your weekend pokin'
screwdrivers at anything you can guess at and still not know what the
problem is. There are a 100 of these 1:100 probabilities that can pull your
chain pretty danged hard.  When hard nosed following of Bentley diagnosis
procedures step by step do not lead in a straight line to the failure,
reconsider how hard nosed you were and if you skipped a step cause you
didn't have handy the right connector and just went on to the the next step.

When all inputs to the CPU have been VERIFIED TWICE during the event,
replace with a BOSCH reman CPU either new or rebuilt by BOSCH, even if the
original CPU is a Triumph/Adler or Fairchild or Telefunken. The BOSCH units
cost more because they are designed not to choke when the others do.
Failure rate of BOSCH CPU's is very much lower than all others. You must
have empirical evidence from every feed to the CPU before trying
replacement because the original was probably fried by something else and
you can fry the new CPU with the first turn of the ignition key in a down
side senerio that is the worst of the possibilities, and all because of a
poor ground somewhere. The first paragraph in the diagnostic section
advises checking grounds before going further. Abscence of rigor =
compromise that can attack the kid's college fund, or Christmas, or Hanaka,
or that planned pilgrimage to the Haig.

If compression is down in one cylinder, it can explain this subtle failure
of bad gas spec. Mechanical empirical evidence must be VERIFIED first. An
ignition module can be going bad and fry the carbon contact in the dist.
cap causing weak spark energy as can many links in the ignition department.
VERIFY ignition second. Only then will you know the problem is with fuel
delivery.
Only then diagnos the F.I. or carbs. Rigorous procedure is required to find
the shortest line to the failure, no matter how long that line is. Spot
simple tests are warrented to attempt a quick diagnosis. If no results
result, the correct result will result from rigor.

DM is using an ox and a plow to turn the soil, rather than a chicken and an
ax. Feathers don't dig deep enough. It may be easier to swing an ax, but
the labor of following the ox will feed you next winter as will the
chickens if you save then for that.

Doktor Tim
Maintenance Repair and Restoration of European Vehicles
San Juan Island, WA