Date:         Wed, 9 Jun 1999 21:59:41 -0400
Reply-To:     John <u1031271@WARWICK.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         John <u1031271@WARWICK.NET>
Subject:      Re: emissions inspection failure(Utah)
Comments: To: john silverman <jsilver@AROS.NET>
Content-Type: text/plain; charset=us-ascii

john silverman wrote:
>
> Well, Vic (90 syncro westy) has been at the local mechanic several times
> over tyhe last few weeks in a (so far unsuccessful) attempt to pass
> emissions.  He was able to get the CO down fine, but the Hydrocarbons don't
> seem to drop, especially at 2500 rpms (part of the test).
>
> Dropped the van off yesterday, and he spent time this AM on it.  He just
> called and said he  couldn't get it down, and he thinks I need a new AFM and
> O2 sensor.  He's also concerned that there may be a problem inthe digifant
> brain.
>
> Any other thoughts?
>
> Thanks...John

John:

My name is John and while its easy to sit back and criticize another's
diagnosis, I have my doubts that your vanagon's oxygen sensor, AFM &
Digifant control module have all failed at the same mileage and the
engine still starts and runs ! Diagnosis by component replacement (AKA
"shotgunning") is a regrettable and wildly expensive method of
troubleshooting ! Typically a motor with low CO and high HC is a lean
misfire and the most common reason is an unmetered air leak. The
Digifant control module(DCM)is the most reliable part of the system and
like any computer it conforms to the GIGO rule. Prior to replacing the
DCM, a pin by pin check should be carried out at the DCM multiplug. If
your tech doesn't know how to perform a pin by pin or doesn't know the
values of the 19 DCM pins, you may be talking to the wrong tech ! The
DCM makes a few assumptions-have these been checked?

        Basic ignition distributor timing correct- 6*btdc

        No unmetered air leaks- what is the manifold vacuum?

        Correct fuel pressure- 2.5 bar with vac line disconnected

        O2 sensor functioning- ~0.2 to ~0.8V "swing" at idle speed

        AFM functioning-~1 to ~5V DCM load signal with engine stopped
        (air baffle fully closed to fully open by hand)

Good luck and I hope this helps !       JP