Re: I5 without oil filler cap

[ejfluhr@austin.ibm.com (Fluhr)]

Fellow listmembers said:
>>>It's not MC only.  The WRs and MBs do it too - both have failed in my own
>>>garage.  Also my 85 CoupeGT (forgot the engine code).
>>>
>  SOMEBODY PLEASE CLEAR ALL THIS UP!  I only know one thing - my '86
>Coupe GT 10v I5 runs happily WITHOUT it's cap. If there is anybody who
>DEFINITLY_KNOWS the correct applications/results/symptoms, PLEASE
>CLARIFY my and all listers confusion.

Well, I just went and looked at the vacuum setup on my '85 Coupe.  From
experience, I know it will run happily with the oil filler cap off and
dipstick off.  This is the 2226cc CIS-E I5, code KX, that is on
many of the '85-'87 Coupes and 4K quattros.

The valve cover, crankcase, and fuel charcoal cannister all connect into
the large rubber multi-point connector underneath the ISV.  This big rubber
collecting point then dumps into the intake manifold via a hard plastic
tube that taps into the middle of the "collapsed" rubber hose.  This
rubber hose is notorious for failure, as it connects the ISV with the
intake manifold, and typically is crushed in the middle when under the
vacuum pressure of the intake manifold.  The ISV connects this hose
(from the intake manifold) to the throttle body intake boot.

Looking at this, I would expect the valve cover & crankcase to be in a
vacuum, venting through the hard plastic tube of the multi-point rubber
collector, into the "collapsed" rubber hose that connects to the intake
manifold.  However, the hard plastic tube is relatively small, and I
suspect it is not capable of enough air flow to cause the engine to stall.
It may stumble, assuming everything else is ok.

Ahh, but from experience, all these areas fill with hardened oil residue,
restricting or clogging many of the passageways (expecially the rubber
collector underneath the ISV, and the crank ventilation tube).  So, I
theorize that older engines with these restrictions may not sufficiently
flow enough air to cause the engine to stall or stumble, and may be
compensated for by the computer.  I guess the best way to determine this
is to measure the pressure actuator current as you pull the oil filler
cap off.  If the current increases, the ECU is richening the mixture to
compensate for the vacuum leak.  Sound about right?

This is my take on the KX engine.  Other engines would be different.
Anyone care to backup or refute this theory?

Later,
Eric
'85 Coupe GT, runs with the oil filler cap off, no problem
---
Eric J. Fluhr                                Email:  ejfluhr@austin.ibm.com
630FP Logic/Circuit Design                   Phone:  (512) 838-7589
IBM Microelectronics Div.                    Austin, TX