There is no reason why the Digital P system would not work with either
regulator. (The vacuum regulator has some advantages, therefore it should
be used with the Digital P system). The vacuum regulator however, cannot be
used with the Pre-HE ECU due to its inability to handle the varying fuel
mixtures that that regulator provides.
Bernie
A thought occurred to me regarding the compatibility of the different fuel>pressure regulators with the different ECU’s.
Kirby claims that the ECU’s are not compatible with both fuel pressure
regulators, either one or the other.
Why then, when my 1980 pre-HE with Digital P was built, was it produced
with the
single non-vacuum regulator, then when it had the fuel rail conversion due to
the recall, it was changed to the dual vacuum controlled regulators? All
without
changing the ECU? Doesn’t this seem to conflict with the theory that they are
incompatible?
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
2
There is no reason why the Digital P system would not work with either
regulator.
Hogwash. The Digital P system has fuel maps based on a constant
pressure differential on the injectors. The earlier regulators,
having no vacuum connection to the intake manifold, will vary the
pressure across the injectors as the manifold vacuum goes up and
down. As a result, a Digital P system fitted with D Jetronic
regulators will run rich when the manifold vacuum is high and/or lean
when the manifold vacuum is low. That last one could be a real
disaster, since that would mean running lean when the throttle is
wide open and the EFI is in open loop.
The vacuum regulator however, cannot be
used with the Pre-HE ECU due to its inability to handle the varying fuel
mixtures that that regulator provides.
“Inability”? Perhaps one’s thinking could be improved by realizing
that it’s the D Jetronic regulator that allows the rail pressure to
vary relative to the manifold pressure. The Digital P regulators
hold it constant, making control simpler.
– Kirbert | Palm’s Postulate:
| If anything is to be accomplished,
| some rules must be broken.
| – Kirby Palm, 1979On 22 Sep 2000, at 13:03, Bernard Embden wrote: