[xj] An Unusual Problem. Fixed!

G’day Gents,

The ‘unusual problem’ I had with my VDP turned out to be nothing more than a
fractured wire in the back of the AFM connection plug. However in the
process of discovery I substituted an ECU, an AFM a resistor pack, had the
whole thing wired up with a substitute wiring harness, (I don’t know why
that didn’t work) cleaned every single connection and component of the
system, had a friend who is an electronics wizard go over the ECU (he
rebuilds them as a part time business) with a test rig and pronounce it fit
all with no success. Even with the AFM cover removed, manual manipulation of
the airflow flap had no effect on the mixture, it should have run
progressively richer as the AFM flap was moved with the throttle at the idle
position, but it didn’t. I was sitting at home feeling at a loss as to what
to try next and I thought “It seems as if the signal from the AFM is not
getting to the ECU, it can’t be anything else” so I went to the workshop
where the car was this morning and peeled back the cover of the AFM plug and
bugger me if the wire from the AFM output from the ECU wasn’t broken. I
soldered that up again and the car ran, though it ran extremely rich. More
questions. The mechanic connected a gas analyser and fiddled with AFM for a
while but with no success. While he was doing this I was thinking about what
happened when I had the ECU tested, with the ECU plugged into the test rig,
varying the air temp input had very little effect on the injector pulse
duration however when the coolant temp input was altered it had a marked
effect on the pulse duration. So I checked the connector to the coolant temp
sensor and bugger me if it wasn’t broken also. I soldered that up and
readjusted the AFM and it now runs sweetly, but what an ordeal.

Jeff Watson.
(EFI expert)

1976 SII XJ6
1984 SIII XJ6
1985 SIII XJ6 Sovereign, (with as new intake bits)
1985 SIII XJ6 VDP that refuses to proceed, EFI problem. I fixed it!!!
1980 GSX 750 Suzuki
1970 Norton Commando Fastback.(under restoration.)
All in Sydney (Bushfires under control) (and raining here at the moment),
The archives and FAQ will answer many queries on the XJ series…
FAQs: http://www.jag-lovers.org/xjlovers/xjfaq/index.html
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