[v12-engine] Spoke too soon {Scanned}

A few weeks ago I was trouble shooting a sudden loss of power in my 1984
XJ6 VdP (4.2L XK engine, not the 5.3L V12) and discovered that the front
three fuel injectors were not firing. Compression, spark, fuel pressure
were all normal. It was odd that three cylinders were affected suddenly
by the same problem. A few weeks prior I had replaced the EFI harness
with a new one and suspected that, but I also suspected the power
resistor pack.

I replaced the power resistor pack first, because that was relatively
easy, and I had a couple of spare ones on hand. Much to my pleasure
all six fuel injectors starting to fire normally again.

Although it’s a different engine, maybe the same principle (or problem)


Paul M. Novak

1990 XJ-S Classic Collection convertible
1984 XJ6 Vanden Plas
1969 E-Type Fixed Head Coupe
1957 MK VIII Saloon
1985 XJ6 Vanden Plas (parts)
Ramona, CA
@Paul_M_Novak1-----Original Message-----
From: owner-v12-engine@jag-lovers.org
[mailto:owner-v12-engine@jag-lovers.org] On Behalf Of Kirbert
Sent: Thursday, August 30, 2007 11:50 AM
To: v12-engine@jag-lovers.org
Subject: Re: [v12-engine] Spoke too soon {Scanned}

Richard Dowling wrote:

A bank has very pronounced 50/50 off/on pulse.
Without more investigation time for the next two or three days my
guess is A bank has one injector circuit out of action so only 3
cylinders firing.

Next item on the agenda is to go over the engine bay and clean every
connector and check injector wiring under the compressor. Just on the
off chance it suddenly comes good I will start the engine and make
sure the miss is still there. Then wiggle the injector wiring under
the compressor and check the result. I hope that identifies the
problem since it is an easy fix.

Anybody got other suggestions ?

Excellent analysis.

It’s not likely to be the wiring in the V, because this would most
likely take out one injector, not three. It’s more likely the wiring
from the V all the way back to the ECU, including the resistor pack
behind the R headlight. You’ll need to check that entire circuit
until you find a cause.

I’m betting on the resistor pack.

– Kirbert

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