[xj-s] One-bank running

I’ve been trying to help a guy by phone, which is always a challenge.
Apparently his engine was running on the right bank only, the left
bank remained cold. He wanted to know what was wrong with his
ignition system. The trick: His car is a 1988 H&E conv with a Lucas
CEI ignition system.

I told him the ignition system cannot have a one-bank failure – but
the EFI system can. I told him he needed to start looking in that
direction.

Turns out that, earlier in the course of trying to diagnose this
car’s problems, the owner had taken it to some auto electrics shop
and the guy there had hotwired something in the vicinity of the fuel
pump relay. Not clear on it, but apparently this involved running
some wires across the trunk to the area with the conv top controls.

Things apparently started to click when I told him that one relay
back there has a red mark on the top for a good reason, it’s not
interchangeable with other relays. He went to someplace where
there’s a parts car he’s been getting parts off of, got all three
relays that go on the right side of the trunk, and put everything in
the trunk back to OEM configuration. Presto change-o, the car starts
right up and runs on both banks. It’s still got lots of other
problems, but that one-bank running issue is fixed.

OK, can anyone here tell me how screwing around with the relays in
the trunk can possibly result in the V12 running on one bank? The
only thing I can think of is possibly one of the relays has two 87
terminals and one serves one bank of injectors and one serves the
other, and it got swapped out with a relay with only one 87 terminal.

– Kirbert

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Hi Kirby,

I’ve sent you the EFI circuit diagram for the 88 model, and yes, there
are two separate 87 pins on the Main Relay. One 87 pin provides 12V+ to
the A Bank injectors, and the other pin 87 provides 12V+ to the B Bank.
He might have had the wrong relay, an internal fault in the relay where
one of the 87 pins was not connected, or a fault in the relay base
wiring where just moving the base restored contact.

George Balthrop, Clifton, VA USA
85 & 89 XJ-S Coupes; 89 XJ40 VDP-----Original Message-----
From: palmk@nettally.com

I’ve been trying to help a guy by phone, which is always a challenge.
Apparently his engine was running on the right bank only, the left
bank remained cold. He wanted to know what was wrong with his
ignition system. The trick: His car is a 1988 H&E conv with a Lucas
CEI ignition system.

I told him the ignition system cannot have a one-bank failure – but
the EFI system can. I told him he needed to start looking in that
direction.

Turns out that, earlier in the course of trying to diagnose this
car’s problems, the owner had taken it to some auto electrics shop
and the guy there had hotwired something in the vicinity of the fuel
pump relay. Not clear on it, but apparently this involved running
some wires across the trunk to the area with the conv top controls.

Things apparently started to click when I told him that one relay
back there has a red mark on the top for a good reason, it’s not
interchangeable with other relays. He went to someplace where
there’s a parts car he’s been getting parts off of, got all three
relays that go on the right side of the trunk, and put everything in
the trunk back to OEM configuration. Presto change-o, the car starts
right up and runs on both banks. It’s still got lots of other
problems, but that one-bank running issue is fixed.

OK, can anyone here tell me how screwing around with the relays in
the trunk can possibly result in the V12 running on one bank? The
only thing I can think of is possibly one of the relays has two 87
terminals and one serves one bank of injectors and one serves the
other, and it got swapped out with a relay with only one 87 terminal.


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// please trim quoted text to context only

OK, can anyone here tell me how screwing around with the relays in the
trunk can possibly result in the V12 running on one bank? The only
thing I can think of is possibly one of the relays has two 87
terminals and one serves one bank of injectors and one serves the
other, and it got swapped out with a relay with only one 87 terminal.

gbalthropxjs@aol.com wrote:

That’s it exactly. See the attached screen print of the EFI circuit
for that model (from JDHT CD, JHM-1123, Electrical Technical Guide).

I’ll be damned. I never noticed that before.

– Kirbert

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