A Bank Injectors not operating

XJ-S
1

I have a 1983 XJ-S V12 Coupe that has developed a fault. The car starts and runs but with much less power than normal. I discovered that the injectors on the A bank were not working (no click). I have checked the following.
Cleaned all three wiring plugs (power resistor connector) plus the injector harness connectors.
Checked voltage at the injectors - 12 volts on both pins on both A and B bank with key in run position.
Checked the main relay working- 12 volts at both pin 87 with ignition key in run position. Does anyone know where the wire from pin 87 runs to? is it the large connector near the power resistors?
Fuel pump operating.
Any suggestions welcome.
Cheers David

2

Hi David,
if it’s the same as with my (6-cyl XK) FI, the injectors will be grounded to “fire”, so maybe bank A connectors just have no wire to ground (as both wires are at +12 that makes sense). Maybe the resistor has an issue; the ECU, according to the manual, fires two groups of six and these groups are mixed between banks, so it’s not at fault.
Can’t find the main relay but 87 is usually the pin that gets switched. Either to the fuses or to the ECU would make more sense; if you are talking about the feedback relay then the w/s cable will go to the starter relay pin, W1 (that’s one side of it’s coil). This relay’s C1 has a w/r wire to pin 26, the other side is ‘hot’ because your fuel pump is connected there.
All of the wiring is taken from the XJ V12, so it doesn’t necessarily have to be identical.
Good luck.
David

3

David,
There should be two Pink-Black (KB) wires connected to the each of the two pin 87 on the Main Relay for four KB wires. One KB wire goes to pin 22 (main feed) of the EFI ECU; the second KB wire on that pin 87 goes to all 6 of the A bank injectors; one KB wire from the second pin 87 goes to pin 86 of the Pump Relay; and the final KB wire goes to all 6 of the B bank injectors.

This information is found on Figure 24.1 of the XJ-S S-57 Electrical Guide (through Model Year 1987). This is a very worthwhile document to own as it shows the electrical components, their locations, and the wiring schematics including all the wire colors. I would not be able to keep my wife’s XJ-S convertible running without it.

Several years ago I had a problem similar to what you are experiencing with my 1984 XJ6 VdP in that three of its six Fuel injectors were firing but three weren’t. After troubleshooting the wiring and finding nothing wrong I swapped out the Power Resistor unit with a spare one I had on hand and that fixed the inoperative fuel injectors.

Your problem could be due to bad connectors, faulty wiring, loose grounds, faulty injectors or possibly a faulty power resistor (DAC2044).

Good luck.

Paul

1 Like
4

Thanks David and Paul,

I have changed the power resistor pack from a known running car and it made no difference. For the avoidance of doubt I put my pack into the running car and it ran fine on all cylinders.
I then changed the ECU and again this made no difference. Again I put my ECU into the running car and it ran fine.
I will now focus on the wiring and I notice what appears to be a single wire running the length of the V from back to front on the A bank side. I will start by checking this out, maybe the feed from the relay??

Cheers David