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John I sent you link to my website, check your email.
Doug I found your writeup about the Sunroof. I too have an issue now about it leaving a gap in the front passenger side and I have done nothing to cause this, (other than replace the motor?).
I have tried forcing the panel forward by the worm cables, and forcing the cables to engage the gear at the motor in a different position and nothing works, the panel always stops short.
I don't want to lower the headliner, there must be a reason for it to stop short. Could it be an adjustment in the motor itself?
there is a thermal switch at the bottom right of the radiator which turns on the auxiliary fan located under the front bumper. It works in conjunction with the Red Relay mounted on the radiator support on the opposite side.
Got the wiring diagram, thanks.
What is the THERMAL SWITCH do and where is it located?
It's at the very rear of the water rail.
One function, in conjunction with the Air Switching Module, is to open the diverter valve at the rear of the air pump. This diverts air from the air injection manifold to the air filter cannister when the coolant temp reaches xxx-degrees. I think it's 157ºF but don't quote me on that.
The other function, I think, is to trigger closed loop versus open loop operation.
I've never been able to fully get my head around the Air Switching Module
I don't think any of this would contribute to a no-start situation
Thank you Doug.
Now I understand the circuit diagram and know where to look for everything. I can start probing around with my meter looking for a broken wire or a bad diode and check the operation of all the components. Knowledge is Power.
The wiring on the Jag seems a bit flaky, the plastic insulation on some of the wires have cracks and the exposed loom covering has disappeared in places.
I found a mystery cylindrical component hanging next the ECU in the trunk and figured out it must be the Altitude Switch.
The wiring on the Jag seems a bit flaky, the plastic insulation on some of the wires have cracks and the exposed loom covering has disappeared in places.
There are two main issues with the wiring on Jags of this era. The insulation cracking, as you've mentioned....which is primarily in areas exposed to engine heat. And non-sealed connections....particularly in areas exposed to the elements.
Luckily, they're easy fixes. Wires with split insulation can be clipped and replaced, and connections can be cleaned. In fact, as you go through your testing process (and any other time you're working on the car) take a few minutes to clean any connections you happen upon. And same goes for the various grounds. You'll be pre-emptively solving most of the much-ballyhooed "Lucas Prince of Darkness" problems.
Again more questions than answers.
I have traced the wires from ECU (with it disconnected) to the throttle switch to discover the throttle switch closes when "the butterfly is almost fully open" and the connection is a bit dodgy without the clip installed. So moved on to the Air Switching Module where I get no continuity across any of the connections in either polarity of the diodes. Indicating that they are all open circuit and dead.
Question: Is this component subject to failure and what would be the cause?
So got a new (used) one on order.
In the mean time, I decided to open the unit up, to find the circuit board and wires are completely potted minimal chance of replacing diodes. But what the hell, lets dig in there any way. Unfortunately, I did cut through some wires. Plan B is to cut wires and solder in new diodes externally.
Question: Does anybody know what these diodes are?
I guess they are the same as the ones in the diode pack which I found a reference as 1N4006.
Also, I note there is a White/Black wire connection which triggers the Cold Start Injector when connected and the Ignition on and with the ECU installed. But with the ECU disconnected, this doesn't work. Indicating that it must be powered or grounded by the ECU. Looking at the wiring diagram, I can't figure that out either.
Much better than extra ground wires. Abig ground cable from the ground on the wing wall to the engine.
When i revised the wiring on my car to accomodate the LT1 i used a various relays. I dreated a rack for them at the fire wall. I also created a ground bus.l All but one of the groud legs on the relays go to the bus. it in turn has a wire that goes to teh ground post on the wing wall.
Also, I note there is a White/Black wire connection which triggers the Cold Start Injector when connected and the Ignition on and with the ECU installed. But with the ECU disconnected, this doesn't work. Indicating that it must be powered or grounded by the ECU. Looking at the wiring diagram, I can't figure that out either.
More to come later.
Your cold start injection should have white/green and white purple wires.
The CSI operates independently from the ECU. It gets "+" voltage from the starter circuit; that is, only with the key turned to 'start'. The CSI is grounded by the Thermotime switch, and only for a few seconds when cold. After it 'times out' it won't operate again for quite some time.
If you have white/black wires going to the CSI, sumthin' ain't right.
So moved on to the Air Switching Module where I get no continuity across any of the connections in either polarity of the diodes. Indicating that they are all open circuit and dead.
Question: Is this component subject to failure and what would be the cause?
I'm not aware of any tendency towards failure but perhaps many have failed without the owners realizing. If memory of discussions from 20 years ago is correct, the Thermal Switch...the one at the rear of the water rail....is often inoperative. Easily tested, as it is simply a open-or-closed type of thing.
Here is a quick video on YouTube to show you what I mean:
That wire goes from the coil to the ECU, pin #1, "Speed signal". From this the ECU knows engine RPM.
The clicking is, I think, the six fuel injectors clicking.
The anomaly described in the video has come up in discussion a couple times in the 20+ years that I've been messing around with old Jags. I don't recall what conclusions, if any, were drawn. The process described in the video seemingly 'wakes up' the ECU. My attention would turn to the connections at the coil and ECU, condition of the wire itself, a possible coil fault, or a possible ECU fault.
ECU faults are rare but not impossible. Coil faults are common so, as guesses go, it wouldn't be too crazy. Wiring faults in this area are common as decades of engine heat turns the wiring insulation to a crumbly mess.
After a Weather delay and Thanksgiving, back to work on the Jaguar.
So, continuing on with my wire tracing. I found the Air Switch did not give me the readings that I expected.
Plan A.
Open up the Air Switch and have a look inside and fix it. Opening it up revealed a completely potted circuit board with "epoxy resin".
So, with hammer and chisel in hand I chipped away at it. DISASTER.
Brock the circuit board, sliced through the wires.
Air Switch apart
Plan B.
Get a new one.
After installing the new one, Put everything back together. NO START.
A little more tracing of wires. The White wire with Black strip, See Above Video, is directly connected to the ECU and goes to the coil.
With the ignition ON, connecting and disconnecting this, triggers all of the injectors and "primes" the intake.
So, with 10 cycles tried to start engine again. BY GOD IT STARTED AND RAN.
It was that faulty switch.
After 30 mins of running, Still does not run smoothly.
I suspect the distributor cap and ignition amplifier. Will replace these later.
Also, could be a vacuum leak.
But it will start and run, again and again. MARVELOUS.
Air Switch apart
Plan B.
Get a new one.
After installing the new one, Put everything back together. NO START.
A little more tracing of wires. The White wire with Black strip, See Above Video, is directly connected to the ECU and goes to the coil.
With the ignition ON, connecting and disconnecting this, triggers all of the injectors and "primes" the intake.
So, with 10 cycles tried to start engine again. BY GOD IT STARTED AND RAN.
It was that faulty switch.
Hooray!
I'm a little confused, though.
Replacing the air switch fixed it? Or repeated cycling of the injectors via the white/black wire fixed it?
I wonder what the specific failure mode was? That is, what failed inside the Air Switching Module that caused the no-start condition?
That was plan A.
My research shows some diodes in there. When I was probing about with my meter, I determined that some had gone open circuit.
My worry is why did they go open circuit and will it happen again.
11-13-2021, 09:33 AM
