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I am back at my garage, figuring out what to do with alternator.
Last weekend, when I was testing wipers motors, looks like I completely discharged the battery. (Tested with DVM -- almost zero.)
No problem, I thought. I pulled a replacement battery (showed 12.3V not connected) from the other car and put it in. However, I did not realize that the set up of the replacement battery was the opposite to the Interstate battery I had in '85 xjs: negative and positive ends were on opposite sides!
While trying to connect the cables (incorrectly, obviously) I saw some sparks. I figured out quickly that something was wrong, just not sure whether quickly enough
After connecting the battery the correct way, I tried to start the engine. It was cranking, but no start.
Is it possible I killed something during those couple of seconds when I tried to connect the battery incorrectly which caused no start? What could it be? Please help!
You might have killed an ECU. A friend had his Rolls Royce "die" on him after he fitted the battery wrong. In his case though, the voltmeter died resulting in a dead car.
You're best to check what you have up front... Spark or fuel... One of two will be missing and you can track it back...
Does the fuel pump activate when you turn the key to "II"?
Oh, crap... Didn't even come to me that batteries of the same could have positive and negative terminals reversed...
How does fuel pump sound like? Would it be very obvious if it is activated?
When I turn the key to II, I hear one click. I think it is coming somewhere from around the middle of the engine. But I could not be sure without an assistant.
I don't have a schematic in front of me, but if I recall correctly, power doesn't go directly to the ECU from the battery, but it gets there via a series of relays and fuses. I would think it more likely that he killed on of those. The ECU in the XJS seems more bulletproof than in other cars.
I don't have a schematic in front of me, but if I recall correctly, power doesn't go directly to the ECU from the battery, but it gets there via a series of relays and fuses. I would think it more likely that he killed on of those. The ECU in the XJS seems more bulletproof than in other cars.
I am praying that you are right, Mac Allan... (It would also make sense, as I remember I did this on another car. Think it was Volvo. Did not do anything to it. But you never know with Jaguars...)
Anybody had to deal with this on XJS recently? Where do I go from here?
I don't have a schematic in front of me, but if I recall correctly, power doesn't go directly to the ECU from the battery, but it gets there via a series of relays and fuses. I would think it more likely that he killed on of those. The ECU in the XJS seems more bulletproof than in other cars.
You're right unless he had the ignition switch on...
It wouldn't be a bad idea to Test the Fuel Pump Relay, as then at least you can eliminate that.
All you need is a Test Light, with a Couple of Clips on the end, like I've done in my Video.
Hang the Test Light somewhere you can see it, while you're sitting in the Car and then take the Wires off the Fuel Pump.
Connect the Test Light to the Wires (That you just took off the Fuel Pump) and then Sit in the Car. (make sure you can easily see the Test Light)
While looking at the Test Light, Turn the Ignition Key to position 2 (So the Warning Lights come on) but DON'T CRANK THE ENGINE.
If the Fuel Pump Relay is Working, the 'Test Light' Should Light for about 3 Seconds and then go off again of its own accord.
You could run this Test a couple of times to be sure.
If this checks out, then the Fuel Pump Relay should be ok.
Then disconnect the Test Light and reconnect the Wires on the Fuel Pump.
There is no need to uncover the Fuel Pump Relay in order to do this Test.
But if you want to know where it is, it's behind a Plastic Cover in the Boot/Trunk near the Boot/Trunk Bulk Head beside the Inner Rear Wing/Fender Drivers Side (UK) Car.
The Black Holder is The Fuel Pump Relay.
The Red Holder is The Main Relay.
If you haven't got a Test Light you could use a DVM Meter.
The Black Holder is The Fuel Pump Relay
The Red Holder is The Main Relay
The Relays are located behind a Plastic Panel in the Boot/Trunk near the Bulkhead Fender/Rear Wing.
My Video of Testing the Fuel Pump Relay 1990 XJS V12
Looks like the design of '85 is slightly different from what you showed in the video (I assume for '89?):
There are no wires/plugs near the pump.
I do however see the relays. I pulled both of them out and they don't appear to be burned or anything.
Are relays in '85 exactly the same as in '86? Can I try to swamp them and see what happens? (Obviously with this horrifying experience due to simple mishap with pos/neg leads, I want to be extra careful...)
UPDATE: never mind, I found the fuel pump wires/leads. The pump was hiding behind the black metal shield that surrounds the battery stand. I guess I will need to use the test light, because I would not be able to see the DMV reading while inside the car...
Last edited by v1rok; 04-07-2017 at 05:34 PM.
Reason: update
Can I get a relay from '86 XJS and swap it? Is '86 relay compatible/same as '85?
Yes, the same.
To verify, look at the terminal numbering. The fuel pump relay will have terminal markings of 30-85-86-87-87. (This as opposed to the more common 30-85-86-87-87A)
Also note, just for reference, that relays with the painted diagonal stripe are for very specific uses. The diagonal stripe indicates the relay has an internal diode and/or resistor. Don't not swap these with non-stripe relays, or vice versa.
Tried do the test on fuel pump relay just like ob described. No light
So this means that the fuel pump relay is fried?
Quite likely.
Or.....
The fuel pump relay relies on a ground from the ECU to operate. It's the orange wire at the relay. It's somewhat common for this circuit of the ECU to fail....even with out mixing up jumper cables.
Repeat the 'key on' test with your test light configured to check for ground at the orange wire.
I don't think any one answered your question about the sound of the fuel pump running when you turn on the ignition , it is a short whirring sound , open the boot ( trunk) turn of the radio you should then hear it as soon as you turn the key. I would also be careful if considering jump starting , my model is an early one but I do not think that makes any difference , it clearly states not to jump start , it indicates you could fry the ECU . I am wondering if , when the ignition is off whether or not it closes the ground circuit if not what harm could happen with a positive current going through the electronic system !!?
The MAIN relay, the one with the Red stripe, turns ON the pump relay. The MAIN relay is the first defence to battery muck ups.
I would swap in a new MAIN relay, and turn ON the ignition and LISTEN, you will hear the pump "whir" if its working.
There is NO direct battery supply to the ECU, it comes from that MAIN relay.
The fact the key was in your pocket deserves a medal at least, maybe a LOOOOOOOONG snort of JD even.
The lack of an assistant is going to require clever thinking, and maybe some very long extension wires to get that DVM to you at the front.
ALSO.
When the shock of your error took hold, you definately "yanked" the battery cables. Now, look at the plastic cover about 6" down the +ve cable. There are 2 heavy Brown cables attached here. They are a simple spade terminal, and in the heat of the moment, maybe one or both have fallen out. If so, simply plug them back in, taking care that they actually slide ONTO the spade, as apposed to down the side. Standing on your head helps with eyeballing them as they slide home.
The MAIN relay, the one with the Red stripe, turns ON the pump relay. The MAIN relay is the first defence to battery muck ups.
I would swap in a new MAIN relay, and turn ON the ignition and LISTEN, you will hear the pump "whir" if its working.
There is NO direct battery supply to the ECU, it comes from that MAIN relay.
The fact the key was in your pocket deserves a medal at least, maybe a LOOOOOOOONG snort of JD even.
The lack of an assistant is going to require clever thinking, and maybe some very long extension wires to get that DVM to you at the front.
ALSO.
When the shock of your error took hold, you definately "yanked" the battery cables. Now, look at the plastic cover about 6" down the +ve cable. There are 2 heavy Brown cables attached here. They are a simple spade terminal, and in the heat of the moment, maybe one or both have fallen out. If so, simply plug them back in, taking care that they actually slide ONTO the spade, as apposed to down the side. Standing on your head helps with eyeballing them as they slide home.
Grant, how did you know???!!! That is exactly what happened! Those two brown cables got yanked and were off! I plugged them back in, ignition to II ... and I hear beautiful whirring sound of the fuel pump. Then ignition on -- engine starts!!! Back in business! (And I have all my spare relays for future emergencies...)
He knows because he is the Wizard. At 12 noon tomorrow, GMT, all forum members to turn to the Southern Cross and bow. FYI chart below: • 12:00 PM Greenwich Mean Time conversion to worldwide times:
will definitely do... (I learned quite a lot about what is happening in the boot of the car and why it is important to understand all of that! thank you all!)
Now back to the Lighting Bolt warning light.
While car was running (idling) I measured voltage at the battery. When I just started the engine, it showed 11.70. Then I check couple minutes later: 11.68. Interesting, I thought. So waited some more. It appears that the voltage was consistently dropping with time: 11.65, 11.62, 11.60... All of that in the span of 15 minutes or so. At that point I turned it off.
Is it normal for battery voltage to drop with time while the car is running? Does it mean that instead of overcharge problem, I might have "undercharge" problem? (My lightning bolt lamp on dashboard always stays on.)
04-07-2017, 01:41 PM
Cranking but no start: what happened?
