I believe the inertia switch is for the fuel pump and probably that only. But I will check it out tomorrow.
Hey hey hey! I’ve got the XJS 1990 Elect Guide in pdf and sure enough the inertia switch does switch off the the main EFI relay and it even shows where that relay is. I never thought of that because I drove my car into a parking spot and that was the last time it ran. Nothing inertial about that action at all.
Nope, the inertia switch does a whole lot more than control power to the fuel pump in some models like your 1990 XJ-S.
Paul
Hi Paul,
Finally got the chance to look at the Elect. Guide and here is what I found. Looks like I have to go at the inertia switch or earlier. Take a look at my diagram and give me answers to items 1 thru 3. Looking at the lower schematic I don’t see any fuse from the relay to the ign. feed and then to the battery if I assume that Diagram is fig.2.1. But, the inertia switch is also not showing and also relay pins 10/30 and 86 are shown ganged together with the ‘W’ wire. Huh? I’m getting confused. Is the EFI MAIN SW. RELAY in picture two, fig. 25.1 the same as the MAIN RELAY, labeled Black base? These diagrams are not too clear on that.
By using my designation of Black base and Red base, do I have the relays designated correctly?
Sorry if my questions seem somewhat dumb, I had to quit and get back to std activities so I didn’t have much time to analyze and sort out what I was looking at physically vs. the diagram and I am now coming up with questions at my computer that I know I could have answered myself if I stayed at it. I will get past this first immersion and be able to carry on much more intelligently but I wanted to get this off rather than wait another day. Let me know if this Guide is what you are referring to. I’m not certain that it is. I found it in my data library that I have been collecting for the last 20yrs God knows where I got it from but I figured it would come in handy.
Thanks, Paul
Don’t trust any of the documentation on how the inertia switch works! It seems to work differently from one car to another. The only thing in common is that it will always shut off the fuel pump since that is its fundamental function. Some shut off the entire EFI system, some shut off the ignition system, and some disable the starter. And we’ve never discovered any rhyme or reason which car has which.
Thanks Kirby. That’s actually a really big help. At least I know I’m really not loosing my mind. You may or may not know how much discovering that is an unbelievable relief. At my age of 76, family, friends, neighbors and strangers when they get a chance are always quick to let you know that you’re getting old and that’s what your problem is.
Got some ideas and I’ll be back on it tonight after work. Talk to y’all then.
Paul,
My hard copy of the S57 Electrical Guide has a couple of pages at the front that provide a legend for the electrical components and the color wiring used in the drawing. For instance the letter “N” is used for Brown wires and “B” is used for Black wires. Doesn’t your digital copy have theses pages up front?
There is no fuse between the ignition switch and pin 86 on that relay.
I will have to look at your other questions later today, I have a bunch of things to work on right now.
Paul
Hi Paul,
I discovered late last night what one of my problems was. The schematics show the main relay to the right of the pump relay and I didn’t take note that the layout showing the trunk has the pump relay to the left of the main relay… Because I used the association in the
schematic, I was actually disconnecting the main relay thinking that was the pump relay. Doing that also shuts the pump off so I figured that I was making a proper test/measurement. Tonight I will disconnect the correct relay, the pump relay and make the test/measurements
again.
When I get home tonight I will check for the legend which I believe is not in my copy. I looked specifically for a legend wondering why ground was labelled B and couldn’t find one on top of the fact that the wires I was testing were Brown, not Black and had +12V and not
ground.
Needless to say, when I gave it all up last night … I was spinning uncontrollably.
Thanks, Paul
I really appreciate the help.
Hi Paul,
Just tested the inertia switch and main relay. Both are working and the main relay delivers +12V on the KB lines. Even with voltage on the KB lines coming out of the main relay, there is no voltage on the WS lines to the full load switches. Without the voltage on the WS lines for the full load switches, there is no switching that occurs on the full load switches and therefore there will be no injector clicking.
I presume the ECU is getting +12V from the KB line coming out of the main relay. I will check to see that there is +12V on the connector at pin 22 of the ECU.
Now the only problem after lifting the ECU out and disconnecting the connector … Where is pin 22???
Paul,
If you look at the XJ-S ROM on page 19-1 of the “Supplement A XJ-S H.E.1979-1984” it shows the EFI ECU pin arrangement. There are two rows of pins in the connector, one row has 18 pins (1-18) and the other row has 17 pins (19-35). Pin #22 is the 4th one from the end on the side with 17 pins. But which end? Make a drawing of the connector and trace a sensor or two to make sure you have the pattern down and the rest will fall into place.
Paul
Hi Paul,
Thanks for getting back to me. I have spent a lot of time searching on the internet to find the pin out with no luck. So here is a photo. Going from left to the right what is the pin# on the farthest left, top row.
My Guide has no legend and no page numbers. I even searched for a better copy on the internet but have come up with nothing so far.
Thanks, Paul
Paul,
This is why I have a hard copies of the XJ-S Repair Operations Manual and S57 Electrical Guide to help me sort out complicated things like this easily and quickly.
Pin #22 is the 4th one from the right on the top row of your picture. I figured that out because there are two empty sockets in your connector and there are two unused pins in the ECU, #2 and #33, so #2 must be the second one from the right on your bottom row and #33 must the third one from the left on the top row. On the bottom row of your picture are pins#1-18 going from right to left and on the top row are pins 19-35 going from right to left.
Paul
Hi Paul,
Thanks. While I was waiting for your return I did find where I probably got my copy on the internet, Scribd. Although I haven’t been on this site for years it still said I had an account there. Knowing that I figured that my copy must be a bootleg of a copy because the pages were copied from a binder copy and show the three punch holes be page for the binder and yet my copy has no page numbers and no legend. For reference a page count on my copy gives 64 pages. I also remember subscribing to them many years ago too.
I also searched the old Jag Lovers archives and Kirby’s book and found nothing. Many years ago I also bought the CD rom but was never able to open it on my computer and that was so long ago I can’t remember if it came with a password or not.
Thanks again, Paul
IIRC, there are actually numbers on that plug. Reeeeally tiny.
Thanks Paul,
I agree with you on the pin-out of the connector. I’m on the diagnosis today, Saturday. I tried opening my ROM again and it still has a problem with Adobe Reader 6 & 7 and will not open.
Could you please email me a copy of the wire coloring code nomenclature?
Thanks, Paul
I have +12V on the injectors and the ECU. Gnds are true for ECU. When I turn the throttle turn table by hand, all injectors do click at the very first action of the turntable on the pedestal and at no other action or position than that.
The full load throttle microswitch is open and when I close it nothing happens with no engine running. This used to also cause the injectors to click when I closed the throttle microswitch by hand but it no longer does. The vacuum full throttle switch is closed with the engine not running and therefore shorts both the throttle microswitch and the vacuum switch for full voltage to gnd which is a fuel enhancement signal. When I place a vacuum on the full throttle vacuum switch, it opens and therefore there is no shorting of the signal voltage to gnd which would be a fuel enhancement signal. This tells me that when the engine is running and there is vacuum there will be no fuel enhancement from the vacuum full load switch nor the full load microswitch. Therefore with the engine running there will be no full throttle fuel enhancement until the vacuum drops due to full throttle. Likewise when under full throttle and full load when the turntable activates the microswitch the microswitch will then give a full load signal to the same pin at the ECU as the vacuum switch and achieve fuel enhancement.
Everything seems perfect.
Now for the ’NO’ spark problem. I have now checked this again by cranking the engine. There is still no spark from A bank or B bank coils at the distributor.
Any suggestions on how to run some tests with no spark and no engine running??? I also presume that the ignition ECU is behind the panel just to the right side of the right foot well and forward from the door post hinging the door. Is this true???
Paul
Paul,
Yes, that is where the Marelli ignition ECU is located, at least on the LHD cars.
In the Marelli ignition cars the Crankshaft Position Sensor (CPS) and Flywheel Engine Speed Sensor provide vital timing signals to the Marelli ignition Electronic Control Unit (ECU), and the Marelli ignition ECU and the Electronic Fuel Injection (EFI) ECU communicate to synchronize their operations. So one test strategy is to test the CPS and Flywheel sensors to make sure that they are doing their jobs and then verify that the Marelli ECU and EFI ECU are communicating properly. The wiring involved is shieled pairs with an inner conductor, an insulating layer, an outer braid grounded at only one end, all covered by an outer insulating layer. If the inner conductor is broken, if the ground is detached or if there is contact between the inner conductor and the grounded shield the vital timing signals will be lost.
The Marelli no-start problem due to signal loss is well documented in the archives along with how others have determined that this was the cause of their problem as well as the repairs that they have done on the shielded pair wiring are covered. This is similar to the no start problem in the Lucas ignition car with the thin white wire near the left side of the fuel rail.
If I were you I would start by reviewing the archives for “Marelli no start” or similar strings of characters. Then have your S57 Electrical Guide in one hand and your digital multimeter in the other hand to look for broken wires, connectivity where it should be and not where it shouldn’t be. Any place where recent work was done should be your first stop as some of these wires are likely fragile with age and heat.
Paul
Hi Paul and anyone.
I have stripped down and cleaned everything around (into and out of) the ignition ECU. Now I am checking out all terminals on the ignition ECU. I only got as far as the Gnd on the connector and it is ground. Went to pin 13, the W wire, +12V and got nothing. No wonder the ign is not delivering a spark.
From the Electrical Guide, S-57/90, there are no fuses or relays between the ignition switch and the ign ECU. Can anyone help me with the color coding on the +12V, W wire from the ignition switch to the ign ECU???
I know I have +12V and it gets delivered to the EFI ECU. I believe there should be a split some where in the area behind the ign ECU but I can’t locate it without the W wire color coding. Please help.
Also on the firewall in the engine compartment there is a 10amp fuse in a fuse holder with brown wires which was blown. I replaced it and have no idea what it supplies +12V to. Can anyone tell me? I have not been able to locate it on any diagrams.
Thanks, Paul
You evidently contend that a single wire goes to the ign ECU and power splits off from there to the EFI ECU. Are you sure about that? Because it’s not what I’d expect. If I were you, the first thing I’d check is the leads right on the back of the ignition switch, seeing that every one of them is getting power when it should.
Remember, the XJ-S ignition switch is a flaky POS.