S type 4.0 won’t turn over

Hi textterry… i tried it already and no luck.
The only way i can start it is thru the starter relay grounding pin 30 and 87. Once i drive it around i can then start it using the key. But once it cools down it goes back to no start again. I really don’t know which route to go next.

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Hello Jed - wonder what caused the wear change to the key - if I am understanding you correctly, you can activate the starter, via the ignition key switch, after the car has been run and is warm, but after a cool-down period, you are not able to activate the starter with the ignition key switch - I will do some research to see what may be causing this, meanwhile, hopefully one of the other listers may have experienced this same condition and respond sooner - Tex Terry, II - 1991 XJS V12 Classic Coupe, 1986 XJS V12 Coupe - 4/12/2020 2229hrs. EDT USA

Tnx textterry…

Hello Jed - try these steps to determine if there is a loss of power to the starter relay coil, with the engine in the “cold” condition, and with the engine in the “warm” condition - look at the starter relay (located in the right hand side of the engine bay) socket to determine where the starter relay coil terminals 85 and 86 are located (leave the starter relay unplugged from the socket) - 1) confirm transmission selector lever is in the “Park” position and remove the key from ignition switch; 2) using a DC volt meter, connect one meter lead to socket 85 and the other meter lead to a “ground” position in the engine bay; 3) place key in the ignition switch and turn key to the “on” position (not “start” position); 4) verify that there is a battery voltage present on the meter; 5) momentarily turn the ignition key to the “start” position and verify that there is no battery voltage present, then turn the ignition key back to the “on” position - the starter circuit, of the instrument pack, provides B+ when inactive, and ground when active, to the starter relay coil terminal 85 - 6) remove the meter lead from socket 85 and place on socket 86; verify that there is no battery voltage present; 7) momentarily turn the ignition key to the “start” position and verify that there is battery voltage present - turn the ignition key off and remove the key from the ignition switch - remove the DC volt meter leads and replace the starter relay within the relay socket - I suspect that you will not have a ground, as of step # 5, with the engine in a cold condition - redo the same steps with the engine in a warm condition and compare the results - (this suggested testing is as per my understanding of the electrical schematic for your 2001 S - Tex Terry, II 1991XJS V12 Classic Coupe, 1986 XJS V12 Coupe - 4/14/2020 0135hrs. EDT USA

Hello textterry
Here’s what i gotimage
That’s step 1 the other steps check out

I’ve been following this but I’m not clear what you’re testing here. If you have the starter relay removed and you are looking between tag 85 and ground, that is what I would expect to see with ignition in position II (on but not cranking). If you now plug the relay in, you should see battery volts at tag 85 via the relay coil. If you do not see B+ there, move to tag 86. If you have 12 volts on tag 86, the relay coil is open circuit, if not chase back towards the selector interlock switches.
Assuming with the relay in, you do see a B+ on tag 85, get someone to turn the key to position III (cranking). If all is well you should see the 12 volts drop to zero. The relay should close and the engine should crank. If when your assistant operates the key to position III the 12 volts remains on tag 85, chase back towards the IP because the required ground is missing.
You can also prove this out by dabbing a ground on tag 85 but make sure you have the right tag or there will be sparks!
BTW, when it won’t start, have you tried it with the selector in N? This will rule out a faulty Park switch.

Hello eric…, with the key on position II no 12 volts on pin 85 the only pin that has 12 volts is pin 30. I have tried neutral start up and still the same. Only way i can start it by tapping 30 and 87 on the starter relay. After i drive for a while it will start with the key then afterwards it’ll be back to no start.

I went through this a year ago.

Click on it. There are some pictures on this thread that may help you.

What volts do you have on tags 86 and 85 with the key turned all the way to position III ie trying to start?

If still nothing move to Fuse#1 in the Primary Junction Box and see if you have volts there when trying to start. If no volts on either side of the fuse when the key is turned all the way to the start position, your ignition switch is suspect and Rob has documented this extremely well in the thread he pointed to. Good information there.

Hello Jed - since you stated that all verified okay with the tests, both in the cold mode and again in the warm mode, I would suspect that the starter relay coil wiring path may be going open when cold - either within the relay case or at the relay socket - remove the relay and test the resistance of the relay coil circuit - set the meter on an ohm setting of less than 1K scale - put the meter leads on the 85 and 86 pins of the relay - generally a reading of 50 ohms to 200 ohms is normal for the coil continuity resistance - I would suppose that you may get a reading of very high ohms (determined by changing the meter scale), or may even have no reading - this would show that the relay coil circuit (within the relay case) is open when cold - reinsert the starter relay, start the engine as you have been doing, then after the warm-up period (when you are able to restart the car with the key, as you had stated before), turn off every thing and again remove the relay - check the ohm reading again, between terminals 85 and 86, and note if you are getting a coil reading between the 50 ohm and 200 ohm reading - if so, then replace the starter relay (as Eric had mention before of possibly a bad relay) - if, during the first cold test of the relay coil, you have the correct relay coil readings, then you may have a bad contact connection between the relay pins and the relay socket - Tex Terry, II - 1991 XJS V12 Classic Coupe, 1986 XJS V12 Coupe - 4/14/2020 1508hrs. EDT USA

Thank you rob the pics really helped

Hi textterry… i got 73ohm on 85 and 86 cold and warmed up. Does it mean the relay is bad? I will check the contacts tomorrow.
Thank you for your patience.

Hello Jed - a short recap of the testing that you have done: when the engine bay area is COLD, the ignition key, in the start position, is providing positive battery to the starter relay coil at terminal 86, and the starter circuit, of the instrument pack, is providing negative ground to the starter relay coil at terminal 85; the test of the starter relay coil confirmed that the coil path, between 86 and 85 is not open; you stated that when you momentarily short the starter relay contacts 87 and 30 paths, with the ignition key in the start position (which is what the normal operation of the starter relay coil would accomplish), you are able to start, and run the engine; once the engine has WARMED up the engine bay area, you stated that you are able to start the engine the normal way (you do not have to momentarily short the starter relay contacts 87 and 30 paths); you stated that once the engine bay area is cold again, you are not able to start the car without momentarily shorting the starter relay contacts path - this leads me to suggest that you may have poor connection(s), at the starter relay socket for terminal 86 and 85; - check the wire connection at the back side of each plug in the socket; check for slight corrosion, and loose fitness, of the socket plug – to verify that your problem is temperature related, make the following test before you remove the relay from the socket for the wire connection condition tests - when the engine bay area is cold, use a heat gun (such as a hand-held hair dryer) and pass warm air over the starter relay area for a few minutes; if the ignition key, in the start position, works as normal, after warming the area, then proceed with the search for the poor connection(s) at the socket wires - Tex Terry, II - 1991 XJS V12 Classic Coupe, 1986 XJS V12 Coupe - 4/15/2020 0330hrs. EDT USA.

Hello Jed - for what it is worth, I had a problem with one of my relays - I had a problem with my turn signal relay not working - turn signals would flash once then stop flashing - after verifying all the electrical paths, I purchased a new relay (cost of $32.00), installed it, and found I still had the same problem - as I moved the relay, within the socket, just to test for a poor connection within the socket, the turn signal flashing was able to be maintained - I took an emery board (fingernail shaper type), cut the board lengthwise, and used this to clean the socket receiver plugs - I then installed the old relay and found all to work correctly - just something you may try for your socket (can not tell, by your picture, if you have contamination within your socket) - Tex Terry, II - 1991 XJS V12 Classic Coupe, 1986 XJS V12 Coupe - 4/15/2020 1311hrs. EDT USA.

Hello textterry… Thank you for your suggestion. I will clean the terminals of the starter relay and keep you posted. Tnx everyone for your support sir eric, sir rob and sir textterry.

Hello textterry… update… i removed all the relays and fuses in the junction box under the hood and cleaned the terminals… its still doin the same thing… i also cleaned the terminal wires on the starter… i still need to jump the starter relay… I’m about to give up and let it be this way…

Hello Jed,

I understand your frustration in trying to find this annoying fault. I’m sure you would be able to locate the problem but if you’ll forgive me for saying so, I think a logical approach is more likely to succeed and will yield results.
You have already established that if you jump the relay, the car will start and that the reason it won’t when it’s cold is that the starter relay isn’t operating. You know that in order to close, the relay requires two conditions to be satisfied. These are a ground on tag 85 and supply on tag 86. To locate the fault you need to find out which one of these is missing when it should be present.

This is really easy to do. When the fault is present, with your multimeter, go onto tag 86 and while an assistant turns the key to the start position (III), measure the voltage between tag 86 and ground. If you see 12 volts or something like it, move the meter to tag 85. If you see more or less the same, the ground is missing.

If you do not have a supply at tag 86, the next place to check is on Fuse #1 in the Primary Junction Box. On my car, (RHD) this is located behind a trim flap in the kick panel in the right hand footwell. Possibly it’ s on the other side on a LHD car, I don’t know.

Anyway, when the key is turned to the start position, Fuse 1 supplies the volts to the selector interlock. Measure on both sides of the fuse and see what you have.

Before you give up, do try these tests and let us know.


Good morning sir eric… i was able to follow your instructions…, i see 12v on pin 86 when i turn the key to start position and nothing on pin 85…put back the relay and it did start. My question is … is pin 85 always grounded? If I don’t see 12v on 86 on startup does it mean my switch is bad?

Hi Jed,

I meant you to do the test with the relay in its socket. Sorry, I should have made that clear. You’ve already checked the coil for continuity. I think you said 73 ohms which sounds reasonable.
Pin 85 is only grounded when the Instrument Pack provides the ground which it should do if all the check conditions are good for starting. But the relay has to be in its socket when you do the test when the fault is present because if you see 12 volts on 86 and on 85 while you’re trying to crank the engine it means the relay isn’t being grounded as it should be.