Hey guys. This might be the first new car forum that I join and I don't have to straight away ask for help with a fix. Well, as the title says, this is kinda true

I recently got an XK8 that has been previously owned for the past 5 years by a friend of mine. I got my eye on it 3 years ago, and waited for the right opportunity to ****** it

Not 8 hours later, the car wouldn't start. She had this habit before, but it was the generic one with the J box not knowing that it was on P. But all those time, the car won't even turn over. This time the car tries to start but just turns and gives an Engine Error. Ok... what was the engine error... Can't quote it but it was about the gear switch micro switch . We checked it, and the cable... everything was fine.

Then the shop saw that the spark coils are not getting any power (positive). As far as I know the car doesn't have any aftermarket immobilizer, but who knows.

Then we checked the relay that gives positive to the coils when the ignition is switched to position 1. The relay wasn't switching. When we switched it normally - the car started. At first the guys thought that the relay wasn't getting enough voltage to make it work (I think it was measuring around 3V), but actually the Ground was missing, or as I understood it the control for the ground, as both the positive and the ground for this relay are being cut off somewhere.

So the "Kinda" solution was to get ignition controlled ground from somewhere else, and this way the car now works fine.

But the question that remains is "Where is this Ground being controlled from, so that I can have my electrical guy pointed in the right direction, to fix it for good." Of course the Engine fault hasn't been resolved, but is still complaining about the gear switch...

 

Kainy, I had a friend sale his XJ8 for just that reason. It would just stop in the middle of nowhere and had it towed to the dealer 40 miles a way a couple of times and it started right up.
I did tell him it would take me a while to find it, but he sold before I had a chance. I really would have liked to find it for the rest of use. Thanks for confirming that this is a problem sometimes.
Will be looking forward to your findings.

 

Which year as there were some changes in the wiring diagrams as they revised the engine .

 

Sorry, forgot to put it in - 1997.

The gear shift issue is easy to spot, as the P won't light up on the J gate and the car will alarm you as if you are trying to leave it not in park, as if it is in N and the key is out. Most of the times it will start on N, but sometimes it will refuse for a while .

As for the no spark issue it didn't go away. We tried clearing the error, disconnecting the battery, other keys, etc.

Interresting enough prior to this happening I was at a keymaster's shop asking for a copy of the remote fob. The guy read the lock/unlock codes, thought that they don't change and tried peograming another remote, sane way as you would program a tv remote Of course it didn't work That ia why I suspect some kind of immobilizer to be at play here.

 

Have you tried a " Hard Reset " of the security system by removing both battery cables and putting together . This resets the system to zero state as it may have got out of sequence in your tinkering .

Pulling print for 97

http://www.jagrepair.com/images/Auto.../jagxk1997.pdf see right side page 33 for ignition relay

The ECU provides a ground to close the relay as the control power source is from fuse # 14 / 10 amp Engine Management fuse box different then the main coil power source of fuse # 18 / 10 amp Engine Management fuse box

 

Thank you! I already have it and it helped us do the quick fix. It helps that the control to the relay comes directly from the ECU/ECM, so this is gonna be the next place to look at.

Does anybody have a schematic of the ECU itself? I haven't went through the hole document but as I see it doesn't have schematica of the units themselves, but just the I/Os. This is in case we need to open and look inside it

 

Ok. I had the same symptoms as yourself. Could not work out what it was. Had to leave the car by the side of the road for a few days as it would not start. Will not say anymore, just read the saga for yourself......

Franks XKR Story. - Page 335

 

The I / O of the ECU can be found on page 76

With the key on you you should see 12 volts on any of the coils Pink / White wires and the other wire on the individual coil is the timed / control ground provided by the ECU .

What I recently found ( as advised by moderator Don B ) on my different engine inline 6 was the starter was shorting out not leaving enough voltage to run the ECU / no spark . Monitor the voltage drop during starter rotation to ensure the voltage doesn't sag below 11.5 volts .

There are X308 / X100 starter rebuilding kits on Ebay , but just a good internal cleaning of the brush residue may suffice , don't forget to replacing the bearing grease .

 

The issue is not at the coils. Originally they weren't getting any power, but the ground is OK. Both the ground and the power are controlled, yes, but that happens before the coil relay, which switches the power wire on/off. The issue is that the relay itself isn't getting ground, which apparantly also isn't a constant but as it seemed is also controlled by the ECU. I'll check the out pin on the ECU, and if it controls the ground, then probably I have a snapped wire somewhere (or immobilizer thingy), and will probably run a new one to the relay. That is the best case scenario. If the ECU pin out doesn't do anything, then things become more complicated. That is why I need the internal schematics of the unit itself, not just the pin outs.

I haven't checked the voltage when starting thecar, and will do it, but it does start perfectly now with very little turning, and everytime is the same.

 

You can put a test meter in the suspect relay control ground socket and after multiple times in seeing the ECU ground you can move on in replacing the possible intermittent relay . Put your finger on the ECM control relay at the same time . I think there is a king relay before the ignition relay itself like a ignition positive termed king relay controlling many things without looking at the print . Yes it's called the ECM controlled relay

Pulling my starter

See page 25 for that termed electrical bus must pass through

Control : point 55 E passes through 5 E on page 29 \ 5 E is provided through the ECM control relay on page 25 .

Power : point 83 passes through point 5 on page 27 / 5 is provided as hot at all times from battery

This must accrue after the ECM gets its " first power " but we'll leave that alone for now for simplicity

 

Pin EM10 - 16 is the pin ( Purple / Pink wire ) at the ECM that provides the ground to close this ECM control relay .

This closing of the ECM control relay enables power to the pulling coil of the ignition relay as it is provided a ground by the ECM at pin EM13 - 22 ( Blue / Black wire )

The inside of the ECM is closely guarded as proprietary information .

To provide these 2 commanding close grounds would be easy as a get it home or shop situation .

 

Hey guys. Sadly again I have a "no start" issue

First of all, about the issue of this thread - I did change the ECU with the one from my donor car, which I know is running fine, and the Ground to the Ignition relay is still missing. So this issue is still "kinda solved"

But couple of months ago I started experiencing selective turning over of the engine but with no starting. I'll spare you the details and get to the two revelations:

1. I am pretty sure this has something to do with the outside temperature. The car started doing this the first cold night of the season, and continuously didn't start in the morning (under 10-12C) but started right away at noon or at the evening (over 12C). Now with constant temperatures under 10, the car was standing at the service shop for a month before being looked at. Through that time it couldn't start once. Friday we got it inside the shop and 5-6 hours later it started . Still the mechanic thinks this is just a coincidence.

2. Friday when we put it inside the shop, we tested the coils again, and no surprises there - they weren't firing. This time it wasn't the ignition relay not working, but there was nothing on the signal wire.

I left it at that and am waiting for the mechanics to have the time to look at her. In the mean time I will appreciate any ideas on the matter. The gear lever switches are working normally (although the ECU is saying they are not) and the car won't try to turn over if it is at anything else other than P and N. What else might tell the ECU to cut the signal to the ignition coils, but to continue trying to turn over, and might be affected by temperature As I understand from the schematics, there is nothing between the ECU and the ignition coil on the signal wire.

 

Does the car eventually start over time or is the spark nonexistent?

 

The spark is nonexistent. Consistently during the first turn over there will be some very small hiccup, as if it is trying to spark a cylinder, but after that is a completely "flat" turning. Only once I was turning the car over for some time (like 3-4 tries) and it started. Otherwise if it doesn't want to start it won't. Also I think that some of the times it did start only when I applied gas exactly at the moment of the small hiccup, but again it was starting from the first try then, so I think it is not a case to review. Otherwise when the car starts, it starts from half a turn basically.

When we measured the signal wire, there was nothing coming on it.

Here is a video of one of my tries. I think I was testing to put more fuel in the cylinders, as I was thinking that the fuel pressure might be low. It shows the hiccup at the first long try and the "flat" turning after that:

https://photos.app.goo.gl/mbv4vHtqf3k2cL9P7

Youtube is a bit slow at the moment, but here is the link for when it becomes available. I hope the google photos link works for now

 

Remember that you have several modules and stuff that work with the ECM for the car to start. you have the crank sensor, shifter position. Body processor, Security module, Exciter ring (not sure this is installed on 97) but if it is you also have a Key transponder module. You also have several relays under the hood, trunk and at the door that are marked for the engine. Have you tested your grounding on the car?


Make this test, lock and unlock the car 2 or 3 times then try to start the car.

 

 

Remember the lights on the shifter get the signal from the transmission control module that gets it from the shifter control switch mounted on the right of the transmission. Have you checked the cable adjustment? Remember that the transmission control module talks to the ECM so all must be good..

My bad I forgot about the inertia switch. The thing about the inertia switch is that it unlocks the doors, turns power off to the engine and fuel pump. If you are going to check it just tap it with the handle of a screwdriver and then reset it but be sure to not hit it hard to break it.

Check your PM

 

Broken record here:

Check the grounds against the wall of the trunk on the passenger side (next to the battery).
Put your OBD II tester on it and crank...A code is likely to show up and point you in the right direction.

What it's not (probably): Your tachometer is moving so in my recent experience, it's not likely to be a transmission issue (which can cause a no start)...But, as Gus pointed out, if the J-gate lights don't light, you have a problem...And what the heck, it doesn't cost anything to row the shift lever and try to start it in neutral.
I believe the other usual suspects, i.e. inertia switch, fuel rail, other grounds and relays (swap the relays in the ECM area) have been mentioned.

Again, I would love to see a No Start sticky. Every time I think that I know all there is to know about getting an old XK8 started, my - and your - XK8 schools me and says not so fast Mr. Know It All.

 

The J-Gate is working fine. After the engine swap I did have a problem with the gear switch on the gearbox itself and at the same time (coincidentally...) the TCM also gave out and had to be repaired. Both issues were fixed. With both issues the car was giving a "Gearbox fault", but was starting fine, although in 3rd or 4rth gear

Now the ECU does complain about the park/neutral switch, after I made the "fix" for the ground on the ignition relay, but the J-Gate operates normally. It lights the gears correctly, and refuses to try to start the car if not on P or N.

The fuel pump also can be clearly heard working, and I checked with an OBD tool for the fuel pressure, which was fine.

The mechanic also said they checked the crank sensor during the car's tries to start, and it was giving correct data.

I will tell them to check the grounds more thoroughly.

My main head scratching is why the car is trying to start... if a module tells the ECU it is not okay to start, it shouldn't even try it. Or there should be any errors at least. And the temperature thing... it is just too weird

 

Just as an after thought have you tried the cut off/inertia switch? If my memory serves me right its n the left side of the car. If you open the door then between the door and the side there is a sort of D shaped panel. Remove that, just pulls off. Top right is the inertia switch. You could see if thats been triggered. I once went over a bump in my other car and it tripped it. Worth a look?