Hi guys. I think I have found my starting issue with my xj40. After a lot of trial and error I think, as posted elsewhere in this forum, that it could be a faulty CPS. I have acquired one from the later models with the smaller plug which just needs to be rewired to the larger plug which seems simple enough, BUT, there is always a but isn't there, when I decided to replace the sensor I discovered that a butcher had already had a go at it. Where the plug connects the black wire (presume this is the earth wire) has been removed from the plug and bypassed and rewired directly to what I don't know. For example when you have one tail light working and the other won't work, instead of tracing the wire to find the fault, run an earth wire from the working light to the light that is not working and connecting them both as a common earth and bingo you have 2 working tail lights. I am a little dubious about doing this as not being confident in my ability and don't want to stuff things up. Any ideas?
Oh and by the way,the reason I got the CPS with the smaller plug was the Jag supplier that I bought it off recommended this as an alternative due to the sensor being exactly the same apart from the plug, was cost NZ$400 plus GST compared to NZ$136 plus GST

 

Hi Moodieblue!

I'm about to head out but if no one else responds before I get back this evening I'll try to help.

Cheers,

Don

 

Hi again Moodieblue,

Sorry for the delay in getting back to you. First of all, the most common sign that there is a problem with the CPS or its wiring harness is that when the engine cranks but will not start, the tachometer reads 0 rpm. If the tachometer reads about 200 rpm or so, the Engine Control Module (ECM) is receiving a signal from the CPS.



I've just reviewed the Electrical Guides for the 1990 model year (like your car) and the 1993 model year (like our car with the smaller connector), and the CPS for both cars has three wires with the same color scheme, so your swap should be easy.

The Blue wire connects to Pin 24 of the Yellow connector at the ECM. I'm guessing the main signal is transmitted to the ECM via this wire, since the schematic indicates the Blue wire is shielded and the shield is connected to earth. You're probably right about that modified black wire connecting to earth. If that earth has a poor connection and is intermittent, it is possible that electromagnetic interference from engine bay components is corrupting the CPS signal received by the ECM, so it would be prudent to ensure that the earth is good. The Red wire is the other end of the coil in the CPS and it connects to Pin 13 of the Yellow connector at the ECM.

From the schematics, it appears that you should be able to simply put the large connector from your old CPS onto the wiring harness for the new CPS and be in business, as long as you figure out that earth wire.

I hope this information is helpful. Please let us know how it goes.

Cheers,

Don

 

Hi guys, especially Don B
Thanks Don you helped me out a lot with my wee problem. Now to put you in the picture as to results, the wire that was bypassing the plug was just that, at some stage the wire had broken and it was way easier to hard wire as the " butcher " did. I tried to reconnect this wire but working with those plugs are a B#@$$. So in the end I cut the old plug off from the old CPS and removed the plug from the new CPS and used some electrical connectors to wire up the new CPS and used bullet connector for the stray black wire, who's the butcher now, but in the end all good ( so far ) So now it is wait and see if my starting issue is finally over but looking at the bright side I have learnt a lot over the last few months trying to track the staring issue down. My thanks to all of you who have taken the time to respond to my questions without your help I would have spent a fortune with an auto electrikery guy to sort things out.

Also that difference in price for the later model CPS is good to know if anyone else has to replace their one, hopefully they see this before buying one with the older plug

Cheers