Hi all,

I spent the day tinkering with dads jag xjs (1991 early facelift 4.0), hoping to get it running and then change the gearbox ecu (see my other thread) but the first thing to solve- it won’t start.

Dad had it idling on the drive a few weeks back and it cut out and wouldn’t restart, the AA man he called a few days later reckoned it was either the coil or the ignition amplifier.

So this morning I replaced the plugs (I tend to do this as a matter of course when trying to get a temperamental car to start) ignition amplifier and coil, testing to see if the car would start after changing each component in turn.

No spark. The coil and amplifier have 12v with the key on. My next suspect is the crank position sensor, which I removed and cleaned but don’t have any way of testing. I’d buy a new one if local places had them on the shelf, but of course it’s too old a car for that.

Any other suggestions before I order a crank position sensor online? I’m only here for the weekend, just wondering if there’s anything else I should try.

cheers

 

Hi, if you have a faulty CPS it will show up as no movement on the rev counter needle when you crank it over. With a good CPS it will normally show a reading of around 300 rpm on the gauge whilst cranking, hope this helps.

 

thanks- the rev counter wasn’t showing any difference between turning the key to position 2 and position 3.

I’ve ordered a replacement cps and dad is going to ask the local garage (that we’ve used a lot) if someone can pop over and fit it.

Cheers

 

Ok, a friend went and swapped the crank position sensor for dad (I live a long way away and couldn’t just pop back to do it).

still cranks with no start, the rev counter isn’t showing any difference when cranking- ie it just reads 0.

I suspect it still has no spark, although my friend left before I could suggest checking for one and dad can’t check on his own.

is there an obvious ecu fuse? Or something else to try? I thought I found all the fuses, but the car has several fuse boxes and they’re not labelled which is fun…

it’ll get towed to jagutech next month, but if there are any suggestions of something obvious to try first let me know…

Cheers

 

Hi, I would check the wiring back to the ECU, on the yellow connector its pins no 13 and 24. 13 red wire is a pulsed signal and 24 the ground. I have exactly the same year car and the rev counter hops up and down when cranking so my money would be on a wiring issue. The ecu’s seem fairly bullet proof but I would check for water damage as the xjs is prone to leaking through the front scuttle . Good luck

 

Forgot to add you should have battery voltage to pin 14 on the blue connector and 12 volts with the ignition on to pin 10 on the same connector.

 

A small suggestion the next time you are back with car, in hopes that you aren't looking in the wrong direction.

Bring a can of spray starting fluid with you, and while someone turns the key for you, spray some starter fluid directly into the throttle body. If the engine just cranks with zero response of any kind -- you have no spark and should focus on the ignition system. If it even coughs or fires briefly -- you have a no fuel problem.

Eliminating 50% of the potential issues, either way, will simplify your next steps.

 

Thanks for the suggestions- delving into the wiring is beyond what dad is capable of doing, so if there is a wiring fault then Jagutech will have to find that when it’s towed to them.

Are sporadic wiring faults common on an xjs? My experience of older cars is mainly on a similar aged Volvo 240, and whilst the electrical components (ignition amplifier, crank sensor, temperature sensor) fail from time to time the wiring is usually trouble free and very rarely the cause of issues (not just on my car, but across all the forums I read etc. wiring isn’t the issue).

The can of starting fluid suggestion is sensible, but the car doesn’t have a spark- I suppose the fuel pump/fuel pump relay could have packed up at the same time, but I’m trying to fix the no spark issue first. Unless there’s some truly bonkers wiring that means if the fuel pump relay fails there won’t be a spark?

Cheers

 

On your early 4.0, there are electrical and physical components that can affect the fuelling, and the same for the ignition, But with the exception of the ecu, they are "relatively" independent.

There is a great temptation for owners to start replacing components without ever properly diagnosing what is the problem. I'll sound like a stuck record but for me the proper initial diagnosis is:

- Do I have a spark at the end of one of the plugs pulled from the engine and grounded against the engine, whilst the engine is being cranked?
- Do I have an injector, pulled from the car and held into a jar, spraying fuel whilst the engine is being cranked?

If you don't first pin down which, or both, of those is the problem, you're just throwing paint at the wall and hoping some will stick.

Good luck

Paul