Hi all, still putting the XJS through compliance, and it’s decided that it won’t start.

Here’s a brake down of what happened, and what we’ve tried.

While I was getting some work done with the panelbeater, they ran it out of fuel (my fault, I should have left more in there) and also ran the battery down trying to start it. Before I left it with them, it started fine, but it was hard to turn over, but it always started after a few seconds.

Now I’ve asked my local mechanic to get it back on up and running. He will put a new starter in it, to eliminate that, but I’m concerned there might be something else going on, as the starter has been tired for a long time, and it’s always eventually kicked to life.

what we’ve tried:
Charged battery.
Fuel: Injected fuel (starter spray) straight into engine. Didn’t start. Engine turned over slowly but didn’t fire (note tired starter)
Air: Can’t see anything stopping air getting where it needs to get to.
Spark: It’s an AJ16, haven’t checked that each plug is firing, but surely they all wouldn’t fail at once?

I guess the question that Im asking, is what (on an AJ16) might be going on preventing spark? Is there anything else I can check.

I’m very much a novice, and my local mechanic will be across things, but just thought it was worth reaching out incase there was an AJ16 specific issue that’s common.

 

A faulty crank position sensor has caused many no-starts on the AJ16.

Observe the tachometer needle while cranking the engine. It should bounce a little. If it doesn't bounce the CPS is on the blink. Replace it.



Cheers
DD

 

I’m assuming that if the CPS is faulty, the spark will either not occur, or occur at the wrong time?

 

Not occur.
Also you may have ruined the fuel pump if you cranked it for more than a few seconds with no fuel. I realise this is nothing to do with your spark problem, just a warning!

 

ALSO.

Knowing its the 1/2 engine, BUT, check the engine earth straps, wherever they are, or add a new strap, dedicated, that YOU know is actually earthing the engine.

NO disrespect to anyone in this section, but., there will be a ton of info re this in the X300 Tech Section, as the AJ16 is the Prime Power Plant in that model.

The Cam Angle Sensor, the whizzy thing where a distributor once lived, is a prime issue for Injector Pulse. The engine cranking too long before firing, is classic Cam Angle Sensor out of time, as it is adjustable. I think????? I did a sticky years ago in the X300 section about that. If not, ask, I will go find and attach here. My X300 was a "cranker", until I retimed that Sensor, then it ALWAYS fired on the 1st rotation of the starter motor, king of scary, considering how is used to be.
The Crank Angle Sensor, as mentioned, is the Prime for Spark.

 

Thanks for all the help.

Ive been looking at part numbers, and it look like the AJ16 had a bunch of different part numbers for the crankshaft sensor based on engine number, are any of them interchangeable?

 

LHE1640AA

That is the number I used on the 3.2 and the 4.0R engine.

SNG had them back in those days.

As mentioned by Greg, that fuel pump has about 3 seconds life IF it is run without fuel, fussy sucker, but they all the same no mater the name on the car.

 

N Bath,

I wouldn't change the starter motor without absolutely verifying that it's faulty. I've not heard of anyone who's needed to change a starter motor on an AJ16 XJS. I'd start by looking at the earth straps and the general +ve and earth points on the bulkhead of an XJS.

As regards no-start, I'd begin with the crank sensor or check the basic plug connection of the ecu.

Good luck

Paul

 

Thanks for all the help, here’s an update, and some more questions….

- Starter was replaced, car turns over properly now, but still doesn’t start - no spark

- I’ve found a crank position sensor, I’ll get that installed

- My mechanic has had a crack at reading the OBD2 codes, but can’t get any reading. My car is a ‘94, 4.0L AJ16, is it OBD2 compliant? It has an OBD2 shaped plug, but does that mean it can have codes read with an OBD2 scanner?

 

Forgot to mention- when cranking the engine (now much faster than before) the tacho/rev counter doesn’t move at all. Hence why I’m planning to order a crank speed sensor tomorrow.

Could this also be caused by an ECU issue (given the mechanic can’t read the OBD2 port)?

 

My understanding is that Jaguar began rolling-out OBDII on 1995 model year cars....which is also the first year for the AJ16 engine. But.....model year designations get fuzzy on cars sold in many different markets with different practices regarding model year. My 1995 USA-spec XJR/AJ16 had OBDII, FWIW.

Some scan tools did not play well wit the early Jaguar OBDII

Or, despite the diag plug being present, maybe the system was not "live" on cars sold in some markets?

Others will chime in with better info.

Cheers
​​​​​​​DD

 

At the risk of being controversial a mechanic that cannot function without OBD isn't a very good one - it is a useful feature and tool but nothing beats basic diagnostics for a no start - guess I'm too old school - I mean how hard is it to detect spark, fuel pressure, injector pulses ,,,,

 

Without a jumping tachometer needle at startup, it would seem to indicate a failed crank position sensor. The $25 cheapies on Amazon have been wildly successful for my daily driver.

LHE1640AA should be the part you want.

 

Turns out It was the inertia switch.

I’ve also learned that if you scroll down too far when you reply to a post, you may end up replying to a different thread.

 

AHA, Simple cars these Jags, even the 1/2 engine ones.

Well found all the same.