Intermittent engine cut out 1989 v12 xjs

[vfr2009]

Dear Friends

My 1989 xjs v12 started to suffer intermitent engine cut outs, it started first after a long run 100 miles, the car was parked for three hours, 10 minutes after restart, as it reached op temp it died, I waited 20 minutes it started and ran all day. the next morning it ran for 10 minutes then died. The intervals got shorter until it would die on every trip, wait 20 mintes it starts again then dies when it reaches operating temp once more. My jag specialist diagnosed a fuel problem. A new fuel pump was fitted, it wasnt that. The Fuel injection ECU was tested, it was good. Engine sensors were replaced, then the Marelli ecu was discoved to have water damage, . This too was replaced. Total cost of £1000+ Fault cured! A mere 300 miles later the fault returns as before. Any ideas please??? I have since discovered the route of water, it came in through rust holes under wiper grill.

Best
Pete

 

[Steve]

My first thought was that the ignition amplifier is no good. I had a similar issue with an XJ12 that I owned. Maybe one of the Jaguar techs that frequent the forum will be able to chime in on this.

 

[vfr2009]

thanks steve, maybe the new amp has failed how to test it?

 

[HEALEYJAG]

Hasd same problem with my 12 cyl e-type....turned out to be vapor lock from using fuel with an alchohol additive.. Ran straight gas...no problem.

 

[Steve]

I don't think that they have the same fuel issues in the UK as we do here....

I don't know how to go about testing the new amp, back in the day the only proper way was to swap it out for another unit which was known to be good. You can put better, more reliable electronics into the original casing nowadays as well. Just in case.

 

[DrEntropy]

Another consideration: the injection system is very voltage sensitive where it comes to supply voltage. Check to insure the battery and alternator are up to standard.

 

[jessebogan]

Were BOTH crankshaft position sensors replaced? Also, check the connections at the coils. The small wires are prone to break where they go into the connectors. The coils themselves are also suspect. The ignition rotors can short to ground. Remove the distributor cap and then the rotor. Look at the rotor closely for signs of burn through at the center shaft. What spark plugs are you using, and what are they gapped to? The CORRECT gap is .025. Most people ignore that little setting. Check these things, and get back to us.

 

[Michael J.]

Jessebogan is on the right track.

1st check the connection for the front crankshaft sensor for corrosion inside the plug. Connector is on right side of AC compressor in the valley of the Vee. The connector is black and looks like one of the connectors on the fuel injectors. I used an emery nail board to clean the pins when corrosion was found.

If not in the connector, look at the top of the sensor. It mounts just under the harmonic balancer at the rear of the under pan. There will be corrosion or other signs that the sensor is failing.

I now carry an 8mm wrench and a spare sensor in the car at all times. The sensor is relatively cheap (about $55) and I have had to replace the front three times in the last 8 years. The rear seldom fails, when it fails it won't count the teeth on the flywheel and the car will not start. The front sensor is exposed to wet conditions and seems prone to failure.

 

[vfr2009]

Jesse, thanks for your reply much appreciated, one question are you sugesting there are two sensors on the crankshaft? the Workshop manual only mentions one?

 

[jessebogan]

As the above post mentions, there are 2. Main sensor is at the front, under the crank pully. The other is mounted at the rear, on the bellhousing cover plate. It is in a prime location to get oil soaked , but it still has a much lower failure rate than the front sensor. It's connector will be found near the large crossover pipe that connects the two intake manifolds.