XJ12 non starting

Moderator: XjRestorations

RyanT24
Posts: 7
Joined: Tue Jan 24, 2012 2:04 pm

XJ12 non starting

Postby RyanT24 » Thu May 25, 2017 7:39 pm

Hi guys i wonder if anyone can help me.

After its winter hibernation my 1978 XJ12 went to the garage to have its headlights replaced, it drove fine to the garage, then back to my house and then to where i keep the car, 15-20 miles in total, on arriving at my storage the car started running very lumpy, down on power and spitting and banging, we managed to get it into the unit and turned it off, after a while we fired it back up and it was still running rough.

My mechanic looked at it and suggested we replaced the HT leads, we done this and the dizzy cap and rotar arm at the same time, come to start it up and it just won't fire, mechanic came back and discovered the fuel pump wasn't giving out a decent flow so we replaced that and still no go, a new set of plugs and fuel filter also hasn't cured the problem and i think hes running out of ideas.

It is seemingly trying to fire now, its not just turning over anymore but it won't catch, i don't like the stuff but a few squirts of easy start up the air trumpets allows the car to run almost immediately but it quickly dies once thats burnt off.

It has a decent spark at the plugs and plenty of fuel getting to the fuel rail but it just won't catch and run. Does anyone have any suggestions for anything else it could be?

Thanks everyone

Brakebuster
Posts: 3131
Joined: Tue Apr 18, 2006 1:17 pm
Location: Gloucester UK

Re: XJ12 non starting

Postby Brakebuster » Thu May 25, 2017 8:16 pm

does your have the swirl pot in the fuel system , if it does there is a pickup gauze in there before it sends the fuel to the pump and then filter , ( this is how an XJS v12 is setup ) , these pickup gauzes inside the swirl pot is known to get blocked

BB?
1989 5.3ltr V12 XJS Coupé FULLY RESTORED
2004 2.1V6 X-Type Saloon in platinum silver for the good wife
1994 3.2S XJ40 in Morocco Red with Doeskin interior

used to have
1999 4ltr Sovereign XJ8 in Seafrost

RyanT24
Posts: 7
Joined: Tue Jan 24, 2012 2:04 pm

Re: XJ12 non starting

Postby RyanT24 » Thu May 25, 2017 8:27 pm

does your have the swirl pot in the fuel system , if it does there is a pickup gauze in there before it sends the fuel to the pump and then filter , ( this is how an XJS v12 is setup ) , these pickup gauzes inside the swirl pot is known to get blocked

BB?
It doesn't as far as im aware

340jag
Posts: 127
Joined: Sat Apr 22, 2017 7:35 pm

Re: XJ12 non starting

Postby 340jag » Fri May 26, 2017 7:09 am

Well if it fires up with easy start it must be a fuel problem right , if there is fuel getting to the fuel rail , then it must have something to do with the injector system , I would start off by looking at what controls the injection !

mike020150
Posts: 2294
Joined: Wed Feb 08, 2006 6:26 pm

Re: XJ12 non starting

Postby mike020150 » Fri May 26, 2017 9:36 am

The simplest and most dramatic fuel fail issue is the temperature sensor. Either replace it or use a multimeter to compare its resistance at a known temperature with the table in the Jaguar workshop or Haynes manual. Typically, these sensors fail 'rich' rather than 'lean' but it's worth checking. Another suspect is the rotor arm. There are several variants, without or with different shaped magnets to operate the fuelling signal. If the original failed and was replaced by an incorrect version, fuelling will be affected. Mike.
2014 XK Dynamic R convertible; 1977 Daimler Double Six Coupe; XE S

RyanT24
Posts: 7
Joined: Tue Jan 24, 2012 2:04 pm

Re: XJ12 non starting

Postby RyanT24 » Fri May 26, 2017 2:11 pm

someone else on another forum suggested the rotor arm could be incorrect and an inspection of it revealed that the parts code in the sng barrett catalogue for the Pre HE V12 rotor arm is for one without a magnet, so we'll be putting the old one back on and see what happens then

mike020150
Posts: 2294
Joined: Wed Feb 08, 2006 6:26 pm

Re: XJ12 non starting

Postby mike020150 » Fri May 26, 2017 2:38 pm

It sounds like you are using a rotor arm for a carburettor V12, not a fuel injected version. Any fuel injected pre HE V12 needs a rotor arm with a magnet. There is more than one version of the rotor arm with a magnet, dependent upon which fuelling circuit board is present! If the car ran OK before the rotor was changed, get a new one of identical specification and you should be on the right track. Mike.
2014 XK Dynamic R convertible; 1977 Daimler Double Six Coupe; XE S

RyanT24
Posts: 7
Joined: Tue Jan 24, 2012 2:04 pm

Re: XJ12 non starting

Postby RyanT24 » Thu Jun 08, 2017 6:45 pm

it did indeed turn out to be an incorrect rotor arm causing the none starting, we've put the old one back in for now and it started up fine. Will certainly be checking parts more carefully in future and not relying on the part being right just because the catalogue says it is

mike020150
Posts: 2294
Joined: Wed Feb 08, 2006 6:26 pm

Re: XJ12 non starting

Postby mike020150 » Fri Jun 09, 2017 11:43 am

Glad it was a simple cure. Mike.
2014 XK Dynamic R convertible; 1977 Daimler Double Six Coupe; XE S

RyanT24
Posts: 7
Joined: Tue Jan 24, 2012 2:04 pm

Re: XJ12 non starting

Postby RyanT24 » Tue Jun 13, 2017 6:45 pm

Unfortunatly while the rotor arm has cured the non starting the rough running once the car has warmed up seems to have not gone away. When it first starts its fine but after going for a run in it it was not running as nice as it should be

https://www.youtube.com/watch?v=gHegJ7JB9FY

mike020150
Posts: 2294
Joined: Wed Feb 08, 2006 6:26 pm

Re: XJ12 non starting

Postby mike020150 » Wed Jun 14, 2017 9:52 am

Cars always behave best if they are exercised regularly. Starting from the point you made about the car running normally before you parked it up for winter, you are looking for something which could have changed when the car wasn't being used. Typically but not exclusively, that means something affected by corrosion. Pre HE V12 injectors fall into this category so check these first. Get a stethoscope (a long screwdriver!) and use it to listen to each injector in turn whilst the engine is running. Place the stethoscope against the body of the injector, avoiding touching the injector rail, and you should hear a clearly audible 'click' each time the injector fires. Small differences in noise between injectors are acceptable. Barely audible or non-existent clicks mean there is a problem with that injector. Many such problems are down to poor electrical connectors and/or broken/damaged wiring (40 years of excessive heat). The volume of fuel injected by the two additional cold start injectors is enormous and that can easily cover up the poor performance of one or two cylinders until the engine warms up. Ultrasonic cleaning is the way to clear a non operational injector whose wiring/electrical connection is sound. It is very rare for an injector to fail electrically. Just check resistances of each injector winding with a meter to be sure. If you do resort to ultrasonic cleaning, have all 12 injectors cleaned to ensure they have identical fuel flows. Still on the fuel side of things, make sure the running pressure of the fuel rails is between 28.5psi and 30.8psi and check both pressure relief valves are working by clamping each one in turn. Don't be tempted to increase the pressure beyond these figures.
Back in the day, a Lucas Epitest unit was used to diagnose these sorts of problems. If you can find one, complete with its test procedure instructions, it would provide a logical way of working through all the possible problems. If not, beginning with the fuel system checks above is an alternative way forward. Let us know how you get on. Mike.
2014 XK Dynamic R convertible; 1977 Daimler Double Six Coupe; XE S


Who is online

Users browsing this forum: No registered users and 2 guests