HI All,

I am currently recommissioning my XJR which has been in a dry shed off the road since 2010 as it developed a high idle. Up until about 2 years ago I started the car at least once a year however recently I wasn't able to get it to start. I initially put this down to dead fuel pumps and a down injector which have now both been replaced. The car will now splutter into life but will not idle or run on all cylinders. From my diagnosis so far I have checked the ECU in the drivers foot well for corrosion on the pins which is completely clean and fine and I have checked the voltage going to the injectors and coil packs with this ignition on to which I am getting just under 4 volts which seems off to me cant find the cause. Im thinking this must have something to do with the issues but looking for advice on where to look next.

Alex

 

Have you given her fresh fuel? 2010 fuel will have gone off by now.

 

4 volts

The voltage " sitting " on the fuel injectors from large # 5 right ECU controlled relay

..................................on the coils from the right engine bay fuse box small # 9 relay in the corner of the box

You could be reading the individual 2 X 6 ground wires the ECU provides to make the coils and injectors sequence / fire

The wire colors to read are fuel ( Black / Light Green ) and coils ( White / Pink )

 

With old fuel not firing off you risk washing off the compression oil seal on the cylinders walls as a bore wash condition and then no start condition

Some but not all X300s you can siphon the fuel from the top with a 1/4 inch by 6 foot hose from the large reels at the hardware store

You are due for a main fuel filter change , as I saw a pic once of set away X300 fuel looking like pancake syrup

Never install battery in backwards , positive post fwd

Never over tighten the positive post bolt , breaks special curved nut underneath

 

Hi All thanks for your responses so far.

Firstly on the fuel I syphoned all the old fuel from the tank when I did the pump as it had defiantly gone off (Although it wasn't 12 years old as I always topped it up when I ran the car previously). SO the only old fuel could of been residual in the lines so perhaps I shall try and used the pumps to pump that out.

On the 4 volt reading I Have read the white and pink wire off the coil plugs, the black and light green off injector plug and the ignition relay in the small fuse box all same reading. I shall try the ECU wires for completion are they same colours as above?

Someone on a different forum also suggested the Crank sensor could be causing this issue but im unsure how?

Cheers

 

" On the 4 volt reading I Have read the white and pink wire off the coil plugs, the black and light green off injector plug and the ignition relay in the small fuse box all same reading. I shall try the ECU wires for completion are they same colours as above? "

No , The power feeds ( or sitting on coils and injectors ) do not come from the ECU , the ECU provides a timed ground sequence ( on 12 separate wires to the ECU ) to operate them

On the old fuel in lines , the fuel pressure regulator will recirculate the overpressure back to the tank unless the pump pressure is under FPR setting to bleed back , You can feel for the FPR to rumble by feel or hear knowing there is a recirculation

Fuel pump will run for 3 seconds only on key rotation

Battery condition ?

Which socket on the ignition relay is at 4 volts ?




With the ignition relay in the right engine bay fuse box at 4 volts need to look at the battery cable post on the rear engine firewall , mega fuse nuts under the rear seat pan , and the mega fuse nuts at the battery positive post right at the turn down

Again do not over tighten positive battery post bolt

Battery Shims ?

Both ends of the battery negative cable tight ?




Are you taking these readings as the starter is trying to rotate ? Starter sag

There is an inertia / crash switch that can trip for no reason always in front of the ECU on the car's far right , you can jumper the inertia switch connector between the 2 white wires with a paper clip , it does not always reset from reading , this crash switch removes " control " power to close the ignition relay , right engine bay fuse box , thereby stopping engine

 

Ah ok that makes sense so I should be able to rule out the ECU.

I shall double check the fuel is recirculating but im pretty confident iv heard it do this when pressurising and would like to think so with the new pumps also.

Battery condition I have tried 2 different batteries one of which was from my daily E36 which was new this year and same results.

SO by looking at the battery posts ect looking for a bad earth in the system basically?

There readings were taken with the ignition simply switched on no starter engaged.

And inertia switch is a good shout perhaps I knocked it getting the ecu out previously. In theory if jumping it is successful I should achieve the desired 12 volts?

 

back to your relay question it is socket 30 which is reading 4 volts

 

" SO by looking at the battery posts ect looking for a bad earth in the system basically? "

not a bad earth ( but can accure when you dig deeper and remove post plastic isolators ) but a loose power " through " connection

On the rear engine firewall terminal post remove the engine side heavy cable and wiggle post indicating the battery cable on the inside of cabin is not clamped tight ( found before in England )

Socket 30 is the muscle / work ( not control ) power into the relay , battery cable source

Bed time in the States

 

The valve cover is not a good ground point for your meter

The valve cover is electrically isolated from the engine block , plastic shouldered / top hat bushings

 

So I continued my investigation today and you were correct that using the valve cover was causing the voltage issue when I tested used a better ground I achived 12 volts at the coils. I still have a car that will not run so I am jumping to changing the crank position sensor?

 

The crankshaft position sensor can fail and not give a CEL code of P0335

The single CKPS signal split up to be used many ways can fail to be discerned by the ECU partially

You can clean the face ( other than connector ) of the sensor of built-up grime that interferers with the clean signal

There is no mounting adjustment on the CKPS , the ECU takes care of that , 10 mm , some keep a spare CKPS in the trunk , not a specific Jaguar part but generic for many cars so cheap

But there is an Andy Bracket ( XJREngineer on the original Jaguar design team ) that can be installed that biases the timing 5 degrees for better engine performance

A good CKPS will read 1300 ohms as a basic meter reading

Starter rotation 300 RPM on the instrument cluster ?

The first 3 seconds of fuel pump on is the rotation of the key , after the CKPS sees engine rotation it will command the fuel pump back on so On - Off - On

You can feal the fuel pump relay click in your fingers and if good enough ears you can hear the pump from the driver seat

 

The Crankshaft position sensor is a fairly common issue on these engines, so worth changing it out, even if only to eliminate it as a culprit.

 

There is a TSB (technical service bulletin) which relates to poor idle and misfiring on cylinders on XJRs
That is caused by exhaust valves getting gummed up and causing poor compression.
This condition is exacerbated if the car is only driven around town.
The fix is to get the car onto a highway and give it a thorough flogging particularly in intermediate gears holding high revs. Some upper cylinder lubricant also helps.
I had this on a deceased estate X300 which had two cylinders badly down in compression at around the 100 psi mark and a leak down check showed it to be an exhaust valve problem
30 miles of hard driving (flogging) fixed the problem