Quickly,,, and I am SORRY to jump in here like this,,, BUT it has been a loooooong standing question of mine. I have replaced the front crank sensor on my 1990 v12 XJS and I want to replace the rear crank sensor. Is it the same sensor? Although the wire OUT on the rear is shaped/angled differently,,, can I use the same style crank sensor used in the front, on the rear? The cost difference is phenomenal...

Speed sensor,,, crank sensor? How is it even described...?

Any answer will be and is MUCH appreciated.

 

Yes the sensors are interchangeable, not sure about the plug. The wire on the flywheel sensor comes off at an angle to keep it high not sure if it would a problem with the wire coming straight out catching on things.

 

Thank you, Warren!

 

I have checked and with the ignition on, there is no injectors click or voltage at the injectors

 

Hi Sososs

You say that you have resistance on the Front Crank Sensor when Tested with your Meter

Now do the same Test again with you Meter, only this time Spin the Engine while you do it, if the Needle on your Meter doesn't Flicker, then it could still be a Crank Position Sensor problem

Another thing that you could and should try is to remove the Distro Cap and look for any signs of Burning or maybe a Crack in the Cap, either of which could be the cause of the problem

And also Check the Plug and Socket of where the Crank Sensor Plugs into the Loom, just in case the Pins got damaged when putting the New Crank Position Sensor in

If none of that works it might help to get a Noid Light (ebay or Amazon)

 

If the injectors do not click when you turn the ignition on then it could be the following and I would check in this order.

1 Shorted wiring in the V
2 Injector resistor pack and plug
3 No 12V at injectors
4 ECU

Have to go to work now I'll check back tonight once oyu have checked these,

 

I checked the front crank sensor - crank sensor wire disconnected, engine cranking, multimeter had readings of mV - fluctuating

I have done the same with the rear sensor - but nothing on the multimeter; should the rear crank sensor register the same output (mV) as the front one ?

 

could you please let me know in details how to check the 4 points you mentioned ?

 

This problem is most likely going to be either a bad connection or bad wiring. So you need to verify ALL wiring and connectors in the injection circuit are working correctly.

1 Shorted wiring in the V visual inspection- look for damaged insulation, or disconnect ALL the connectors - Every injector and the other end which I think is behind the RH headlight and check the 12V supply wire continuity to ground with an ohm meter it should be open circuit.
2 Injector resistor pack and plug visual inspection, pull the plug out and check the pins for corrosion
3 No 12V at injectors measure with a multimeter


With fluctuating mV reading I suspect you had the meter on DC volts. The meter needs to be on AC. The fact you got fluctuations most likely means the VR sensor is ok.

 

back crank sensor should have the same voltage as front one ?

 

Hi Sososs

The Rear Sensor Monitors the Engine RPM for the ECU

The Front Sensor Triggers Injectors and the Spark

Since I've never had a Rear Sensor go wrong, I am going to have to pass that one over to 'Warrjon' but 'thinking out loud' No resistance doesn't sound good, although the First thing I would do (which has actually worked for me before)

Is to remove the Silver Box Resistor Pack@Warrjon and give the Plug and Socket a really good clean with some Vinegar

Although its a bit of a PIA to get to and remove, you can't give it a proper Clean In-Situ as all those pins need to be 'Shiny Bright' and if it's been on a Buggy, the chances are that it got hammered and splashed with plenty of crud

There are no Shortcuts as a Squirt of Contact Cleaner won't do it, so try that first and let us know what happens

 

My apologies I missed this, yes it should have voltage but it will be different from the front sensor as there are more teeth on the flywheel.

Meter MUST be on AC volts

 

I disconnected and cleaned up all the connections that I found
Measured front and read crank sensors - AC and both had voltage
Checked the continuity of both injector wires to ECU - OK
Checked the continuity of both front crank sensor wires to ECU - plus was ok, but the other - blue wire was not - I could not found a correspondent in the ECU

 

finally the electrician fixed it

had water/moisture in the ECU

 

now I have problems with the 4L80E transmission - with Jake's standalone controller

- with driveline connected - when trying to put on Park is making a lot of noise
- oil come out from the dipstick

please advice

thanks

- l

 

Hello again

Now, after 5 years of not running I manager finally to start it
very hard cold start, initially no spark

After warming it starts fine, but next day had the same issue at cold start - no spark and managed to start it after 5 tries

Please advice

 

*Reading over the thread* So, your eventual problem was that water ingress had moved along the harness and into the Marelli ignition ECU? And that was solved (I presume). You've checked the connectors in the years since?

Basic principles still apply. All XJS V12's have a separate Ignition and EFI system. The EFI system is DOWNSTREAM and DEPENDENT upon the Ignition system (as you may know, or may not be clear on). The EFI can ONLY function if it knows the engine is running via the RPM pulse from the Ignition system (in this case, a square wave output from pin 25 I believe of the Marelli ECU passing over a white shielded wire, into the engine bay, near where the Lucas Ignition system would have intercepted it on pre-Marelli cars, and then to the ECU via the rear harness.

Just things to know: When you turn the key on, ignition power goes to the coils, the two Marelli amps, and to the CONTROL side of the Main Relay in the trunk causing it to pass battery power to the injectors (always energized and ready), the EFI ECU, and if I remember, the Marelli ECU - causing them all to wake up. It also passes available battery power to the control side of the Fuel Pump Relay (FPR) next to it, which is then turned on BRIEFLY by the EFI ECU as part of it's wake up routine, for just a moment or two, pre-pressurizing the fuel rail. Absent the RPM signal, the EFI ECU will de-ground the FPR, causing the fuel pump to shut off, and will not turn it back on until it sees that RPM single (in which case it can also begin calculating needed injection pulses).

Now moving on to hard starting / rough running. 1. Are you sure that the ignition / spark is consistent? NO RPM pulse, no injection.

You can always test the injection system (a bit) and kind of pre-enrichen start up by using the ONLY feature besides an RPM pulse that will cause an injection burst. With key on, activating the WOT (wide open throttle swtich(s)) will cause a single enrichment burst from the injectors whether the car is running or not. With everything quiet and only key on, it's a quick sanity check to know that that the EFI ECU is alive, and capable of commanding the injectors (as long as it's getting the right inputs).

Otherwise.... 5 years.... how is the fuel in the car? Have you changed the fuel filters? Could ignition be fine but you have bad fuel?

Also with regards to the EFI system alone, you might want to check your coolant temperature sensor connection, as it is BY FAR the biggest input into proper enrichment - startup or otherwise - besides the MAP sensor. Many no-start situations that are not ignition related comes down to a CTS with excessive resistance (due to connector/corrosion/failed cts) that causes the EFI ECU to think the engine is FAR colder than it is, (off the chart really) and causes massive over-enrichment to the point of non-start. You can test this somewhat by shoving about a 480 Ohm (or paperclip in a pinch) across the CTS sensor connector to simulate a warmed up engine.

Air related issues aren't uncommon - are leaks, stuck IAV (idle air valve) too - usually causing excessive idle RPM or RPM bouncing once started.

At some point if issues arent' solved there other things to look at are ensuring there's good connection at the power resistor block so that the "hold" phase of injector opening works as well as the "open" high current circuit pathway.

~PK

 

I have replaced Lucas ECU (had moisture în it)

What is now strange after 5 years is that after the engine is hot it starts right away, no problem

But when is cold I have no spark, only after 3 or 4 times of long crancking start to have some sparks and then starts, but is not running as it should untill is hot

I have Put fresh fuel

 

Some ideas: have you renewed:

• the coils
• the dizzy cap, rotor, HT leads and plugs?
• installed decent engine earth
• serviced, by carefully cleaning, the connector prongs of the resistor pack?
• as above mentioned, renewed the CTS and the ATS
• checked the fuel pressure and/or renewed the fuel pressure regulator?
• checked the lamda sensors are operating properly?

 

I ordered new sparks, new sparks wires, new distributor cap and rotor

Do you know the codes for CTS (coolant temp sensor) and ATS (air temp sensor) to order them also

ECU is receiving info s both from CTS and ATS ?

Thanks