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Juan Crespo
Juan Crespo, Tech Trainer
Category: Car
Satisfied Customers: 1526
Experience:  A.S.E. Master Technician, Advanced Level, Emissions - Asian, Domestic, & European
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Jaguar XJ6 Sovereign: jaguar sovereign 1988 6cyl. can not get

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jaguar sovereign 1988 6cyl. can not get to fire. has power to coil but not out
Connect a test light to the negative side of the coil and crank the engine. Does the light flicker?
Customer: replied 4 years ago.

with the key in the on position but not turning over the test light is on, on both sides of coil

turning the motor over the light goes dim and bright


The negative side of the coil (-) should be momentarily grounded as the engine turns; this in turn should collapse the field inside the coil and produce a high tension spark. Just to check, try another coil and let me know what happens.
Customer: replied 4 years ago.

have taken a coil from my other running car with the same result


The pick/up coil inside the distributor sends a signal to the amplifier, which in turn grounds the coil. Are you getting more than 11 volts at the positive (+) side of the coil?
Customer: replied 4 years ago.

without turning the motor over 11.78

turning the engine over an average of 7.0 (low 6 high 8.5 approx)
That should be enough. Since you have also replaced the Ign Amp, the only thing left that might be preventing that coil from creating a spark is the pick-up coil inside the distributor. To test it, turn ignition off; disconnect pick-up coil connector from amplifier module; measure resistance between the two pick-up coil harness terminals; resistance should be between 2200-4800 Ohms; if not, replace the pick-up coil and harness assembly.
Customer: replied 4 years ago.

Sorry but not sure as to the pick up coil inside distributor, as the only thing that i can see inside the distributor is the rotor button,

have replaced cap and rotor


Perhaps you're looking at the shield under the rotor? Your distributor should be like the one depicted in this graphic:



Customer: replied 4 years ago.

sorry that is not the type of distributor on these cars all three have a similar type distributor.

No vacuum advance unit or pick up coil assembly. or anti flash shield.


type lucas

part nos 4199od

35DHT6 1589



OK. 3.6L. Have you checked if the Tachometer reads at least 200 RPM as the engine cranks? If not, either the signal from the Crank Sensor is bad, or the wiring between it and the ECU, or the ECU itself is faulty. If you have access to another ECU, swap it and retest. Another thing, you said the test light went dim and bright when testing the Negative side of the primary circuit. It should flicker ON and OFF. Also, try another high tension coil wire; connect it to the coil and place the other end about 3/16" from a good ground. Is there a strong spark?

Customer: replied 4 years ago.

have taken the coil off and have had it checked out it is ok.

can not get a reading on the reves as there is no reading on the tachometer on the dash have changed the crank sensor and the first part of lead over,with a spare

Are you recomending that i change the lead from the coil to the distributor?

The ECU is out of a car that runs only have the one


The tachometer receives its signal from the Negative side (-) of the coil; was it working before this happened? If it was, the Ignition Amp may be at fault now. Try swapping it with the one from your other car. If that doesn't work, try a new lead (high tension wire) from the coil and test for spark as previously indicated.

Customer: replied 4 years ago.
/Sorry for the delay
Have changed the Amplifier,checked and changed coli both test ok no help with new leads from coil
Voltage on the neg side of Coil 9.5 to the car body. Coil does not seem to be getting pulses stays constant at 9.5 when turning motor over.
Tacko still not responding
no voltage across the coil.
how can we test wiring from the crank angle sensor to ECU
Can we check ECU
confirm the amplifier is next in line to coil
Check the Blue and Red wires from the Crank sensor to the ECU terminal 24 for Blue and 13 for Red. If no continuity, repair the circuit. If continuity is good and the Crank sensor, the Ignition Amp, the Ignition coil and its lead are all new, the only component left to try is the ECU.The way the system works is the ECU controls spark and injector pulse based on Crank sensor signal. Another way to see if the ECU is bad is to check for injector pulse with a noid light, if no pulse, you've got a bad ECU.
Juan Crespo and 2 other Car Specialists are ready to help you
Customer: replied 4 years ago.

Have checked all the above all wires read ok, have tried a different ECU and the other unit next to it.

There is a red relay unit have tried to buy pass this as it appeared not to respond


Are the injectors working as the engine cranks?

Customer: replied 4 years ago.

any advice on how to check?

In a previous posting I had indicated how - "Another way to see if the ECU is bad is to check for injector pulse with a noid light, if no pulse, you've got a bad ECU". Noid Lights are small LED lamps that connect to the injector harness connector - they're sold at most auto parts retailers. Another tool that can be used for the same purpose is a Logic Probe - also sold at parts retailers. The reason these tools are used to check injector pulse are: 1- They're rated High Impedance and won't harm the transistor inside the PCM that "drives" the injector. 2- Both incorporate LEDs which can be visible even when being switched ON and OFF for a few milliseconds. At each injector connector you will find the "power" wire (White/Brown) that should have Ignition System voltage with the Ignition switched to ON. The other wire at the connector is the "control" side (different color for each injector) used by the PCM to open and close it. If you're going to use a Logic Probe, you would touch this "control" wires to check for injector pulse. The noid light just plugs in place of the injector.
Customer: replied 4 years ago.

Missed that one.

Have purchased a noid light

There is no responce from the light on the injector, have previously changed the ECU unit from the car that runs with no difference.


I noticed in your postings that the battery voltage is decreasing. These "cats" can get finicky regarding battery condition. Make sure the battery is fully charged.
Customer: replied 4 years ago.

when buying the noid light also purchased a new battery


Switch off engine.
Wait 10 seconds.
Switch on ignition - do not try to start engine.
Fault code will now be displayed on facia panel
Any codes?
If codes won't display automatically, press the VCM button.
Customer: replied 4 years ago.

no further responce may this be due to the battery having been taken in and out over time


So what do we have? Vehicle Condition Monitor (VCM) not working?
Customer: replied 4 years ago.

it would appear so


Something is not adding up. Can you give us a little background history on how this Jag became so ill? What happened that rendered it so?
Customer: replied 4 years ago.

I was given it when i purchased another jag the same model which was and is licensed and on the road but is rusty in the boot and needs the rust removed other wise it runs well this is a 1989 this car if it all works out is to be sold in time.


The problem fee car is a 1988 i am told it has a crook motor head, the coil the amplifier and a silver box near the ECU had been taken off the car as well as a head light.This car it has been my aim to regester and keep due to its good appearance. i wanted to get the motor to at least run before doing the repairs on the engine as i thought that by not doing so i would have far to many problems


i then purchased another jag the same model but different year 1992 unlicensed running after i replaced the large rubber boot near the injector bar not sure what it is called this car i have now nearly stripped looking at wiring etc

What I can't understand is if you have replaced the components that make the engine start and run. Why is there no spark at the plugs or pulse at the injectors? My suspicion is that some of the parts are not exactly the same number, and therefore can't be exchanged from one vehicle to the other, especially the ECU. Let's start at the beginning: the usual cause of this problem is either the Ignition Amplifier or the Crank Sensor. You can test them both with a meter. First, the Ignition Amplifier; you should have Battery power on the White/Pink, ground at the Black, 5 volts with the Key ON on the White/Green, a pulsed signal from ECU on White/Red, and the White/Black is the coil trigger. For the crank sensor you should have ground on the Blue wire and a pulsed AC voltage signal on the Red wire when cranking.

I wish I was there by your side getting my hands dirty. Keep me posted.