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[Doctor Gollum]

So . . . would/can either of the mauve relays (fuel pump & injectors)
if faulty . . . cause a no spark situation ?

Yes, I believe so, as one of them powers the ECU and all related systems (although the coil packs are fed straight from the ignition switch).

Coil pack primary comes from the ignition but triggers are from the ECU likewise the injectors, power from relay feeds them, and the triggers are from the ECU.

[Terbs]

That is the beauty of this forum, and the wealth of knowledge of you chaps. I know this thread is a bit long winded now, but by 'eck, have I picked up some really useful gen, not normally found
Never got chance to try relays today...peeing down, then visitors.

[Bigron]

I second that whole-heartedly, "terbert" - nowhere else would you uncover those hidden secrets, nor would you find better, more obliging folks,
Thanks to all from me, too. 

Ron.

[JamesV6CDX]

Only asking for my own learning here, but if there were an issue with power not reaching the ECU, how come I'm able to connect to it, interrogate it for its software version / fault codes,  and get live data readings / perform actuator tests such as running the fuel pump, etc?

It's a genuine question as my simple brain tells me if the ECU wasn't being powered, I wouldn't be able to interrogate it in that way

[Kevin Wood]

Only asking for my own learning here, but if there were an issue with power not reaching the ECU, how come I'm able to connect to it, interrogate it for its software version / fault codes,  and get live data readings / perform actuator tests such as running the fuel pump, etc?

It's a genuine question as my simple brain tells me if the ECU wasn't being powered, I wouldn't be able to interrogate it in that way

Good point. Had missed that. If the ECU is getting power (and it must be, as you say) but there's no spark it's most likely the crank sensor.

[Doctor Gollum]

Only asking for my own learning here, but if there were an issue with power not reaching the ECU, how come I'm able to connect to it, interrogate it for its software version / fault codes,  and get live data readings / perform actuator tests such as running the fuel pump, etc?

It's a genuine question as my simple brain tells me if the ECU wasn't being powered, I wouldn't be able to interrogate it in that way

Again, the ECU having power is very different to the injectors getting power

[Marks DTM Calib]

So . . . would/can either of the mauve relays (fuel pump & injectors)
if faulty . . . cause a no spark situation ?

Yes, I believe so, as one of them powers the ECU and all related systems (although the coil packs are fed straight from the ignition switch).

Coil pack primary comes from the ignition but triggers are from the ECU likewise the injectors, power from relay feeds them, and the triggers are from the ECU.

Spark firing is from low side drivers inside the ECU, injectors positive supply is via the relay with again low side drivers to pulse them.

Hence relay failure should see no fuel injection but spark present.

[Terbs]

Crank sensor fitted. Vehicle started first turn of the key.
Sensor only cost £11.80 from the bay. I intend to use it as a guinea pig and see how long it lasts. (I shall carry a spare with all three cars now !!!!)
Thanks to all who contributed to the thread. All ideas tried, and a lot has been learned and we got there in the end .

[Doctor Gollum]

Job jobbed then 

[terry paget]

My impression is that only the 2.5s are fussy about crank sensors, I fitted my 3.2 with an e-bay sensor five years ago and it's still running. Doubtless others will correct me.

[Bigron]

Mr. Terbert, could you please lik me to where you got that budget sensor from - I am getting nervous! 

Ron.

[Steve B]

Mr. Terbert, could you please lik me to where you got that budget sensor from - I am getting nervous! 

Ron.

I was thinking that too...They are £70+ from main dealer on TC ...

[omega2018]

delphi brand ones are £20 on ebay 10K miles on mine so far no problems.

[terry paget]

That is twice in the last three months that a V6 has refused to start, and has caused many wise men to puzzle over it, to turn out to be failed crank sensor. On straight 4 Omegas cam sensors are the usual culprit.

Funny how we never learn, isn't it?

[JamesV6CDX]

Only time will tell, but upon fitting this £12 sensor it looked to be well made to me. As long as you have a spare, not much to be lost IMHO. As I said to terbs - would cost that in petrol just to get to the dealer!