After extensive testing on 1999 V70 the cause of motor dying after firing is still unknown. It cranks fires and then runs for a few secs or less and suddenly dies.
I tried unplugging the camshaft sensor to see if there was any difference when it was unplugged
(such as the motor no longer firing for instance) but the motor still fires and dies IDENTICALLY to how it does when the cam sensor is plugged in.

Could anyone advise whether this could be a sign that the cam sensor is as fault? As it appears that exactly the same fault state exists when it is unplugged as when it is connected.
Advice greatly appreciated.

 

Cam sensor failure was common with the early 1991-1998 cars, and always set a cam sensor code. 1999+ cam sensors with the Denso fuel injection system had almost 0 failures.

Have you scanned the car with a compatible scan tool? A quality can tool can give you live data - when the engine is running or cranking - The free VIDA with a $100 DICE unit is your best choice.

Fuel pressure can't be checked with a scan tool (on your car) - that would be a good first step after scanning - does the pressure drop off right before the engine dies? Is the car low on gas? (many cars have been towed in due to lack of gas in the tank, and many techs have spent hours checking stuff - until they figure out it's out of gas!)

Does the spark stop right before the engine dies? -

 

Thanks, I'll try and get the Vida/Dice to work.
I have tried a couple of diagnostic systems on it that failed to sync with it (which according to the system's owners was through the vehicle's age being pre 2000 and the systems only syncing to vehicles from 2000 on) but I have not tried a Vida/Dice set up on it. It is a mk1 V70 born in May 1999.

​​​I haven't checked if the spark stops just before the engine dies. I will remove a spark plug and check exactly when the spark stops when I can get someone to key the motor for me.

​​​​​​I checked for fuel reaching the injector fuel rail by disconnecting the fuel line at the fuel rail and cranking it. The fuel pumped out normally.
But as all the attempts to start it will have now lowered it's fuel level, just to be on the safe side I will put more fuel in it.

 

I have now checked this and found that the spark continues right up to (and even slightly after) the motor dies.

I have also noticed hearing two donks from somewhere below the dash on the driver's side low down and far back close to the firewall, just before the motor cuts.
The donks sound like a vacuum system device or valve shutting. This is petrol but I know diesel motors have a magnetic valve that shuts off the fuel supply. Does anyone know if a petrol motor has the same and if the valves operation would cause donk sounds from the area of the vehicle where the two donks are heard just prior to the motor cutting?

I have tried cranking it with the antenna ring unplugged and removed from the ignition and it fires and dies in the exact same way it does with the antenna ring connected and in place. Does this indicate a fault exists somewhere in the key chip - antenna ring - control module, circuitry?

 

You are looking in the wrong place - as you said "it's the same result with the sensor plugged or unplugged"

No magnetic/electric fuel valve - just an electric fuel pump - What is the Fuel pressure?

Don't waste your time futzing with the antenna ring/chip/random immobilizer ideas - that's not your problem. What's the fuel pressure? What codes are stored?

 

What do I use to read the fuel pressure? I know from checking that when cranking the fuel is pumping to the connection into the injector fuel rail. I won't be able to read codes till I can get a reader. Have requested on local volvo forum if there are any Vida/Dice owning members near my location.

 

A gauge that connects to that valve on the injector rail - maybe something like this -

 

Have tested fuel pressure which I believe should be 55 psi? but compound meter I used only measures fuel pressure up to 10 psi.

Nevertheless the following may give a clue to what could be the fault.

When the motor cranks and fires the meter needle showing the fuel pressure shoots way past the 10psi max and sticks there while motor is running.
When the motor starts to die and the idle speed drops the needle showing fuel pressure begins falling to a much lower pressure and the first time it will drop to around 5psi, then the dying motor suddenly recovers and the idle speed increases again and the pressure needle shoots back up to ​over 10psi (10psi is max fuel pressure on meter) then after running normally again for only a short time the motor begins to die again, and the idle speed drops again, and as the idle speed drops the fuel pressure needle drops back below 10psi, but unlike the first time it does not suddenly recover at 5psi but instead keeps dropping until by 3psi or before, the motor has completely died.

After motor has died, while the ignition is switched on, the fuel pressure needle very slowly climbs back up to just after 10psi and stops there (see photo below), then when motor is cranked and fires again the needle shoots up even higher while motor is running normally.

In photo below the 10psi mark is shown immediately to the right side of needle when looking at photo. The 25 visible to the left of needle is not part of the fuel pressure section of meter, but it is where the fuel pressure needle shoots to when the motor is cranking and after motor has fired and is running normally.

 

Sounds like flow is restricted, doesn't it?

 

Or a bad fuel pump after 22 years! Check the pressure with a real gauge - stop guessing!

 

The fault has finally been identified.
A failing fuel-pump controller.
To help anyone in the future who has this problem who finds their way to the end of this thread.
The controller is located in the left rear corner of engine bay (on a RHD model) when viewed from front looking under the hood. It is under the cover that houses the fuse box. To remove the cover unscrew the 4 torx screws then lift it off. The fuel-pump controller can then be seen. It is salmon pink with the number 103 on the top (see picture below) It will feel tight like it may not pull out but it will.

After removing it, you can test that it has a fault by connecting a short jump wire between terminal 15 and terminal 87 in the connection that the controller plugs into. If the vehicle then starts and runs normally it means the controller is faulty (often intermittently, so sometimes by
unplugging it, then reinserting it, it will start to work again albeit temporarily)

My thanks to everyone on this thread who gave advice to try to help me find the motor killing fault

 

Thanks for telling us your solution - those relays get cracked solder connections, and usually fail after being driven a while - the cracked solder joint get larger with heat - and prevent current flow to the fuel pump.