Car will turn over but wont start

To check that the pump is doing its job, all you would need to do is slack back the fuel filter or the orange push connector (I think it’s orange but I’m 75miles from exhibit A) which is the send to the fuel rail. Make all attempts to mitigate the potential rush of fuel but if you have petrol pumped at pressure & consistently that section can be considered working.
Turn now to the return from the pressure regulator. There are two push connectors, if you’ve found one look for the second (is it green?) open that & that’ll show fuel being returned to the tank.
As I’ve said I’m on holiday & 75 miles from my car, so can’t go with a bag of spanner’s to check, maybe one of our number would like to verify these comments.
M

Airportable is correct, the fuel feed pipes are orange connectors and return pipe connectors are blue.

The fuel pump pressure is 3 bar (44psi) so disconnecting a pipe under pressure is too brave for me. I would crack the fuel filter nut with pump/ignition off to release pressure , tighten it back up, ignition on to pressurise, ignition off, crack fuel filter nut to see if it had re-pressurised immediately (3 seconds) for a normal start. Not a recommendation, just what I would do. Please be safe etc. I was about to say make sure engine is cold, but then realised it won't start--- slaps forehead and exits.

Can I chuck in a curved ball? The other day my daughter rang me to say her car wouldn’t start, turn over yes, but no life. I went over as dutiful father’s do & was presented with a brand new key & fob, I’ve covered this elsewhere but the upshot was having transferred the electronics over she hadn’t changed the coding chip over. She had no idea that it existed, why should she.
It might be worth a look at that network, either with the key/fob or the ring around the lock & associate gubins.
M

These are all really helpful and insightful suggestions. This community is amazing and I'm very humbled by how helpful [and sometimes funny] you all are.

My update is thus: The car is back to starting on first attempt but doesn't on the second (ignition off, ignition on and cranking but no life). I don't dare drive it for fear of breaking down so these tests are done on the street outside my house: I disconnected the Engine temperature sensor (black horizontal plug near the cylinder head) and the car started every single time that I started and shut her down. Whether it was for 2 seconds of running or 10 minutes. This went on for about 30 minutes of intermittent/random test intervals just to be sure it was the engine sensor causing the problem. Then it wouldn't start again (starter motor going but not starting engine) just as if the engine temp sensor had been re-connected (it hadn't). I googled some info about how an engine temp sensor works and someone on Quora explained that when disconnected the ecu gives a best guess of how much fuel to inject. The user then suggested trying a little throttle when cranking. Sure enough the car roared into life and I could smell fuel (and probably damaged cat converter) but the engine was alive!

Turned off the engine and re-connected the temp sensor (engine was very hot) and predictably it wouldn't start. Tried giving it some gas and the engine once again started without problem.

I think my mechanic's guess [replace the engine temp sensor] was right. What do you think? Is this conclusive proof that I need a new engine temp sensor?

Sorry if that sounds thrifty but I'm unemployed atm so i'm trying to avoid any unnecessary part purchases :dry:

P.s. I had a cheap wired ORB2 wired in for the duration. It gave me a p0115 "engine temperature sensor 1 circuit" error but then about 15 minutes into testing (before I plugged the sensor back in) the error disappeared, without me clearing it, and I couldn't get the ecm to give me the error again despite exiting the program and trying to scan again. Not sure if this is useful info but through I'd include it.

With the mechanic and the OBD code pointing to the ECU water temp sender, as well as your results by disconnecting it that would be my next item to try. Intermittent faults are a pain in the butt, as you never know if your action has made a change or it has randomly changed. If you have to fire the parts cannon, this is one of the the cheapest items to try. They are £9.99 at DMGRS at the moment Pt No MEK000030.

Good luck

"... and the OBD code pointing to the ECU water temp sender"

My earlier message about the fault logger was misleading. What i meant was I couldn't get a consistent error code when the ETS (Engine Temperature Sensor) was unplugged i.e. the ECU wouldn't consistently generate an error code that the ETS was discconnected/faulty. Not sure if this is a sign of a bum ECU or the fault detector only detects every so often e.g. checkss for faults every 10 minutes.

ANYWAY, I've replaced the sensor (thanks for the item no/ @markvrs ) and have seen no change in the cars behaviour. Still starts beautifully from cold but will not start when hot AND i mean HOT. I think my previous message can be ignored as I wasn't actually driving the car between stop starts so I don't think it was getting hot enough. Running the engine, shutting down and trying to start the car works. It had nothing to do with engine sensor being connected or disconnected I just wasn't getting the engine hot enough. That's why it would start after stopping. This was a false positive - I was connecting dots that shouldn't have been connected. I now know to drive the car before stop starting to get the problem to rear its head.

Problem is the problem's still there. Do I have any other options?

If this was a carburetor car I would have a guess at vapour lock.

It's a long shot but is the tank venting properly?

Does the car still cut out at any point whilst being driven or is the issue now limited to being unable to restart if you have driven for a while with the engine up to temperature, stopped and then tried to immediately restart?

Hi R40. I've thought that maybe the charcoal filter might have something to do with the issue but I closed off that line of the investigation as it didn't seem to align with the symptoms. My MG has always sucked in a lot of air, when opening the fuel cap after a long drive, and still does that even now so I don't think anything has changed.

@Nota The car has only ever cut out during a long drive (2 hours), i let it rest for 15 minutes, it would then allow me to start it. Drove for another 15 minutes and cut out again. I left it overnight then drove it home the next day, stopping for an hour to let the engine cool so it wouldn't cut out on me while driving. I've not had it cut out since.

So the issue is both that it cuts out during a long drive (2 hours or more) AND "being unable to restart if you have driven for a while with the engine up to temperature, stopped and then tried to immediately restart". Quoting you as you hit the nail on the head perfectly.

R40MGF wrote:

It's a long shot but is the tank venting properly?

My MG has always sucked in a lot of air, when opening the fuel cap after a long drive, and still does that even now so I don't think anything has changed.

Next time it won't start, try taking the fuel cap off...

This a question I really feel I should know the answer to & it leads on to a discussion we had on here a good while ago, possibly David might recall. Firstly, should the petrol tank gasp for air when removing to refuel, secondly is it detrimental if it doesn’t?
My car amongst a lot of others on here, if historic posts are anything to go by are irritatingly slow fillers. I reasoned that providing there were no kinks or restrictions in the pipe work venting was the problem & that could be exacerbated by the flap through which you insert the filler nozzle. The Japanese spect cars don’t have this & as Rimmers had these on offer at the time I thought I’d give it a go. I didn’t. So when I noticed that two out of the three spot welds which hold said flap had failed I carefully cut the third & rived it out, causing the cap not to seal as it did. Hence the question.
And did it’s removal overcome the slow filling problem? No, it created another, it is better but if you’re being profligate & filling up up, once near “my cup runneth over “ point on the fuel gauge, it does & blows back slopping fuel down your freshly polished paintwork.
M

Tried your tip David. No dice.

@Airportable I have seen some of the discussions about whether the fuel tank should gasp for air when opened. Mine only does it when drained from a long drive. Otherwise its quiet.