Topic

My car cranks but doesn't start. I've checked ignition and I've checked fuel pump is supplying by filling up a measuring jug. I've had the fuel rail out today and confirmed the injectors all have the same resistance (15.2 ohms) and they are firing (fired them onto some a4 paper). Put the fuel rail back together and car starts immediatly. Revved it and all sounded good with all pistons firing. Turned car off and back on and is back to cranking with no start.

Thinking an empty fuel rail caused the fuel pressure regulator to allow enough fuel into the car to start it. How can I confirm something is up with the fuel pressure regulator?

Engine is an MGF 1.8 MPI mems3 from 2001

Edit: should add the car starts for a second if I spray easy start spray into the intake.

Experimenting with an adjustable fuel pressure regulator is one of the jobs on my to do list. I’ve had a flat spot ever since I’ve had the car & my box of sensors, replaced in an attempt to cure the problem, attests to the tenacity with which I’ve tried to rectify it.
The FPR forms part of the fuel circuit; the pump lifts fuel into the fuel rail, which is common to all the injectors. The injectors meter the fuel when required by the ECU & the excess is returned to the tank via the regulator. In a closed system it doesn’t really matter where the regulator is, the pressure is dictated by the setting & that setting should remain constant.
I can’t see any reason for the regulator to work cold but not hot, the unit is little more than a spring acting on a diaphragm & when the pressure is reached the valve opens & fuel is returned to the tank.
This, at least is how I understand it & it’s this information on which I’m basing my adjustable system.
Any advance on this anyone?
M

"I can’t see any reason for the regulator to work cold but not hot, the unit is little more than a spring acting on a diaphragm & when the pressure is reached the valve opens & fuel is returned to the tank."

I hear what you're saying but maybe this isn't a problem caused by overheating but caused by a certain situation i.e. the fuel system doesn't work properly if its primed after the engine being run recently. Something is not resetting to default causing the fuel to not get to the engine?

What's frustrating is the fuel was spraying every time I cranked the injectors while outside of the engine. I can only presume something is different inside the piston heads. Although I would assume the pressure in the head is very much the same as outside the engine block when first cranking?

For my upcoming experiments with the adjustable FPR I bought, off eBay, a fuel rail complete with the regulator, which will be discarded for the experiment & replaced by a blank. This cost me £10, although there were others available for quite a lot more, they are out there & that was only a couple of weeks ago. Have a look, your luck will be every bit as good as mine. And as with all these things keep us informed.
M

Contact Darren at ‘Bitz in Glossop, a penny to a pound he’ll have some spare & he may also be able to give you a pointer to your problem.
There are few who have the single minded reputation with supply of parts, repair & restoration of our cars.
M

I've just had a thought. Clamp the fuel return line (like you would when replacing brakes) and see if that gets the engine to start. I'm gonna try it tomorrow. Maybe not full clamp but enough to artificially increase pressure. You said it doesn't matter where the fuel pressure valve is located so I'll clamp just after the fpr.

I’m an experimenter & not a pundit, my experimentation is based on knowledge gained over years of interest in a number of fields & is inspired by the work of others much in the ways my experiments have inspired.
I would be reluctant to close off the return feed as this would increase the line pressure to that capable of being supplied by the pump, that could easily damage the pump & injectors.
I would advocate caution
M

I used caution and only 3/4 clamped it with some mole grips. Did not fix.

Also tried disconnecting the Manifold Absolute Pressure (MAP) sensor and the Idle Air Control (IAC) valve to put the engine into limp mode in case one of these was the problem. No fix. I did note the quiet, high pitched whine when an MG's engine is off (key removed), comes from the IAC valve. Does your engine do this?

Dunno what to do next as I don't think it's a compression problem as engine runs fine once its going. I'm gonna have a look for oil in the combustion cylinder and double check i'm still getting a strong spark when cranking a second time.