my 1983 944 will only start if I clamp the fuel return hose to tank and spray easy start at air filter, once engine is at temperature car will start easy, but if I leave it for a while, I'll have to resort back to the Clamping fuel return hose and spraying easy start in air filter
I have replaced plugs rotor, distributor cap, and leads, i have replace speed and reference sensors, I have fitted a pressure gauge at fuel rail and I have 2,5 bar with pump/engine running. I noticed that the Pressure drops instantly, when I stop the engine, is this a faulty FPR? any help would be welcome, as I've been working on this issue for a while.
When car warm it runs

 

Do you lack fuel or do you lack spark? This should be the first step to any no start diagnosis.

Its all here:
https://www.clarks-garage.com/shop-manual/ts-01.htm

 

Since you suspect the FPR, try this test: pinch the return line and see if the pressure holds when the engine is off and the pressure drops. If it does, the FPR is likely faulty and needs replacement.

Also, check for leaks in the fuel injectors or the fuel lines. A leaking injector can cause similar issues by releasing pressure when the engine is off. Remove the spark plugs after shutting off the engine and see if any are wet with fuel.

Plus, inspect the check valve in the fuel pump, too. If it fails, it can cause a pressure drop.

A weak battery or poor ground connections can cause weak spark and fuel delivery issues.

 

Your symptoms indicate a leaking check valve at the fuel pump and a faulty DME coolant temperature sensor.
The leaking check valve allows fuel to return to fuel pump outlet, bleeding down the fuel pressure. The DME coolant temperature sensor is not sending the proper signal to increase FI pulse rate to make the fuel/air mixture richer for cold starting

 

[QUOTE=mark Harper;19435229]my 1983 944 will only start if I clamp the fuel return hose to tank and spray easy start at air filter, once engine is at temperature car will start easy, but if I leave it for a while, I'll have to resort back to the Clamping fuel return hose and spraying easy start in air filter
I have replaced plugs rotor, distributor cap, and leads, i have replace speed and reference sensors, I have fitted a pressure gauge at fuel rail and I have 2,5 bar with pump/engine running. I noticed that the Pressure drops instantly, when I stop the engine, is this a faulty FPR? any help would be welcome, as I've been working on this issue for a while.
When car warm it runs[/QUOTE]

OOPS ...I see that T& T got there before me !... I should have checked through the thread first sorry..

sounds to me like the non return valve in the fuel pump may have failed allowing the fuel pressure to drop when ignition switched off.
Either that or you have a fuel leak somewhere in the system.
The fuel delivery system should hold pressure for at least 20 minutes or more.


. Have you checked both the FPR and Damper for leaks into the vacuum system ? just pull the vacuum hoses off the FPR and damper just before you switch off and see if they release any fuel when you switch the ignition back on to the ignition light position