Residual fuel pressure overnight?

[alpinewhite318i]

I connected a fuel gauge to my 86 325es overnight and the fuel pressure went from the uppper 30s PSI to 0 PSI. Is this normal? I connected the gauge at the cold start valve. I am having issues with cold starting the car when it has been sitting. After is has been running I can turn it off and it starts up right away.

[jlevie]

What is more important than the residual pressure is how fast the pressure comes up when you start the car. It should (in this case) hit 2.5bar or very close to that in a turn or two of the engine. If that doesn't happen the filter is clogged, the high pressure pump is weak, the FPR is bad, or something is blocking fuel flow into or out of the pump.

In most cases hard cold starting will be due to intake leaks. Other players on this car include the time-temperature switch or cold start valve. For all E30's a faulty ICV or engine temp sensor can be players. It is also possible to have injectors (or a cold start valve) that are leaking and flooding the engine when it sits for an extended period.

[alpinewhite318i]

How do you check if fuel injectors are leaking? I have a new ECU, ICM, ICV, coolant sensor and sender.

[jlevie]

The injectors are best checked by sending them to a shop that can clean and test them. But just to see if they are leaking you pull the injectors, connect them to the rail, jumper the fuel pump, and see if they leak.

The definitive test for intake leaks is to have a smoke test run on the intake and crankcase. if you don't want to or can't do that, replace every hose and seal associated with the intake and crankcase. That would include the intake boot, valve cover gaskets, crank case vent hose, evap control hose, throttle body gasket, intake gaskets, injector seals, oil return tube seals, dip stick o-rings, oil filler cap seal, brake boost hoses, and ICV hoses.