Slow starting-Fuel pump not priming

Post Sun Nov 30, 2014 9:46 pm

My 1988 318 has always had trouble with poor starting when cold (but is fine when turned off and restarted fairly soon after).

Today I decided to look into the problem, I pulled the rear seat and pump cover and found that when the ignition is turned on the fuel pump does absolutely nothing.

When the car is cranked over power is fed to the pump and when running continues to feed power to the pump.

I have been looking into the relay power feeds but so far have only worked out that it seems to use 2 relays.

Should this system provide power with the ignition turned on for a short while until pressure builds up to prime the system for startup?

Thanks
Ben

Post Sun Nov 30, 2014 10:08 pm

BenG wrote:, I pulled the rear seat and pump cover and found that when the ignition is turned on the fuel pump does absolutely nothing.

When the car is cranked over power is fed to the pump and when running continues to feed power to the pump.

Exactly as it should be.
Your problem could well be related to low/no fuel pressure when starting from cold, but the system should hold pressure for several days after being stopped.
Fuel pressure can fail for several reasons: A leaking non return valve in the fuel pump, a simple leak in the fuel delivery pipe or hose, the fuel pressure regulator leaking fuel into the fuel return pipe, the fuel pressure regulator leaking fuel into the small vacuum pipe to the inlet manifold, and one or more injectors leaking fuel into the inlet manifold.
The last two can cause additional starting problems by the fuel in the manifold making the mixture too rich for the engine to start.
The diagnostic tool you need for this is a £10 ebay fuel pressure gauge kit (plus a few inches of rubber fuel hose.)

Post Mon Dec 01, 2014 12:45 am

BenG wrote:My 1988 318 has always had trouble with poor starting when cold (but is fine when turned off and restarted fairly soon after).

Check the blue temperature sensor resistance at the ECU.

http://www.e30zone.net/e30zonewiki/inde ... or#Testing

Ben

Post Mon Dec 08, 2014 11:12 pm

Thanks and sorry for the slow response, I now have a fuel pressure gauge. Where would the first place to start from here?

Post Mon Dec 08, 2014 11:27 pm

Disconnect the rubber fuel hose from the fuel rail, connect the hose to one branch of the tee piece of your gauge, then connect your few inches of hose between the other branch of the tee and the rail.
Start the engine, note the reading on the gauge, then switch the engine off and see if and how long the pressure takes to decay.