CIS Lack of Fuel Pump Buzz at Startup

[rjm65]

I've had my 79 for the better part of 3 years. My starting ritual goes like this,

1. Turn key on
2. Engage starter for a second and release.
3. Engage starter again and engine fires right up.

When I do #2, I mean step 2 not the other #2, when I release the key I can hear the fuel pump run for about a half second then shut off.

Should the fuel pumps come on at step 1 for 2-3 seconds to pressurize the system? This weekend when I was over at Leo's aka MPDano, I noticed his Euro's pump would come on for a couple seconds when you went key on engine off. What's normal for CIS cars?

My car has never done that. Should it? What triggers the pumps to come on with key-on, is it something inside the fuel relay?

[Fischer_76_911S]

If you are having to build pressure like that before it will start you probably need a new fuel accumulator. I had to replace mine. They are in the rear passenger wheel wheel and simply bolt on / bolt off affair. As far as the relay, I think it just pressurizes once on the first time. Swap out a relay with another on the same board and see if that solves the 2nd problem.

[928Shane]

My 78 does the same thing. I am switching fuel pumps to see if I have a bad check valve or if I need an accumulator.

[rjm65]

I have a new fuel accumulator and check valve. System holds pressure beyond spec. This isn't a hot start issue.

Most new cars that have FI, when you turn the key on/engine off you hear the fuel pump kick on for 2-3 seconds and then it shuts off. I noticed with MPDano's 81 Euro (also CIS) that his car did this. I've never heard the fuel pumps kick in with key on/engine off in my car ever.

I just wanted to see if this was normal for a 79 or if perhaps I have a faulty fuel pump relay that isn't triggering the fuel pumps on prior to engine start.

I don't think the fuel pump relay swaps out with any other relay on the panel.

[Fischer_76_911S]

I remember the fuel pump relay has an extra little pin. Start pulling to see if you have one that matches. Also, make sure yours DOES have the extra pin. I'm sure the wrong relay has been installed more than once in the fuel pump spot.

[DPW928]

The Porsche CIS system has a circuit in the relay that powers the pump for a short period when the key is turned to the on position. This charges the fuel system since the pump does not run during cranking (no 50 circuit to the fuel pump relay). If there is a leakdown and the system doesn't fulling charge you get a no start. When my 78 has sat for a long time, I will turn the key on and off for about 3 cycles and it starts with no problem.

[rjm65]

Thanks, that's exactly what I wanted to confirm.

The installed relay is the correct part number and has the extra pin that gets the signal from the ignition, but the relay has gone bad as it doesn't do the initial power up on the pumps.

Thanks again all.

[928Shane]

Looks like I need a relay also, Mine only powers up pumps when I crank it,or when it starts.

[rjm65]

So here's the final verdict.

I replaced the fuel pump relay and now when I turn the key on/engine off, the fuel pumps power on for 2-3 seconds and then shut off.

[MPDano]

Good deal, but does it start upon first crank?

[rjm65]

Sure does, cause now I don't have to do my "priming" crank any more.

[928Shane]

Same here,now on to the next thing on the list...