Resident 1.8 L-jet experts, a little help please... Options

[Blue6]

My 1974 1.8 completely stock has a problem. Every couple of days it will only stay running about three seconds. No mater how many times I try to start it, it just runs for three seconds then dies. Other days it will run great.
I checked the power to the fuel pump, and get 10.86 while cranking. When I plug the fuel pump back in and crank the engine, it doesn't do anything. No noise, no vibration. I removed the pump and jumped it with a battery, and it spins like it should. What am I missing. Thank you...

[timothy_nd28]

Sounds like a failing dual relay

[timothy_nd28]

Grab a voltmeter and set it for DC. Put the positive meter lead on the positive battery post. Insert the negative meter lead on pin 88d of the dual relay, should be a big black wire with red stripe. With the car off, you should be reading a solid 12 volts. Monitor the voltmeter when cranking and with the engine running, you should see 0 volts. Anything higher than 0.5 volts would indicate a resistance drop internal of the relay and should be replaced.

It's also worth checking if the fuel trigger points inside the airflow meter are working. With the ignition switch set to on, deflect the airflow meter flap. You should hear the fuel pump engage.

[Bleyseng]

Maybe a loose wire in the dual relay connector. Those wires get loose with all the pushing in an out over the years. Check to make sure they are not corroded too.

[Blue6]

Thank you Timothy and Geoff for the info. I should be home on Sat and will check all of your suggestions...

[Blue6]

Geoff, checked that dual relay. Everything looked great, no corrosion, wire and pins like new.
Timothy, 12 volts from 88d with the key off. Cranking, it flutters a little but stays around .03. With the ignition on, when I deflect the AFM flap the fuel pump does run. Experimenting, if I spray a small amount of starting fluid into the rubber elbow btw the AFM and the throttle body, the car will run but only with the AFM unplugged. As soon as I plug the 6 pin plug into the AFM, it kills the engine as if I turned the key off...thank you

[timothy_nd28]

Interesting, how long will it idle with the AFM connector unplugged?

[Blue6]

When I start it using starting fluid, it will run until I turn the motor off or plug in the AFM. I drove it around the block and found under load, it only will pull till approx 3 grand, then fall off to an idle. When I plug in the AFM, it doesn't backfire, sputter, or fade away, it is as if I turned the ign off...

[CooltimesJr]

not sure if this will help you or not, but the person left some contact info in the thread. Might be able to help you with it.

http://forums.pelicanparts.com/porsche-914...ng-diagram.html

[CooltimesJr]

or maybe Dave will chime in since he is an admin there and posted the diagram in the link.

[Blue6]

Thank you Cooltimes, everything helps. With the help from other members, I'm chasing these gremlins. Hope to catch and squash them soon. The car was running fine, don't know what happened...

[timothy_nd28]

This seems odd. The fuel pump is turned on by two methods. When you turn the ignition key to crank, the dual relay supplies power to the fuel pump momentarily (we tested this earlier and is proven to work). The fuel pump is only on when the key is turned and engine cranking. Once you release the key (hopefully engine now running), the air flow meter engages the dual relay to keep the fuel pump active.

What you are describing is that the car will start and stay running with the airflow meter connector off. What's keeping the fuel pump on? You may need to post some pictures of your engine bay, perhaps the fuel pump wiring is not original and has been bypassed.

We need to solve this problem first before any other diagnostics. Do you own a fuel pressure test gauge? We will need this too.

[Dave_Darling]

Sounds like you have good avenues of inquiry here. Figure out the answers to the questions above and you'll be a lot closer to understanding WTF is going on.

...Of course, if some PO re-wired the pump and such, things get much more complicated...

--DD

[Blue6]

Been chasing wires, and so far everything looks stock. I understand the two ways the fuel pump is activated, and they both are working correctly. I agree with you that the car shouldn't run with the AFM unplugged, but even more puzzling is why it kills the engine when I plug it in...I'm off to NASCAR in Phoenix in the morning, returning Monday, so Tues I'll get back to chasing. Thanks again guys...