I run a pretty strong concentration of like two cans of it in a half a tank when a K-Jet starts kicking up.

 

Do you still have a wide-band O2 gauge connected? Does it indicate you are going lean when the engine dies?

 

Yes, it does. Yesterday as it was starting to die, the gauge was cycling up and down the whole right half of the gauge (normal to lean to normal to lean, etc).

 

That does suggest intermittent fuel delivery. To confirm, there are directions in the shop manual to jumper the fuel relay and measure the volume of fuel being provided at the motor. It specifies so many ml per minute.

You disconnect a fuel line on its way to the fuel distributor and run it into a graduated cylinder or a bottle. Your assistant jumpers the relay for 30 seconds and you see how much gas you get. That will confirm the fuel delivery is correct or not.

 

See diagram on page 20-6 in volume 1A

The Fuel Pump volume/delivery test starts on page 20-3 in volume 1A

 

Pete --

Do you have a set of CIS pressure gauges? If so hook them up and compare readings with WSM values. Fuel pump is jumpered, WUR unplugged, cold engine. Then start it as normal (WUR plugged in again and fuel pump relay reinstalled) and let it warm up. Watch the pressure vs WSM values.

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Maybe before doing that, put the jumpers into the fuel pump relay socket and try a local drive again, something that will let you get home easily if the situation repeats. In my Stupid Stuff list, besides no gas in the tank, is a tired fuel pump relay. The pressure gauges would catch it if you tested with the original relay in place, but the first test has the jumpers in anyway so it's probably worth a try before opening the system for the gauges.

 

I think I did buy a set of CIS test gauges with the hope that having them meant I wouldn't ever need them - so much for that theory. Guess I'll be digging in.

Doesn't my '79 have a dual fuel pump setup with one pump pumping to the other. That first pump being the one some people replace with a strainer or screen? If that pump has gone bad or is going bad, would this be how it manifests itself and why even though I can hear a pump buzzing (the second one) it can't deliver fuel to the motor properly?

 

It's not hard to find out if your car has an in-tank pre-pump or not. Dropping the fuel pump is just removing two M6 nuts that hold the tray and pump in place. It swings down, and you can get a good look at the pump, filter, and the outlet of the gas tank.

If there are two wires going into your gas tank, then you have an intergal pre-pump. If not, you don't.

 

The Porsche PET suggests that you DO have a in-tank pump...

 

I'm going off-line for a while now Pete. Time to take the wife to her Valentine's Day dinner.
You've got my cellphone number, text or call me if you have questions tonight.

 

The gauges will tell you, as low fuel pressure. There may be enough at idle though, suggesting that you do the fuel delivery test (detailed in the WSM...) to be sure.

 

Looks like I'll be trying this out this weekend


what else do I need other than the WSM?

 

I had a similar issue on my Audi that turned out to be a dying fuel pump. The pump would work intermittently making it very difficult to diagnose. Eventually the pump quit completely.

 

I haven't dug into anything yet, but had another thought I wanted to bounce around. Even though with the current fuel pump relay, I can hear the pump buzzing when I turn the key, is it possible that it only runs for a couple seconds then quits due to an internal fault or if they work at all, do they usually work correctly? Tuesday night, I swapped the relay for a new one and then the car started and stayed running. When I switched back to the old fuel pump relay, the car also started and ran, so I assumed it wasn't the relay, but the next time I drove the car around the neighborhood, it died.

My question is whether it's possible that when the new relay was in the car, it moved enough fuel though the lines and into the filter and fuel accumulator that it let me drive around the neighborhood for about 3 minutes, but then no additional fuel was being delivered with the old relay back in there, so it died after the 1 lap?

I can test this by trying to drive the car with the new relay in it and see how far I get but was looking for some feedback before doing so. Alternatively, I can just idle it in the driveway. How long will it run when idling before depleting all the fuel from the lines, filter, and accumulator if additional fuel is not being pumped?

Also, if I'm going to jumper the fuel pump relay for some of this testing to make it run continuously, which pins do I jumper (I'm assuming someone has a photo of the relay board with some red arrows pointing to the appropriate sockets).

Thanks everyone for the help.

 

Lessee, I think it is some old guy on here (his initials are James Bailey) who says "relay, relay, relay" over and over again. Stick the good one back in and drive it until it fails. Or doesn't.