smshirk

MY 80 SC is running great during warm daylight hours, but as soon as the sun starts setting it starts to lurch, backfire, lose power, especially with an open throttle. I can keep it running smoothly if I gradually increase speed by holding each gear longer with limited right foot input. During the day it starts and runs like a singer. Any thoughts? I have an order in to Pelican for various electrical parts......

JV911

sounds like bad photovoltaic cells

mo_gearhead

Odd... there is NO reason for any Porsche to fear the night! Let us know what the new parts consist of and if they help.

ked

you may have an ignition/elect system somehow exposed to water vapor / humidity / dew. also possible that a vacuum leak (gasket, sensor, or hose) is coming & going w/ the wide change in temp over the course of these spring-like days / winter nights... also could be a simple case of "co-incidence that behaves like causation". trouble-shooting is an exercise that fights off the effects of old age, but be careful w/ those fingers!

jimq

maybe its a some problem when you turn on the lights at night? Ground or short?

GothingNC

Do you have a Permatune Box or a Bosch CDI?

John

Mike Murphy

What is the temperature difference between day & night?

smshirk

It has a Bosch CDI. The temp change is 20 degrees or so and the problem occurs before turning on the lights. The car has been sitting for the better part of ten years until recently. I am awaiting new dist cap, rotor, ignition wires, coil, among other things, and have plenty of tubing for vacuum. I plan to spend the day replacing things one at a time and just hope it's not a fuel related problem. I don't really understand the CIS well enough to fix it. I'm really amazed it runs as well as it does, during the day that is. I've already cleared out the bad gas, air filter, fuel filter, critters in the airbox.

Mike Murphy

I hate to tell you this, but if its been sitting for 10 years, you might as well go through the entire fuel system. I'd start with the tank and make sure that it is completely clean and rust free. Next, I would think about replacing all the rubber fuel lines and flushing everything out. As far as a fuel filter goes, you might have to replace it very often at first. you might also have to thoroughly test and/or replace the fuel pump. Finally, you're at the CIS system, and that's where my experience stops. I would guess it would require a thorough cleaning as well.

smshirk

I think I have all the fuel issues resolved, but you're right I had to take care of that first. I am now at the after dark problem, although this afternoon it ran well only for 15 minutes or so, until about 6PM. The temperature really hadn't changed that much.. I've resolved to leave it alone until my parts order arrives. I'm going to take everythinng off the top and inspect all hoses, wires, fuel lines, etc. I may still have some critters hiding in there somewhere.

It took me a month to get the rats out of my wife's Miata last year. They had built a nest around the gas tank which is under a steel plate, under the rear carpeted area. I would never have found them if they had not eaten the fuel gauge wire. I still have no idea how they were getting in and out, but they had a half pound of dry dog food stored all around the tank.

This car was part of someones estate and had been sitting for longer than anyone could remember. I have a lot of work to do, both mechanically and cosmetically, but the body is sound and all the Weissach specific details are in good condition except the rear seat bottoms.

Mike Murphy

Boy, that is strange. The only thing I can think of that would affect night driving would be lights.

RedShadow

That's hilarious (and unfortunate sorry). Have you tried garlic and a crucifix?

smshirk

No but I have been trying to locate some holy water