Help my SC is sick

CindyDuck · 04-06-2005, 06:55 AM

I have a 79 SC 3.0 Some times it runs great other times it misses, backfires, and stumbbles, under acceleration and or cruising. Some times it runs great cold sometimes it runs great warm It always runs good sitting still but underload I just hope for the best. I have read troubleshooting books and have a set of shop manuals but this one has me lost. Can you Porsche gearheads help my baby?
Any help or sugestions would be appreciated.

Thanks,
Mike

MotoSook · 04-06-2005, 06:58 AM

Hmmm...might start with cleaning the fuel system. from tank to injectors.

Also check timing and advance.

SC-targa · 04-06-2005, 07:39 AM

How old are the plug wires, dist cap and rotor?

Jerry Kroeger

bigchillcar · bigchillcar's Garage

problems under load sound like ignition-related to me. i second the suggestion to check timing and advance. what's the maintenance history of your ignition components: plugs, wires, etc.?
ryan

jwetering · jwetering's Garage

ditto the popoff valve (if you have one). A cracked airbox could behave like that.

stlrj · 04-06-2005, 12:17 PM

Replace your ignition cables with Clewetts.

CindyDuck · 04-06-2005, 03:03 PM

The ignition wires, plugs, cap and rotor are new last summer. I have only had the car since july of last year and drove it a few weeks before putting it in storage. this problem has always existed and it driving me nuts. first I thought EGR thats what it feels like. Not there. The problem in intermitant, and has no consistancies( is that a word) but it feels like a vacuum problem. The popoff valve looks like it was put in by a 6 year old kid. I think that will be my morning project.
I will also check the timing, I checked and the vacuum advance is working. My timing light doesnt have a 10 foot cord, are there terminals in the rear?
Thanks
Mike

Early_S_Man · 11:48 AM

Mike,

You can find power for your timing light at the fuse block on the electrical panel on the left side of the engine compartment.

Intermittent ignition problems can often be related to the condition of the green coax signal cable from distributor to CDI unit. If it is discolored or cracked ... vs fresh, viper green ... it can be causing problems! To test, remove the CDI 6-pin connector and check for 600 Ohms +/- 10% at room temperature ... between terminals #7 and #31d. Additionally, you can test for a 1- 3 Volt AC signal during cranking. Make sure the connections are secure ... fabricate test jumpers to the 0.25" Faston connectors to the multimeter! Flex the green cable at the distributor while testing to see if there are any fluctuations or dropouts. Pelican has a new signal cable for around $30.

The following diagram may help:

CindyDuck · 04-07-2005, 08:42 AM

S man,
At the box connector with the multi meter set at 2K I have nothing, set at 200 I read 00.7. I unhooked the two connectors in the green wire between the dist. and the box, at the box connector the same numbers, to the dist. I have .575 on 2K.
Does this sound right?
Mike

CindyDuck · 04-07-2005, 09:21 AM

S man,
Disreguard that last message. I was testing 31/1 and A, I read my diagram upsidedown. I have 575 ohms and it drops 2 points when I bend the wire at the dist. it appears to have been replaced.
Thanks,
Mike

CindyDuck · 04-07-2005, 01:02 PM

I think I got it, with a little help from you guys. The timing was the big issue I believe. Some how the wrong vacuum line was attached to the advance, applying vaccume under acceleration and not allowing it to advance at low speeds. The idle speed was turned up to help it idle decent. I cleaned every connection and ground I could, adjusted the timing and idle and now she runs great. I'm still redoing the popoff valve, it doesn't look to tough.
Thanks guys,

Mike