1983 SC No Start - help!

Toolmaster · 07-30-2003, 02:24 AM

All -

My ongoing issues with this car are neverending.

Car died on me while driving it a couple weeks ago. System pressure with the fuel pump running and car off is 50psi. Already changed the fuel pump. Same system pressure. Fuel filter is new within last 1000 miles. I opened the old fuel filter which was prolly VERY old, and didn't see any rust or anything like that.

Car ran fine last year, but this year I've had issues like no Porsche ever gave me.

I've read prior posts saying there's a screen in the fuel tank, and also that the fuel accumulator could be plugged. I have a spare fuel distributor that I can try too, the one on the car now came off a working engine though it had been stored for a while. The car ran fine for a bit prior to fuel dist replacement to try to figure out what was happening with the car - it was bucking and low on power, in addition to backfiring sometimes.

A number of people have told me to check the CD box, which is in fact firing all plugs according to my timing light, but that wouldn't explain why my system pressure is so low.

How does one get at the screen in the tank? Could the accumulator be the issue? Are there tests that I can perform to identify the real issue before I have to throw any more parts at the car? I've tried the injectors, air box, and a myriad of other parts with no joy. According to Bentley, I have to get system pressure right before I can do anything else.

Car is an 83 SC Cabriolet, with about 150k miles on it.

thanks.

chuckr · 07-30-2003, 05:24 AM

What about your Warm Up Regulator ??

Superman · 07-30-2003, 05:50 AM

If you've got ignition, and 50 psi of fuel, the engine should start. At least START. If I were in your situation, I might turn the ignition on, and raise the air flow sensor plate with my finger to see if the injectors whine. If that works, then the engine should start and run. I'd then go back to basics. Verify that a hot spark is happening at the proper time (ignition timing). If the spark is happening, and the injectors are spraying, then your engine runs. At that point, driveability problems might be associated with poor mixture adjustment, or perhaps a serious vacuum leak.

Here's another tip. Your frequency valve needs to be operating, otherwise your mixture will be very screwy (severe driveability problems). The frequency valve on mine is located behind the throttle body. It vibrates. It has one of those square, Bosch "injector" plugs on it. This device MUST be operating properly in order to use the fuel distributor that comes on an '83. If you use a FD from another car that did not have the frequency valve, it will not work unless you eliminate the frequency valve. The FV is controlled by the O2 sensor system and computer. There is a FV relay, less than an inch cube, located under the passenger seat. Cheap. Replace it. Even if you unhook your O2 sensor (like most of us have), your FV and relay still need to work properly.

makaio · 07-30-2003, 05:53 AM

Don't just throw parts at it.

You say your system pressure is highat rest, but have your performed a complete fuel pressure test?

The fuel tank screen is accessed under the car, on the bottom of the fuel tank. Make sure the tank is almost empty before opening it though.

1fastredsc · 07-30-2003, 06:28 AM

I thought the late model sc's wouldn't run correctly if you unhooked the o2 sensor? Does it go into a default frequency or something?

Lorenfb · 07-30-2003, 06:42 AM

You don't need the O2 sensor to start! Did you check for spark?
Ground pin 15 of the Lambda unit. This makes the mixture very
rich for starting. Check pin 15 and 8 with a test light first. They
shoud have power. Also, you need to check the control and system
pressures.

Check out this website (systemsc.com) under Diagnostics. It
may be helpful.

Good Luck
Loren
'88 3.2

Superman · 07-30-2003, 06:54 AM

Indeed, the '83 SC runs just fine with the O2 sensor unhooked. It's probably best to not have a working CAT for this, since unhooking the O2 sensor will allow the fuel system to delivery a richer mixture, and rich mixtures can plug, overheat or otherwise damage a CAT. The frequency valve must still be operating, but you do not need the O2 sensor. Without it, your system becomes essentially a "K-Basic" CIS system. Without the O2 sensor, your engine can be tuned so that the fuel mixture is not so terribly lean.

1fastredsc · 07-30-2003, 06:59 AM

Hmm, good to know, cause i was thinking about where i was going to mount the o2 sensors on rsr headers if i purchased them.

1fastredsc · 07-30-2003, 07:02 AM

BTW, if you have an 83, you could ground the negative lead of the cold start valve to make sure you get extra fuel when you crank. I don't remember if it's on the left or right but that cold start sensor has the negative lead of the valve on it. When your motor get's below a certain temp, it grounds the wire so that when you crank it shoots extra fuel in. so just disconnect it and then connect it to a permanent ground and then give some cranks.

Toolmaster · 07-30-2003, 08:50 AM

Hey all -

The car sorta starts, rund for a couple seconds, and dies as soon as I try to hit the accelerator. I know the injectors are firing, and that the ignition works.

What could be the causes of my low fuel pressure? I guess that's where I think I need to focus. I know that the O2 sensor and Freq. valve are working, and the cold start valve and thermotime switch have been replaced.

thanks!

Toolmaster · 07-30-2003, 08:57 AM

All - the part numbers on the fuel distributors match exactly... And the car that it came from had an O2 sensor on it.

thanks

Toolmaster · 08-05-2003, 02:14 AM

Hey all.

Turns out that there were TWO issues, and perhaps a third when the car warms up.

1) Fuel pump helped a bit.
2) The ignition COIL died. Funny part is that it tests FINE out of the car. But when hit with high voltage, it basically opens.

3) The CD box might be an issue when it heats up, but I have to drive the car for a little now to see.

Thanks for the aid though, at least she sorta runs.

Jay