1980 SC 1979 engine, no DME?

[tevake]

I need some help figuring this out. My 80 SC is having hot starting problems.
It starts cold just fine. then after warming up just cranks and cranks, it may sputter and start, but not on all cylinders at first.
Or not start at all.
Then I can open the air cleaner, lift the air control valve? to prime the injectors. then it will start. So I am thinking it may need a new fuel accumulator. or check valve. How do I test to tell which it is?

And if the problem is the fuel accumulator, as I suspect. There is one part # for up tp 1979 then a different part # for 1980 and up It seems that the engine is a 1979 eng # is 6292116, plus there is no DME under the passenger seat. there is one large but empty plug


Also the fuel accumulator in the car looks just like the pic in the catalog for the 79. there is no pic for the later part. But it is twice the price as the earlier part????



So, your thoughts?? Do I go with the 79 part? Bite the bullet and go with the 80part?
Is there a real difference?
Thanks Richard

[pcar9119]

There may have been a 3.2 in that car at some point. Your hot start problems, mine was a crap load of vaccume leaks. Good luck!

[tevake]

I thought that the DME started with the 1980 SC ??

[slodave]

DME started with the 3.2 in '84. CIS was the predecessor, then MFI....

[tevake]

OK I am confused now. What is the black electrical box under the passenger seat??

Also what about the fuel accumulator 79 vs 80 ?

[slodave]

I'm DME, sorry and I can't find the thread that mentions what it is. It has to do with the CIS system - I want to say altitude compensation, but that's usually a bell looking thing.

[Walt Fricke]

The DME started (in our 911s) with the 3.2, which has full electronic fuel injection and ignition control. That's what the DME means.

But the later SCs had what I call a mini-brain. Still CIS motors, but with a "frequency" valve and oxygen sensor. The brain told the frequency valve to raise or lower the CIS control pressure depending on if the O2 sensor read lean (reduce pressure with a higher frequency) or rich (lower frequency, raise pressure). The valve allowed more or less fuel to escape the WUR back into the return line, which is what altered the pressure (the better name for the WUR is control pressure regulator, which is what it does to deal with warming up). It must be a fixed pulse width so there is more open time at higher frequencies.

I can never remember exactly when the change happened, but it was after the '79s, and for sure by the '81s. Looking at your picture, I bet it was for the '80s. Euro SCs never got this - straight CIS.

Someone took that out. Left just the wiring. The "black electrical box" is just a big connector.

When I put an '82 in my '77, I left this out too. Mistake, as I had starting troubles. Though others have tuned things so it works OK, I think. You should be able to identify the frequency valve to the rear of the WUR.

Walt

[slodave]

Originally Posted by tevake

Isn't this under the driver's seat, not pax?

[James Brown]

The box is under the passenger seat, you do need that along with a O2 sensor. There should be a small plug by the tunnel for a relay also. Concentrate on this first before you get a fuel accumulator. Wish I still had mine I would donate it to the cause! Check the engine for the frequency valve on the rear of the engine and is there a big plug between the rear shocks behind of the engine. That will give you a clue as to what engine you have.

[tevake]

Yep that is under the passenger seat, there is a stereo amp under the drivers seat.

Here is a shot under the pass. seat of my 1980 SC targa. It still isn't running yet ( waiting for a fuel tank). This car is in original condition, and has the box still plugged in.

[slodave]

Okay, so you have 2 911's.... this is a bit confusing.

That said, you are missing the CIS box, not a DME.

[tevake]

Thanks guys for the suggestions. I do want to make it clear that the car has run very well in this configuration. I don't think there is an O2 sensor in this car either.
I was hoping that the engine # might turn up some info from someone out there.
Engine # is 6292116

[jwakil]

I believe the 80+ accumulator is a lot bigger than the earlier one. The problem you will have is that if you buy the pre79 accumulator, you won't be able to mount it properly in the holder of your 80 body which is made for the bigger one. I had the same problem (my engine is 77 and body 83). Luckily, the steel pipes that attach to the top and bottom do a pretty good job of holding it in place so you can just have it floating there. When I replaced from the 83 version (which I thought had problems but actually did not) to the pre79 version, it didn't make any difference in performance. (I had other issues, not hot start problems). So I think going with the 79 should be fine if you are OK with having it hanging or rigging up your own attachment bracket. I still have my old 83 accumulator and would sell it very cheap, but for you the shipping might make it more worth while to just get a new reasonably priced 79 version which matches your engine. That's if you determine the accumulator is the problem,. The easy way to test it is to remove the bottom pipe and see if a lot of fuel comes out. There are a lot of previous postings that describe how to do it if you search accumulator testing.

[James Brown]

Hummm ok, well then forget the box!!! Do you have the CIS pressure gage?

[tevake]

I did some checking on FA testing and will give it a go in the morning. should be able to clear that up. Thanks jwakil

SlowDave sorry for the confusion, I thought the pic of the other car might be clarifying.
It does help me some what to be able to look at the factory stock car. My coupe has so many mods that I get lost some times trying to follow the discussions here.

James, No gauges yet. will have to put those on the list.

I'll check back in once I test the FA.

[psalt]

But the later SCs had what I call a mini-brain. Still CIS motors, but with a "frequency" valve and oxygen sensor. The brain told the frequency valve to raise or lower the CIS control pressure depending on if the O2 sensor read lean (reduce pressure with a higher frequency) or rich (lower frequency, raise pressure). The valve allowed more or less fuel to escape the WUR back into the return line, which is what altered the pressure (the better name for the WUR is control pressure regulator, which is what it does to deal with warming up). It must be a fixed pulse width so there is more open time at higher frequencies.

Hello Walt,

You are right that lambda CIS needs a pulsing FV to get anywhere near the correct fuel curve, but the frequency valve does not effect control pressure or the WUR. Control pressure remains constant after warm up. The pulsing FV controls lower chamber pressure in the FD, and the fuel delivery at the injectors is varied by the pressure differential at the slits. In closed loop, a higher duty cycle means the mixture is lean and the system is trying to richen it up by bleeding off more lower chamber pressure. In open loop, a higher duty cycle means richer than stoich. The "K-basic" part of CIS lambda is calibrated way too lean, and the "mixture trim" part (FV) is designed to push toward rich. The system is designed to accomodate a failed O2 sensor, but not a failed FV or ECU.

[boyt911sc]

Originally Posted by tevake

OK I am confused now. What is the black electrical box under the passenger seat??

Also what about the fuel accumulator 79 vs 80 ?

tevake,

CIS-E or Ketronic system (911 '80-'83) with lambda system (OXS) has an oxygen sensor control unit called ECU (electronic control unit) while the 3.2 Carrera ('84-'89) is known as the Motronic system or digital motor electronics (DME) has the ECM (engine control module). In layman's lingo, these are commonly referred as the ' brain'. Both are ECU's.

The electronic box under the seat for Carrera's (3.2) is called ECM, but inadvertently referred by many as DME!!!!! The fuel management system is Motronic/DME.

BTW, there is practically no difference in the FA (fuel accumulator) application for SC's. Actually, most of these FA's are interchangeable for most CIS engines with very slight modification in the plumbing system.

Tony

[70SC]

Yes Lambda system plug. My Sc runs great without the Lambda system. O2 sensor bung must be pluged without a o2 sensor.

[tevake]

OK I had a chance to check out the fuel Accumulator. It does continue to leak fuel out the bottom while the pump is on. So time for a new one. I am planing to order fuel pressure gage while I am at it. Is there a good choice in gage , that works well for most porsches?

Walt and Paul, I was cracking up at myself while trying to understand some of the details you shared in your posts. I've got a lot to learn! However with your help and that of others on PP BBS. there is hope for those of us just getting into this game. Thanks

Richard

[tevake]

I want to touch in with an update. As usual when asking here for help in sorting out an issue with my SC, I ended up learn a bit more about the inner workings of and how to take care of the car. Thank you all so much.
Just replaced the FA. with the later part for the 1980-83. It went right in easily. And what a difference. The engine started right up, idled smoothly, runs more smoothly thru the rev range with lots more grunt than its had in months. Plus it restarts when hot
Seems the FA has a lot more to do the engine than just hot starting!!

Also I have the pleasure and satisfaction of sorting this out and getting the SC running well again.

Thanks again to all here who make this such a fun and helpful forum.

Cheers Richard