'80 SC injection question

[Wout_RS]

Hi all,

I'm new here, and since 3 months the happy owner of my first porsche.
It's a 1980 SC coupe (American Version)

But i have some questions.

I've got some problems starting the car, benzine pump is running, but it starts and dies after a couple of seconds. After a few tries mostly the engine starts to run and to keep it up you have to keep the throttle up a minute or so.
Then when i go out for a drive, when pushing the throttle it produces constant backfires.

I think the problem is the K-tronic. But what do you guys think?
Should i look first at other things before looking to the K-tronic?

I don't know how long the car hasn't been driven. I've bought at from a merchant who bought the car in America, so I think the car has been underway to EU for a couple of months.

I hope someone can help me!

Regards!

Wout

[ninelevenick]

Welcome to Pelican. Is it backfiring through the intake or the exhaust? Also, when the engine is warm and at idle, remove the oil cap. Does the engine RPM decrease or stay the same?

[Wout_RS]

Thnx,

it is backfiring through the intake I think.

I have to check the last thing you mentioned.
Why is that?

[Pazuzu]

Sounds like a Jetronic issue, as you suspect.
The Jetronic brain is powered by the same fuse that runs the interior lights (dome lights). Do they work?
The brain and power relay are under the passenger seat, remove the seat and check that they are there, intact, and have power.

[ninelevenick]

Backfiring through the intake suggests a vacuum leak. Also, opening the oil cap while the car is idling compromises the vacuum of the system thus leaning the air fuel mixture. The idle should drop after the oil cap is removed.

[Bob Kontak]

Originally Posted by Snipernick

Backfiring through the intake suggests a vacuum leak. .

This is correct except if is not a vacuum leak. Your mentioned oil cap test is great but should be done when warm as you mentioned in the first post.

Right now I am leaning towards Pazuzu's thoughts. This is because Wout indicates constant backfires. If they are intake backfires, I am betting the freq valve is not getting juice. Could be as simple as the fuse in the front trunk.

[fred cook]

The problem could also be caused by shorting plug wires. An easy test is to start the car at night in a relatively dark area and look at the engine while its running. If the wires are bad, you will see little lightning bolts going from the wires to the closest ground. This may not be the answer, but the test is easy and free!

[RDM]

Welcome to Pelican. Please post pictures- it's a tradition.

If the car is just off the boat and still has the old gasoline (benzene) in the tank, that may be creating your problems.

If you want to search the forums, your fuel injection system is usually called "CIS" (Continuous injection system) by most on the board. There are many great resources.

[Wout_RS]

Thnx for the advice guys!

I will have a look at each of the suggestions you tell!
There's already new gasoline in the tank, also a new air filter and oil.

here are some pictures of the car. Didn't know it was tradition.

[Wout_RS]

Maybe a dumb question (i"m not that technical educated, but i'm happy to learn it).

How do I know if these fuses are working? Do i have to read them out with a multimeter or something?

The box is there, I removed the passenger seat this weekend because it wasn't flipping when pressing the handle. And i found it funny that there was an electronical box underneat it. i thought the SC was the last 911 without ECU.

[RDM]

Starting in 1980, there are two components of the Lambda system under the passenger seat. One is the Jetronic box, one is the oxygen sensor relay.

The Lambda system uses the output from the oxygen sensor (in the exhaust gas stream) to give the correct air-fuel ratio by adjusting the amount of fuel injected. The system is not active until the engine warms up, so if your car starts its poor running a few minutes after cold starting, replacing the oxygen sensor relay is a good (and simple, and cheap!) first step. I had trouble with my oxygen sensor relay not long after I got the car, and replacing it made a huge difference!

I assume BE means Belgium; if so where specifically are you? Will you be going to the Spa 24?

Dru

[Wout_RS]

Is this the same fuse as Pazuzu is talking about?
As he is talking about the brain fuse?

I'm getting really confused about all this information

Yes with BE I mean Belgium, I'm living near Ypres.
Spa 24 hours i'm going to miss this year, because of renovations on the house ;-)

And work on the car

[boyt911sc]

Originally Posted by Wout_RS

Is this the same fuse as Pazuzu is talking about?
As he is talking about the brain fuse?

I'm getting really confused about all this information

Yes with BE I mean Belgium, I'm living near Ypres.
Spa 24 hours i'm going to miss this year, because of renovations on the house ;-)

And work on the car

Wout,

Get familiarize with the fuse panel in the luggage compartment (front). There are 21 electrical fuses (8 + 10 + 3). Starting from the front of the car, you should find the first section with 8 fuses, second with 10 fuses, and lastly 3 fuses (total = 21). Get a reference manual like Bentley for SC and that would help you get familiarized quickly about your car.

Fuse #18 is the circuit that supplies power to the FV relay, courtesy light, clock, and glove compartment light. Some people call this relay as OXS or ECU relay. The fact is that both oxygen sensor and ECU don't need a relay but the FV (frequency valve) does. Whatever name we use to call this particular CIS component is irrelevant at this point as long as we understand each other.

Get the engine to warm up close to engine operating temperature. And perform these simple tests:
a). While the engine is idling between 800 - 900 rpm consistently (steady), remove the oil cap and observe any noticeable idle speed change.
b). Next, disconnect or remove the relay (FV, OXS, ECU, etc.) under the seat. Observe for any change in the idle speed behavior like rough idling. Repeat this test a couple of times.
c). Is there power at the plug connector to the relay when engine is idling?
d). Locate the FV behind the motor and feel if it is vibrating or pulsating when the engine is running. You could do this test without running the engine if you know how to test run the FP (fuel pump).

Keep us posted.

Tony

[Pazuzu]

One reason that I mentioned the OSX relay is because those symptoms are 100% what I found on the two times that I had problems (once the fuse had blown, once the relay died). You could get the engine started, sometimes with some extra throttle while cranking, it would idle but barely, and you could theoretically drive it down the street with full throttle, but it would be backfiring and bucking continuously and violently.

So, there is 3 things in that "system" that could fail suddenly (or because of a bumpy trip across the ocean). The fuse under the hood (#18 per boyt911sc), the relay itself that is under the seat (the small cube, not the bigger controller), or the controller itself (unlikely, I think that would kill the engine completely). also could be wiring, etc.

Quick fuse check is: Do the dome light and/or glove compartment light work? If so, the fuse is good. If not, the fuse is bad, problem solved

Quick relay check: Remove relay, do symptoms become much much worse? If no, then relay is broken, replace. If yes, then move on.

I assume that the car didn't get washed with seawater or anything, since that relay sits on the floorboard, it's susceptible to minor flooding.

[Wout_RS]

Thanks guys, I've just got out of the garage without reading your tips.

I was feeling a little stupid because I was looking at the box under the passenger seat.
But couldn't find any fuse on the box. Stupid stupid me! They are all in the front.

Here's a picture of the box under the passenger seat. So the small one rightabove, with the wiring is the relay? If I'm correct? What is the bigger box for?



Now I'm going back to the garage to check the inner lights and check fuse number 18.

[Wout_RS]

Fuse # 18 is working: glove comp. lights are working...

Tomorrow I'm gone check it with the engine running.
I'm just afraid that the engine won't start and that I will flood it because of trying to much.

One thing I noticed when turning the key to check the lights and fuse is that the fuel pump is working constantly. Doesn't this shut down after a couple of seconds?

[fred cook]

Originally Posted by Wout_RS

Fuse # 18 is working: glove comp. lights are working...

Tomorrow I'm gone check it with the engine running.
I'm just afraid that the engine won't start and that I will flood it because of trying to much.

One thing I noticed when turning the key to check the lights and fuse is that the fuel pump is working constantly. Doesn't this shut down after a couple of seconds?

The fuel pump should only be running during cranking and while the engine is running. A common problem is that sometimes owners will unplug the safety valve (located on the back side of the CIS just to the left of the air plate). This is done as a "fix" when the system doesn't hold fuel pressure when the engine is shut off. You should be able to reach behind the left end of the rubber boot on the top of the CIS and find the disconnected plug. Just plug it back in and test by turning the key to the run position. The fuel pump should not be running. Remove the air filter cover and filter and manually lift the air plate a bit and the pump should come on.

[RDM]

Originally Posted by Wout_RS

Here's a picture of the box under the passenger seat. So the small one rightabove, with the wiring is the relay? If I'm correct? What is the bigger box for?

Yes, the small silver cube with the wires going into the connector is the relay. The ECU is the brains, the relay is the switch that the brain turns on and off to regulate the fuel pressure, and as a result the amount of fuel injected.

Originally Posted by Wout_RS

Tomorrow I'm gone check it with the engine running.
I'm just afraid that the engine won't start and that I will flood it because of trying to much.

One thing I noticed when turning the key to check the lights and fuse is that the fuel pump is working constantly. Doesn't this shut down after a couple of seconds?

I don't know if it's possible to flood the engine. I've never done it anyway.

Question- how do you know the fuel pump is running? If you are hearing a high-pitched whine from the back of the car, that is the Capacitative Discharge Ignition (CDI) box, not the fuel pump. The fuel pump is under the front of the car, near the steering rack.

My family and I have been to Ypres several times; beautiful town, sobering history. We also go to Malmedy on a regular basis to replenish our food (everyone), beer (me) and chocolate (her) supplies. I'll be going to the Spa 24 with my 2 sons and some other friends. Hopefully we'll see you another time!

[Wout_RS]

It's a high pitching noice, but it's from the front of the car I think.
I think they told me that was the noice of the fuel pump when you turn your key on, but not start the engine!?

@ RDM: there is indeed a possibility that we can meet one time. As I go also on regular base.
But I go more when there are Porsche related or historic events on Spa or sometimes to the Nurburgring.

[Bob Kontak]

Originally Posted by Wout_RS

It's a high pitching noice, but it's from the front of the car I think.
I think they told me that was the noice of the fuel pump when you turn your key on, but not start the engine!?

Sounds like the fuel pump. It is not supposed to turn on until the key is turned to "start". It is not critical to repair this right now. Here is a quick test to confirm. Remove the front trunk round relay closest to the steering wheel. It feeds the fuel pump. It is probably red. If you remove and the noise goes away when you turn the key on, it is in fact the fuel pump. Fix later.

You are receiving a lot of information. Just be patient. No one expects you to understand the system immediately.

Lambda relay........ Here is a video that I made several years ago unplugging the Lambda relay. Listen to my car. It drops down in rpm and "pops" when I give it gas from intake backfires. Maybe this is close to the problem you have?