Is it harmfull to let the engine run when the car stands still?

I may not legally to drive on the road, as I didn't have the car MOT/TUV (don't know how to call it in English) because of the problem with the backfire i will wait to go there.

So for the test where you need a warm engine, i would turn it on and wait a few moments.
If this isn't harmfull for the engine.

Only if you did it all the time. For troubleshooting purposes it's okay.

Ok,

i'm gonna try to start the car tonight and see if there is a difference when pulling out the relay.
And also try to film the process, so there can be a good judgment

Trouble shooting.........
 

Don't forget to check for cross firing plug wires! If the wires are bad, it will be pretty evident with lots of little lightning bolts going here and there!

Hi guys SmileWavy,

I did my homework tonight :) but I'm not wiser after the test.

1. Trying to start up the engine, trying to crank after 5 times didn't start or barely started the engine.

2. Removing the air filter and pressed the plate in the injection system, then cranking, and immediatly the engine started, but no trouble with shooting.
Here you see a movie of the engine turning.

View My Video


3. Once the engine was stable, I removed the oil fill cap. Also no difference.
See video.

View My Video


4. The last test was made removing the relay. Also when removing the relay nothing happened. Turning back on the relay made the engine stall.
See the video.

View My Video


5. I found it really strange that the engine was more normal then otherwise. So I turned back on the engine and immediatly it was back shooting, backfiring like otherwise. But damn I didn't made a video now. So I turned it off. Then I filmed again, now I'm in the car and start the engine up. You'll see that it up banging and popping. So then I pull out the relay and nothing changes. I put back on the relay and the engine stalls again. Then I forgot to shut down the camera. Sorry for the long video. But I'm no video expert and editing :D

View My Video


Hopefully someone finds a clue in the explanation. Thnx!

Nobody? :(

Backfiring..........
 

That sounds to me like it is backfiring thru the exhaust. That would typically be indicative of a system that is running much too rich. At this point, I believe that you need to either get a set of test gauges and check the fuel pressures and use an exhaust analyzer to check the CO reading from the exhaust or take it to a shop to have the tests done. The information on how to do these tests is available on this forum, just do a search. The air bleed adjustment screw is just above and to the right of the throttle linkage in the side of the airbox. The fuel enrichment screw is located just to the right of the fuel distributor. It will require a long 3mm allen wrench to make enrichment adjustments. The screw is down in a hole and can be difficult to find. Turning the screw in (clockwise from top) makes the adjustment richer and out (counter clockwise from top) makes it leaner. Good luck and keep us informed of your progress!

But how can you tell the difference?

Sorry for all the questions, I'm a scientist, so I like that everything I know, happens for a reason :D

If it's running to rich, Is this why it mostly starts when opening the airfilter box? So it sucks more air? So when pumping more fuel, you have more air needed to have the correct mixture?

Air fuel ratios.......
 

Questions are good! At this forum you will get lots of answers!

The theoretical ideal air/fuel ratio is 14.7/1. That may be a bit too lean for some engines to run properly so carburetors and fuel injection systems tend to run a little richer, closer to 14/1. Under hard acceleration, the mixture needs to be richer, maybe down in the upper 12 or low 13 range to keep from burning a valve or piston. When you open the air filter box, do you pull up on the plate or push down? Pulling up will allow more air to the intake temporarily leaning the mixture, pushing down should make the a/f ratio temporarily richer. At this point, before you start turning adjustment knobs, etc, you need to know where the fuel injection is set now. One thing you can do, is to find the air bleed screw/knob on the left side of the air box just above the throttle linkage. Turn it all the way closed while counting the turns. Then, back it out about 3 turns. That should be close to the correct setting for your engine. The fact that the engine did not change rpms when you removed the oil cap indicates to me that the air bleed screw is too open. Normally, when you remove the oil cap, the engine will choke down and quit running. Since your engine did not do that, it indicates that an excessive amount of air is getting into the box somewhere else. I hope this helps. Try adjusting the air bleed screw and then restart the engine. Let us know what happens!

Sounds like electrics,start with plugs,cap and rotor as they are relatively cheap,if it runs better but not great check the leads and replace if required.
Is your engine timing correct?
You need to get the car in the best state of ignition tune before you look @ the fuel injection,this is a mistake many make and just blame that.
You might want to change your fuel filter also,I always give a new purchase a service,hard to believe some past owners have done this and that,when YOU do it you really know then,good luck.

@ Porschetub: When I've purchased the car, they told me they already had new oil, oilfiters en spark plugs. And indeed everything looks fine. So I think I can trust them on that.

Don't know what the sate of ignition tune. Is it something you can do easily yourself?


Just thinking next to the to rich state of the car, sometimes when you push the throttle it feels like the car is somewhat coming behind in its reaction and sometimes the rpm stay to high when releasing the throttle. Then dropping again to stable rpms. i've experencied this when driving the car home from the garage.


When I did open the air box I pulled the plate up! I didn't know that you can pull it down. As i thought in the box it's always at the lowest point.

Problem is found.

I went with the car to an OPC to have a diagnose.

They found out I have broken cylinder head stud.
That's why the engine sounds like it's backfiring.

Oh no. I'm sorry to hear that. You didn't get a chance to have some driving fun with your car. A rebuild is in its future.

[QUOTE=RDM;8708992]Welcome to Pelican. Please post pictures- it's a tradition.

" its a tradition "
This must be new as Ive never seen this in all the years of surfing this site. :)

Wout,

A broken head stud won't account for all the symptoms you describe. However, I've had that experience, and learned a lot. Are you considering fixing it yourself? It is do-able. And while you're doing it, you have much better access to all the other things that cause these kinds of problems.

Here's the thread describing my head stud adventure, There are many others!

http://forums.pelicanparts.com/porsche-911-technical-forum/789817-start-maintenance-end-disaster-opportunity.html

I am surprised one broken stud would cause that.

Problems with the bad running is disappeared without any reason.

After i posted the video, I haven't touched the car for a month.
until i contacted the OPC. I had to wash the car before they came to collect it.

And with the first turn of the key the engine started. Since then no problem with difficult start.
The technician only reset the fuel/oxygen ratio and it starts smoothly.

Only problem is the studs you here in the engine when pushing the throttle.
So no more driving or very very calm if necessary