Missing at constant speed
 

Hi all,

I have owned my SC for about 2 months now and it has a small miss when at a constant speed and up to temperature.
I've gone through the forum trying to find a fix but have not been successful.
First I changed the fuel filter as it was in a pretty bad way, will drain the tank once the light comes on.
http://i237.photobucket.com/albums/f...925_162452.jpg
There are no more shims left on the inside so will be replacing the belt tomorrow, could that cause a issue with voltage?
http://i237.photobucket.com/albums/f...925_165118.jpg
Do the earth's from the HT leads need to have good earth (not coated in paint)
I know the LS1's have poor earthing and with a kit you can gain a few kw.
http://i237.photobucket.com/albums/f...925_165033.jpg
Can the earth's become fragile and not work as well as new.
http://i237.photobucket.com/albums/f...925_165337.jpg
I've read that the T/B gasket and air box can crack. causing an air leak, looks ok will spray something flammable around lines and T/B to see if there are any leaks, also the diaphragm on the distributor is clicking in and out and it is holding pressure. Will look at replacing all vacuum lines.
http://i237.photobucket.com/albums/f...925_165221.jpg
http://i237.photobucket.com/albums/f...925_165248.jpg
I've heard of people having a blown 02 fuel sensor relay but my interior lights work and there are no fuses under the seats, so unsure what one it is in the trunk.
All else fails ill take it to an auto sparky and get him to look over the car leads etc.
Thanks again for any advise or pushes in the right direction.

Cheers Shannon.

that ground needs to be cleaned of the paint.

with a miss, i would start with a tune up. plugs, cap, rotor and check the wires and ends.
timing also needs to be checked and verify the advance is working

make sure you have no air leaks. an air leak miss might be a mnifold gasket, or lose manifold or injector seals or sleeves.

inejectors tops the list after tune up. check for spray pattern, leaking injectors and volume of each injector. (use 6 containers to catch fuel from a ll 6 at once.)

spark plug inspection may give you and idea if a cylinder is running lean or rich.

have the mixture checked. could be lean. very important. never adjust the mixture without first checking fuel pressure, hot and cold.

when was the last time the valves where adjusted?

What year is your SC?

Valves were adjusted 6k miles ago , it has a new rotor and cap could still be the issue.
I cleaned the tb and float ? With a 3m cleaner as it was pretty dirty,
I'll check for leaks with some spray and make some additional earth lines.
Sc is a 1983 .
Thanks again.

I'd unplug the O2 sensor as an easy first step.

Also, you should have an oxs relay under passenger seat. Wouldn't hurt to swap with new one - keep old as a spare.

There are no sensors in the exhaust system or are the 02 sensors somewhere else.
Also where are the oxs relays in 83 as both my seats have nothing under them.
Anyone replaced the vacume lines with silicone ones, 30 year old rubbler lines might not be up to scrach.
Thanks again.

Hmmm. An 83 with no oxs / frequency valve. Do you have carbs on that thing? Do you have more pics showing entire engine compartment?

I'll post some pictures when I get home and after I try new vacuum lines,
Earthing kit and belt should be here tomorrow.
I think "garage" has a few photos not to detailed though .

Right hand drive '83 euro model from GB and AUS now in New Zealand!
No O2 sensor, no cat and probably a few less US or japan smog requirements.
Original engine? Or backdated ? High HP engine higher compression etc.
Need a lot more info on what is in there to be able to assist.

Original engine I backdated it myself, Factory tune/output.
Did all the heater covers and airpump plugs, only thing I've really changed is the exhaust side of things, I added a K&N but TB, intake, injectors and lines are all stock.
Last owner changed dizzy cap and rotor, also the electronic ignition is a permatune item not a trusty bosh one.
Thanks again for any help.

Did you say Permadoom?
Do a search on permatune, you may be describing one of the failure modes. I have no experience with them, but I've read a number of threads talking about their failure symptoms.
MSD 6AL and a Blaster 2 coil will cure permatune troubles. ;)

^^ Yep. Look at the permatune.

I still don't understand your engine though. How did you exclude the lambda?

Most likely because he has a 83 SC ROW (perhaps UK model). No O2, no lambda, no air pump, 204hp.

If he has set mixture and timing following this boards advice he is off as most on here describe US models. It got me fooled once.

I have no idea on the Permatune as I only use original Bosch but what he describes I had a while ago and it turned out to be timing and too rich mixture. I assume the hesitation is only present when at constant speed at low to mid rpm? Does it go away if you maintain constant speed at 4.000 rpm?

Is the WUR a 089?

Michel

My SC was UK new , It had air pump and a/c.

Michel, you mention the WUR has me thinking, it use to idle realy low like 750od the whole car would shake like my drag car.
So I adjusted the idle once warm still a little low 800-900 but on cold start will sit on about 2000rpm.
Will check if it’s a 089 tonight.

The miss is in the entire rev range (double check tonight) and only seams to do it when warm (WUR off?)
I put new vacuum lines on it last night and will go for a test today, one had a dodgy joiner the other a crack at the end.

Is it possible that it just needs a tune with the blocked cat and sitting for 3 years and only doing 6000 miles in 9 years . Could do with a birthday?

Thanks again pelicans

Edit 916 ?
http://i237.photobucket.com/albums/f...927_160810.jpg
After fitting the new 3mm silicone vacuum lines the problem has all but gone, with out taking on the highway to see 100%.
Now it just runs like an old car, have got new plugs and some intake gaskets on order.

Wasn't aware that you could adjust the WUR maybe I can drop it down a bit and put another 100 in the idle adjuster.
The WUR is vacuum assisted 089.

Check if you have a 089. It can also be a O90.

You had low revs before adjusting your WUR. Next you adjusted. How did you adjust?

I had low revs once at cold start, this turned out to be too low cold control pressures. This flooded the engine. I have now increased it to almost 2 bar at 15 degrees celcius. Low revs are gone.

2000 rpm at start up is a little excessive but nothing too worry about if they gradually come down to 1.000 over the next 5 to 10 minutes. It makes you look a bit like a fool dough at traffic lights :D

Check out my fight with CIS in this post.

http://forums.pelicanparts.com/porsche-911-technical-forum/678022-euro-sc-troubleshooting-over.html


As I said if you follow the US specs for a ROW car you will always have issues.

As you can read above (and when you look at my graph in the other post) my car is happiest with a cold control pressure slightly above what the graph says for that temperature. If this points to an issue in my car I do not know. I only know that is the only way for my car.

For know I would say fuel or ignition. On the Permatune I know nothing.

But as Tony would always say" We need fuel pressure readings and you need to check carefully for any vacuum leaks".

Changed the plugs last night, Number 3 and 5 were wet with fuel also two other HT leads had a green build up.
Cleaned them all up and they are all drawing? the same current now.

Are the injectors or the k jet system serviceable, the injectors seam very loose in the intake.
Have looked into parts and there a 2 orings available per injector are there any more parts that I will need.
Thanks again.

Add Injector sleeves and the o-rings for them.
They are usually very brittle or cracked by now and are known to leak.
Injectors are serviceable, there are a few threads on how to do it.
Title search on injector cleaning will find some for you.

How do people normally take the sleeves out, I've read some guys grind or punch the 3 tags out of the way, but how are you to reverse that? no one has really gone into detail about "replacing" them.
Thought Porsche would do a cir clip or similar to hold them back in. As Putting a centre punch on it could crack the new tubes.
Or just take off the intake tubes are replace them from the bottom ?

Just trying to get my cart together as shipping can be pretty decent, but the prices are 1/4 of what parts places here charge.

With the engine out and the intake off of the car, I put each runner in a vice and used a punch or small screwdriver to make the tabs flush with the boss and pushed the sleeves out.

I then cleaned it out with a brass wire wheel on a drill at slow speed.

Installed the new sleeves wth their o-rings and then used a flat screwdriver blade and a hammer to make new tabs.

I wouldn't try it with the intake in the car.

That makes me a little nervous but if it's what you have to do then that's it.

Sprayed some flammable stuff around the loosest injector and the rev's picked up so hopefully new o rings and sleeves will fix this “missing” issue.
But along the way I think I have fixed problems that I never new I had.

Will be getting a dyno run when complete to see if I have anything over stock.

And how do you search for stuff on this forum I found it easer using google?
Because everyone likes pictures.
http://i237.photobucket.com/albums/f...psd4e3b6f5.jpg