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

I usually click on search, then advanced search and then do a title search. Choose your words well!

So after a full gasket rebuild I still had this annoying miss.
http://i237.photobucket.com/albums/f...ps0a96e268.jpg
Got my hands on a smoke machine today and I found the hole/leak!
http://i237.photobucket.com/albums/f...ps0b040318.jpg
http://i237.photobucket.com/albums/f...ps0b795aef.jpg
My friend has a 450SEL 116 Mercedes with the smiler CIS set up.
Note the gum coloured plug.
http://i237.photobucket.com/albums/f...ps3202cc71.jpg
Is there a plug that goes in this hole, I tried looking in the parts section but no luck.
I put some silicone in the hole to see if it stopped the miss, but motorway was blocked and couldn't sit on 120.
But it does feel like it has gone.

That hole is not on the vacuum side of the intake system. (Before metered air)
It is the access hole for the richness adjustment.

Did you service your injectors?

Yes injectors have been cleaned.
There are no other leaks that I can see.

One last bump before I sell intake and convert to an efi conversion kit.
Things I have done ,
All new gaskets, reconditioned injectors, o-rings new vacuum lines and has has a smoke machine air leak test.
The issues:
When it's warm it misses at constant speed and once warm when you re start it, it has a high idle 2k+ for about 5 minutes.
Are these two problems related.
I've read the bosh k-jetronic book cover to cover and It's a reasonably simple system.
So there must be a simple fix ?
Any help would be hugely appreciated.

Simplistic approach - What brand plugs are you using and have you changed the whole set, no matter how new they were? I had a similar issue with my 914-6 once; right after tune-up, an irritating miss at constant/trailing throttle. Hard acceleration, no problem; pulled great right to the limiter (7300 in this case).

Put the old plugs back in, problem gone. Threw out entire new set, installed another set, no problems.

My friend is the New Zealand importer for NGK , just called him and there are 3 listings for 911 78-83.
One plug is 3 dollars each and the other 20.
Will look into what I have in there and hopefully the end of this problem.
Also I'm running M&K shortys would not enough back pressure cause this problem?
Cheers

Test and confirm......
 

esonefoure,

If I were in your shoes, I would check the following:
1). Check the AAR and test it. It might not be closing completely when the engine is warm.
2). Check your fuel pressures (control and system pressures), both cold and warm condition.
3). Your airbox has been opened or fixed before. Look at the screws, they are not the OEM ones and you could see the glue around the perimeter. I have recently purchased several CIS air boxes sellers claimed in good working condition when removed. And they all failed the pressure test. Even a smoke machine has trouble locating the leak underside of the air box. A good way to test an air box is water immersion method.
4). Try to borrow a good CDI (Bosch or permadoom) and do a switch.
5). Inspect your ignition distributor's rotor, spark plugs, and ignition timing.
6). Inspect the fuel injectors' spray patterns.
7). Have your exhaust gas analyzed by someone with a gas analyzer.

Keep us posted.

Tony

Nice car mate, hope to see you on the streets of Auckland

http://forums.pelicanparts.com/uploa...1386279243.jpg

You will hear me before you see me.
http://i237.photobucket.com/albums/f...ps5e2b966c.jpg
Boyt911sc, thats a decent check list but so worth it if this problem is fixed.
Ill pick all the easy ones off first and go from there.
Thanks again for the input.

I also had some frustrating missing issues. They were completely cleared up by installing a set of Magnecor ignition wires. It's a pretty affordable way to rule out your wires as a source of fault. There is also a lot written about the annoying and tricky problems that can be caused by those "grounded" wires.

Before you do anything expensive... try the Magnecors. They're great, and even if you do decide to go the more extreme direction with your fix, the new wires won't work against you in any way.

Good luck. It's a great looking car and engine!

-Dan

I'm of NO help, but man, thats a nice color!

replace injector sleeves and Orings.

then i would do some injector flow and leak tests.

with each injector in its own container, power on the FP and check for leaks. then raise the sensor plate about half way and hold it. while filling the containers, check the spray pattern of the injectors. when done, compare each injectors fuel volume to each other.

So a small update,
Pulled the plugs out and they looked ok, but got some iridium to replace them.
http://i237.photobucket.com/albums/f...ps4tjacogk.jpg
http://i237.photobucket.com/albums/f...psgkofh2yo.jpg
New plugs look space age apart.
http://i237.photobucket.com/albums/f...ps1mcgenvk.jpg
http://i237.photobucket.com/albums/f...psj5z5jwsw.jpg
This didn't fix the problem but I guess im getting through the list.
Also ran some race gas left over from the drag car,
Smells so good.
http://i237.photobucket.com/albums/f...psymyxskjc.jpg
Been to a well recommend auto sparky shop and they think it's in the permadoom unit.
So might throw a msd kit at it and go from there.
Also these are definitely going to make any problem go away.
http://i237.photobucket.com/albums/f...sptm1vyiw.jpeg

Back on track to finding the air leak/electronic miss.
Bought a MSD blaster coil, rotor and cap.
Had it installed buy a autosparky friend of mine.
http://i237.photobucket.com/albums/f...psqg37chjo.jpg
It sounded so much more crisp and clean but still high idle and not running right.
So some new leads were the next on the list, as I found some that just fell out of the lead.
still running ruff and my patience was wearing thin, so I found a bumper to finish my clone.
http://i237.photobucket.com/albums/f...psbkoejvv0.jpg
My dad was down for the day to collect his drag car, We went over the electronic system started with
finding TDC with a paint brush in number one and for some reason the cap location was out.
Pulled dizzy out and made TDC right with number one and the mark on dizzy.
It started and for once I could see the timing marks with the timing light but still way out 10-11 o'clock.
Begining to get very frustrating and started to google EFI conversions.
Started to look into the MSD and Coil green wire, found a page on Pelican were someone was having issues "Green to Green and Purple to outer wire.
Dun Dun Duunnnn !
http://i237.photobucket.com/albums/f...pslsxcqiac.jpg
Temporarily wired it up, and it started no high idle TDC and 5deg were bang on never been happier and 2 days on still smiling, so happy I have this monkey off my back.
http://i237.photobucket.com/albums/f...psjuhxqebr.jpg

That was a bit fast.

What is the green to purple and outer wire problem?

Bad connection? crossed wires?

Glad to see those issues are over.

Green wire from dizzy goes to green wire on msd and the outer sheath? to purple.
There is no real clear instructions on this, unless I missed it in everything I read.
Was the permdoom unit wired in wrong, or was it just so faulty that a wired incorrectly msd preformed the same.
It's been a long road but fixing everything contributed to the making the issue disappear.

MSD calls the Violet + and the green -. on the porsche, the inner green wire is considered + and the outer braid is -. so you would think violet would go to the center or green conductor but it is wrong. here is why.
MSD wants a neg to pos signal. the bosch unit uses a pos to neg signal. normally the output of the dist has a slow rise to pos then a very sharp drop to neg. this transition is what triggers the MSD or bosch unit. the difference is bosch wants a pos to neg transistion and MSD wants a neg to pos transition. dont think of the signal like battery voltage were you have pos and ground, its more like AC in your house.
the problem with leaving it connected wrong is that due to the shape of the wave form, the slow rise to pos will trigger the MSD BUT, it will also advance the timing at idle AND as RPM's go up. i image there are a lot of people out there that just pulled the dist, like i amost dod, and just re-time the ignition. this is very bad due the the advance that is added in.

as RPM's go up, the voltage out of the dist goes up. as it does, that slooow rise of the "up side down" side happens sooner and sooner thus advancing the timing.

this is hard to explain typing, hope it helped.

Wonder if permadoom use the same pickups.
That made sense as to why a sparky can get it wrong.
Just over the moon it's sorted, need to get some k's (miles)on this thing.