Porsche 911sc 1982 misfire/hesitation

[hardwick63]

Hi Guys,
Need some help with this. My 911sc has a slight misfire at low revs which clear at 2000rpm. Seems like a slight splutter/hesitation. I have changed the plugs,rotor arm, dizzy cap, air filter and run some cleaning additive in the fuel-however the problem is still there. After 2000rpm the problem clears and the car drives really well. Its not just when the car is cold/just started-it can be mid-journey.

Need some advice on where to look next.
Any help much appreciated
Colin

[boyt911sc]

Originally Posted by hardwick63

Hi Guys,
Need some help with this. My 911sc has a slight misfire at low revs which clear at 2000rpm. Seems like a slight splutter/hesitation. I have changed the plugs,rotor arm, dizzy cap, air filter and run some cleaning additive in the fuel-however the problem is still there. After 2000rpm the problem clears and the car drives really well. Its not just when the car is cold/just started-it can be mid-journey.

Need some advice on where to look next.
Any help much appreciated
Colin

Colin,

I doubt you'll ever have any decent reply to your inquiry. One of the protocol has been blatantly committed by not posting a picture of your car.........but since this was your first post, we'll ignore it for the meantime. I'm just kidding. Welcome to the forum. This type of problem you are currently having is just peanut to these guys!!!!! They are good and a few are critically nasty so be informed. You just joined the best 911 forum in the Internet.

Tony

[Bob Kontak]

If it sound like "putting" out the tail pipe there may be a vacuum leak. My 81 had the putting but no hesitation or change in the engine rpm - but as the RPM's increased the putting went away. One of my intake runners was not fastened down all the way at the head and I found it by spraying starting fluid on hose connection points. RPM's went up a little.

If not a vacuum leak, you can look at your wires and distributor cap in the dark with the engine running. Don't wear a necktie. You can see arcing if you have any type of insulation issues with the wires. Let your eyes adjust for several minutes.

If you are running a fat spark plug gap you will increase the chances of the juice arcing to something (another wire, etc.) before it gets to the plug.

[hardwick63]

Sorry just added picture today. I will check the arching but I don't think the problem is 'putting'.
Thnaks

[hardwick63]

hi,
I have checked for arching in the dark, but couldnt see anything sparking at all. However one of the ht leads has a bit of a melted end-could this be the problem? What leads do you guys recommend?
cheers

[hardwick63]

hi,
I have checked for arching in the dark, but couldnt see anything sparking at all. However one of the ht leads has a bit of a melted end-could this be the problem? What leads do you guys recommend?
cheers

[Groesbeck Hurricane]

The melted end could be indicative of needing to replace the wire. Take them off, one at a time, and measure resistance. You just want to ensure no wires are broken. If they are older I would replace as soon as possible.

Also, is there a heat source where the wire is appearing melted?

I am thinking of a possible vacuum leak in the CIS (Continuous Injection System/fuel injection). Run through your hoses, again one at a time so nothing gets missed, and make sure they are not old/brittle/broken. do not remove them if you cannot easily see/get to both ends. You will likely need to take off the air filter and some of the larger pieces that are on top.

Another thing I just always suggest is blowing our fuel filter out backwards (don't apply much pressure). If junk comes out the in bound side then I would definately replace. Fuel accumulator can take the same treatment.

Best of luck and report back, there are so many more smarter folks here than I...

[prebordao]

I would like to check mine for vacuum leaks... what is starting fluid ? some kind of gas ?

[Bob Kontak]

Starting fluid comes in a spray can and contains ether. It is used to help start internal combustion engines that benefit from a quick burning fuel. It is very volatile and ignites easily.

Note that very knowledgeable folks warn of flash fire risk and do not recommend the test. However, it works. Your choice.

[Bob Kontak]

I would perform the test Groesbeck recommends.

I recently bought Clewitt wires and I am really happy. They are price well compared to the competition, have a nice appearance and receive good feedback.

Pelican Parts - Product Information: CE-9192-28-R

[hardwick63]

I brought a new set of ignition leads, problem solved.
Checked for broken wires on old set, only 3 out of 6 were working correctly.

Thanks

[jwakil]

Disconnect your vacuum retard line on your distributor (you will have to plug it up of course). You will have to lower your idle setting since idle will go up. This has significantly reduced my low rpm hesitation, engine seems to run cooler, idles smoother. This is a free 3 minute modification which you can always reverse if it doesn't work.