fouling only one plug

[GMR911]

I having a problem fouling only the #2 plug. I changed the plugs and it did the same thing. All the other plugs looks ok. All parts are new including the wires, cap, rotor. The car stumbles for a few 100 RPM upon accelerating. Then seems to run fine. The car is a 77 911S with a euro 3.0 Any ideas? Thanks Jerry

[ruf-porsche]

You could have a leaky injector on #2.

[350HP930]

My car started to foul plugs around the 120K mile mark.

At first I assumed the worse such as cylinder damage or extremely bad valve guide wear.

After my engine break down I discovered that the problem was that the oil control rings on the pistons were completely coked up and had lost most of their tension. It was quite a reminder of how important those oil squeegees are on a piston when big oil squirters spraying the hell out of them.

You could be looking at anything as minor as this or something as serious as a broken piston and/or gouged cylinder or a really bad intake valve guide or seal.

Start with a compression and leakdown test. It will at least give you an idea of what kind of condition the cylinder is in.

[david c.]

Does the car have Webers?

[GMR911]

No, the car has standard CIS with SSI's

[Joe Bob]

Check the plug wires....could not be firing right due to resistance problems......

[david c.]

Mike is making a good point; just because the ignition parts are new doesn't really resolve whether they are functioning properly or not.

It wouldn't hurt to check the resistance of the wires, swap plugs, etc. to eliminate the possibility of ignition problems before delving into the more sinister culprits.

[GMR911]

I checked the resistance today on 3 of the plug wires, the #2 wire was 3.99 ohms, the other 2 were 3.94 ohms. THey should be 3 ohms per the wire sheathing and the bentley manual. Are these out of spec or are they OK> I am going to test the other Tues. By the way, the plug in question is black and dry, not wet or oily, Thanks Jerry

[GMR911]

Also, what is a good method for testing a fuel injector. i am thinking maybe it has a cloggeg fuel injector. Thought maybe I try a can of techron.

[ruf-porsche]

Black and dry or sooty would indicate that you are getting to much gas in that cylinder. An oily plug would indicate a broken ring or bad valve guide. Have you pull the injector to test the spray pattern and to see if it is leaking?

[Jdub]

I'd vote for the oil control ring. Have you dropped 20oz of Techron in the car and taken it for a spirited min. 1 hour drive to REALLY heat up the engine and drive out the buildup?

Be sure to dump your oil after doing this. I typically do the 20oz twice before an oil dump at 2,000 miles if I am really picky about things. The stuff is pretty amazing.

John

[ChrisBennet]

In a well ventilated area pull the "bad" injector and put it in a tall clear glass container (gas will melt some plastics bottles).
1. Turn key on, is injector leaking?
2. Lift air plate in airbox with your finger briefly (*), does injector spray nicely?
You may want to replace injector O-ring when you have injector out.

-Chris

* While you are spraying fuel in the bottle, they other cylinders are filling up with fuel also, hence do this briefly.

[Superman]

Good suggestions here. I yawn at resistance specs for ignition wires. Somewhat meaningless in a way. For example, our cars would run fine with NO resistance in those wires. Our radios would cackle, but the engine would run just fine. Even if a wire had infinite resistance (not conducting low voltage electricity at all), it might perform just fine when passing high voltage sparks.

Again, there are good suggestions here. Pull injectors and put them in jars, turn on ignition and raise the sensor plate. Look at the spray pattern. Measure the volume. Play with the ignition system a little. Do the Techron dance. You're likely to solve the problem and even if you don't, you'll have better information.

[BGCarrera32]

Check injector first like Chris says. That's my vote. Little plastic and steel parts with fuel forced through it after a few million hours are suspect. Kinda like after several days of bad food, coffee, and pizza...things at the back end eventually lose seal and start heading south...

[Skip Newsom]

I've got a 72 T with MFI that fouls #1 consistantly and also stumbles a little between 2200-2700 RPM. With lots of fine tuning, air flow balancing between stacks, CO adjustments on the pump, and new injectors it is much better than where I started. Once I hit 3k and up, she sounds and works well. I've also gone through the entire ignition system and replaced anything questionable.
I still need to do a leak down test because I suspect a leaky valve guide.
I always use Chevron, but I think I'll try the "techron dance" just prior to oil change too.

One question I did not see asked is when was your last valve adjustment?

[echrisconnor]

The injectors on my Euro 3.0 are EXTREMELY difficult to remove. I've pulled a couple of them by prying them out, but then had to tap them back in with a soft mallet. It looks like there's a small piece of metal in the intake which locks them in place. Is there a good method of easy removal/installation of injectors?

[cyprusx]

Quick question... Why change oil after a Techron run? I just changed my oil and happened to treat my baby with a bottle of this juice. Do I now need to change my oil again?

Thanks...

[Superman]

I'd say yes. Techron is pretty nasty stuff. It does not burn or boil off. I'd run another bottle through, and change oil. If you just lift the oil filler cap and sniff, you'll be able to smell the stuff.

[GMR911]

Thanks to all! I am going to test the # 2 wire with a new spark plug tonite to see if there is spark. I may try to remove the injector also to see if it is clogged, leaking. I will definitely use the techron and see how this works also. Will let you all know how this turns out, Thanks Jerry

[350HP930]

Originally posted by Skip Newsom
I still need to do a leak down test because I suspect a leaky valve guide.

A leak down test will indicate if a cylinder is leaking at the valve seats and/or rings but it will not tell you anything about the condition of the valve guides.