911SC Engine Misfire HELP!!!

1987M505 · 07-01-2006, 09:36 AM

Okay Here's the story. I picked up a 911SC with the original 3.0 a couple weeks back. The car has 106,000 and had been driven about 4k miles in the past ten years, otherwise stored. It does not leak a drop of oil or burn oil. The fuel in the car was probably 8 months old when I test drove it. The car was running and driving great on my 45 minute test drive. The engine pulled strong in all the gears and I figured with a basic tuneup it'd be set. I trailered the car home and drove it another 5 miles then parked it in my garage. The next morning, I fired up the car and it started misfiring. The misfire got slightly worse as I put on another 15 miles or so. I changed the oil. I put in new plugs, plug wires, dist Cap and rotor and it's still misfiring in the Number 1 (according to valve adjustment sequence or rear Left) cylinder. I did a compression test and here's what shows:
#1- 148psi
#2- 142psi
#3- 143psi
#4- 140psi
#5-139psi
#6- 141psi

This tells me that the cylinders are strong and I shouldn't have a valve problem. I have fuel going to the #1 injector but didn't pull the injector to inspect it. The plug in that cylinder also seems pretty dry when I pull it after running the car for a few minutes. What should I do next? Is there an easy way to get the injector out? My Bentley shows a special puller... Any way I can replicate this at home?

JP911 · JP911's Garage

I was able to pull mine out by hand, but I know that in some cars the puller is helpful. Other thoughts: Did you check the timing after your tune up? And, where did you gap the plugs?

CliffBrown · 07-01-2006, 10:03 AM

I'd start with a complete change of the old fuel and a fuel filter change.

Fuel that old is a hazard to your CIS system. You might even need to clean the fuel tank and pump. Get the CIS fuel pressure gauge set and see if you're system is getting the fuel pressure it needs to operate.

It could be that your fuel filter is becoming restricted and depriving the motor of fuel because of contaminated fuel.

1987M505 · 10:20 AM

Did not check timing after tune up and I gapped at .008 . I also visually inspected the fuel tank and it looked very very clean. There was half a tank of old fuel so I topped it off with Shell 91vpower and a bottle of injector cleaner. That number 1 cylinder isn't firing at all anywhere from idle up all the way thru RPM's... It was firing great on all cylinders on my test drive.

DDD · 07-01-2006, 10:54 AM

I've had clogged injectors twice in my 12-years with my 911SC. Both times, the car ran ok at start up, but would miss badly running up from 2000 RPM. No idea what caused the clogged injs, but I can tell you my car ran perfect one day, and then for no reason, it just started missing the next. First time took me awhile to figure it out (I think this forum helped me find it). Second time it was obvious.

My recollection is that the injectors pull pretty easily. There is an o-ring in there that holds them tight, but a good tug got them out. I don't think I used vice-grips or any other kind of tool, but I do have some V-Gs with rubber tubing pushed onto the teeth to use for just this kind of purpose.

My car sits every winter for 3-4 months, so that may have something to do with what I have experienced. Your car sounds a lot like mine, what with old gas and missing.

Oh, and the injectors are easy to clean -- I just soaked mine in fuel injector cleaner or carb cleaner for a few hours. Good as new.

Good luck. -DDD

1987M505 · 07-01-2006, 01:45 PM

Thanks DDD,
I think this is right on track. I'm going to pull the injector and soak it right now. Are you by chance on Mnaudi.com ? I am located in Minnesota as well...

2.7RACER · 03:07 PM

Tell me the plug gap is .028". The .008" must be a typo, right?

DDD · 07-01-2006, 06:30 PM

1987M505 -- I do check out MNAudi.com every once in awhile. I spend most of my time here or at AudiWorld.com. I have been thinking about APR flash for my A4. Are you an Audi owner?

1987M505 · 07-02-2006, 02:26 AM

Well I've tried soaking two of the injectors with no great results. There are definite differences in the spray patterns on the injectors and I don't get any spray until about 48psi on either of them. Could a fuel filter cause 1 cylinder to suffer misfire. The car seems to run a bit rough in general but that #1 cylinder seems to be the culprit... Any more ideas?

In response to DDD. I am an audi owner as well. 99 A4 avant and had a coupe quattro for a while.

Rick V · 07-02-2006, 04:02 AM

You may have some crap in the injector pump. Same theroy as the injector. Do a search for the pump, some fellow(I forget who) just did a rebuild on his pump. Lots of pics and text. One of the best posts I have seen in a very long time, it should answer all the questions you have about your fuel system.
I would recomend changing your fuel filter just as a maint. item.

fred cook · fred cook's Garage

I found that the easiest way to pull the SC injectors was to remove the fuel line from the top of the injector and put a nut with the correct thread on the injector. That will give you a shoulder to pry against using a long square shank screwdriver. Getting the injectors back in without cutting the new seals is somewhat more difficult. I found that the best way to insert the injector was to leave the large nut on the top of the injector and put a short socket over the nut. That give you a nice flat surface to press against.

Good luck!

1987M505 · 07-03-2006, 07:49 AM

Hi Fred,
I got the injectors out no problem although 1 was much easier than the other.

In response to 2.7racer "Tell me the plug gap is .028". The .008" must be a typo, right?" I gapped at .8mm or .032". Sorry about that typo. I'm going to plug in two of the injectors that have been soaking for a while now... We'll see if it helps.

Bones · Bones's Garage

Have you checked for spark on that cylinder? It could be a plug lead or a bad connection at the dizzy cap or plug cap.

1987M505 · 07-03-2006, 03:06 PM

Well after notorious troubleshooting I finally figured out the problem. It was a clogged injector and fouled out plug after all... It was not the one I pinpointed the other day though... I also wanted to note my Bentley manual states the distributor spins clockwise. This led me to pulling all of the plug wires and totally mixing everything up with the firing order... I pulled the diz cap and turned the engine over to find it spins counterclockwise... Needless to say I got everything back in line and the problem is fixed. Thanks for all the input the car is running great!