'86 Carrera running rough...

david914 · 06-23-2012, 10:19 AM

Been a LONG time since I've posted here for help. My 911 hasn't seen much action the past few years, staying parked most of the time. Life's been getting in the way of me enjoying my car.

I try to start it and run it regularly and it's been increasingly difficult to start, eventually getting to where it wouldn't start at all. The exhaust smells like gas, so I figured ignition. Replaced cap and rotor with parts from our host and no improvement. Replaced the Bosch platinum plugs with NGK's and it now starts, but runs rough like one cylinder isn't firing well. It runs better at higher RPM, but like it's on 5 cylinders at idle and backfires like excess fuel is building up at idle.

I'm still leaning toward ignition (bad cable?) as a possibility. Have pulled each plug wire while the engine's idling, but get the same result with each wire (car stalls).

david914 · 06-23-2012, 11:04 AM

Ok, here's one thing that worries me. Look at these two plugs. First is from cylinder #4.

This is from cylinder #5

Could a stuck (open) injector do this?

david914 · 06-23-2012, 11:48 AM

Just pulled the injector cable on cylinder #5 while the engine was running and nothing changed. Hmmm...

Tippy · 06-23-2012, 12:16 PM

Was the plug wet from fuel or in that condition when you pulled it?

david914 · 06-23-2012, 12:23 PM

It hadn't been started in a while when I pulled it, so it was dry.

Porchcar guy · Porchcar guy's Garage

Are those the NEW plugs you just put in as they look pretty crusty ?

david914 · 06-23-2012, 12:37 PM

No, the plugs in the pics are the old plugs. The remaining four plugs not shown look pretty "normal". The two above looked the most different. The first (cylinder #4) looks like it was running a little lean compared to the others. The second (cylinder #5) looks the worst. Looks to me like a lot of deposits and some corrosion of the plug electrode. I'm thinking of trying new (rebuilt from our hose) injectors for these two cylinders.

KFC911 · 12:42 PM

I can tell that those are the old plugs. Since you've put in the NGKs, have you given her the old Italian tune up? If not, get her warm and drive her hard

.

edited...

ps: Did you go with the NGK copper or platinum?

Porchcar guy · Porchcar guy's Garage

KC911 beat me to it. Starting and running the car whithout driving it for a period of time to get all the junk out...so to speak..... doesn't do the car any good...Italian tuneup first and then start your process of elimination.

david914 · 06-23-2012, 12:54 PM

Haha, "Italian car tuneup" is exactly what my buddy said.

The NGK's are copper (BPR6EY). Car had Bosch platinums in it before.

KFC911 · 06-23-2012, 01:58 PM

NGK copper is good! Not sure about BPR6EY though...BPR6ES are what I've always used. Good luck!

david914 · 06-23-2012, 02:13 PM

Well, Italian tune up seems to have cleared things up! Bellissimo! Bought a can of Seafoam treatment on the way home and added some Shell 93 octane for good measure. Gonna take her out and run her hard some more.

KFC911 · 06-23-2012, 02:28 PM

Excellent!!!

Jdub · 06-23-2012, 02:37 PM

Be sure to charge your battery all the way up - a low battery will play havoc with your alternator and then its $$$. Dump the oil after your next spirited ride to get condensation and injector cleaner runoff out, then fresh filter and oil.

Finally, you MUST change the fuel filter - if you can't remember when it is time to do it.

Laneco · 06-23-2012, 03:37 PM

Don't overlook nasty old gas in this process as your initial posts seems to indicate the car hasn't really been driven (only started) for quite some time.

New oil anda few drives to run the gas in the tank through. Then get rid of the old fuel filter and put in a nice fresh tank of fuel. Enjoy!

angela

gregwils · gregwils's Garage

David - how long has it been since you replaced your DME relay. Old DME relay's can cause a rough running motor. If you have a spare, swap it. If not, I would suggest a $30 investment in a new relay. Keep the old one as a spare if you don't have a spare.

david914 · 06-23-2012, 07:00 PM

Well, took her out on a drive and ran her hard. Purring like a kitten now! Luckily, it didn't have much gas left in the tank, so I put in just 10 gallons of Shell 93 octane to keep the Seafoam to gas ratio higher. I'll put in another can of Seafoam on my next fillup for good measure.

The battery is an Optima and in great shape as I put a maintainer on it when it's not being driven enough, so no worries there.

The DME relay is also fine. I looked at that (I'm an electronics technician by trade) awhile ago when this problem first arose. It wouldn't hurt to carry a spare though...

I'm just happy the problem seems to have cleared up! I've promised myself that I'm going to drive the car much more often so this won't happen again, at least not due to lack of being driven!