Help! 85 911 with misfire

[Andy Minihan]

Hi Folks,
My newly acquired 1985 911 has developed an issue.It started by very occasionally misfiring when hot.It is not really noticeable while under way,while at idle it puffs every other beat.It is still quite minor,but is getting worse.I have already replaced the Spark plugs,the plug wires,the distributor cap and rotor.

[steely]

Hi Andy and Welcome.

Can you tell us what the rpm is at idle, and a little background about the car (it's condition)?
Are there any other issues.
In your first post you looked for a pedal - are you having any other issues with the car?
It could help us help you.

[pete3799]

How many miles are on the motor?
Any chance you could record the noise and post it?

[bkreigsr]

My 85 exhibits much of the same symptoms - turns out that every so often, I have to reach in and seat the #2 plug wire to the plug. It has a tendency to work itself loose enough to cause a miss. When I hear the difference in the idle, I know it's time for a firm push.
I suppose I should get in there and do a permenant fix.
Bill K

[T77911S]

could be an injector. try soem injector cleaner. i like to put a bottle in with about a half tank of gas. then i try to drive it with more sustained hi RPM's. like 4-5k between stop lights.
then got a few tanks without, then do it again.

check the mixture.

check for air leaks.

since it is new, i would do a compression and lekadown test, jsut to see where its at. also doa valve adjustment. the valves first.

[Andy Minihan]

911 misfire - YouTube

[Andy Minihan]

Hi guys,The Car has only 65000 miles on the clock,it is in very clean and unmolested condition,other than some nasty after market bits and pieces(pedals,gearshift,94 cup wheels)very original.The only other problem is the blower motor stopped working,I think it is just a loose wire,was working fine,would cut out when I went over a bump.

[Drisump]

If the symptoms are what I think they are, as T77 says, try some injector cleaner. These low mileage cars often have been "too" babied and you'll find that these cars like the redline every now and then. I usually use Techron and take her for an Italian tune up. That does the trick for my car. I find that if I use the car for short runs and never open her up for many weeks, I often have a rougher idle. What fuel are you using? I generally put in the highest octane available wherever I am. If I'm at home, that is 93 at Chevron ( and that is the one fuel available around here that has no ethanol). Also at idle, the air cooled 911 is definitely not the most smooth sounding engine. This is what I'd try first.

Cheers

[DRACO A5OG]

Get some BG44K, it is Techron on steroids, it should clear it up just nicely

+1 on the italian tune up after she is good an warmed up

jim

[Andy Minihan]

I tried to post a video twice,I'm not sure why the link is not there.If you search youtube for ''Andydelapoer 911 misfire'' you will find it.Thanks Guys.

[DRACO A5OG]

[IMG][/IMG]

[Drisump]

Sounds like it needs classic "needs some injector cleaner/ Italian tune up" love. Try this first before going anywhere else. Very common on these cars. Cheers

[Andy Minihan]

Rpm at idle is 800-900rpm

[Andy Minihan]

Just been out for a spin to half empty the tank, I put in a bottle of techron and then topped her up.

[DRACO A5OG]

Good if that doesn't work get some BG44K and after warmed up enough in 2nd take her to redline, check the mirror you should see a ploom of white smoke aka carbon

[T77911S]

that may be more than an injector cleaner fix.

check for air leaks.

have the mixture checked to see where its at.

are you running with an O2?

[Andy Minihan]

Running with an o2?,not sure what you mean by that.How do I check for leaks,bar replacing everything that could leak.How do I check the mixture?.

[Drisump]

O2 is the oxygen sensor on the exhaust. It's function is to tell the DME some info about the current running of the car and consequently the DME adjusts. Some on the board believe it to be a critical system for proper running. My 85 is a Euro model and the O2 sensor had been disconnected since before I got it...and she runs great. Perhaps the different engine in the Euro means that it has little or no effect on the running whereas the American market spec may require the system to be fully functional.

[Andy Minihan]

I ordered all the gaskets and nuts for the valve adjustment,I figure this is worth doing anyway,whether it is the issue,any tips ?

[Drisump]

If you've ordered (I presume from our host) I hope you ordered the funky feeler gauge tool as well (with a couple of extra blades). The 3.2 has limited access and visibility to do the valves, consequently getting a normal sized feeler in there may pose a challenge, also, it has a hook so you can hold on with one finger while turning the wrench and holding onto the screwdriver. You will have to drain the oil out of the car unless you do one side at a time and lean the car over. Myself, I run the car to running temperature, drain oil and leave over night to cool for proper adjustment. I'm thinking you should probably change the oil, plugs, air filter,fuel filter, cap and rotor so you have done a 15000 mile tune up to properly baseline the maintenance schedule. Anyway, good luck