1987 911 3.2 misfiring when engine is cold
 

So i´ve already posted about this issue a while back (not sure what happened to my old account). These problems first started in the year 2014 (66,000 miles), just a couple of times the car misfired after startup but it quickly went away. at the end of 2016 (74,000 miles) the misfiring suddenly appeared after a brutal wheel hop when accelerating in wet conditions. That misfire was fixed with new plugs, cap and rotor.

Then in the first drive of 2020 (77,000 miles) the misfire had come back. The weather was quite damp and cold, so i immediately thought that could play a role with the misfire. Funny enough the misfire cleared itself after i drove the car to its operating temperature. Then we got a two month streak of warm and dry weather here in Finland, and during that period i got zero problems with misfires. Then came the first proper rainy day at the end of June and there it was again...Weird thing is, even in extremely wet conditions, the misfire goes away when the car reaches its operating temperature.

The misfire has always situated at a rev range of idle -> 2500 rpm. At least there it is at its worst. Car has had a major service by a local Porsche Center at 66,000 miles where they did a variety of the "bigger" services i.e adjusted the valves. After that the plugs, cap and rotor were changed at 74,000 miles and now at 78,000 miles i´ve changed the ignition wires, ignition coil, plugs (Bosch WRR4C) and lastly the DME relay. The parts have made 0 difference to the misfire, but the car runs noticeably better when warmed up and has more power after replacing the old 33 year old parts so that´s something.

At the moment i am running out of ideas what could be the cause of these persistent misfires after so many parts have been replaced. Tried to search the forums for same kind of problems (misfiring only when engine is cold or in wet weather) but did not find any threads. So does anyone have any idea what could be be the reason for this weirdness? Any help would be greatly appreciated.

The attached picture shows the terrible condition of the 4000 miles driven spark plugs that i just changed for new ones.

https://i.imgur.com/HKasEt8.jpg?1

Oh, i´ve also installed a steve wong chip (correct model, yes) at 70,000 miles and adjusted the ignition for RON 98 fuel from the Motronic box.

i would start with the correct type of spark plugs..What was the last time you have changed the fuel filter..............?Also is that oil on the number 2 spark plug...?
Ivan

It almost sounds like you are getting moisture in the distributor when the engine is cold and it is damp weather. Don’t ask How I know. 🙄 My first recommendation would have been to replace the distributor cap, but you said you did that.

Next time you have the misfiring, if practical, remove the distributor cap and see if there is condensation inside the cap. If you do have moisture inside the cap, and you know the cap is good, put a bead of dielectric grease around the sealing base of cap (where it fits over the distributor) and see if that keeps out the moisture.

Also, make sure the cap is fully seated into position. I’ve seen them mounted improperly allowing moisture inside the distributor.

Also, check the connection under the cap on the coil; you could have a lose or worn connection there. Pull your coil wire from the coil. Take a clean shop rag and spray it with some electrical contact cleaner. Then insert it into the female connector on top of the coil and clean out the connector. I wrap the rag around a small screw driver to assist in throughly cleaning the inside of the connector.

Good luck.

Well i thought i could remember the code correctly but apparently i could not. The correct product code for the new plugs i installed (not the bosch super 4´s pictured) is Bosch WR4CC, original factory plugs for -87 carrera i believe. Forgot to mention the fuel filter, it was 32 years old when i changed it for a new Mahle filter last summer. Oil indeed, i believe it has accumulated to the plugs during the misfiring, i´m not an expert though. Drove about 30 miles with the car misfiring, of course it did not misfire all the time but enough to ruin the plugs?

I really do hope that is the problem. Did not uninstall and inspect the cap and rotor while replacing the ignition wires because that was the last part of the ignition i suspected to be failing, because they are so fresh and were installed by a professional automotive electronics workshop.

Thanks for the tips with the cap, will try them immediately when i get home from work.

i though you have written there is a new cap and rotor.....??Yes the plugs are correct for non catalyst 911 but on the picture are not wr4cc plugs you have 4 electrodes it should be one...like this
https://images.matthies.de/mike/c1b/1000_1290477.jpg

Yes well the cap and rotor are relatively new, only 4000 miles old. They were installed back in 2018. At the moment i only have a spare rotor in stock.

My car is the non-catalyst version and i have replaced the old Bosch Super 4 WR78's (shown in the picture i posted above) with the WR4CC's. WR78 was suggested to me by a local porsche part dealer so i think they can't be too much off.

Look's to me that 4 of your plugs are running rich. I'm guessing, but possibly injectors, engine temp sensor. Did you take those plugs out after warm up and good running for the photo? The two at the bottom right look correct the others not good.

Consider some fuel injector cleaner. Drive a while and recheck the plugs. Looks like four running rich and two lean. Can also pull the injectors and send out for cleaning. If you pull them, consider flushing the fuel lines from filter to injectors.

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ok for the plugs ....if you had those 4 prong we had a lot of problems with those..but back to the basics all this and did not changed a thing ,correct?
Also look inside the cap and take a picture so we can see it before cleaning...any white smoke on 1st start in the morning...i`m asking because the spark plugs colors is all over.....pointing to the valve guides.Do not want to scare you- i did back in the early 1990` 3x 1987 with worn out valve guides with under 40K miles.... It never does it warm?
Ivan

I took the plugs out after horrible wet weather misfires, the misfires were so bad, that i did not even start the car before changing the plugs. The temp sensor sounds possible, i´ve bought some contact cleaner and planned to service every electrical contact point i can find in the engine bay. Also bought STP ultra fuel system cleaner, people seem to have got great results with it.

As stated above, i initially went with the easiest (STP) option, but maybe should consider disassembling the injectors and cleaning them thoroughly if nothing else helps to get rid of the misfires.

Could the plugs have gotten contaminated because of the misfires? I read that incomplete combustion could contaminate them in oil and carbon deposits, im not an expert yet again just a thought.

And yes after all the parts i´ve changed the issue remains almost unchanged, the car is a lot more responsive and smooth running when hot, but the cold engine issues remain. And in the first drives of 2020 season after oil change i got crazy amounts of white smoke in the first few starts, but after that normal amount (Barely noticeable, sometimes 0). Sounds fun, hopefully my problem is a bit more simple. The car indeed never misfires when warm, runs perfectly smooth.

I´ve attached pictures of the cap and rotor, found out there was some carbon deposits and rust, normal wear or not?



http://forums.pelicanparts.com/uploa...1595578657.jpg
http://forums.pelicanparts.com/uploa...1595578657.jpg
http://forums.pelicanparts.com/uploa...1595578657.jpg

One more picture of the rotor mount, guess it is a bit too rusty? The contact can´t be too good. After taking the pictures i cleaned the contact points in the cap and rotor mount, replaced the rotor with a new one and assembled the whole thing. Will test the car today after cleaning all of the other electrical contact points.
http://forums.pelicanparts.com/uploa...1595579090.jpg

on the distributor there not contact use on the shaft.But remove the fabric and spray inside the saft some wd40 or similar liquid -not too much.
Your cap and rotor looks fine regular wear.
For the injector it would have to be a professional shop to have them clean-it would not hurt but the problem is most likely there...is your 911 parked indoor or outside by the house?

Ivan
while you are there replace the left camshaft oil line and install missing sheet metal screw under the distributor;-)

There isn´t? But the rotor has a metal contact point inside of it :confused:. Oh ok i have CRC multi purpose oil or what was it called, should do the trick. Leaving it to the professionals could be a good idea with my experience. It is parked outside in an open garage.

Thought about the oil line actually, but the missing screw i didn´t even notice haha.

the shaft of the distributor is used on earlier types which have points and the shaft open and closes the points.

Johan, where are you located?

Since only two spark plugs look normal and the rest are hopelessly carbon fouled it seems possible your mixture might be running extremely rich.

My take on seeing the spark plugs is that intake bolts are loose on 1,2,3 & 6, bringing in air & thus having the dme compensate by adding more fuel to those cylinders.

Oh ok good to know.

I'm located at Finland, should probably ad some info to this new profile.

The car running rich sounds possible, intake bolts mean the bolts that connect the intake manifolds to the engineblock right? Should check the torque on them first thing tomorrow. Could the mixture be off because of the air volume sensor is acting up?

Today i cleaned every single electrical connection i found in the engine bay, also the ground points. I also tightened some screws around all the air hoses in the engine bay just in case, they seemed to be very loose.Will assemble the air box after oiling the cleaned air filter tomorrow, hopefully all this + intake bolt torque check will do the trick.