Damp, wet weather = engine misfiring. Help please.

[JCFL]

SINCE JUNE 23rd approx., HAVE NOT BEEN ABLE TO START THE CAR

Hello guys,

I am writing for help - members of this Forum have unbelievable knowledge and I live in a rural area where Porsche resources are simply nonexistent. I am located 600 miles East of Boston, in the province of New Brunswick, Canada.


CAR INFORMATION
1 Porsche Carrera Coupe, 1986.

2 Mileage is approx.152,000 miles.

3 Bought from BAT in May 2022, from owner for 29 years.

4 During June 2022, I thought there was a bit of misfiring.

5 In early July 2022, I put in NEW – ignition rotor, distributor cap, spark plug wires, spark plugs, and ignition coil.

6 Car ran very well after that, and I drove approximately 7000 miles since then (in 6 months of driving).

7 The only item I would mention that has not been perfect - the car sometimes seems hesitant at low RPM.


CURRENT SITUATION
1 Car out of winter storage in April 2023 – started on the very first turn of the key after 5 months parked.

2 Got new tires, turbo tie rod kit. Big increase in driving pleasure.

3 Car has been running extremely well since May 2023 – a real pleasure to drive, both on the highway, and in my small town (daily driver).

4 Around June 6, I drove the car in heavy rain (on purpose) to test my new wiper setup – I have removed passenger side wiper, and driver wiper now parks on the passenger side. I did this while my gauges where out for new LED bulbs – much simpler than going through the front trunk. I like the result.

5 We have had very unusual wet weather for a few days, so the car was left parked in the garage for a couple of days.

6 When the sun came back, I went to start the car and it started immediately, but it is MISFIRING badly. It is as if there is only 3, 4 or 5 cylinders working, depending on the moment. If I leave it running, it will end up stalling.


THIS IS WHAT I HAVE DONE SO FAR RO TRY AND FIX PROBLEM
1 Checked the resistance of the coil, and it is within specs, clearly.

2 Checked the voltage to the coil with ignition on, and it is at 12.1 volts.

3 Cleaned the connections to the coil, to the distributor cap, and used dielectric grease to improve contact.

4 I have ordered a new DME relay – I should receive it next week.


CONCLUSION
The car was running very well, but after 2 days in wet (damp) weather, it suddenly misfires quite badly. And yet, the car was NOT in the rain, it was parked in my garage. I have done fair amount of research on the Forum and have not found similar situation.

I would like to insist - the car always starts, whatever the problem. It is not a starting problem. It is after having started that one can notice that all cylinders are not firing. Some people mentioned that the plug wires could be the problem – but that would not have happened all of sudden.

Do you guys have any suggestion as to what I could do further to solve the issue ? I am leaning towards faulty relays but I do not know how to proceed.

Thank you a lot.

Jacques

[EC900]

Some basics with my limited experience…I wouldn’t grease the rotor contact (for sake of collecting dirt) but would use a silicone paste around the distributor gasket. Microscopic moisture could be seeping in and since driving is limited there’s no time to sufficiently dry out. Then the same applies to gasoline. Could timing be a bit off or distributor loose, maybe one of wires are mixed up?
Also - check for vacuum leaks and determine if you’re experiencing and over-rich condition with blackened exhaust smoke.

[JCFL]

Thanks EC900
Will check those items that I have not already verified.

[pete3799]

Spray some WD40 in the dist. cap and see if it helps.

[r_towle]

Skipping ?
Remove and clean the inside of the distributor cap
Remove and clean the crank and reference sensor connections.

Possibly replace all ignition wires with new ones
Check all grounds , clean and tighten (all ground on engine)

[JCFL]

Thank you r_towle,

I have new ignition wires from July 2022. Can you please say what are the reference sensor connections ? Thanks.

[PeteKz]

IME, these are often symptoms of a coil going bad. After checking the distributor and cap for any condensation, try swapping the new coil you installed for the old coil you took out. Was there anything wrong with the old coil? Or did you just swap it for the sake of having everything new?

[JCFL]

Hello PeteKz, and thank you for your comments.

I did not try swapping coil this time, as specs of the new coil were well within the specs.

Last year, I changed the coil as I was having minor ignition fire problem (nothing like this time).

But I will take your suggestion at heart, and add it to the list of possible solutions (before I start trying them one by one). I am expecting a new DME relay within a week and I will try it on to see if it helps the situation.

Thanks again.

[r_towle]

Looking into the engine bay, left side, rear
You will see a short metal bracket with three electrical connectors.
Crank sensor
Reference sensor
Temp sensor

When I had weird behavior I replaced the dme relay, nope
I replaced the reference and crank sensors
The wiring is old, so are the sensors

This is all part of your bonding with your car

[JCFL]

Thank you again - will look into it for sure.

[Mike80911]

You must have already done it but if not inspect the cap very carefully for cracks. It might not be visible when cold but expand a little when hot

[SpyderMike]

For my 85, I found condensation was traveling down the wires towards the cap. It found its way in the cap through the top of the boots. My solution was red RTV where the wires meet the boots. It has not happened again.

[brighton911]

First thing I would do is pop the cap and check for condensation inside. If the cap is dry inside, then I suspect spark plug wires and/or cap issues. I find this works well:

With the engine running in the darkest outdoor environment you can find, lightly spray the wires with water. If there is a problem, you will see arcing on the offending wires and/cap.

[911obgyn]

Check plug gaps. Too big a gap and the spark tries another path. I had ngk plugs in mine and after a year the electrode had worn enough to replace coulda just re gapped but…

[JCFL]

Hello guys,

Weather around here has been terrible - not a good set up to follow up on your recommandations.

In my starter post, I did mention that the car would always start, although it was stuttering (or misfiring). Well now, it is no longer as keen to always start.

Regarding the DME relay, I read in another thread (much older) that the relay had nothing not to do here. If it works, the car can work. If it does not function, the car will not run. There is no middle ground apparently - a relay would not cause interrupting or misfiring engine... Is that the case ?

Thanks again.

[Showdown]

At the risk of sounding obvious, have you checked all the ground connections? I’ve definitely wasted a day chasing an electrical issue only to find a ground that was lousy.

[JCFL]

Hello guys,

To fix my issue of misfiring in damp weather, with issue now gone over to no start in wet weather, I have been following advice received on this thread, and conducted several verifications in last few days. I have also done fair amount of research on the Forums to gather all possible info.

2020 - new fuel pump, new injectors
2021 - new fuel filter
June 2022 - new ignition rotor, distribution cap, spark plug wires, spark plugs and coil

NOW DONE:
- remove and cleaned DME relay, re-installed
- no condensation in distributor cap, has now been cleaned
- no visible cracks in cap (to be reviewed again)
- speed sensor resistance is ok to specs
- reference sensor resistance is ok to specs
- ignition coil resistance is ok to specs
- WD 40 in distributor cap

TO GO
- check and clean all grounds
- plug gap
- plug wires arching
- temp sensor resistance
- sensor connections to be cleaned again

As mentioned before, I am awaiting on a new DME relay but I now doubt it will help me. Thank you all for making some more suggestions / possible avenues to further explore to solve issue.

[davemath]

Your car was inside, but don't forget the CIS intake gaskets on top of the cylinders for those of you that park outside. These are paper and can fail from moisture then allow water into the combustion chambers, which then cause a nice water/fuel mixture and can also pit your cylinders.

[JCFL]

1986 model - no CIS. Thanks.

[almostordinary]

May be worth looking at.... I just got my 3.2 motor for my build and am finding a lot of small things that I need to replace/repair.

One such thing was a broken clamp on the back bottom portion of the airbox, the second I saw that I knew I needed a new unit, I could see water/moisture getting in there on wet drives.

May be worth looking at while you're digging around for solutions.

-Ian