Misfire after storm

[ejp]

(Disclaimer: I'm still pretty new to 911's, but know just enough to make me dangerous...please excuse my ignorance.)

My '88 Carrera endured sitting outside during Hurricane Sandy here in the DC area. No biggie, just some rain and wind (I was quite lucky, considering what others experienced in the northeast). I drove it to work today and noticed that it was missing under low RPM load and a little under idle. It seemed to clear up a little as the car heated up, but it was still missing a bit.

It seems very likely that there is some moisture causing ignition problems in the engine compartment - the interior is dry, so a soaked DME is unlikely. What seemed most obvious to me was the distributor cap. I popped it in my work parking lot and it was bone dry. I ran a dry rag over it just in case, and no moisture. It started right up and it sounded better. Idle was smooth, but still a little stumble here and there as I revved the motor.

Working logically, next up for me are the ignition wires. Does this make sense, or should I look elsewhere? I saw nothing specific in the service records to indicate if or when the wires were changed out, so this is definitely a possibility. If wires are the culprit, are there any recommendations for wires? (OEM-style Beru vs Genuine Porsche vs Magnecor, etc)

More importantly, since my knowledge is limited, what am I overlooking?

Are these cars typically susceptible to moisture? This was an unusual amount of rain and wind - and the car has previously performed flawlessly while driving in heavy rain. Should I just chill and wait for things to dry out more before throwing money at this or, is this a sign of something that perhaps needs to be tended to sooner rather than later?

[twistoffat]

Give you Dizzy a clean. With all that rain possible the Dizzy Cap got some moisture in it.

[DRACO A5OG]

Definitely look under the distributor and dry it out if needed. Use Bosch dizzy grease to make a tighter seal when the cap is on. The Bosch grease is a high temp grease to help keep moisture out of the dizzy.

When was the last time you had replaced the Fuel Filter?

Better yet, take her for a long drive to completely dry her out and give her an Italian tune up, when she is up to optimal running temps 194F .

If you are going to leave her out in the pouring rain, you may want to consider cover the engine vents. Just my 2 cents

[Craig_D]

Originally Posted by DRACO A5OG

Better yet, take her for a long drive to completely dry her out and give her an Italian tune up, when she is up to optimal running temps 194F .

Being Italian/American, I resemble that response. When you're done, get out with a grin, get an espresso and say loudly "She's-ah running-ah fine-ah!"

...you might want to also check the air filter to make sure it didn't get wet with the blowing wind...and to make sure something didn't try to take shelter in your airbox.

Cheers-ah,

- CraigD

[ejp]

Originally Posted by DRACO A5OG

Definitely look under the distributor and dry it out if needed. Use Bosch dizzy grease to make a tighter seal when the cap is on. The Bosch grease is a high temp grease to help keep moisture out of the dizzy.

When was the last time you had replaced the Fuel Filter?

Better yet, take her for a long drive to completely dry her out and give her an Italian tune up, when she is up to optimal running temps 194F .

If you are going to leave her out in the pouring rain, you may want to consider cover the engine vents. Just my 2 cents

Thanks for the replies. I popped the distributor cap in my office's parking lot (yay, factory toolkit got some use) and checked underneath as well as on the rotor. They were both bone dry. I wiped it down with a rag just to make sure.

To answer the question about the fuel filter, the service records do not specifically indicate that the fuel filter has ever been replaced during the car's 168k mile lifetime. Then again, there are unspecified entries for regular service - but that neither confirms or excludes that the filter has been replaced.

The Italian tune up seemed to work. No misfiring after running good and hard for a little while.

Next time I have to endure a hurricane, I'll try to at least cover those engine vents. Better yet, maybe I'll have a proper garage by then

[emac]

You cannot see hairline cracks in the cap. Replace a few bucks. Also a little WD40 sprayed in the old cap will take care of your issues. Replace the cap
Ernie 81 sc

[audi]

Originally Posted by DRACO A5OG

If you are going to leave her out in the pouring rain, you may want to consider cover the engine vents. Just my 2 cents

I used to do this before I got my garage completed - I had similar symptoms to what you describe, and covering the engine vents helped. I had checked the dist cap, too, and it always looked dry.

I ended up replacing the cap, rotor, and original plug wires anyway later on, and haven't had a wet start problem since (but garage is now done and the car hasn't sat out in a year).

[boba]

I had a similar problem with my 356, one rainy evening I was working on it in my garage when there was a lightning strike and the power went out. Dark garage and the most gorgeous St Elmo's Fire in the engine compartment.
A new set of plug wires and the miss was gone.

If the humidity is not very high spray a fine mist into the engine compartment, running with the lights off. It could be your answer.

[EMJ]

Apply Permatex dielectric grease to the dis cap spark plug connection points, and to the inside of each plug boot connected to each spark plug. Had the same issue, applied this grease, never had the issue again.

[Craig]

I would also check and make sure the connections at the coil are dry, seeing as how it is right up there close to the engine vents.
Craig

[larrym]

similar problem - just happened after driving in storm in Reno 2 days ago - '89 3.2

- misfire under load only - in higher gears, when pulling at 1500-2500 rpm

no misfire at idle, nor when free revving

- injectors tested & OK

cap & wires & dme connectors all DRY,

cleaned cap inside with electramotive & checked wires for spacing but no change

no evidence of wires crossfiring in the dark

more ideas ???

[dentist90]

When another car of mine missed under load it turned out to be a plug wire. A fault can be very hard to spot... it only takes a small crack in the insulation and the current can go to ground, say on your fan shroud, and you won't see a spark. Even harder to find burn marks on black wires. The other likely possibility is a weak/fouled spark plug. Hope it's something simple like this.

[DanielDudley]

Check your plug gap. If you don't know how old the cap rotor and wires are, replace them.

You have sensors that read the rotation of the flywheel, check and clean the connections. I suppose they could fail in such a way that they would have a harder time at higher RPMs, and I have seen some types of pickups fail in that way, but not on a Porsche.

It takes more spark to fire the mix at higher rpms. It is still a misfire, but it is from weak spark rather than no spark.

[larrym]

tho't about this more today - 1. the wires & cap are oem (maybe 80K miles on 'em) & cap has a bit of carbon/dirt residue showing inside, (fyi plugs are recently new & correctly gapped)

2. add a little moisture, and some carbon-based grime on the old oem parts

3. put the plugs under severe cyl pressure load at low rpm and with much throttle opening

= PREDICTABLE RESULT = voltage tracking wherever it can more easily go instead of across the plug gap under high cyl pressure, and once those tracks are laid in the damp grime on old parts, my experience with oldtimers says new parts are often the only good answer

today - nice dry hot day so it had a chance to dry out on it's own - ran the thing a few miles up to full temp

- also did today - pulled back all the boots, sprayed all the secondary stuff with wire dryer, cleaned up the inside of the cap as best i could,

again ran the thing a few miles up to full temp;

RESULT - it's not misfiring much anymore - still stumbles a bit on "tip-in" pulling uphill at lower rpm in 4th-5th

- will buy a new cap (have a better/newer used one on another engine, but why bother swapping)

I still need to ohm-test the old oem wires & plug ends - will order a set of 3.2 magnecors if the oem's test sketchy

(... have a near new set of 2.7 magnecors but they won't fit the cap)

note to self: Build a portable, quick-setup "rain cover" to throw over the engine & dizzy just in case i ever get caught in a downpour storm again

... so it goes

Originally Posted by larrym

similar problem - just happened after driving in storm in Reno 2 days ago - '89 3.2

- misfire under load only - in higher gears, when pulling at 1500-2500 rpm

no misfire at idle, nor when free revving

- injectors tested & OK

cap & wires & dme connectors all DRY,

cleaned cap inside with electramotive & checked wires for spacing but no change

no evidence of wires crossfiring in the dark

more ideas ???

[wacko]

I had this same problem earlier this year. Replaced the spark plug wires and it fixed it completely. I went with magnacore.

[larrym]

an update - replaced the cap & rotor; wires & connectors all tested good - per spec

runs perfectly again !

and I built myself a rain cover for the dizzy that packs away under the trunk carpet