Peter R.

After my wheelchair adventures I finally got back in the 993 today. The weather is utter crap over here, but after six weeks of inactivityI fitted the new AGM battery yesterday evening and fired her up. She sounded a bit rough, but started up immediately. So this morning there was a bit of protest, and I had to blip the throttle but off she went.

Drove her to work, but upon arrival I noticed there was a misfire in the exhaust note.

I hope all will be well tonight after she's had a chance to dry out, but I'm a bit worried.

Could it be a spark plug that's gone off, or do we suspect something worse is afoot ?

Peter R.

Peter R.

Update

Got away early at work, 't was still light. Difficult starting, but it fired. Stopped on the corner to make a turn. The smoke was horrible. You used to see these Rumanians here with 25 y.o. 200.000 mile third hand Lada's thatdidn't smoke that hard.

Misfires wile driving. Got on the motorway and it cleared up, pulling returned. Added 10 gallons of fresh 98. Hope it goes away.

Peter 'mild panic' R.

Peter R.

No one ? How bizarre...

Peter R.

Garth S

Peter,
Glad you retired the two wheeled chariot .
Re. the four wheeled one, perhaps the first thing to confirm is that the distributor caps are dry inside .... and have not developed signs of arcing/'tracking' from moisture that was likely there. Similarly, check the connections to the two ignition modules - and refresh with dielectric grease if confirmed bone dry.

Fred's 964

You might want to make sure your dual distributor belt didn't fail. That could cause the misfire or much worse. Do a search for more info.

Peter R.

Okay. I know what to do...thx !

Been running diesels for the last 10 years...neet to bone up on Otto engines ;P

Peter R.

Peter R.

Well, there's news.

Saturday I decided to take her out and not come back 'till I sussed what's going on. And I did just that.

It's overfuelling. In olden days, Porsches had this extra injector that added fuel when very cold. I suppose all this is now taken care of by the air mass flow sensor.

So either this is on it's way out, or there's some other gizmo that's palying up.

I've been looking through the parts list, but haven't come up with a suspect yet. Tips welcome !

Peter R.

c993k

What's the weather like where you are? If moist, you should examine your spark plug wires.

FotoVeloce

OK. I know this is sort of 'out there' but did you fill UP the tank with fuel.. like all the way? Sure.. why not, right?

OK. so I bought thist 964. The next day it ran like complete trash when you put more than 3/4 of a tank of fuel in. Sometimes, smoke, sputter, stall, lose power.. not fun.. especially if you forget to tell the guy to STOP at 3/4 when he's filling it up.

To make matters worse.. mine got so bad fuel was dripping out of the eval canister in front of the left-rear wheel!

Turned out that is was a failed check valve on top of the fuel tanks expansion chamber. Replaced that and viola.. all is right with the world.

Just tossing that out there.... I was when I thought the 964 had gone TU 1 day after purchase..

Good luck, and congrats on dumping the 2-wheeler!

Peter R.

Been pissing down for weeks !

I checked the wires on the distributor end, everything very clean that side. Can't say for the other side. I'm picking up a spare air flow meter for testing purposes. I'll see where that lands me.

Peter R.

JasonAndreas

The cylinder head temperature (CHT) sensor controls the amount of extra fuel used during startup and warmup. You can read the sensor output/resistance with a multimeter if you don't have an OBD tool (hammer,PST2,DougB).

Gbag

I am not sure what year you have (OBDII?),l but if it is throwing the misfire code it can be a little tricky to track down the culprit. I did the search and followed a few tips which resulted in good luck-

My plugs and wires were fairly new, so I felt safe to leave those alone other than checking all the connections as best as possible.

After that I put new distributor caps/rotors. Also put a set of new PORSCHE OEM belts on. I had read about this and it was also a topic of conversation I had with a trusted dealer mechanic.

It did the trick. No more misfire codes- passed smog. All is well.

Good luck and search around. Should find a handful of other parameters to guide you to success.

G

Peter R.

Although a very good tip, it's overfuelling on both banks (same amount of ugly smoke out of both exhausts).

I'll take apart the distro caps this weekend, if that doesn't show anything I'll try and sort out a spare massflow.

I'm pretty confident it's humidity related.

Thanks and keep 'em coming

Peter R.

GabiOsz

It could possibly be the O2 sensor on the catalitic converter or the MAF sensor. The O2 sensor is a fair bit cheaper than the MAF, and I believe that some have had success with cleaning the MAF sensor with PCB cleaner. Incidentally what air filter are you using?

If you want to test the distributer belt, with the engine off, unplug the wire from the ignition coil to the primary distributer, if the engine starts then the belt is in tact.

JasonAndreas

I don't think your problem is CHT related but you wanted to know what the current day equivalent was of the cold start injector. The DME control unit uses the temperature reading from the CHT to increase the opening time (i.e. add extra fuel) of all the injectors.