Melchior

The o-rings he is referring to are attached to the spark plug tubes. The tubes are inside the cylinder and are what the spark plugs slide into. You can remove the tubes by first removing the spark plug and then popping the tube out. Some people have come up with interesting methods to do this, the best way I found was to gently twist the end of a small rubber-handled screw driver into the tube and then pop the tube out. The tube has o-rings on either end. You may also have a crack in one of the tubes since they are plastic and can get cracked if the spark plugs are inserted abruptly at an angle.

htny

if it is good at higher RPM, it really screams coil pack to me

do a code test, it will tell you which cylinder is misfiring (if any) and you can then inspect that coil more extensively for cracks or wear

JCF

I have some news.
Yesterday, my father drived the car to his job because we planned to make a default code read during the afternoon. When he arrived at his job, the 996 was running very smooth. We test the quick full load at idle, there's always a noise but not the misfiring like before (I think the noise is a flap or simply the air acceleration in intake). Today, the car is still working well, the problem seems to be fixed, and we don't know exactly why...
Maybe the "learning" is complete by the DME (after a bad learning with bad plugs given by a BAD SUPPLIER), but we drive the car more than 50 km and for about an hour, and it would be a long learning.

JCF

Since this issue, I changed a coil which the resistance was different from the other ones, and after 30 minutes of running, the car was running as good as before.

Some news :
I don't drive the car enough to keep the battery power (winter) and then, it was down when trying to start.
Ok, disconnected it, pluged the charger for some hours. After connecting the battery again, the car start but my misfires problem came back !
After some minutes of running, the Check Engine Light lights up. I plugged my OBD reader which shows me 4 codes :
- P-0318
- P-031E
- P-031D
- P-031C (not sure, just remembering)

The P0318 gives a "rough road sensor". I don't have a PSM, and even, no link with the misfires. I don't know what P0318* are.
So If I replaced the 0 by 1 (for specific manufacturer codes), I read P1318 for the first one, and it could be a Misfire at the 6th cylinder. But no result for the other ones.

What do you think about it, and these codes ? (before removing the coils, especially the 6th).

Pac996

I'd just replace the sparkplug wires. Normally a person doesn't know these parts wear out too. It is even a higher likelyhood of a faulty wire after messing with it after it sat in the same position year after year getting baked. There are a few types of spark plug wires. Plain wire, exotic carbon filled tubes and maybe a couple other varieties. Any of them flake out. If you or anyone else pulls on the wire section instead of the hard socket its asking for trouble. It's pretty much the same thing as yanking the wire if you pull only the plug then bend and stress the junction. Did I mention I believe in replacing spark plug wires every few years since they carry a very important part of ignition?

Plainly if you installed correct plugs for either cold or hot weather it shouldn't be running rough. Most likely problem is the spark plug wires. If they have never been replaced...............

JCF

Ok, but there's no High Tension wire because of the "one coil per plug", so what do you mean by "spark plugs wires" ?" The harness ?

Pac996

Yes the individual wires for each spark plug.

JCF

I tried 2 other softwares to read the DTC codes. Seems the yesterday one shows wrong codes as the new codes are these :
P0300 - Random/multiple cylinder misfire detected
P0304 - Cylinder 4 misfire
P0305 - Cylinder 5 misfire
P0306 - Cylinder 6 misfire
They don't appear at cold idle, but when some rpm are reach (but the engine is still rough at idle).

So what do you think about it ? I often had misfires problem when disconnecting/connecting the battery.
Lambda sensor ? ECU (hope no...) ? Variocam coil ? Wires eaten by mouses ?

ivangene

hold on there... this has been a year and a 1/2?


have you driven it during this time?

Macster

If a car has sat a while unused and the engine acts up, runs rough, and just generally misbehaves for no *apparent* reason, if there are any electrical gremlins then rodent damage is always a possibility.

A thorough inspection of the car's interior spaces and under the car on top of the under body panels for any signs of rodent nesting material or droppings, etc. is called for.

Another possibility, if car has sat outside, is water has gotten into the cabin or some interior space (inside the door) and is causing the symptoms.

Lastly, there was one case where one cylinder bank was generating misfires and the problem turned out to be a MAF. You can disconnect the MAF at the wiring harness and run the engine, normally, and see if the misfires reappear.

If they do not then the MAF becomes the likely suspect.

I do not know why a failing or bad MAF would generate misfires on just one cylinder bank but at least in this one instance it did.

Sincerely,

Macster.

JCF

After running the car several minutes after my first problem, with the correct plugs, it disappear and the car runs perfectly after for some month. But this rough idle occurs one more time between today and my first problem. After checking the coil resistances, one were different to the others. After replacing it, as the first time, after a little road test, all was fine.
The car is parked indoor, and safe. I was joking about the mouses but obviously, I visually checked plugs and harness. I didn't think that the MAF fails because I would have not only problems at the right side cylinders. I also checked the value measured and it increases as I push the throttle. The air temperature seems also to be fine.
Car running, I checked the O2 sensor values : one changes during throttle actuation, other one stays at 0. I will checked futher about it, but maybe is there my problem. I will let you know.

Thanks !

dallison28

mine too, i thought that the harness "clicked" and it didn't. ran the codes and fixed it.

JCF

I made some tests today.
At cold, my two 02 sensors are working. But when the engine gets hot, one drop to 0 et stay (it seems that it indicates lean mixture, but somes sources gives rich mixture...). So I tried to unplugged this sensor. Starting the engine, and... absolutely the same. Plugged it again and try to unplugged the MAF, same same same... Ok, according to the behaviour of the value of the 02 sensors and the fuel trim, I think the ECU "remember" the last x minutes of running for making it's modification. I also think my two O2 sensors are OK.
So I disconnect and connect the battery again and start with MAF uplugged.... the car run smoothly, even when actuating the throttle. Of course, it's not perfect, but it's better. After I plugged it again and, as before, the engine runs very rough. After connecting, the fuel trim and lambda were more and more bad, then returned to 0. When plugged, the air flow is about 6 g/s at idle (if I remember), and grows as I accelerate. Does somebody know the correct value ? The intake temperature shows -40 (or as disconnected) when ignition on but engine off and shows around the ext. temperature, not quickly fluctuating but increasing slowy as the engine heats. I think it's just a correction which measure the air warmed by the engine compartment. So the MAF seems to works properly...
I must notice that since this battery disconnection, the CEL never lights again. Worse, the car never give me a fault code for the MAF or the O2 sensor unplugged...
I don't know what to trust in all these measurment.
That's all... for today.

Macster

If O2 sensor voltage reading drops to 0 exhaust gas oxygen cotent is higher than ambient air oxygen content or sensor tip is too cold (below 575F (300C).

(The sensor only generates a voltage if ambient air has higher oxygen content than exhaust gases and the sensor tip is above 575F.)

If O2 sensor voltage reads ok then drops drastically this suggests a problem with the 02 sensor heating element.

Unplugging various sensors even O2 sensors may not produce an error code right away. The engine controller require time in closed loop mode to be able to complete all tests/checks before it can flag an error.

There are tests one can do to verify the O2 sensor's heating circuit is working properly and the sensor is seeing the proper voltage to its heater circuit.

Sincerely,

Macster.

JCF

The sensor shows voltage at engine starting, then drop to 0. The 0 voltage increases when I unplug the MAF. I tried to hold a 2500-3000 rpm during several seconds but nothing changes.