Misfire Cylinder #3 AGAIN! It's a full time job

hollywood953 · Post by **hollywood953** » 04 May 2010, 14:37

As I last left you fine gentleman I had a misfire on cylinder #3 so I did the logical thing. I replaced the plugs (6) with new Denso plugs and replaced the coil pack on that cylinder. Well, you guessed it! It's back. Same code, same cylinder. I have read a few threads talking about everything from vacuum hoses to cam position sensors but none of them sound like this. FYI, I bought the 1996 960 in May and the service records show that coil pack being replaced before I got it. So now it's on it's 3rd one. Please help! I don't have any electrical testing tools but will get them if needed. Thanks
ps.. the problem is intermitent, it's fine right now, later tonight it will start missing.

Post by **billofdurham** » 04 May 2010, 15:49

ps.. the problem is intermitent, it's fine right now, later tonight it will start missing.

Is there a reason why you think it will start missing tonight? Does it do this in particular weather conditions or does it occur more frequently when the temperature is lower and possibly the air has more moisture in it?

The ignition coils and the wires to them are under the cover. Have you checked the wires to #3 cylinder for breaks in the insulation? This has been a problem on other cars with the wires trapped in an area of high heat.

As for electrical testing tools the most important one is a digital multimeter. With this you can check the resistance of components, which is a good indication of their state of health, and both AC and DC voltage. You don't need to spend a lot to get one. My last one was bought about 2 years ago for the princely sum of £3.99 which is about $6.00.

Bill.

Post by **JDS60R** » 04 May 2010, 15:59

Hi,
Sorry you keep having to go back to this. Maybe we can go outside the box on what is causing this.
Heres a few questions if you have the time. Once you have put in quality parts the problem shoudl have resolved itself. There are a few other things like a pinhole in the head gasket that can cause this type of annoying random issue and I was hoping to rule them out with these questions.

Did you get a chance to look into the cylinder #3 when changing the plugs?
Did the piston top look very clean and gold colored or flat black?
How about the rest of the cylinders?

Do you have the old plugs and can you post a pic of them?

My hope is that you find a worn/shorting wire on cylinder 3 like BIll suggested.

Best Wishes

DanR · Post by **DanR** » 04 May 2010, 16:28

Try swapping the front and rear power stages. If is a bad power stage then it will move to a different cylinder, one with an even number.

Check and make sure the pre heater valve door is set for cool intake air. It is located below the air filter. They can stick in the pre heat position and cause miss at idle, also will cook the MAF over time.

DanR '94 964 350,000 miles (116,000 on the new engine)

hollywood953 · Post by **hollywood953** » 04 May 2010, 19:13

thanks for the quick replies fellows. I will try to answer in order.
Bill, thanks so much. I guess I am being pessimistic because my wife has been telling me it does shudder every once in a while. Last time this happened i changed the plugs and the problem went away then came back. It ran fine yesterday until I pulled it in the garage and it did it again. The wires to the coil on #2 #3 #4 look a little stretched or tight and I can see the yellow and red wires but I don't see the insulation broken. As for the temperature, the first go around was in the winter (it get's around 20 F) here and this time it's 85 F. I will definitely get the ohm meter.

hollywood953 · Post by **hollywood953** » 04 May 2010, 19:20

JD, I used an OEM coil pack and Denso plugs. I used auto lite at first and the local Volvo man slapped me in the face and made me get Denso. Do you think these are ok? I do have the old plugs but they all look the same to me. I did not look at the pistons. Should i do so? The air box thing is new to me. I read about the pre heater but didn't quite understand what it does. To be honest I have never worked on a computer driven car. Can you tell me how to check it? I have read that some guys prop this in the open position at all times. Is this ok? Lastly, when the car it at it's worst i smell gas, like my truck when the choke it stuck. Is there a way to check the injectors? Locally the are $186 each (that hurts)
Thanks very much for your time.

hollywood953 · Post by **hollywood953** » 04 May 2010, 19:23

Dan, sorry I got your question with jD's. Where is the power stage and how do i changed it? I took the cover off of the middle of the engine. Should I see it there?

Post by **JDS60R** » 04 May 2010, 19:44

Good,

If you happen to pull the #3 plug please let us know what the cylinder top looks like. As for Denso's being right I will let one of the others chime in. I would use stock plugs but am usure what was stock on your car.

If you ever need an injector go to www.fiveomotorsports.com The owners is very much on top of things and he sells discounted, balanced sets as well as single injectors. ( who could ask for more). When I was modifying cars and bikes this is where I went and ended up very satisfied.

In order for it to studder you would have to have bad or no spark or its running way to rich or lean.
If the piston top is black I would start with cleaning the MAF with MAF cleaner when it is cold.

If its gold then we need to check for a pinhole in the head gasket.

hollywood953 · Post by **hollywood953** » 06 May 2010, 18:50

OK, so I added some Lucas injector cleaner and the check engine light went off and stayed off. While cleaning the MAF sensor I noticed a small tear in the film. It's about as wide as a hair and about 2 mm long. Can this be part of the issue? I don't want to give up just because the light went off. Any suggestions?

danr960 · Post by **danr960** » 07 May 2010, 17:05

At first I would think so, but with your symptom being only at the number 3 cylinder, no. You would have poor idle and overall running on all cylinders if it was the MAF. One test for a MAF is to disconnect it and run the engine, if the MAF is bad it will run better with it not connected than with it connected.

DanR