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Random misfires only at idle

N

Nchristopherson

New member
I figured I would start a new thread for this since the old thread is irrelevant.

OK. So I did a camshaft swap on my car. Did the VS cam with SD Headers and a 3.4" pulley. I also replaced the front cover gasket, SC gasket, and LIM gaskets with the aluminum ones. New Autolite 104 plugs and OEM wires. I have not tuned the car.

When I first start the car, the misfires aren't bad, hardly even noticeable if any. Once it warms up, they start to become much more apparent, I can hear the car stumbling. Using Torque, I got the number of misfires for each cylinder, and cylinders 3 and 5 have by far the most misfires. 1 and 4 misfire very seldom. 2 and 6 not at all. Codes P0300 and P0305 (Random misfires and Cylinder #5 misfire) get set eventually. However, when the car moves, I get no misfires at all that I can account for. My OBDII software does not pick any up, the power is smooth and plentiful, and it doesn't set any codes.

Things it could be due to? :
Because the SD headers relocated the front O2 port, I did do a chop job on extending my O2 sensor, but it reads a full 0.1 to 0.9 volt range.
The car sat for 4 1/2 months and the fuel filter was changed 30,000+ miles ago. Possibly bad fuel? But again, the car has great power.
Leaking LIM gasket? God I hope not..that would be depressing.


Solutions attempted:
I tried to re-seat the injectors with lubing the o-rings and a rubber mallet, but that didn't seem to help.


Ideas:
Change the fuel filter
Do a compression test to check for just that
Fuel pressure test
Injector cleaner


Any information would be extremely helpful. Thanks.
 


Question. Could a faulty front O2 sensor cause misfires at idle? Here's my reasoning:

Because I got SD Headers, I had to extend my front O2 sensor. Instead of being intelligent and buying an extension from ZZP, I thought i would solder in an extension myself. Well, the wires are steel, so soldering wasn't gonna happen. Instead, I twisted the wire pairs as tight as I could, lubed them up with some dilectric grease on the outside, and heat shrinked them shut. Yes, rigged as ****.

Now I am thinking the O2 sensor is giving an artificially low reading because of the added line resistance, which is telling the PCM that the car is running rich. As a result, the car is leaning out the mixture, causing misfires at idle when the car is in open loop. When I drive, the car goes to closed loop, disregarding the O2 sensor. As a result, absolutely no misfires.

I will try replacing the O2 sensor next if misfires at idle can be a result of a faulty one.
 
Scottydoggs said:
re do the 02 extension with wire, solder and shrink tubes. a solid wire and no solder at all is not gonna work well.
Click to expand...


So the added resistance could be a culprit of misfires at idle? I'll go ahead and re-do it.


Also, if there was one gauge you could buy, what would it be? I'm thinking buying a wideband O2 or an AFR controller (until I have tuning software).
 


the whole way its connected is a problem. like you said rigged lol lets un rig it and make it right, see what happens.

id try to match the wire size too.
 
Scottydoggs said:
the whole way its connected is a problem. like you said rigged lol lets un rig it and make it right, see what happens.

id try to match the wire size too.
Click to expand...

Unfortunately, unrigging it is not that simple. I am fairly experienced in electronics and soldering, but steel wires do not accept solder at all, even with flux. The only way to un-rig it would be to buy another one and buy an extension. Got any ideas on bonding steel and copper wires together?
 
butt connectors but use the crimp tool so its good and tight, then add shrink tube over it. make sure your using the right size butt connector for the wires too.

if you can tug on the connection and it pulls a part it was no good to start with. good test before you shrink tube it.
 
Scottydoggs said:
butt connectors but use the crimp tool so its good and tight, then add shrink tube over it. make sure your using the right size butt connector for the wires too.

if you can tug on the connection and it pulls a part it was no good to start with. good test before you shrink tube it.
Click to expand...

Wow. I wish I had known about those, they look like they'll work no problem. Thanks for the help, I'll return with results later!

P.s. - Did you happen to see my question about a second gauge?
 


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