MissFire Cold Weather Only?

[JayRolla]

I was having problem with misfiring at about 6k rpm's after I swapped some new MSD and NGK plugs gapped at .028. That day I did the swap was our first day under 40* and it missfired for the next few days.

As soon as the weather warmed up the missfire is gone. What would cause this to happen. Im running 12psi with a spike to about 14 so im pretty sure its not fuel cut, but it does seem to feel like it. Some times it would miss real hard like fuel cut and others it would hesitate. What would cause the cold weather to make me misfire at high rpm?

Jason

 

[spyderturbo007]

I'm guessing that you can't swap back and see if that takes care of the problem?

 

[JayRolla]

I have, it only missfires in cold weather. Works great anyother time as long as its 40* or hotter. Thats with my old wires or new. Gap is at .026 and it still has a slight missfire at around 6k rpm only if its below 40*.

 

[Dsm78]

It is still possible that you are hitting fuel cut. The air is denser when it is cold and you will pull more air. I have that problem with my car @ about 6k and 16psi but hopefully a fuel pump rewire will help.

 

[spyderturbo007]

Have you taken a look at a log? As Dsm78 stated, the colder it is, the denser the air will be. It could also be that the ECU is severly pulling timing in that area. A 3 or 4 degree timing drop at higher rpm's will feel pretty nasty.

You should be able to tell a significant difference between fuel cut and a misfire.

 

[JayRolla]

Oh I know the difference in fuel cut. Im pretty sure its a missfire because it miss's hard but not as hard as fuel cut. Fuel cut is like a brick wall. I have no knock on my log and the timing pulls to 24* and holds with no dips.

It is still possible that you are hitting fuel cut. The air is denser when it is cold and you will pull more air. I have that problem with my car @ about 6k and 16psi but hopefully a fuel pump rewire will help.

Fuel cut is a madder of overreading the maf not how much fuel you have. The pump rewire will not fix it at all. You need a maf that can read more air like a 2g or evo. You cant fix it by adding fuel at all.

 

[spyderturbo007]

Actually, fuel cut occurs when the ECU "sees" a preset airflow value. Increasing the flow of the MAS will not change the airflow value at which the ECU cuts fuel.

Anyway, back to your problem. Hummm.....with no knock and solid timing, I guess we can rule that out. Do you get this type of log even when you have the misfire problem? You should see something in the log that would reflet the misfire.

Are you sure it's not mechanical?

 

[JayRolla]

Actually, fuel cut occurs when the ECU "sees" a preset airflow value. Increasing the flow of the MAS will not change the airflow value at which the ECU cuts fuel.

Yes and adding fuel will not do anything. Swapping to a maf that has a higher preset airflow value will correct his fuel cut. Not rewiring the fuel pump.

I do need to log in cold weather to see what is happening and what do you mean mechanical?

 

[nightspeed87]

i thought you had a keydiver chip, that would push back fuel cut if you told jeff to set it up that way.Also, since its colder your actually going to run richer ( on stock ecu at least ) could be fouled plugs. See if your car is even leaving warm up mode when its cold like that, because that also tells the car to run richer.

 

[spyderturbo007]

I do need to log in cold weather to see what is happening and what do you mean mechanical?

Post up the log when you get a chance. By mechanical, I mean something that's broken.

We can explore this more in depth if we can get a log of the problem. But you know how that goes, as soon as you hook up your logger and it's cold out, the car will run fine.

 

[JayRolla]

We can explore this more in depth if we can get a log of the problem. But you know how that goes, as soon as you hook up your logger and it's cold out, the car will run fine.

yea I can see that happening. Our weather is warm again of course, but it should cool down soon. I dont think its mechanical, because I have new plugs, wires, coil, and transistor.

i thought you had a keydiver chip, that would push back fuel cut if you told jeff to set it up that way.Also, since its colder your actually going to run richer ( on stock ecu at least ) could be fouled plugs. See if your car is even leaving warm up mode when its cold like that, because that also tells the car to run richer.

Nope, no keydriver chip. Also I dont like to turn off my fuel cut, because its there for a reason. When I get my dsmlink and 2g maf installed Ill be fine but I know this is not fuel cut. Expecially at 14psi with no boost leaks.

 

[Dsm78]

Yeah about that miss at about 6k... It turns out that my 16G Evo III is boost creeping up to about 22psi. I am going to either port the exhaust inlet side of the turbo and go with a 34mm flapper or just go with an external waste gate and weld the internal shut.