CJ:

I'm way out of my element here, but I think your guy may be talking about adjusting the sensitivity of the "scanner" and not really modifying the sensitivity of the ECU to detect a misfire.

If you do find that your guy can adjust the sensitivity for detecting a misfire, that would be some info that could be very helpful to the forum.

Regards,
JS

 

How does the computer 'sense' a misfire? Is there a signal coming back from the coil to see if it actually discharged?

I'm sure if the EVO continually 'misfired' the motor would be ... rough? Or...this happens so rarely there is nothing to 'really' worry about?

Tanks,

jcnel.

 

JC:

It is certainly annoying. I'm sure you could live with it. But it is definately something I am going to find a fix for.

Regards,
JS

 

Why do you have DROVE on your avatar?

 

He totaled it. No more Evo.

 

No. The ECU monitors how long it takes for one revolution of the crank from revolution to revolution. A decrease in time from one revolution to the next that was not expected (i.e. not normal acceleration) means that there was a misfire.

Toyota had a hard time figuring out how to do this on OBDII manual transmission Supras because road noise was making it back through the transmission and making the crank rotation vary. That is why you could only get an automatic Supra for a year or two while they figured it out. The torque converter shielded the crank from the road noise.

 

Thanks Shape,

That's interesting because as a electrical engineer (with some background in signal processing) at 9000 rpm (assumed max. for the EVO), one would get a signal from the crank at 150Hz. (9000 cyclespermin / 60 secpermin). Anyways...a 100 rpm difference would equate to approx. 1.67Hz variation.

My gut feeling is this would be a hard situation to 'test' for in the computer, requiring a lot of engineering development, hence your Supra comment.

One would have to 'hold' the car under load for 'long' enough so that the computer can think it made a good estimate as to if the rpms 'should' be steady, increasing, or decreasing. If the sensitivity were turned up on this algorithm, I'm sure a good front gust of wind could cause a load wild enough for the computer to kick off a misfire error.

Its interesting to note also that some here have actually used the misfire code to check for sparkplug gap problems. Is that just happenchance, or is the misfire algorithm doing what it should be doing?

Hmmm...food for thought.

Later,

jcnel.

 

Are you getting the misfire codes at wide open throttle, or when you are just putting around?

With 2G DSMs, the misfire check (I have it turned off), is only performed under certain circumstances. Usually at steady cruise or at idle, etc... But never in open-loop operation.

 

If you're referring to me Shape,

I'm not getting misfires yet...but as I 'continue' to modify the EVO I may. To be prepaired as to what the computer is actually doing to determine a misfire, may help me hopefully treat, or ignore a problem.

BTW This is a great board, with really good expertise on hand!

Thanks again,

jcnel.

 

I just went to the dealership and they confirmed that I was getting the 0300 cel also. They installed some new spark plugs (correctly gapped this time) and wires. It has been about 100 miles since....no cel.

Symptoms= brief but random engine hesitation at various rpm's and load. But it mostly occurred while accelerating moderately in 5th around 75-85mph.

SC~

 

Just what mine was doing....so the fix was the plugs huh?

 

I may do the plugs and gap them, I have no had the error in a few days. I bet because I posted I will get it now

 

p0300s drive me nuts. I wish the xedeflash will get rid of them

 

I have only gotten one CEL in the 3000 or so miles I have put on my car since installing my Stage 1. It occurred exactly as SC described above. I went to Pep Boys and bought an OBDII reader/clearing tool and had the 0300. I thought I would probably get a bunch of CELs so that's why I bought the damm tool for over a hundred bucks instead of Autozoning it. Hopefully, it was a one time deal.

 

Sorry guys. The cel came back on this morning. So it was more likely that the dealerships clearing of the cel from the ECU was the reason it didn't come back on right away. But after the ecu did some 'learning' the cel came back on....and the stuttering....and the annoyance of knowing that I have a 10 month old car with an electronics problem.

SC~