I want to know how misfire detection works. I've been having trouble with my converter, becuase it won't lock when its over 150 degrees. I talked to Bryan at pcmforless.com and he told me that misfire detection comes on at 150 degrees, and when it detects a misfire, it will not lock the converter. That makes sense to me, does anyone else have any ideas? If my car is doing a misfire, i know in ls1's it flashes the ses light on and off. My car hasn't thrown a misfire code on the last time i've scanned it. Would it have to throw a code for the misfire detection to do anything? Or could it be picking up false misfires and thus not locking my converter? Thanks.

 

Your car will throw a code or flash the light when a misfire is detected. Several misfires are required before the PCM decided to NOT lock the converter.

 

the computer detects misfires using the crank position sensor. when there is a miss, the engine will slow down for a very very small fraction of a second. when the computer notices this slight drop crank speed, it knows which cylinder is not firing and causing the pulse. when there is a miss, the computer wont let the TC lock up because the pulse can put stress on the tranny and other parts of the drivetrain. when it's not in lockup, the TC absorbs the pulse, because the is no mechanical connection, only fluid connection.

 

Once a misfire is detected, will the converter not lock anymore until the code is thrown? Or will it lock after the car is turned off and then started again. I just can't figure out how it will lock when its under 150 degrees, and then as soon as it hits 150, it will not lock until it cools down under 150. The misfire detection seems the most promising, but now it doesn't sound too good . Anyone else have any ideas?

 

ttt!

 

Could you give us the symptoms of your problem? Any codes

 

Tranny and converter work fine when the tranny temp is under 150 degrees, converter locks and unlocks perfectly. As soon as the temp gets over 150, the converter will not lock. The car doesn't throw any codes. Right when I put the converter in, it did a tranny slip code, but hasn't done one since, and I heard thats common when the pcm is getting used to a new converter. Only code my car throws sometimes is a rear bank 1 o2 code, p157 i think. O2 sensor seems to be goin bad. Other than that, no codes. I can't think of any reason why the converter would lock when its under 150 degrees, then as soon as it hits 150, will not lock. If i'm driving when its cool, and the converter is locked, and the temp gets over 150, and I have to speed up and it unlocks, but then I let off the gas and it should lock up again, it doesn't. Makes no sense.

I just remembered, that the night we put the converter in, it through a couple codes. 2 were the p0100 and p137, which turned out to be from my o2 wiring hittin my headers, and shorting it out. Also, it did a P0719 Brake Switch Circuit - Low Input D *DTC P0719 will be stored in PCM history . Searched and found nothing about it, cleared it and it hasnt' come back since. It also did the p1870, tranny slip code, but hasn't thrown one since either. Anything in there that will help?

Something else I noticed, is that sometimes after driving it awhile, and it gets pretty hot, like around 200, it starts shifting really hard. Like I can be moving at 10 mph, slowly accelerate, and when it shifts to second, it can chirp the tires like a WOT shift does. Once the car cools off, its fine. Any ideas there?

 

There's an AAMCO on Broad St and on Laburnum ave. Take it to them for a diagnostic.