Leaner = cooler? Whaaaaaaa????

[Guest bastaad525]

Been fiddling around with my AFM some more lately. I had done a TON of adjusting on the AFM in the past, in the futile quest to get rid of my light misfire at idle, get rid of my super rich smelling exhaust, get some better gas mileage and throttle response.

 

Anyways, I've been running around with it set just two teeth... two-measley-gearteeth leaner than the stock setting for the longest time. That setting seemed to give the smoothest idle. Anyways, for some random reason I don't even remember, I decided last night to just set it back to the stock position, and see what happened. Well, first thing I notice is idle is a little down, secondly, the misfire is still there, and I can swear that it's actually more pronounced, louder than usual. Well, I drive it to work that way, and I notice that when I get on boost, the temp climbs FAST. I would get on it in very brief spurts on the freeway, and every time the temp would rise like two needle widths, a bit more than usual, and also unusual, they were taking way longer to come down if I just drove normally for a bit. My temps always seem to run a bit warmer on the freeway (about 1 needle width above the middle on the street, 2-3 needle widths at 75-80mph, I figure it's an airflow problem), and if I get on boost even for just a few seconds it will climb even more, up to about 2/3's of the full gauge, but usually come down pretty much right away once I get back on the streets, but this time, once I got off and drove the last couple miles to work, the temps took forever to come down. By the time I got to work and idled down before shutting off, temps were still a good 10-15 degrees higher than what I'm used to seeing when I drive this exact same route and pattern.

 

Well, I didn't really give that any thought, was thinking maybe I just got on it a bit too much or something I dunno. At any rate, I wasn't satisfied with the more pronounced poppity pop at idle (probably all in my head), so decided to try going the other way with the AFM. Leaned it back out to where I'd had it set before, plus one tooth (so now three teeth lean from the stock setting). After leaving work and car gets to regular operating temp, and I notice that a) the audible misfiring seems to be happening less, and less pronounced, BUT the idle seems generally lumpier.... whaaaat?? idle has also gone up about 50rpm, and the temp is hovering a little bit lower than usual for being on the street, right at the middle instead of one needle up.

 

Then I get on the freeway, and of course every time I get a safe opening, I gun it. Well I'll be damned if the temps were BARELY rising even after going WOT several times in a row, only up about a needle width. At it's highest point on the whole drive home, I estimate the gauge read ~20 degrees less than the highest point it had registered on the way to work. I was baffled and honestly delighted. And by the way the outside temp this morning was just about the same as it was on the way home last night, mid 70's.

 

So... does this make sense or is my guage playing tricks on me?

 

Something to bear in mind: I know for a fact my car runs pretty rich pretty much all the time. I've discussed it here many times... and the odd thing is it seems really happy that way. If I try to lean it out very much, it runs like crap. Also, I'm not sure how big a difference adjusting the AFM such small amounts makes in the a/f ratio but I wouldn't think it does much. Then again, from the stock setting, leaning OR richening it up much more than 3 gear teeth the idle becomes noticeably worse, so even a few teeth does make a noticeable difference, at least at idle.

 

So, does it make sense that leaning the mixture even a tiny bit, would cause the car to run much cooler like that????

 

 

One possible theory I have, involves the placement of the coolant temp sensor/thermostat housing, right above the exhaust manifold. I know I've read here before that running rich like this will cause your EGT's to rise... maybe my manifold is getting hot enough to affect the coolant sensors reading, and leaning out even a little bit lessened the EGT's enough to cause this? Or is the motor just running too warm from running so rich?