Well I will start I am new here and am not a Camaro owner but please don't hold that against me because my truck is TBI. I have been recommended by quite a few other people to post here because of the vast knowledge you guys have of throttle bodies. Well this is my truck, its a 92 TBI 350 and has a performer intake and Edelbrock TES headers, dual exhaust, filter and small ignition upgrades. The truck ran great until I had it repainted and then everything started. First it was popping out one tailpipe really bad and running like crap. I fixed that by rebuilding the TBI. Now it runs pretty good and has lots of power but stil gets horrible mileage compared to what it used to. At idle cold it spits black out the tailpipes indicating to me it is rich which disappears as it warms up. The mileage is at 13 mpg when before it used to get around 20. The O2 is only 6 months old and I figured maybe it was damaged when the truck was running really rich( the popping thing was a combination of the base gasket and the regulator) but without hooking the truck on a scanner it is hard to tell. The motor is in excellent shape, good compression and whatnot, but the mileage sucks. There are no codes. The truck does warm up slowly however it always has since new and it never affected mileage in the past, and neither did winter. I am running a 195 stat and a winterfront on teh truck and cruising it runs about 70-80 degrees C. I have access to a Snap On scanner and am going to check O2 crosscounts as well as open/closed loop operation but I wanted some other ideas. Sorry for the long post but I hope someone can help me with this, Thanks.

 

Only thing I can think of is a small Vaccum leak. I may be wrong, but its all I can think of. I'm sure someone else here may know of something else.
Good luck,

Minion

 

I again tried finding a vacuum leak and it seems to have none. I checked everywhere with the good old can of carb cleaner and I have found nothing. It has to be something else, I don't know if the IAC can cause everything wrong with it but I think it may be partially at fault or maybe its just the O2, I will have to find out.

 

Sounds like your on the right track with the O2 sensor. It may be coated with crud from running poorly. There fairly cheap, probably woulddn't hurt to change it anyway.

Steve

 

what about the coolant temperature sensor? If you unplug the sensor the car will run rich. I unplugged mine (on a car i no longer own) and the car ran so rich it smelled like I was pumping gas in the car. The O2 sensor would be my next guess. If it is reporting back bad readings the car will run rich and the mileage will go down the drain.

 

Definatly use a scan tool or better yet log the data with winaldl.
Exhaust leaks before the o2 sensor, actual o2 sensor, CTS sensor, MAP sensor (or vacuum leak, one in the same basically), or maybe even a IAT problem.

 

I should be able to scan it tommorrow finally. I have a scan tool i can use but don't have the windows program. I will post what I find and hopefully fix it's problem, and the btw the headers do not leak. Also I don run my air cleaner lid flipped however this is the 2nd or 3rd winter it has been that way and that has never mattered and this is too severe for that so I don't think the IAT is affecting it much. Definetly CTS, MAP or O2 hopefully.

 

Well scanned the truck and everything looked normal except the O2. It kept kicking in and out of closed loop all the time and had basically no crosscounts. New sensor and it stays in closed loop and the crosscounts are low from what I want to see but i will see what mileage does. The truck runs a lot better and cold starts seem to show no more trouble but tommorrow will really tell.

 

how does the vacuum hose from the tbi to MAP sensor look? I just installed headers on my TBI and I broke the vacuum tubing that goes between the two. My service engine soon started right up. I went home and replaced the tubing and the light went away. I want to say something that is not related to this subject. I pulled the EECS, EGR, and AIR crap out. I plugged every vacuum hose up and had the cat AIR piping welded shut. I dont get the code 42 when I'm cruising on the freeway. After I reconnected the map to the TBI my service engine light has not returned. I thought that pulling that crap would make the ecm give up a code 42?!

 

Tube is fine and like I said it has no codes, I think it might be fine but I have to drive and see what my mileage is.