Scott Long
Registered User
My theory: colder t-stat causing my car to run rich and lose performance due to keeping the computer in closed loop mode almost constantly.
In my 92 SC I have a problem. Its nothing major, just that it runs a little rich and the gas mileage sucks. Now the CE light is off, never comes on, so its getting at least some sort of signal from my O2's. Granted my A/F gauge stays lean most of the time, its obviously in range enough that the computer is still getting a signal from them. Now when I replace them in a few weeks this will help me diagnose this problem.
I also have a 160 degree thermostat in my SC and the low speed fan constantly on w/ the ign. Around town the temp guage stays like 1/16" below the N. Car runs cool, has decent power (until the ic gets heat soaked), but the gas mileage sucks.
If I get on the highway and go long distances the temp ever so slightly raises up until it gets around the RM on NORM. It then seems to get much better gas mileage, like it seems to be about 8 mpg more than in the city (i always reset my trip meter when I fill up to monitor my mileage, just something my dad showed me when I was younger about keeping track of fuel economy.) Better on the highway but not where it should be like only 19 mpg. I do have 3.27's in this 5-speed, but still my friend w/ 2.73's gets almost 30 mpg constant at 80 mph. I followed him to St. Louis and I went through a tank and a half of fuel, he was on his first tank. Thats what led me to believe I have one or two problems, caused by one or two things.
Here are my thoughts:
I have been told time and time again that engine temp has no relation w/ the computer coming out of closed loop mode and that its based on a time limit rather than temp. I know that in closed loop mode the engine dumps a bit more fuel than normal and may even ignore the O2 sensors until its out of closed loop mode. Now, around town it runs cold but on the highway its running warmer probably because coolant is passing through the radiator faster than it can exchange the heat. I thought this fan was restricting it at speed and I unplugged it. Made it hotter so I plugged it back in.
Around town if I get on it hard I notice it puffs unburnt fuel. I can see the puff of black smoke in my mirrors. Its not terrible, but its something I notice. On the highway when I stomp it even on a downshift, its not blowing unburnt fuel at least not that I can tell. But then again the temp is up there. I believe the computer runs on engine temp, since its monitoring the O2 sensors and the temp is up, it doesn't have to dump extra fuel because the mixture is being monitored.
When I had the stock 195 t-stat in my SC, if I ran into the store for a minute and came out, the car would restart and imediately go to 900 rpm idle speed. Now with the colder t-stat, even if I shut it off for like a minute, when I restart the car, it does the cold start high idle thing. Everytime. Maybe the engine is too cold and the comp goes back into closed loop mode which has to run high idle BASED ON TIME. The idle speed always comes down about 35 seconds later. I believe that is the only thing based on time.
Watching my A/F guage around town, I notice it stays red and when I hit it, it only jumps to stoich (yellow). Green (rich) is almost impossible to light up. I think the O2's are shot since its obvious the car is running rich. Thats why I'm going to change the O2's and I know it will get better mileage, but I wonder if it will get much better. Either the O2's are shot and causing the poor mileage and rich running, or the colder t-stat is keeping the computer in closed loop mode around town due to engine temp, also causing poor economy. On the highway I expect MUCH better mileage w/ new O2's since the temp is up and the O2's are reading more accurate. But..... around town maybe I'll still get the same bad mileage due to the O2's being ignored from closed loop mode. I mean why else would this SC pull high idle all the time when restarted and my 90 w/ 195 t-stat only does it when you first start it after its been parked for hours?
I believe my O2's are bad so when I replace them I can rule them out, but for now the way the car is I may have two problems. bad O2's and too cold t-stat. I like the car running cold since I'm paranoid about HG failure due to overheating but I also am sick of using 10 dollars a day to drive this car. I put in about 5 gallons of gas, and get maybe 60 miles before its on E again. So yeah the mileage I assume is low for this car even when driven easy and no boost.
After I switch the O2's, I'll probably put a 195 t-stat back in just to test my theory. If it all goes well and runs better, no more high idle when warm restart, etc... and keeps the temps reasonable w/ the fan on. I'll leave it and be happy. Other wise I am not sure what I'm going to do.
I used to think the 160 t-stats were good for these cars but now I'm wondering if I'm not hurting my mileage and performance by keeping it so cold and so rich. I know leaning it out would show more power than having it flood out rich. My tail pipes have soot at the ends so I know its too rich.
Anyone experiment w/ colder t-stats and fan mods like I did? Did you notice a direct drop in mileage, performance, and a high idle on restart when warm like I did? My car just feels too slow for the mods it has. I mean I have trouble racing some cars I should just embarass. Makes me want to get nitrous or have a chip burned for my car but I think I better find out the cause of this running rich problem first. A $350 dollar chip might be a waste of money if its burnt to correct this problem that I need to fix first. So I'll see what I can do with it first and then maybe later get a chip burnt. I should still be ok w/ stock programming for now.... read my member page for my 92 if you want to see my mods. Let me know if anyone thinks I could benefit from a chip at this point.
In my 92 SC I have a problem. Its nothing major, just that it runs a little rich and the gas mileage sucks. Now the CE light is off, never comes on, so its getting at least some sort of signal from my O2's. Granted my A/F gauge stays lean most of the time, its obviously in range enough that the computer is still getting a signal from them. Now when I replace them in a few weeks this will help me diagnose this problem.
I also have a 160 degree thermostat in my SC and the low speed fan constantly on w/ the ign. Around town the temp guage stays like 1/16" below the N. Car runs cool, has decent power (until the ic gets heat soaked), but the gas mileage sucks.
If I get on the highway and go long distances the temp ever so slightly raises up until it gets around the RM on NORM. It then seems to get much better gas mileage, like it seems to be about 8 mpg more than in the city (i always reset my trip meter when I fill up to monitor my mileage, just something my dad showed me when I was younger about keeping track of fuel economy.) Better on the highway but not where it should be like only 19 mpg. I do have 3.27's in this 5-speed, but still my friend w/ 2.73's gets almost 30 mpg constant at 80 mph. I followed him to St. Louis and I went through a tank and a half of fuel, he was on his first tank. Thats what led me to believe I have one or two problems, caused by one or two things.
Here are my thoughts:
I have been told time and time again that engine temp has no relation w/ the computer coming out of closed loop mode and that its based on a time limit rather than temp. I know that in closed loop mode the engine dumps a bit more fuel than normal and may even ignore the O2 sensors until its out of closed loop mode. Now, around town it runs cold but on the highway its running warmer probably because coolant is passing through the radiator faster than it can exchange the heat. I thought this fan was restricting it at speed and I unplugged it. Made it hotter so I plugged it back in.
Around town if I get on it hard I notice it puffs unburnt fuel. I can see the puff of black smoke in my mirrors. Its not terrible, but its something I notice. On the highway when I stomp it even on a downshift, its not blowing unburnt fuel at least not that I can tell. But then again the temp is up there. I believe the computer runs on engine temp, since its monitoring the O2 sensors and the temp is up, it doesn't have to dump extra fuel because the mixture is being monitored.
When I had the stock 195 t-stat in my SC, if I ran into the store for a minute and came out, the car would restart and imediately go to 900 rpm idle speed. Now with the colder t-stat, even if I shut it off for like a minute, when I restart the car, it does the cold start high idle thing. Everytime. Maybe the engine is too cold and the comp goes back into closed loop mode which has to run high idle BASED ON TIME. The idle speed always comes down about 35 seconds later. I believe that is the only thing based on time.
Watching my A/F guage around town, I notice it stays red and when I hit it, it only jumps to stoich (yellow). Green (rich) is almost impossible to light up. I think the O2's are shot since its obvious the car is running rich. Thats why I'm going to change the O2's and I know it will get better mileage, but I wonder if it will get much better. Either the O2's are shot and causing the poor mileage and rich running, or the colder t-stat is keeping the computer in closed loop mode around town due to engine temp, also causing poor economy. On the highway I expect MUCH better mileage w/ new O2's since the temp is up and the O2's are reading more accurate. But..... around town maybe I'll still get the same bad mileage due to the O2's being ignored from closed loop mode. I mean why else would this SC pull high idle all the time when restarted and my 90 w/ 195 t-stat only does it when you first start it after its been parked for hours?
I believe my O2's are bad so when I replace them I can rule them out, but for now the way the car is I may have two problems. bad O2's and too cold t-stat. I like the car running cold since I'm paranoid about HG failure due to overheating but I also am sick of using 10 dollars a day to drive this car. I put in about 5 gallons of gas, and get maybe 60 miles before its on E again. So yeah the mileage I assume is low for this car even when driven easy and no boost.
After I switch the O2's, I'll probably put a 195 t-stat back in just to test my theory. If it all goes well and runs better, no more high idle when warm restart, etc... and keeps the temps reasonable w/ the fan on. I'll leave it and be happy. Other wise I am not sure what I'm going to do.
I used to think the 160 t-stats were good for these cars but now I'm wondering if I'm not hurting my mileage and performance by keeping it so cold and so rich. I know leaning it out would show more power than having it flood out rich. My tail pipes have soot at the ends so I know its too rich.
Anyone experiment w/ colder t-stats and fan mods like I did? Did you notice a direct drop in mileage, performance, and a high idle on restart when warm like I did? My car just feels too slow for the mods it has. I mean I have trouble racing some cars I should just embarass. Makes me want to get nitrous or have a chip burned for my car but I think I better find out the cause of this running rich problem first. A $350 dollar chip might be a waste of money if its burnt to correct this problem that I need to fix first. So I'll see what I can do with it first and then maybe later get a chip burnt. I should still be ok w/ stock programming for now.... read my member page for my 92 if you want to see my mods. Let me know if anyone thinks I could benefit from a chip at this point.
