What else could be causing bad gas milage?
02-19-2003, 11:39 AM
#1
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Location: Lilburn, GA, USA
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What else could be causing bad gas milage?
My girlfriends 90' TBI Formula is still getting bad gas milage even after the changing of the O2 sensor that I thought was the problem. What are some other things to look for? Keep in mind that there is a new air filter, plugs, wires, coil, cap and rotor, and fuel filter. Thanks.
02-19-2003, 12:36 PM
#2
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Location: Southern MN
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Air pressure in the tires could be low 
... I am sure that you checked this. Also an alingment that is off, a tranny that needs a fluid change, Injectors that are bleeding down, a hole in the fuel pressure regulator diafram(very comman), long term fuel trim too rich.
Do a fuel pressure test KOEO, and see if the system holds PSI, if it does not, you have a leak somewhere, wither back into the tank(would not cause bad milage), a leaky injector, or a bleeding regualtor. Look at your exhaust, if there is a lot of carbon this is a sign of hi HC (unburned fuel) and you have a problem somewhere. Also I would do a compression test...
There is a lot of possibilties,
Erik
... I am sure that you checked this. Also an alingment that is off, a tranny that needs a fluid change, Injectors that are bleeding down, a hole in the fuel pressure regulator diafram(very comman), long term fuel trim too rich. Do a fuel pressure test KOEO, and see if the system holds PSI, if it does not, you have a leak somewhere, wither back into the tank(would not cause bad milage), a leaky injector, or a bleeding regualtor. Look at your exhaust, if there is a lot of carbon this is a sign of hi HC (unburned fuel) and you have a problem somewhere. Also I would do a compression test...
There is a lot of possibilties,
Erik
02-19-2003, 09:16 PM
#4
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It is definatly running rich but of course I don't know why. It has to be with the fuel delivery because all the mechanical possibilities have been checked. Could the timing have anything to do with it? I am not sure if this is normal but when i look at the throttle body with the air cleaner off, I see fuel being sprayed on the closed throttle body at idle and it kinda pools up and I guess leaks through, down into the intake and so on. But when i increase rpms, the amount of fuel seems to be constant and only the throttle blades are opening more. i don't know what the deal is but somewhere too much fuel is being used.
02-19-2003, 11:24 PM
#5
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Your timing is set and should not move unless the chain jumps, but if that happened you would be havin a whole new set of problems. It is entirly possible for the ECM to be commanding the injector pulswidth to be too long, driving up the long term fuel trim and causing your real ritch condition, but for this a Scan tool and four gas analizer are needed to diagnose the problem. Make sure the sytem holds PSI for at least two minutes with the key on and engine off first and go from there, thats my suggestion.
Peace,
Erik
Peace,
Erik
02-20-2003, 10:22 AM
#7
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Is the Fuel Pressure Regulator (FPR) adjustable? If so then maybe it is cranked up too high. I found that this was one of my problems. THe O2 sensor can only do so much when you run rich enough to shoot black smoke (unburned fuel) out of the tail pipes.
02-20-2003, 04:09 PM
#9
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Could the Baro sensor be a problem? The car just threw a code for it. The code used to come up all the time but it went away for a few months and now it seems to be back. This is getting very frustrating.
02-21-2003, 11:16 AM
#13
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Hmmmmmmmmm. Maybe that is a problem. I always thought the car ran incredibly cool. In normal driving it stays around 130 and it seemed to me that the cooling system was a bit screwy.........or maybe I am just wrong and everything is the way it is supposed to be. I bet that the sensor is pretty cheap so I think it is not that big a deal to replace.
02-21-2003, 11:27 AM
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The sensor is less than 10 bucks and its located on the thermostat housing. Another thing now that you've mentioned it... If the car isn't getting up to operating temp then you will get sh!tty gas mileage too.
Heres where to start:
Get a new thermostat and gasket. I'd get a 180* or a 195* thermo and install it. Get the new CTS and install it also. Now flush the colling system with water until only clear water starts coming out then drain it and fill with 50/50 antifreeze/water.
I am almost positive this is your problem.
Heres where to start:
Get a new thermostat and gasket. I'd get a 180* or a 195* thermo and install it. Get the new CTS and install it also. Now flush the colling system with water until only clear water starts coming out then drain it and fill with 50/50 antifreeze/water.
I am almost positive this is your problem.
