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I have a 1994 Pontiac Firebird Formula, 6-speed manual, 5.7L engine 119K miles. I recently bought this car three months ago and have finally gotten it road worthy. It had minor issues the previous owner didn't want to deal with, so he sold me the car for 400 dollars, the amount he would've got if he had junked it.

I have driven this car myself about 500 miles and on average I get about 14.5 miles to the gallon. I have almost replaced everything in the ignition system:
Spark plugs
Plug wires
Coil
Optispark

I have treated the gas with Techron once. It runs very well now but is there anything else I can do to improve gas mileage?  

I remembered that the integral numbers are off. As soon as you start the car, left and right are at 128. After it enters closed loop, right is at 120 and left is at 138. Also, one of the o2 sensors are jumping all over the place, like hundreds of numbers at a time. the other reads constant. Being as they are both in each of the exhaust manifolds, I should think they'd read constant, and probably be about the same. I know that it probably is the o2 sensor, and probably the right one, can somebody confirm?  

duped  

still there..?????   i blinked my eyes and missed you

i have more

print this chart

 

the oxygen sensors when working properly switch rapidly from 0.1 volts to 0.75 volts many times a second...  faster tan most meters can display..

with the scan tool look for oxygen sensor cross counts...

a few basic things to check..

engine off.. key on...  look at the TPS minimum voltage..

it should be 0.53 volts..  it has to be there or very very close to that...

but what's more important..  is that the tps minimum idle voltage returns to the EXACT same fractional voltage... or the computer will not know that the throttle is not closed.. so it will keep the fuel injection pulse width wide like you are ready to accelerate instead of on the idle program...

look at your injector pulse with ... 1.3 to 1.4 Ms   shows it at idle...  

if your TPS voltage is above the minimum setting it also won't return to idle programming..

what is your idle air count..    at idle.. warmed up..

should be 20 to 50 IAC  i know the chart does not show that number..  but thats where it has to be...

if your TPS voltage varies between each time its closed..

engine off.. grab the throttle lever... open it part way... wiggle it.. does it move around any.. if so.. you may need to have the throttle body shaft bushed.. there are places that do that..

stilll there?????  

next.. do you have any exhaust leaks ???

does your engine have an air injection system into the exhaust..????

that can leak air into the exhaust manifolds and dilute the exhaust stream in closed loop throwing off the oxygen sensor data...

do not remove and throw away the air injection system as it will set a code and leave you in LIMP HOME and reduced fuel economy....

more to come... still there????

you can disconnect it and plug the check valves going into the exhaust manifolds...  for a test...     blocking those in the long term.. again will set a code and may melt the cats...  

I don't have the scanner anymore, it wasn't mine, it was my cousin's. But I did get my exhaust welded on, it's a lot quieter. The integral numbers are still off and that o2 sensor is still reading all over the  place. The a/c still needs to be charged, but I'm having that arranged. Other than that the car runs great.  

I check all this tomorrow, my internets being screwy with me, sorry for the reply delay.  

the oxygen sensors range widely as the system goes lean and rich.. lean and rich... to average the air fuel ratio...

disconnect 4 and 16... plug the check valve 7 with a section of heater hose and something.. see if the block learn and the intergator even out..



Pontiac 1994, Firebird formula, Fuel system-exhaust-emission system, 1994   F A.I.R. PUMP & RELATED PARTS (LT1/5.7P)   (MF03-092)  

click the image for a large view...

this kind of stuff requires a scan tool...

get on C L  type in OTC  then select tools..  or auto parts..

you will also want to check car parts there as people put them in that area...

or post what is the closest CL to you.. i will look up something that will work for you...


if you can get the system operating properly..  you might be able to get much better fuel mileage..

do you own a decent volt meter and some probes.. perhaps some piercing probes..



i usually have to make my own...






you will want to pick up one of the following...

a snap on MT2500 with the proper cables and cartridges..



one of the OTC monitor 4000E variations...    monitor extended, extended monitor... enhanced monitor...   you will probably need a domestic 96 cartridge. a 93 cartridge will not work with your car..




this is an Actron CP9110.. with the GM cartridge and cable. you have a decent consumer scan tool .. i have one of these.. its really handy... i also have a extended monitor... its really handy...




this is an early autoXray unit...  the later ones kinda have problems reading live data on 94 and 95 models.. they just give you codes.. and you cannot fix problems with just codes.



this is an OTC genesis ..  there are a bunch of models.. and a LOT of variations in cables..  they are a true professional scan tool like the snap on MT2500 above...



this is a consumer unit from OTC.. called the OTC 3499N..  they are just over 500 bucks.. and will do an amazing number of different cars.. both OBD1 and obd2...





warning....  DO NOT buy one of the MONITOR 2000 models.. they only cover up to 89... they are still a decent scan tool for 89 and earlier GM cars.. but they only have two lines to display.. instead  of 4 or more..  GM cars from 81 to 89 can use these..  if they have the proper cartridge..
this one has a LOT of cables that can be used with the monitor 4000E variations..  the cartridges also fit the 4000E variations..

 

I do have an accurate digital multi-meter, I have a lot of experience using them as well. My cousin was letting me borrow his snap on tool, the same one in that picture. I can see about getting my own OBD tool but money will definitely be an issue there. I will be wary about the one I get and make sure it's compatible with my car. Thanks for the help.  

print the chart...

drive over and plug the scan tool in.. write down the numbers... some of the snap on tools may have the USB cable to upload snap shot data to a PC...  or write the data on the printed sheet...

take the time and post the data line by line...
i can decipher it..

take it cold engine off..

warmed up and idling..

warmed up and running about 30MPH steady...
RPM
TPS
IAC
ECT
MAF or MAP
injector PW.
block learn
intergator.
open loop/closed loop.
and a few more..

that model has 2 oxygen sensors...

see if they are both displaying the a similar but slightly out of phase oxygen sensor reading..

do it again with the air injection elbows i mentioned above.. disconnected and plugged to block any upstream air from entering the exhaust manifolds..

get some numbers.. post them...  

What gear when doing 30?  

30/35mph..

does not matter.. just in drive.. if its a automatic... if its a 5 or 6 speed... i need around 2500 rpms with a steady throttle... so i can see the numbers...  be sure to throw in the speed sensor data...

no speed sensor data.. no fine tuning and reduced fuel economy..

actually so you can see the numbers...   this is usually done with 2 mechanics... one driving.. the other with the scan tool pushing buttons...  

I don't have the scanner anymore, it wasn't mine, it was my cousin's.  
I heart which I could not help him