i have an 85 car with an 87 TPI 305 in it, it has an LT1 cam (.451 lift) as well as headers and a 3 inch exhaust system and 19 pound multitec 2 injectors. here's my problem, the car starts and runs beutifully, revs fast and hard and its VERY smooth and has plenty of power. sounds wonderful right? heh, here's whats bothering me, my A/F ratio guage is reading VERY lean and when i punch the gas it shoots up to stoich, then drops back off the chart when its warming up at idle in park, when it hits closed loop, it even reads pretty lean, in drive with my foot on the gas it switches between stoich and lean. my BLMs stay around 128 -130, my iac counts are all good. i put an AFPR on it which put me in the sweet spot im in now with the way it runs and i HAVE adjusted it too far in a d adversely affected the run qualitfy, the the A/F guage did NOT show much different. what do you guys think? (im also posting this in the Prom board for their opinions)

 

I would think you have the original 85 chip in there and it thinks its running a 305. I would be looking at the computer rather than the engine.

 

is it a wideband guage???


cause if its not then it will just jump around from lean to stoich..they are pretty much just a light show inside your car

 

no it's a single wire, but the o2 readings from the ALDL match what the gauge shows on my scanner, also its an 85 body, but i have an 87 ECM with an 87 305 w/ auto Prom. the engine IS a 305, just modified with an LT-1 cam, headers, and a 3 inch exhaust system w/ cat and A.I.R delete and 19 lb/hr multitec 2 injectors. what stumps me is i dialed the fuel pressure into a sweet spot where it runs EXTREMELY smooth and revs fast and hard, if i got any more it bogs and if i go any less it gets very rough, but the 02 doesnt seem to respond to it.

 

I had a similar problem with my 89, the o2 sensor was too far down stream and not getting hot enough. I swapped in a three wire heated o2 and the problem got better, but not completly solved as it would still throw a lean code when it was very cold outside.

 

now THATS the info i needed! ill get to swapping a heated 02 ASAP, ill use a bosch unit from a 1995 Cadillac deville 4900. its a 4 wire heated o2 and it costs only 20 bucks

 

the o2 is usually a secondary reading though your main reading would be from the maf or map depending on the car...the o2 sensor is just backup info for the computer it mainly just monitors it doesnt send a signal to the computer in the car to tell it to add or remove fuel...if you are running lean i would look into the maf i believe in your case...

in my vette im only running an o2 sensor for the wideband afr it doesnt even run to the engines electronics...you can usually unplug the o2 and the car will run fine it may just throw a code but thats it...

 

maf is reading perfectly, and actually the 02 is very important in A/F monitoring and adjusting.

 

the o2 is good for monitoring but the maf is what adjusts the af ratio im willing to bet that you change the o2 sensor and it doesnt fix the problem...if it does then thats great but o2 sensors arent a part that just goes bad either

 

no but they CAN be too far down stream and not being properly heated, and in that case it will read improperly. as i said the engine runs GREAT

 

see then that kinda falls under the "if it aint broke dont fix it category"


if i were you id leave the o2 where its at..buy or piece together a wide band air fuel ratio gauge install the o2 sensor that will run to the gauge a little closer or find a good spot for it somewhere that will get you a way more accurate reading of the air fuel ratio which will be a lot different than the single wire afr gauge readings...