94 formula firebird gas issues

I just bought a 94 formula firebird. Its all stock except for headers and a kn filter. As i was working on my car i noticed the fumes from the exhaust were very strong. In idle i burned through almost a whole tank of gas. The car seems the run very well with no issues. No sign of a misgire no sputtering. I did check the regulator but i couldnt really tell if its sucking gas in the vacuum. Please help im so lost

what?

In idle i burned through almost a whole tank of gas.

I had 3/4 tank when i started to work on it. Just leaving idle while working on it. By day 2 or 3 i had about 1/4 left.

So basically half A tank.....Also gas gauges are not the most accurate.....

Time-wise an estimate of how long you had it running?

What work are you doing on it, that it needs the vehicle to be running?

I was rewiring the brake lights and turn signals in the rear. I had it running so id have power there... My battery is not so good in that car

remove the vac hose to regulator plug the hose run it see if it still has excessive fuel in exhaust .

another reason is exhaust leaks must not have any leaks

then the O2 sensors may be damaged [wiring] because of the headers ..
94 is a PITA to see codes/engine fuel trims etc...

Ok so i had it at a shop the check engine light says the knock sensor is bad. The fuel trim is at 128. They fixed several vacumm leaks that i didnt know were there. Could the knock sensor make my gas issue that bad? Can it be the sensor or the module?

what is the code # ??? the KS may have other issues like wiring or bad grounds etc.. these sensors will very easy fail if whacked , even a small hit..

The code was 43

FYI, a fuel trim of 128 is PERFECT.......

ABOVE 128 means you have a lean condition and fuel is added....

BELOW 128 means you have a rich condition , and fuel is being subtracted....

It's impossible for the FT to stay at 128....what it will do is vary a little above/below 128......but there are limits, and when the limits are exceeded a code will set....

I have seen more harness problems than knock sensor problems....

Im gonna check wiring tomorrow for the sensor... See if any is messed up... Then i gotta fix those damn pins in the steering wheel so ot stops wobbling

Fuel trims (BLM) at 128 might indicate the PCM is in Backup Fuel and Spark mode, a.k.a. "Limp Home" mode. You'll have an intentionally rich fuel mixture and no spark advance in this mode.

As a test, you can unplug the connector from the knock sensor and rig a 3.3KΩ resistor in its place, grounded at one end. The PCM will accept the 3.3K resistance as a valid sensor.

If the code can be cleared and operation returns to normal, the knock sensor may have failed. If that works, don't leave the resistor in - Replace the sensor.

From my memory only, if both sensors are disconnected the voltage at the KS circuit should be around 4.5VDC.

Blue, I never heard of that test......

I would just pull out my old timing light(yes there is still a use for them), and I would give an engine lift hook a rap with a hammmer and look for a corresponding change in timing on the balancer....

T2 - I know this works on OBD I and earlier OBD II ECMs and PCMs, I'm not sure about '99-up versions, however.

It obviously does not report detonation signals, and on the earliest EST systems the ECM creeps the timing up in PE mode to check the sensor(s) until a knock is detected. This is done on L98s and some of the Buick SFI systems. Obviously, the resistor replacing the sensor will fail this test as well, but if it clears the initial scans on power-up for a valid and connected sensor, it's a quick/dirty way to see if the rest of the system and wiring is intact.


People may laugh at old timing lights and dwell meters, but there are still uses for them, even if an older model never crosses your floor.