Raw Gas 'steam' coming from exaust

I have raw gas vapor coming out of the tail pipe, I have performed a major tuneup (plugs, wires, distributor cap and rotor) thinking one or two wasn’t firing almost sounds that way. Btw it is a 93 blazer s-10 with a 4.3 vortec engine. Engine also has a slight vibration at idle speed and doesn’t want to shift smoothly (automatic trans 4x4).

Any lights going on? My first guess would be a bad injector. Better to get it checked sooner than later.

The fuel injection system in your vehicle is the Central Port Fuel Injection system. This means there’s a central main fuel injector, and off this injector are six tubes that go to each cylinder. At the end of these tubes are what are called poppet valves. These poppet valves are forced open by the fuel pressure, and that’s how fuel is injected into the engine.

This CPFI system is called a spider assembly, and is located under the intake manifold. If there’s gas coming out of the exhaust, and with this type of fuel injection system, I would tell you that one or more of these poppet valves are stuck open, and the spider assembly requires replacement.


How do you know it isn’t water vapor coming out of the tailpipe? Did you use a tailpipe sensor (like used for emission testing)? If so, what kind of readings did you get? Some unburned fuel is normal.

I also suspect what the OP is seeing is not “raw gas”.

You can see a mist coming out of the tail pipe and when you stick you hand in front of it then smell it you can distinctly smell gas.

Capture some of this “raw gas” and see if it burns. Having your hand take on a smell of combustion after holding it behind the tailpipe of a running car is normal.

Some gasoline making it through the system unburned is normal. Water mist is another byproduct of the combustion-catalyzing process. So if you have water mist with a little gasoline in it, your car might be operating normally. Any mechanic with a tailpipe sensor used in emission testing can test your exhaust fumes to see if the amount of fuel is normal or too high. I suggest you give that a try to find out if something is really wrong.

I took it down to O’reilly’s and put a code reader on it, it was saying the usual O2 sensor lean, O2 sensor rich. Then it said Throttle position sensor low and electric spark control failure. I cleareed the codes and the only thing that came back up was the electric spark control failure. I told them about it and they said to take the distributer apart and clean it and try that. I hope it works. Thanks for your help