How serious is an upper plenum leak (found upper

injectors are leaking under the plenum comon problem with the vortex

You have an interference motor. If you had to replace the heads due to the valves possibly touching the motor, you have to consider rechecking the compression after you replaced the heads. I had the same motor that had an intake leak. I found frozen rings on the number 1 piston as well as a bent pushrod. Ultimately, the camshaft had broken due to coolant getting to the bearings. If the spark is good, the fuel is good, then the only other problem you'd have would be compression.

This code indicates a large vacuum leak. You can sometimes find a leaky gasket by spraying ether on the gaskets while the engine idles. If the engine changes speed while the gasket is sprayed, you have found the leak.

had a similar hard-running problem with a 96 ES 3.8 V6; pulled the front valve cover and rocker-arm tube over #5 had split and no longer controlled the i/o valves. had to replace and re-machine #5 valves in the head.

Possible causes: Fuel Delivery or air leak in throttle body. These engines have a problem with the plenum in the throttle body tearing and causing a rough idle and usually codes P0171 & P0174.
Spray carburetor cleaner around the throttle body with the engine idling. If the idle improves for a few seconds that's it. $30.00 and about 2 hours to repair.

A common problem is the fuel injector leaking fuel into the lower intake and also the plastic fuel lines will crack inside the intake.Remove the upper intake plenum and have a assistant turn the ignition to the run position.Check for any fuel leaks,if its just a fuel line that has burst you can purchase a fuel line kit from napa.They also sell the fuel injector assembly also.

DO A LITTLE TUNE UP.CHANGE SPARK PLUGS.CHANGE FUEL FILTER.CLEAN FUEL INJECTORS.FILL FUEL TANK UP.AND ADD A BOTTLE OF FUEL INJECTOR CLEANER IN FUEL TANK.WHEN YOU DRIVE CAR AROUND.THE INJECTOR CLEANER WILL CLEAN OUT FUEL INJECTORS.IF CAR STILL RUN ROUGH IN DRIVE.YOU COULD HAVE INTAKE LEAK.

These 4.3L W motors are common for fuel leaking inside the plenum causing them to run rough and smell like raw fuel. The fuel pressure regulator leaks internally, also the injector spider leaks and the two fuel lines feeding the fuel to the spider. You have to remove the plenum and look for the clean spot. Where the fuel leaks it cleans the oil off. Before you try this check your EGR valve. The EGR valves on these get stuck open with carbon and cause a rough idle. Remove it and look for the plunger it is a small round piece that you can push in and out, make sure it closes fully. You can also clean it with carb clean and they make a replacement gasket with a screen in it to keep chunks out of it. Start with the EGR because it is easier. The parts for under the plenum are available at most any parts store. If you have any problems just ask, and if you can not find the parts I will give you part numbers. Let me know what you find I will be back tomorrow.

The vortec motor has been known for the so caller spider assembly which is the fuel injection set up inside the intake manifold going bad.The regulator starts leaking wich puts extra fuel into the motor.If that is it you should change the whole assembly.

a faulty fuel pressure regulator might be the cullpret too much fuel will also throw a misfire code