94 jimmy

94jimmy

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What is the part located directly under my "vortec" engine cover ? it has two star bit screws and a fin looking piece under it that fits in a hole on top of the engine. ...for my 4.3l vortec engine
 
What is the part located directly under my "vortec" engine cover ? it has two star bit screws and a fin looking piece under it that fits in a hole on top of the engine. ...for my 4.3l vortec engine

It's called a Intake Manifold Tuning Valve. The Intake Manifold Tuning Valve (IMTV) to open up the intake manifold plenum when engine rpm is above 3,000 rpm and the throttle position is above 36%. The boost in breathing helps the engine develop more horsepower. The tuning valve was discontinued on the second generation CSFI system (another cost-cutting measure, no doubt).

There is no specific diagnostic trouble code for the IMTV circuit on pre-1996 trucks, and a scan tool only shows the control valve on/off status. But if the system is not working, the engine will not develop its normal power above 3,000 rpm.

On the early 4.3L Vortec engines was a “linear” exhaust gas recirculation valve. The valve does not use vacuum to open the EGR valve, but instead uses a solenoid controlled by the PCM. The PCM varies the duty cycle of the solenoid to vary EGR flow as needed. A problem here may cause spark knock (detonation) if the EGR valve fails to open or becomes clogged with carbon, or misfiring or rough idle if the EGR valve fails to close.

Hope this helps and good luck. ;)
 
thanks for the great feedback, that helps alot! i need to take out my transmission to get a rebuild or find a new one, and thinking of a complete over haul on the 4.3 (time willing) any other advice you are willing to give would be a great help! Thanks again
 
thanks for the great feedback, that helps alot! i need to take out my transmission to get a rebuild or find a new one, and thinking of a complete over haul on the 4.3 (time willing) any other advice you are willing to give would be a great help! Thanks again

When swapping out the transmission, remove the transmission cross member and tilt the engine and transmission back to remove the two top bolts that hold the engine and transmission together. Your going to need to use a long extension and a swivel to get to the two bolts. As for your 1994 engine, there is not much you can do with it other then improved intake and exhaust and a tuned chip for your PCM that will give you better engine performance.

The cam come's big enough from the factory to give the engine a great low end and mid range torque. Good luck and keep us posted. ;)
 
more awesome advice, i have one more question however. I am trying to get the truck started before i remove the transmission just so i can get everything cleaned up (oil change, filters). It turns over and feels very close to starting but just won't catch. I have heard starting fluid is a no no. So i think i will steer clear of that. Any step by step instructions? Thanks again!
 
more awesome advice, i have one more question however. I am trying to get the truck started before i remove the transmission just so i can get everything cleaned up (oil change, filters). It turns over and feels very close to starting but just won't catch. I have heard starting fluid is a no no. So i think i will steer clear of that. Any step by step instructions? Thanks again!

Carburetor cleaner will work and is not as explosive as the starting fluid. The issue is that the intake platinum has a larger volume then the old school intake on a carb set up. If there is a back fire, it goes up through the carbs on the old school set up.

On the CPFI that you have, if there is a back fire you can blow out your puppet injectors from it's place and at worst blow up your upper intake causing your upper intake platinum gasket to fail.

Hard start could be a week spark from and bad coil and also weak fuel pressure. Start with the simple and replace your fuel filter, check the ground wire to your fuel pump and check your fuel pressure.

Here are a few things you should know about this system:

1)Low fuel pressure (by even a few pounds )can cause a hard start/no start, especially cold. PSI is critical, should be around 58-62 for proper starting.

2)The fuel pressure regulator is prone to leakage (inside manifold,on injector assembly). Remove access cover on top of manifold to inspect. Signs of leakage should be obvious. Replacement regulators can be found at Auto Zone, Napa, ect.

3) The actual injectors are "poppet" nozzles that open when pressurized by the electronic injector at the top of the 'spider" They are prone to sticking. If stuck, you will probably need a professional injection cleaning done. Techron by chevron is good to prevent this problem.

So, check your fuel pressure for proper psi and to see if it holds.
That should help your diagnosis.;)

This system has to have 58-60 psi fuel pressure in order to run, that means with your accurate fuel pressure gauge connected to the rail, key on or fuel pump diagnostic lead jumped, fuel pump cycles/running and primes the rail, you -have- to have at least58 psi showing on the gauge.

Common and expected failures include;

1) Weak fuel pump, can;t deliver necessary pressure or volume.

2) Torn or ruptured pulsator, the pulsator is the piece that connects the fuel pump outlet to the steel tubing that exits the fuel sending unit on top of the tank, the diaphragm in the pulsator tears leaking fuel back into the tank, insufficient pressure and quantity to feed injector assembly.

The pulsator is best eliminated with a length of proper high pressure flexible fuel hose and clamps. It's merely there to dampen noise.

1) Plugged injector poppets. All you can do is replace them with new or re-manufactured CPI unit.

2) Leaking fuel pressure regulator, evidenced by observing a washed clean area inside the intake plenum as viewed by removing the vortec tuning valve.

3) Cracked or broken fuel nuts. The fuel nuts are the semi-rigid plastic tubes that connect the frame mounted fuel lines to the CPI unit inside the intake manifold, the fuel pressure test port is part of one of the fuel nuts.

When they crack and leak, raw fuel leaks into the intake manifold to the point where it will puddle a few inches deep in the lowest points of the manifold. This extra fuel does nothing to assist the engine in running but
may has been evidenced at an earlier time by indications of rich running conditions such as extremely poor fuel economy or a check engine light on with a rich mixture code (45) stored -or- by monitoring the O2 sensor and having observed high O2 sensor voltage. (above paragraph applies to ruptured fuel pressure regulator also.):eek:
 


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