TOPIC: 1990 5.7 TBI General Motors

Grooved a 1990 Chevy 5.7 TBI Yesterday, Pre groove this Truck very rough and had a heavy gas oder. Removed TBI and reduced Idel Air Pathway to 1/8" befor cutting the grooves, Vaccuum tested all lines and found 2 leaks, Was able to cap one, The other leak is the BRAKE BOOSTER! Plan to install new Booster soon, Also rerouted MAP sensor to (PCV) PORT, Regaped new spark plugs 25%,Post groove this truck run very smooth, NO MORE GAS FUMS.

Hello, Frank.

Make SURE your MAP sensor is as far away from the Throttle Body as possible. We want the LEAST amount of air getting to the sensor so it gives an accurate representation of the call for fuel by opening the throttle.

HIGHER vacuum is far better for the MAP than the extreme variations occurring in the vicinity at the throttle.

If that's the case with your engine's PCV connection, then great!

And GET THAT BOOSTER REPLACED! That is the prime location for overlooked vac leaks!

Keep us posted!

Ron

Hi Frank,

I recommend you move your MAP connection farther away from the throttle body and extend the tube into the middle of the intake. Check to see if the intake has a pipe fitting plug behind the throttle body. If it does, purchase a brass hose barb fitting that will fit in the tapped hole the plug is in. The MAP tube will need to be able to slip onto the hose barb. JB weld a tube to the fitting on the side that would extend into the intake. (I've taken an empty 22mag case and cut off the closed end) The goal is to get the MAP to read in the middle of the intake air. This will lower the readings measured by the MAP as the readings along the wall are higher. I have had positive results using this technique. Let us know the results.

What Nick is saying to increase the depth within the intake manifold the sensor picks up the vacuum.

The purpose is to get the sensed zone into the lower pressure area that occurs in the center of the intake air stream. The pressure is always higher at the walls, lower to the center of the stream.

Make sense?