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Fuel System Leak: Low Pressure and Fuel-Injector (CPI) Repair A Chevy Blazer with low fuel pressure and "reluctant" start-up gets a fuel system repair. From "Weekend Mechanic" episode WKM-408

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When checking the fuel pressure, a steady reading indicates the absence of a fuel leak. If the level drops during the test, a leak is probable.

Diagnostics: Visual Inspection and Fuel Pressure Test

To hook up the fuel pressure tester, we go under the car and remove the "in" and "out" fuel lines that are connected to the fuel filter. The two hoses from the fuel pressure gauge simply hook onto the fuel lines with the supplied hairpin clips. (Fuel tester kits come with a variety of adaptors for different applications.) With the tester connected, we turn the key--but without turning the engine over--and look for any drop in fuel pressure. If everything is operating properly, the fuel-pressure reading should remain fairly steady. Ours drops drastically, identifying our problem as a probable fuel leak.

Bruce conducts a visual inspection and checks all the fuel lines. Not finding any evidence of leakage there indicates that the problem is likely somewhere the fuel injection assembly.

On this vehicle, the fuel injection assembly underneath the upper intake manifold, and it has a two piece intake manifold making it difficult to see. In order to gain access to it, we'll need to take the upper intake manifold off. We begin by removing the duct. With the duct removed, we'll be able to access and remove the upper intake manifold, first removing the wiring harness and throttle cables.

Important: Before removing the wiring harness, disconnect the negative battery cable to shut off power.

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Following is a basic summary of the steps as shown in the Weekend Mechanic demonstration.

• Disconnect the a/c pressure switch (figure A) and the a/c compressor clutch connector (figure B).

  Figure A

  Figure B

  
  

• Earlier, we also disconnected the mass air flow sensor (figure C) and the intake air-temp sensor from the air duct assembly.

• Next, the throttle position sensor and the idle air control valve (figure D) are disconnected.

  Figure C

  Figure D

  
  

  Figure E

• The coolant temp sensor is disconnected as well as the MAP sensor--the "manifold absolute pressure" sensor.

• Important: Always be careful when removing these connections to avoid breaking the locking clips.

• After removing the connector safety lock, disconnect the fuel injection harness (figure E). The ignition coil wire is disconnected and the wiring harness can be moved out of the way.

• After removing the bracket mounting bolts, the upper throttle cable bracket can be removed.

• The two throttle cables are disconnected and the throttle cable and bracket assembly can be moved out of the way. Continue the disassembly by removing the power brake hose and the PVC valve tube.

• To remove the old throttle body, first detach the fuel lines from the fuel meter body by removing the torx screws. Use needle-nose pliers to squeeze the poppet nozzle tabs and remove the fuel injector line from the intake valve socket.
  

  Removing the throttle body mount seal

• Our plan is to replace all of the fuel injectors and lines as well as the fuel meter body and the fuel supply lines.

• It's always important to clean parts before reinstalling them. Carb-cleaner makes quick work of this, but check the product label and part information for the proper cleaning agent. Some can damage parts.

• Also clean the upper intake mounting surface. Use a cotton swab soaked in cleaner to clean out the injector ports.

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