More then likley you have a clogged injector. Try cleaning the injectors, if that does not work, you may have to replace them. There is a problem with these injectors on this engine. They have a updated part to replace them, not a cheap fix. You may want to have a injector drop test performed to make sure the injector is the problem. The test is done by firing each injector wile watching how much fuel pressure is lost during the test, each injector will be tested and compard to each other, if there is a problem with the number 7, it will not drop any pressure of have a lower drop then the others.
This is a GM bulletin for the injector concern.
#00-06-04-003B: Rough Idle After Start, And/Or A Service Engine Soon (SES) Light (Unstick And Clean Central Sequential Fuel Injection (CSFI) Poppet Valves or Convert to MFI) - (Jan 30, 2003)
|Subject:||Rough Idle After Start, And/Or A Service Engine Soon (SES) Light (Unstick And Clean Central Sequential Fuel Injection (CSFI) Poppet Valves or Convert to MFI)|
|Models:||1995-2002 Chevrolet and GMC S/T Models|
| ||1996-2002 Chevrolet and GMC C/K, M/L, G, P Models|
| ||1996-2001 Oldsmobile Bravada|
| ||1999-2000 Cadillac Escalade|
| ||with 4.3L, 5.0L or 5.7L Engine (VINs W, X, M, R -- RPOs L35, LF6, L30, L31)|
| ||Except 2002 VIN X -- RPO LU3 Models|
This bulletin is being revised to update the Correction and Warranty Information. Please discard Corporate Bulletin Number 00-06-04-003A (Section 06 -- Engine).
Some customers may comment on rough idle after start-up, especially if the vehicle has sat overnight. These symptoms may be intermittent. The Service Engine Soon (SES) light may also be illuminated. Current misfire or history misfire codes may be detected with the Tech 2 scan tool.
A deposit build-up on the CSFI poppet valve ball and/or seat may cause the poppet ball to stick open or closed. In either case, the specific cylinder will be mis-fueled, resulting in a cylinder mis-fire condition.
A new injector unsticking and cleaning process has proven to be effective in restoring poppet valves to an "as new" condition. CSFI injector replacement should NOT be considered as a correction for this customer concern.
Check the vehicle history to determine if the vehicle is returning for a second fuel system repair for this condition. If the fuel system has been repaired for this condition previously, then inform the customer that an alternate fix is available. A new MFI fuel system has been developed that will back service the CSFI fuel system. The MFI fuel system eliminates the CSFI poppet valve ball and seat. The CSFI fuel system will need to be replaced as a unit. Refer to Central SFI to MFI Conversion instructions in this bulletin.
Notice: Individual CSFI injectors can not be replaced with MFI injectors. The entire CSFI fuel meter body will need to be replaced. The bracket used to retain the injectors in the fuel meter body is different between the CSFI and MFI unit. The unit may not seal if you mix injectors. Severe engine damage could result.
Cleaning the CSFI injectors is the preferred repair. The CSFI unit should not be replaced until cleaning has been attempted. If the vehicle should return for the same repair, then the CSFI unit can be replaced with an MFI unit. If the vehicle is out of warranty, the customer should be given the option of which fix to pursue.
Important: "GM of Canada" dealers require District Service Manager approval prior to replacing the CSFI unit with a MFI unit under warranty.
The first step of this process is to use the J 41413 Evap Pressure/Purge Station, in conjunction with the J 44466-10 pressure regulator/hose assembly, to provide the required high pressure (150 psi) source to perform the unsticking procedure. The J 39021 fuel injector tester and accessories provide the means to "energize" the injector. Some later model-year vehicles may utilize the Tech 2® to "energize" the injectors.
The second step of this process is to run the engine on a solution of 10% Top Engine Cleaner and 90% gasoline. This will effectively clean any deposits from the ball and seats of the poppets. It is very important that the engine fuel system is separated from the vehicle fuel system. Top Engine Cleaner may have detrimental effects on the fuel pump.
This procedure should be performed before any attempt to convert the fuel system to MFI.
S/T and C/K Truck
- Loosen the fuel filler cap to relieve vapor pressure in the fuel tank.
- Remove the Positive Crankcase Ventilation (PCV) clean air tube from the air inlet tube and set aside.
- Remove the bonnet and inlet tube from the throttle body.
- Remove the brake booster vacuum hose and connector from the intake manifold.
- Remove the electrical connector from the CSFI fuel metering body.
- Remove ignition wires 1, 3, 5, (7) from the distributor cap.
- Remove the fuel line bolt (4) at the rear of the intake manifold.
- Relieve the fuel system pressure at the service fitting on the fuel line. Use a shop towel to contain any fuel that may exit the service fitting.