GM’s 4.3-Liter Vortec V6 - MOTOR

1 20 July 2000 CURINGTHE fuel INJECTORBLUESCURINGTHE fuel INJECTORBLUESIn 1992, General Motorsintroduced a very uniquefuel injection system on Vortec V6 truckengine. Dubbed CentralPort injection , or CPI, thesystem looked and functionedmuch differently than previousdesigns. The CPI system utilizesone main injector that pressurizessix plastic tubes housed in the in-take manifold. Each tube termi-nates in a spring-loaded poppetBYJEFFMASTERMANA rmed with a pressure gauge, a goodscope and a working knowledge of itstrouble spots, you can purge thedemons that plague GM s CPI with a pressure gauge, a goodscope and a working knowledge of itstrouble spots, you can purge thedemons that plague GM s CPI s Vortec V6GM s Vortec V621 July 2000valve that supplies fuel to its cor-responding cylinder.

2 The main in-jector is pulsed twice per crank-shaft revolution, with pressurizedfuel opening each poppet as sys-tem pressure approaches approxi-mately 48 main injector and fuelpressure regulator on the CPI sys-tem are housed in a molded plas-tic piece with the six plastic tubesattached. GM dealers service thisassembly as a single part number,and it s quite expensive to good news is that replace-ment pressure regulators, as wellas fully reconditioned assemblies,are available via the aftermarket,which can save your customerssubstantial dollars on their ProblemsLeaking pressure regulators arefairly common on the CPI sys-tem.

3 Since the regulator ishoused in the intake, a ruptureddiaphragm often results in fuelbeing dumped directly into thecrankcase or passenger-side cylin-ders. Fortunately, the manifoldtuning valve (MTV) can be re-moved to allow easy inspection ofthe regulator if leakage is pressure leak-down withno external signs of leakage is an-other common problem on theCPI system. Like most injectionsystems, leak-down can result inlong crank times or a stumble af-ter restart.

4 A quick way to isolatethe cause of a leak-down problemon this system is to cycle the keyand allow the fuel pump to runfor a couple of seconds. Once thepump stops, simply pinch off thesupply line. If the pressure holds,the cause is in the tank. If itdoesn t, the intake will have tocome off for a closer look at fuel pressure or vol-ume can also cause long cranktimes or a no-start condition. GMlists the pressure range for the22 July 2000 CURING THE fuel INJECTOR BLUESThe manifold tuning valve (MTV) can be removed from the top of the intake toallow visual inspection of the pressure regulator area without removing theplenum.

5 If there s fuel laying in the intake or if the area around the regulatoris very clean, the regulator diaphragm is probably in this photo how the passenger side of the intake is much cleanerthan the driver s side area. This is partially due to PCV flow, but can also bean indication of a leaking fuel pressure regulator (arrow).Photos: Jeff MastermanCPI system at 54 to 64. However,many techs have encounteredhard-start or no-start complaintswith pressure readings as high as56 to 57 psi on a cold engine.

6 Thisproblem is amplified by the factthat many fuel pressure gaugeshave seen a rough life and can beoff by as much as 2 to 5 psi. So al-ways check the accuracy of yourgauge before working on a CPIsystem. Finally, remember thatthe fuel pressure shouldn t dropduring heavy acceleration. If itdoes, the volume of fuel being de-livered needs to be ll find that many customersdon t replace their fuel filter as amaintenance item, and it s not un-usual to see a filter that s rackedup 100,000 miles.

7 Running forlong periods against a restrictedfilter can kill even the best of fuelpumps. It can also cause big-timeproblems for the CPI has shown that evenslight changes in operating pres-sures can result in significant dif-ferences in the volume of fuelflowing through the WoesEGR valves have been known tostick open on CPI engines due tocarbon buildup. The result will bea rough idle, often accompaniedby a failed emissions test due tohigh HC levels.

8 These enginesuse an electronically controlledEGR valve with a built-in positionsensor. Scan data can provide aquick check for this type of the key on and the engineoff, just compare the EGR De-sired percentage to EGR Actu-al. If the Actual percentage ishigher than the Desired, the valveneeds to be cleaned or poppet valves on the CPIsystem have a tendency to stickopen. If this occurs, a largeamount of fuel will enter the com-bustion chamber. Fouled sparkplugs can be a tip-off to this prob-lem.

9 If you look at the scan data,23 July 2000 The EGR valve on the Vortec V6 sticks open frequently as a result of carbonbuildup. While the intake is off, it s always a good idea to remove the valve andclean off as much carbon as possible to prevent rough intricate design of the CPI plenum can make it difficult to use propane dur-ing a cylinder balance test to determine if a misfire is due to a lean ll find that the Long TermFuel Trim number will be nega-tive, as improper spray pattern cancause one cylinder to run leanerthan the rest.

10 Which could resultin a rough idle and high HC dur-ing an idle emissions test. Per-forming a cylinder balance testcan help you isolate the problemcylinder. Once the cylinder isidentified, add propane at thethrottle body until the rpm repeat the test. If the weakcylinder now contributes, thepoppet valve for that cylindershould be suspect. One caveat:The intake design of the V6 can prevent thepropane from being evenly dis-tributed among the can result in misleading test24 July 2000 CURING THE fuel INJECTOR BLUESThis ASNU machine used by Linder Technical Services can be used to both testand recondition CPI injector assemblies.