Hi, you still may have injector poppets that are sticking and not opening.To check this properly would require a fuel injector test setup. You may get some results by turning the key on and recording the pressure,then crank the engine it should drop slightly if the injectors are opening. I will send you some info on testing the signal to the injectors I would make sure that the battery is able to delivery the proper voltage when you are cranking over the engine.Make sure it has 12.6v before cranking and stays above 9.6v while the engine is being cranked over,a lower voltage will cause problems. Make sure that both battery cables are clean and tight and that the ground connections are in good shape.
Back in 1992, General Motors introduced a new type of fuel injection system known as "Central Port Injection" (CPI), which GM also refers to as "Central Multi-point Fuel Injection" (CMFI). The system was used on 4.3L V6 Vortec engines through 1995, and was redesigned in 1996 and renamed "Central Sequential Fuel Injection" (CSFI). The system was also added to 5.0L and 5.7L Vortec V8 engines.
Though the CPI system supplies fuel to each of the engine's intake ports like other multi-port fuel injection systems, it has only one centrally located fuel injector, called the MAXI injector. Some bean counter at GM probably came up with the idea as a way to reduce costs. Fuel injectors are expensive, so using one injector instead of six seemed like a good idea at the time.
Here's how it works:
The MAXI injector is mounted in the center of the intake manifold on the 4.3L engine, and is hidden inside the split plenum manifold. Instead of spraying fuel directly into the manifold like a throttle-body injector, the MAXI injector routes fuel into six nylon fuel lines that have poppet-style spray nozzles on the end. When the pressure inside the lines reaches the opening pressure of the poppet valves (43 psi), fuel sprays out of the nozzles into the engine's intake ports.
In the first generation CPI system, all the nozzles spray simultaneously when the MAXI injector opens (three times per crankshaft revolution). In the second generation CSFI system, the injectors are controlled individually and fire only once every other revolution of the crankshaft. This allows the system to provide sequential fuel injection for better emissions, performance and fuel economy.
In ways, these systems function sort of like an old-fashioned diesel injection system except that there is no mechanical fuel pump, fuel injection is controlled electronically, and the operating pressures are much lower. Fuel pressure in the CPI system with the key on and engine off (KOEO) should be about 58 to 62 psi. Some specs say 54 to 60 psi is OK, but some fuel injection experts insist that to start and run properly, most CPI systems really need at least 58 psi. Pressure is generated by a tank-mounted electric fuel pump. A fuel pressure regulator on top of the MAXI injector maintains operating pressure at about 55 to 57 psi when the engine is running.
The CPI system is a speed-density system, so there is no airflow sensor. The powertrain control module (PCM) estimates air flow using inputs from the MAP sensor, throttle position sensor, temperature sensor and engine speed. Fuel delivery is controlled by pulse width modulation. The PCM varies the on-time or dwell of the MAXI injector to control the air/fuel mixture. The injector driver circuit uses the peak-and-hold method, providing 4 amps to open the injector and about 1 amp to keep it open.
The important point to note about the CPI system is that if anything in the CPI system fails (the MAXI injector shorts out, goes open or leaks, the fuel pressure regulator leaks, any of the lines that connect the MAXI injector to the nozzles leaks or breaks, or any of the individual nozzles leak or become plugged up), the whole system must be replaced as a complete assembly.
Warning: If the engine compartment smells like gasoline, remove the manifold tuning valve located on top of the intake manifold and look inside with a flashlight. If the inside of the manifold is shiny or you can see fuel stains or leaks, the CPI is leaking and needs to be replaced without delay.
To replace the CPI assembly, the top of the intake manifold plenum has to come off. There are 10 Torx fasteners that hold it in place. Once that is out of the way, the six individual spray nozzles can be pulled out of the bottom half of the manifold by squeezing the plastic prongs together and pulling (sort of like pulling apart an electrical connector).
Caution: When installing the CPI system, make sure the poppet nozzles are securely locked in position in the lower half of the intake manifold. If one comes loose, it can spray fuel where fuel doesn't belong and create a potential fire hazard.
Second Generation CSFI
On the second generation Central Sequential Fuel Injection (CSFI) system (1996 and up), the MAXI injector in the central housing has been replaced with six individual injectors, each of which feeds fuel to its own poppet spray nozzle. The system also uses a mass airflow sensor to monitor airflow. Fuel pressure in the CSFI system is a bit higher than the CPI system (60 to 66 psi with key on engine off), and the regulator maintains the operating pressure at 55 to 57 psi. The poppet valves in the spray nozzles also open at a slightly lower pressure (about 40 psi). The injectors fire just before each intake valve opens.
The bad thing about the CSFI setup is that the nozzles tend to gum up more than the nozzles in the older CPI systems because they spray less often. The heat soak period between sprays allows fuel varnish to build up inside the nozzles and restrict fuel delivery causing a lean fuel condition, misfiring, hesitation and a loss of power. The good thing about the CSFI system is that the injectors and nozzles can be replaced individually if any fail.
In recent years, an aftermarket replacement system for these applications has been developed that converts the CSFI system into a conventional multi-point fuel injection system. The aftermarket system looks similar, but the troublesome poppet valve spray nozzles on the ends of the fuel distribution lines have been replaced with conventional electronic mini-injectors.
Common problems on the first generation CPI system includes fuel leaks at the pressure regulator (which can leak fuel onto the passenger side of the intake manifold and create a potential fire hazard), fuel leaks in the fuel supply and return lines (which tend to leak fuel onto the driver's side of the intake manifold), leaks or electrical faults in the MAXI injector, leaks in the fuel lines between the MAXI injector and the spray nozzles, and gummed up poppet valves.
If one poppet nozzle leaks, it will cause a drop in pressure to the other poppet nozzles, too. The cylinder with the leaking nozzle will run rich and may have a wet fouled spark plug. The others will likely run lean and may misfire.
Common problems on the second generation CSFI system include leaky O-ring seals, leaky fuel pressure regulator, leaks in the fuel pulsator or damper inside the fuel tank (causes a loss of fuel pressure), and leaky or gummed-up spray nozzles.
General Motors has issued several technical service bulletins that deal with these issues, including TSB 99-06-01-022 that covers procedures for cleaning CPI poppet valve spray nozzles, TSB 00-06-04-003B for cleaning CSFI poppet valve spray nozzles, TSB 56-63-06 and TSB 66-63-09 that cover diagnosing hard-starting/no-start problems with the CPI system, and Special Policy 99034A that extends the factory warranty on California-only CPI systems (RPO L35 VIN Code W) to 10 years or 100,000 miles. The latter blames CPI problems on the use of California's reformulated gasoline, and covers both repairs and cleaning.
GM also issued a recall (99066F) on 1996 to 2003 CSFI systems, and extended the warranty to 10 years or 200,000 miles (whichever comes first) to cover problems with the poppet spray nozzles. The recall covers free injector cleaning and/or replacement as needed to correct driveability or emissions problems.
Fuel Pressure Problems
The CPI and CSFI systems are both very sensitive to any loss of fuel pressure. If the fuel pump is weak, is not getting enough voltage to run at normal speed, or the fuel supply line is restricted because of a clogged fuel filter, a drop of only a few psi can be enough to create a hard-start or no-start condition. The first step in diagnosing a hard start or no start on a GMC or Chevy truck with one of these systems, therefore, would be to check fuel pressure. If fuel pressure is less than the KOEO specification, you need to test the fuel pump and its voltage supply circuit.
Dead head pressure from the fuel pump should be 70 to 80 psi or higher, and the pump should be capable of delivering a quart of fuel in 30 seconds. If the pump is not delivering the required pressure or volume, check the pump's voltage and ground connections. You should see battery voltage at the pump when the key is on, with no more than a 1.5 voltage drop for the total circuit (ideally less than 0.5 volts). No voltage at the pump could be due to a blown fuse, an open in the pump circuit wiring or a bad fuel pump relay. If the relay isn't closing, check the oil pressure switch. Power to the relay is routed through the oil pressure switch to kill the pump if the engine is not running (a safety measure to cut off the fuel in an accident).
Sometimes the pump wires inside the tank can also overload and short out. The wires are a small gauge and were not designed to handle high amp loads (as can occur when a worn pump starts to pull more than its normal current). That's why some aftermarket replacement fuel pumps now include a new tank wiring harness for these trouble-prone applications. If the fuel pump is okay, the next thing to check would be the fuel pressure regulator. When the key is turned off, the pressure in the fuel line should hold for at least five minutes. If the pressure drops off, the fuel pressure regulator or fuel pump check valve may be leaking. If pinching off the fuel return line produces the same results, the problem is the check valve in the fuel pump (replace the pump). If pinching off the return line stops the pressure loss, the problem is a leaky regulator.
The next step would be to check the MAXI valve (CPI) or the individual injectors (CSFI), and the poppet valves. If the MAXI injector or CSFI injectors are not buzzing, check the power supply to the injector(s) from the PCM. You can use a noid light to see if the injectors are being pulsed, or connect a digital storage oscilloscope to the injector harness to see what's happening in the circuit.
The MAXI injector can also be tested with an ohmmeter. The resistance specification is 1.9 to 2.1 ohms, and the coil voltage should be 3.3 to 4.8 volts. On the CSFI systems, injector coil voltage should be 5.4 to 7.5 volts.
If an injector or poppet nozzle on a CSFI system is bad and you have to replace it, make sure the poppet nozzle is securely locked in position in the lower half of the intake manifold.
On the CSFI systems, a dirty or defective mass airflow sensor can also cause problems (typically lean codes, hesitation, misfiring or rough idle). The airflow sensor can be checked with a scan tool, and should read about 5 to 7 grams/second airflow at idle on a warm engine. If the sensor is reading low, it can be cleaned by spraying the sensor element with electronics cleaner (do not use any other type of cleaner or solvent as this can damage the sensor). If it is still misbehaving after cleaning, replacement is your only option.
Next, I have attached a TSB that talks about the crankshaft sensor can cause a no start, hesitation etc for your review.
File In Section: 06 - Engine/Propulsion System
Bulletin No.: 00-06-04-014
Date: April, 2000
No, Hard, or Slow Start, Backfire or "Kickback" During
Crank/Start, "Grinding" or Unusual Noises During Crank, DTC P0338
(Replace Crankshaft Position Sensor)
1999-2000 Cadillac Escalade
1995-2000 Chevrolet and GMC SIT Models
1996-2000 Chevrolet and GMC C/K, M/L, G, P Models
1996-2000 Oldsmobile Bravada
with 4.3 L, 5.0 L, 5.7 L or 7.4 L Engine
(VINs W, X, M, R, J RPOs L35, LF6, L30, L31, L29)
Some customers may comment on one or more of the following conditions:
^ Backfire during crank/start
^ "Kickback" during crank/start
^ "No" start
^ "Slow" or "hard" start/crank
^ "Grinding" or unusual noises during crank/start
^ Cracked or broken engine block at the starter boss
^ Broken starter drive housing
^ Broken starter ring gear on flywheel
^ Any combination of the above
A condition may exist that allows the crankshaft position sensor to command up to 50 extra degrees of spark advance during engine cranking only. This in turn exposes the engine to higher than normal cylinder pressures which may result in an inoperative condition to the starter drive housing, the engine flywheel starter ring gear, or the engine block at the outside edge of the starter boss.
Inspect for a stored powertrain DTC code P0338. This DTC will NOT illuminate the "Service Engine Soon" light. If this code is stored, the Crankshaft Position Sensor, P/N 10456607, MUST be replaced and the remaining components inspected for damage (engine block at the starter boss, the starter drive housing, and the engine flywheel starter ring gear).
Notice : When DTC code P0338 is set, failure to replace the Crankshaft Position Sensor could result in repeated inoperative conditions of the starter or flywheel.
I have also attached what it does but we need to see if any codes are thrown.
The Crankshaft Position (CKP) Sensor is located in the front engine cover and is perpendicular to the crankshaft target wheel. The air gap between the sensor and the wheel is preset and not adjustable. The target wheel has three slots 60°apart and is keyed to the crankshaft. As the target wheel rotates, the slots passing by the sensor create a change in the magnetic field of the sensor which results in an induced voltage pulse. One revolution of the crankshaft results in three pulses (3x signal). Based on these pulses, the VCM is able to determine crankshaft position and engine speed. The VCM then activates the fuel injector and provides a spark to the Distributor. The relation between the crankshaft position sensor and the target wheel is crucial. The sensor must be exactly perpendicular to the target wheel with the correct air gap.
The crankshaft position sensor provides the VCM with crankshaft speed and crankshaft position. The VCM utilizes this information to determine if an engine Misfire is present. The VCM monitors the Crankshaft Position Sensor (CKP) sensor for momentarily drop in crankshaft speed to determine if a misfire is occurring. When the VCM detects a misfire, a Diagnostic Trouble Code (DTC) P0300 will set. The VCM also monitors the CKP sensor signal circuit for malfunctions. The VCM monitors CKP signal and the High and Low resolution signals. The VCM calculates these signals to determine a ratio. When the VCM detects that the ratio is out of normal operating range, the VCM will set a Diagnostic Trouble Code (DTC) P0337 or a DTC P0338.
Now you are still getting a good strong spark......yes? When pull a plug wire and insert something into the end of it and have someone try to start the car and have the metal object really close to a piece of metal on the engine you are getting a good strong popping blue spark. Yes?
I located another TSB recall that ran out in 2007 but, it is on the fuel injectors sticking. I have attached for your review.
Campaign - Fuel Injector Sticking Closed
File In Section: 06-Engine Emissions
Bulletin No.: 99066F
Date: March, 2003
99066F - SPECIAL POLICY ADJUSTMENT - SEQUENTIAL CENTRAL PORT
FUEL INJECTION (SCPI) FAILURES IN CALIFORNIA ONLY (YF5
CERTAIN 1996, 1997, 1998, 1999, 2000, 2001, 2002 S/T, M/L, C/K, G,
P, W4/NPR TRUCKS AND 2003 NPR TRUCKS EQUIPPED WITH 4.3L
(RPO L35 - VIN CODE W OR RPO LF6 - VIN CODE X), 5.0L (RPO L30
- VIN CODE M) OR 5.7L (RPO L31 - VIN CODE R) ENGINE AND
CALIFORNIA EMISSION EQUIPPED (RPO YF5)
This bulletin is being revised to add the 2002 and 2003 model years to the SCPI Special Policy on certain S/T, M/L, C/K, G, P and W4/NPR truck models. Please discard Special Policy Bulletin Number 99066E, dated February, 2003.
Some customers of 1996, 1997, 1998, 1999, 2000, 2001, 2002 model year S/T, M/L, C/K, G, P, W4/NPR trucks and 2003 NPR trucks, that are registered in California, equipped with 4.3L (RPO L35 and VIN Code W, or RPO LF6 and VIN Code X), 5.0L (RPO L30 and VIN Code M) or 5.7L (RPO L31 and VIN Code R) engine, and California emissions (RPO YF5), may experience a "Service Engine Soon" light, misfire, rough idle or hard start due to a deposit build-up on the Sequential Central Port Fuel Injector (SCPI) poppet valve(s). The deposit build-up may cause injector poppets to stick closed. Certain fuels have been found to interact with the SCPI system to cause the deposits.
SPECIAL POLICY ADJUSTMENT
This special policy covers the SCPI failure condition described above for a period of ten (10) years or 200,000 miles, whichever occurs first, from the date the vehicle was originally placed in service, regardless of ownership.
The repairs will be made at no charge to the owner. This special policy applies ONLY to repairs requiring SCPI system servicing, injector cleaning and/or MFI assembly replacement of the SCPI system. The customer should not be charged for performing a system check when it is determined that the SCPI system is not the cause of a customer complaint (labor operation T5532 is provided to submit claims for such system checks). Any additional necessary diagnosis and repairs that are not related to the SCPI condition are not covered by this special policy. The customer should be informed that any further service that is not covered by new vehicle warranty will not be covered by this policy.
Involved are certain 1996,1997,1998,1999, 2000, 2001, 2002 S/T, M/L, C/K, G, P, W4/NPR and 2003 NPR model vehicles, registered in California, equipped with 4.3L (RPO L35 - VIN Code W, or RPO LF6 - VIN Code X), 5.0L (RPO L30 - VIN Code M) or 5.7L (RPO L31 - VIN Code R) engine; and California emissions (RPO YF5). This Special Policy covers all vehicles within these model years, with these engine and emissions RPO's.
Have you had your injectors cleaned?
Okay, last - Looks like you may have some recalls on your vehicle. The dealer may fix these for free. Please contact the dealer service department, give them the VIN number of your car and have them check on these to see if they apply to you.