96+ Hard Start, No Start, Rough Idle Info
blazee
08-28-2005, 07:03 PM
Fuel problems are the main cause of hard starts, no starts, rough idle and stalling in 96+ engines......This is assuming that regular maintenance has been performed:
Plugs
Wires
Cap
Rotor
Fuel filter
Air Filter
PCV valve
You can also clean various individual componets for improved performance:
Exhaust Gas Recirculation (EGR) valve - Simply remove - clean with brake cleaner, carb cleaner, etc. - reinstall with new gasket
Idle Air Control (IAC) valve - Remove - clean pintle and port with brake cleaner, carb cleaner, etc. - reinstall
Mass Air Flow (MAF) sensor - Gently clean with brake cleaner or electronics cleaner - don't use carb cleaner or similar products because they will leave a residue that will have a negative effect on performance.
Here are a few articles about CSFI:
Those Vortec equipped GM trucks are work horses, as long as you keep ’em well fed. That would be with fuel pressure and plenty of it. The Central Sequential Fuel Injection (CSFI) system used on 1996 and newer trucks helps make driving fun again. The system complies with the stringent emission requirements, starts good, idles smoothly, increases the horsepower, and the torque makes you feel like you were throttling one of the old high performance engines again.
Some of our troubleshooting procedures and test equipment will definitely be rearranged as the vehicles make their way into our repair shops. Troubleshooting steps that were once second on the list may be moved up front in the diagnostic procedure. For example: if I were diagnosing a no-start, hard start, surge or stalling condition with one of the mentioned vehicles, I would be looking at the fuel system pressure first. Low fuel pressure has been a real problem.
Unlike some of the earlier Central Port Systems used on the 4.3L engines, which contained a single throttle body type injector which fed all poppet nozzles, the new system includes an injector for each poppit nozzle, attached by a plastic tube. Each injector is pulsed sequentially. When the injectors are mounted in the fuel meter assembly they are surrounded by fuel with the exception of the top and bottom. When the injector coil energizes, the fuel under pressure is forced through the injector and a plastic tube attached to a poppet valve. The fuel pressure overcomes the spring tension in the poppet valve forcing it from its ball seat, thus spraying fuel for a given cylinder. When the injector de-energizes, the poppet valve spring forces the ball seat closed, cutting off fuel at the poppet nozzle. If the fuel pressure drops below the minimum, the poppet nozzles will not receive adequate pressure to overcome the spring tension, thus no fuel spray. A poppet nozzle which sticks open results in a pressure loss once the engine is shut down. This can promote dieseling, long crank times or plug fouling.
FUEL PRESSURE IS IMPERATIVE
The regulated system pressure calls for 60–66 PSI with the pump running and engine off. If the fuel pressure falls below 60 PSI the system is in trouble. Most of the time the engine will not start, especially when cold. If it does, the system will be lean and DTC codes will be set. A definite hard start or poor performance will occur. We have encountered systems that would start and idle, when hot, at 50 PSI. But idle is all it would do. It was not driveable. If the pressure drops while driving, the engine will usually surge and stall. A restricted fuel line or fuel filter would be a suspect. When performing the fuel pressure test do not allow the system pressure to exceed 75 PSI or damage to the regulator will occur.
When the ignition switch is turned to the on position, the Vehicle Control Module (VCM) energizes the fuel pump relay for 2 seconds, allowing the fuel pump to pressurize the system. If the VCM fails to see ignition reference pulses in 2 seconds the module shuts off the pump relay. As a back-up to a defective fuel pump relay or VCM signal to the relay, the oil pressure switch will activate the fuel pump when the oil pressure reaches 4 PSI. However, a long crank time would be encountered.
FUEL PULSATOR
Many complaints of hard starts or no starts have been registered on 1992-1996 GM trucks. When the technician performs the diagnostics, a low fuel pressure may be encountered. The fuel pump is usually diagnosed as the culprit. Removing the pump will often reveal a split in the pulsator/dampner which will result in a loss of fuel pressure. The mentioned pulsator is the flexible connector positioned between the fuel pump and the metal line in the fuel tank. The split is due to high concentrations of alcohol in the fuel attacking the material. GM has a new pulsator (#25175836) constructed of Viton which is resistant to the alcohol. Instead of the pulsator, some pumps incorporate a rubber hose approximately 1⁄4 inch thick which attaches the pump to the metal line. Examine the hose for deterioration or splits.
WHEN THE PRESSURE DROPS
Likely suspects for a dropping pressure condition would include:
a) Leaking fuel injectors or poppet valves
b) Damaged injector O-rings which seal the injectors in the fuel metering body
c) Leaking pressure regulator valve
d) Damaged or split fuel pulsator/dampner
e) Leaking fuel pump check valve
f) Leaking fuel lines
DIAGNOSTICS
When diagnosing engine performance symptoms, we establish a history of pattern failures. While this can save diagnostic time, it can lead to a premature diagnosis. It happens to the best. Failing to make an accurate diagnosis puts our integrity in jeopardy and some unnecessary expense upon the customer. Imagine…a customer arrives in a 1995-2002 GM truck or SUV with a complaint of a cold start-up miss that clears within a few moments. It may or may not be accompanied by an illuminated SES lamp and stored diagnostic trouble codes (DTCs). A fuel injection related problem would be a likely suspect. And there are some good reasons to take that diagnostic approach. Hours and many parts later, you may determine that the condition was cooling system related. Does that sound weird? Trust me, the symptoms can mirror one another.
PLUGGED INJECTORS
Pintle style fuel injectors were the popular injector in the mid 1980’s. Thousands of test miles were performed by GM without a single failure. But, when the vehicles were put into service, plugged injectors became a common failure. The failures would occur following engine shut down and heat soak. The olefins and diolefins in the fuel would bake on the injector tips, forming a crusty deposit that would restrict fuel flow. The reason this condition failed to surface during the test miles was due to the engines never being shut down. They just racked up mileage. Cleaning was a short-term fix.
MULTEC INJECTORS
By the late 1980’s, a new design injector was introduced that was supposed to eliminate injector plugging. It was referred to as Multec, and its metered disc design would not become restricted. Initially GM advised against cleaning this style injector, as it would offer no benefit and solvents could damage the coil windings. Later, due to injector plugging, they supported injection cleaning, providing certain cleaners were not used.
FRETTING CORROSION
Another condition that has plagued the injection system is “terminal fretting corrosion.” This is a corrosive condition that is microscopic in nature, making it virtually impossible to detect in the field. Fretting is a rubbing motion that occurs between two surfaces, promoting a build-up of insulating debris that accumulates on the electrical connections. Engine vibration, fuel injector vibrations and wiring harness movement all contribute to the fretting condition. The level of contamination determines the performance symptom. The condition may vary with wiring harness movement, resulting in an intermittent condition. Wiggling a connector may initiate or correct a performance condition. If you recall, Nissan had numerous failures with the Maxima, involving fuel injector terminal corrosion and intermittent performance problems.
POPPET VALVE DESIGN CSFI
GM trucks and SUV’s from 1995-2002 equipped with the 4.3L, 5.0L, 5.7L engines equipped with the Central Sequential Fuel Injection (CSFI) may encounter injector plugging. This system utilizes a fuel meter assembly equipped with fuel injectors. When the injectors are pulsed, fuel under pressure is forced through an injector and a plastic tube attached to a poppet valve. The fuel pressure overcomes the spring pressure in the poppet valve, forcing the ball from its seat, thus injecting fuel into a given cylinder. Fuel system pressure is critical, as the pressure range must be between 60-66 psi with the fuel pump running and the engine off. Pressure below 60 psi will usually result in a no-start condition, or the system will be lean and will barely run above idle, and DTCs may be set.
The CSFI system may encounter symptoms of rough idle or missing, especially following a coldstart. The SES lamp may be illuminated and misfire codes may be stored. The condition is due to deposit formations on the poppet valves and seats. Assuming that the injectors are pulsing and the fuel pressure is to spec, GM has a recommended cleaning procedure and chemical that will clean the poppet valves. If the cleaning procedure does not produce satisfactory results, or if the condition is repetitive, a system conversion to Multiport Flexible Injection (MFI) is available. The conversion eliminates the CSFI poppet valves.
COOLING SYSTEM CHECK
For a cold-start miss, would you have considered checking the integrity of the cooling system, prior to pursuing a fuel injection problem? With GM’s track record of leaking intake gaskets, it’s a good possibility that the intake gasket could be the culprit. When the gasket fails, coolant will leak internally into the engine oil, externally down the side of the engine, or into a combustion chamber. The cold start-up miss may be due to coolant seepage into a cylinder after engine shut-down. It usually involves cylinders #1 or #2. Following a cold start-up, an engine miss will be encountered until the coolant is consumed. The symptoms mirror that of a sticking poppet valve or plugged injector. Spark knock is not uncommon and DTCs may be stored. There may not be any physical evidence on the spark plugs to indicate coolant leakage into the chambers. A pressure test should be performed. Once removed, a visual inspection of the intake gasket will reflect the leakage. GM has an updated intake gasket. Make certain that you follow the proper tightening sequence and torque load on the bolts. Otherwise, you will be pulling the intake again.
I've gotten a lot of requests for the TSB that covers the GM procedure for cleaning the poppet valves or converting to the MFI system. I finally got it hosted so now anyone can get it with out having to email me and wait for me to check my inbox. The cleaning procedure is pretty pointless, it is over priced and was only conceived as a way for GM to save money. The MFI conversion is about $200 for parts and well worth it.
http://www.myfilehut.com/userfiles/13931/059041%20CLEAN%20CSFI%20POPPIT%20VALVES%20OR%20CON VERT%20TO%20MFI.pdf
Plugs
Wires
Cap
Rotor
Fuel filter
Air Filter
PCV valve
You can also clean various individual componets for improved performance:
Exhaust Gas Recirculation (EGR) valve - Simply remove - clean with brake cleaner, carb cleaner, etc. - reinstall with new gasket
Idle Air Control (IAC) valve - Remove - clean pintle and port with brake cleaner, carb cleaner, etc. - reinstall
Mass Air Flow (MAF) sensor - Gently clean with brake cleaner or electronics cleaner - don't use carb cleaner or similar products because they will leave a residue that will have a negative effect on performance.
Here are a few articles about CSFI:
Those Vortec equipped GM trucks are work horses, as long as you keep ’em well fed. That would be with fuel pressure and plenty of it. The Central Sequential Fuel Injection (CSFI) system used on 1996 and newer trucks helps make driving fun again. The system complies with the stringent emission requirements, starts good, idles smoothly, increases the horsepower, and the torque makes you feel like you were throttling one of the old high performance engines again.
Some of our troubleshooting procedures and test equipment will definitely be rearranged as the vehicles make their way into our repair shops. Troubleshooting steps that were once second on the list may be moved up front in the diagnostic procedure. For example: if I were diagnosing a no-start, hard start, surge or stalling condition with one of the mentioned vehicles, I would be looking at the fuel system pressure first. Low fuel pressure has been a real problem.
Unlike some of the earlier Central Port Systems used on the 4.3L engines, which contained a single throttle body type injector which fed all poppet nozzles, the new system includes an injector for each poppit nozzle, attached by a plastic tube. Each injector is pulsed sequentially. When the injectors are mounted in the fuel meter assembly they are surrounded by fuel with the exception of the top and bottom. When the injector coil energizes, the fuel under pressure is forced through the injector and a plastic tube attached to a poppet valve. The fuel pressure overcomes the spring tension in the poppet valve forcing it from its ball seat, thus spraying fuel for a given cylinder. When the injector de-energizes, the poppet valve spring forces the ball seat closed, cutting off fuel at the poppet nozzle. If the fuel pressure drops below the minimum, the poppet nozzles will not receive adequate pressure to overcome the spring tension, thus no fuel spray. A poppet nozzle which sticks open results in a pressure loss once the engine is shut down. This can promote dieseling, long crank times or plug fouling.
FUEL PRESSURE IS IMPERATIVE
The regulated system pressure calls for 60–66 PSI with the pump running and engine off. If the fuel pressure falls below 60 PSI the system is in trouble. Most of the time the engine will not start, especially when cold. If it does, the system will be lean and DTC codes will be set. A definite hard start or poor performance will occur. We have encountered systems that would start and idle, when hot, at 50 PSI. But idle is all it would do. It was not driveable. If the pressure drops while driving, the engine will usually surge and stall. A restricted fuel line or fuel filter would be a suspect. When performing the fuel pressure test do not allow the system pressure to exceed 75 PSI or damage to the regulator will occur.
When the ignition switch is turned to the on position, the Vehicle Control Module (VCM) energizes the fuel pump relay for 2 seconds, allowing the fuel pump to pressurize the system. If the VCM fails to see ignition reference pulses in 2 seconds the module shuts off the pump relay. As a back-up to a defective fuel pump relay or VCM signal to the relay, the oil pressure switch will activate the fuel pump when the oil pressure reaches 4 PSI. However, a long crank time would be encountered.
FUEL PULSATOR
Many complaints of hard starts or no starts have been registered on 1992-1996 GM trucks. When the technician performs the diagnostics, a low fuel pressure may be encountered. The fuel pump is usually diagnosed as the culprit. Removing the pump will often reveal a split in the pulsator/dampner which will result in a loss of fuel pressure. The mentioned pulsator is the flexible connector positioned between the fuel pump and the metal line in the fuel tank. The split is due to high concentrations of alcohol in the fuel attacking the material. GM has a new pulsator (#25175836) constructed of Viton which is resistant to the alcohol. Instead of the pulsator, some pumps incorporate a rubber hose approximately 1⁄4 inch thick which attaches the pump to the metal line. Examine the hose for deterioration or splits.
WHEN THE PRESSURE DROPS
Likely suspects for a dropping pressure condition would include:
a) Leaking fuel injectors or poppet valves
b) Damaged injector O-rings which seal the injectors in the fuel metering body
c) Leaking pressure regulator valve
d) Damaged or split fuel pulsator/dampner
e) Leaking fuel pump check valve
f) Leaking fuel lines
DIAGNOSTICS
When diagnosing engine performance symptoms, we establish a history of pattern failures. While this can save diagnostic time, it can lead to a premature diagnosis. It happens to the best. Failing to make an accurate diagnosis puts our integrity in jeopardy and some unnecessary expense upon the customer. Imagine…a customer arrives in a 1995-2002 GM truck or SUV with a complaint of a cold start-up miss that clears within a few moments. It may or may not be accompanied by an illuminated SES lamp and stored diagnostic trouble codes (DTCs). A fuel injection related problem would be a likely suspect. And there are some good reasons to take that diagnostic approach. Hours and many parts later, you may determine that the condition was cooling system related. Does that sound weird? Trust me, the symptoms can mirror one another.
PLUGGED INJECTORS
Pintle style fuel injectors were the popular injector in the mid 1980’s. Thousands of test miles were performed by GM without a single failure. But, when the vehicles were put into service, plugged injectors became a common failure. The failures would occur following engine shut down and heat soak. The olefins and diolefins in the fuel would bake on the injector tips, forming a crusty deposit that would restrict fuel flow. The reason this condition failed to surface during the test miles was due to the engines never being shut down. They just racked up mileage. Cleaning was a short-term fix.
MULTEC INJECTORS
By the late 1980’s, a new design injector was introduced that was supposed to eliminate injector plugging. It was referred to as Multec, and its metered disc design would not become restricted. Initially GM advised against cleaning this style injector, as it would offer no benefit and solvents could damage the coil windings. Later, due to injector plugging, they supported injection cleaning, providing certain cleaners were not used.
FRETTING CORROSION
Another condition that has plagued the injection system is “terminal fretting corrosion.” This is a corrosive condition that is microscopic in nature, making it virtually impossible to detect in the field. Fretting is a rubbing motion that occurs between two surfaces, promoting a build-up of insulating debris that accumulates on the electrical connections. Engine vibration, fuel injector vibrations and wiring harness movement all contribute to the fretting condition. The level of contamination determines the performance symptom. The condition may vary with wiring harness movement, resulting in an intermittent condition. Wiggling a connector may initiate or correct a performance condition. If you recall, Nissan had numerous failures with the Maxima, involving fuel injector terminal corrosion and intermittent performance problems.
POPPET VALVE DESIGN CSFI
GM trucks and SUV’s from 1995-2002 equipped with the 4.3L, 5.0L, 5.7L engines equipped with the Central Sequential Fuel Injection (CSFI) may encounter injector plugging. This system utilizes a fuel meter assembly equipped with fuel injectors. When the injectors are pulsed, fuel under pressure is forced through an injector and a plastic tube attached to a poppet valve. The fuel pressure overcomes the spring pressure in the poppet valve, forcing the ball from its seat, thus injecting fuel into a given cylinder. Fuel system pressure is critical, as the pressure range must be between 60-66 psi with the fuel pump running and the engine off. Pressure below 60 psi will usually result in a no-start condition, or the system will be lean and will barely run above idle, and DTCs may be set.
The CSFI system may encounter symptoms of rough idle or missing, especially following a coldstart. The SES lamp may be illuminated and misfire codes may be stored. The condition is due to deposit formations on the poppet valves and seats. Assuming that the injectors are pulsing and the fuel pressure is to spec, GM has a recommended cleaning procedure and chemical that will clean the poppet valves. If the cleaning procedure does not produce satisfactory results, or if the condition is repetitive, a system conversion to Multiport Flexible Injection (MFI) is available. The conversion eliminates the CSFI poppet valves.
COOLING SYSTEM CHECK
For a cold-start miss, would you have considered checking the integrity of the cooling system, prior to pursuing a fuel injection problem? With GM’s track record of leaking intake gaskets, it’s a good possibility that the intake gasket could be the culprit. When the gasket fails, coolant will leak internally into the engine oil, externally down the side of the engine, or into a combustion chamber. The cold start-up miss may be due to coolant seepage into a cylinder after engine shut-down. It usually involves cylinders #1 or #2. Following a cold start-up, an engine miss will be encountered until the coolant is consumed. The symptoms mirror that of a sticking poppet valve or plugged injector. Spark knock is not uncommon and DTCs may be stored. There may not be any physical evidence on the spark plugs to indicate coolant leakage into the chambers. A pressure test should be performed. Once removed, a visual inspection of the intake gasket will reflect the leakage. GM has an updated intake gasket. Make certain that you follow the proper tightening sequence and torque load on the bolts. Otherwise, you will be pulling the intake again.
I've gotten a lot of requests for the TSB that covers the GM procedure for cleaning the poppet valves or converting to the MFI system. I finally got it hosted so now anyone can get it with out having to email me and wait for me to check my inbox. The cleaning procedure is pretty pointless, it is over priced and was only conceived as a way for GM to save money. The MFI conversion is about $200 for parts and well worth it.
http://www.myfilehut.com/userfiles/13931/059041%20CLEAN%20CSFI%20POPPIT%20VALVES%20OR%20CON VERT%20TO%20MFI.pdf
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