EXTENDED CRANK TIME/FUEL PRESSURE LEAKDOWN DIAGNOSIS
Models Affected: 1985 - 1988 FIREBIRD MODELS WITH 5.7L (VIN 8)
This bulletin is being revised to add information on tank pressure control valve diagnosis. Please discard bulletin 88-6-84 issued 12/88.
Some 1985 through 1988 Firebird models equipped with 5.7L (VIN 8) engines may experience long engine cranks when attempting to start the vehicle after soaks longer than 30 minute. There are several possible causes of this condition. These include but are not limited to: cold start injector not operating; fuel pump check valve, fuel pressure regulator or fuel injectors leaking down fuel pressure on shutdown.
Diagnosis
Diagnosis should begin by performing the "Cold Start Valve" test listed in section 6E3 (Chart A9) of the appropriate Service Manual to determine if the cold start injector is functioning properly. If not, the appropriate repairs should be made.
Next, the tank pressure control valve should be checked for a torn or leaking diaphragm. This may be accomplished by attaching a hand vacuum pump to the signal port on the valve, pumping to 15" Hg vacuum and checking for leakdown. No leakdown should occur.
If the cold start injector system and the tank pressure control valve are found to be functioning normally, the following procedure should be used to determine whether a fuel pump check valve, fuel pressure regulator, or leaking injectors are the cause of the long cranks.
1. Install a fuel pressure gage on the fuel rail schraeder valve, (such as that supplied in the injector plugging test kit).
2. Pressurize the system by turning the key on for a few seconds.
3. Turn the key off, and time the pressure reduction on the gage. (Initial pressure should be approximately 40 pounds per square inch (PSI), note the time it takes for a pressure drop of twenty PSI to occur. If the time exceeds twenty minutes, check valve, regulator, and fuel injectors are free of excessive leakage and the Service Manual should be referred to for other causes of long cranks.)
4. If the system pressure is reduced by 20 PSI or more in 20 minutes or less, then one or more of the three components mentioned are suspect.
5. Turn the key on for a few seconds to repressurize the system and clamp the rubber portion of the supply line closed using a pair of vise grips and a shop towel (to protect the fuel line from damage by the vise grips.)
6. Turn the key off, and again note the time it takes for a reduction of twenty PSI. If the time is a lot longer than the time noted in step 3, then replacement of the fuel pump is indicated.
7. If the times are similar, then repeat steps 5 and 6, only this time clamp the return line instead of the supply line. Once again note the time it takes for a twenty PSI pressure drop. If the time is a lot longer than previously, a faulty pressure regulator is indicated. If the time remains shorter than twenty minutes, leaking injectors are suspected. To confirm that there are leaking injectors, raise the fuel rail slightly out of the inlet manifold without disconnecting any fuel lines and place a small napkin or piece of paper under each injector. Pressurize the system by turning the key on for a few seconds then turn the key off and allow to sit for about 10 minutes. If a leaking injector is indicated by one or more drops of fuel on any of the napkins, all eight injectors should be replaced with service injector, P/N 10108481.
Parts are currently available from GMSPO.
Warranty Information
Labor Operation Number: T1404
Labor Time : 3.7 Hours
General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.
