97 sierra: Fuel pressure

[ESKYMOPACK]

HI GUYS,

New here.... but having a big problem with starting the vehicle. 1997 GMC 1500 5.7 E.C. 4x4. 157,000 miles. Turns over nice, but hard starting especially when cold. Pressure tested (fuel) on rail @ 62 lbs (when key is turned to idiot lites) but B4 I actually turn key to starter, it drops down to nothing and as soon as I turn vehicle over (rotations) it goes back up to 60 lbs. So, what I'm wondering, is whether or not the fuel pump holds pressure with some sort of check-valve, because we replaced the battery, FPR, the map-sensor and did a tune-up already.

We checked the fuel pressure at the rail on a similar '98 3/4 ton with the same engine and it held pressure from when you turned the key to the idiot lites, until you tried to start it. Need your help!

[silveradotrailblazer]

How about your fuel filter? I would start back just before the fuel filter and check pressure and see if it hold pressure. If it doesnt its most likely fuel pump. If you have good pressure and it hold move to other side of fuel filter and check. Sometimes the little things (fuel filter) are the problem.

[Z71_guy]

i would just change the fuel filter and then check your fuel pressure on the rail, filters are not that expensive and it probably needs to be done

[GaryL]

Sorry this is so long, but here's what the service manual has on the fuel system.

FUEL SYSTEM PRESSURE TEST
1) Perform On-Board Diagnostic (OBD) System Check. See ONBOARD DIAGNOSTIC (OBD) SYSTEM CHECK in G - TESTS W/CODES - 5.7L article. After performing OBD system check, go to next step.

2) Turn ignition off for 10 seconds with A/C off. Relieve fuel pressure. See FUEL SYSTEM PRESSURE RELIEF. Connect Fuel Pressure Gauge (J-34730-1A) to fuel pressure test port. Turn ignition on with engine off. Fuel pump should run for 2 seconds. Bleed air out of fuel pressure gauge into container. Turn ignition off for 10 seconds. Turn ignition on with engine off. Cycle ignition to obtain highest fuel pressure possible. Observe fuel pressure with fuel pump running. Fuel pressure should be 60-66 psi (4.2-4.6 kg/cm

�� ) on CSI fuel system and 56-62 psi (4.0-4.4 kg/cm �� ) on SFI fuel system. If fuel pressure is as specified, go to next step. If fuel pressure is not as specified, go to step 8).

3) Turn ignition off for 10 seconds with A/C off. Turn ignition on with engine off. Fuel pump should run for 2 seconds. Observe fuel pressure after fuel pump stops running. After fuel pump stops, fuel pressure should stabilize and remain constant. If pressure is within specification and holds, go to step 5). If pressure is not within specification, or is within specification but does not hold, go to next step.

4) Relieve fuel pressure. See FUEL SYSTEM PRESSURE RELIEF. Disconnect fuel filter. Drain any remaining fuel from fuel pipes into container. Install Fuel Line Shutoff Valve (J-42873-1) in place of fuel filter. Open valve on shutoff valve. Turn ignition off for 10 seconds with A/C off. Turn ignition on with engine off. Check for leaks at shutoff valve. Start engine and idle for 30 seconds. Turn ignition off for 10 seconds with A/C off. Turn ignition on with engine off. Wait for fuel pressure to build. Close valve on shutoff valve. Fuel pressure should be as specified and remain constant. If pressure is as specified and holds, go to step 12). If pressure is not as specified, or is as specified but does not hold, go to step 6).

5) If fuel pressure is suspected of decreasing during acceleration, cruise or hard cornering, go to step 27). If fuel pressure is not suspected of decreasing during acceleration, cruise or hard corning, go to step 26).

6) Check fuel feed line between shutoff valve and fuel pipes. If fuel feed line is faulty, go to step 25). If fuel feed line is okay, go to next step.

7) Open valve on shutoff valve. Relieve fuel pressure. See FUEL SYSTEM PRESSURE RELIEF. Disconnect fuel return pipe union located near fuel filter. Drain remaining fuel from fuel pipes into container. Install Fuel Line Shutoff Valve (J-42873-2) in place of fuel return pipe union. Open valve on shutoff valve. Turn ignition off for 10 seconds with A/C off. Turn ignition on with engine off. Check for leaks at fuel shutoff valve fittings. Start engine and idle for 30 seconds. Turn ignition off for 10 seconds with A/C off. Turn ignition on with engine off. Wait for fuel pressure to build. Close valve on shutoff valve installed on fuel return pipe. If fuel pressure remains constant, go to step 22). If fuel pressure does not remain constant, go to step 29).

8) Turn ignition off for 10 seconds with A/C off. Turn ignition on with engine off. Fuel pump should run for 2 seconds, and then turn off. Observe fuel pressure after fuel pump stops running. If fuel pressure is present, go to step 13). If fuel pressure os not present, go to next step.

9) Turn ignition off. Connect a fused jumper wire between battery voltage and fuel pump test terminal. Listen for operation of fuel pump. If fuel pump operates, go to next step. If fuel pump does not operate, see FUEL SYSTEM ELECTRICAL CIRCUIT under G - TESTS W/CODES - 5.7L.

10) Check for plugged fuel filter, plugged fuel pump strainer or restricted fuel line. If a problem is found, go to next step. If a problem is not found, go to step 12).

11) Repair or replace as necessary. After repairs, go to step 30).

12) Replace fuel sending unit assembly. After replacing fuel sending unit assembly, go to step 30).

13) Turn ignition off for 10 seconds with A/C off. Turn ignition on with engine off. Fuel pump should run for 2 seconds. Observe fuel pressure. If fuel pressure is greater than 66 psi (4.6 kg/cm

�� ) on CSI fuel system or 62 psi (4.4 kg/cm �� ) on SFI fuel system, go to next step. If fuel pressure is not greater than specified, go to step 15).

14) Relieve fuel pressure. See FUEL SYSTEM PRESSURE RELIEF. Disconnect engine compartment fuel return line. Attach a flexible hose to fuel return line. Place other end of hose in container. Observe fuel pressure within 2 seconds after ignition is turned on. Fuel pressure should be 60-66 psi (4.2-4.6 kg/cm

�� ) on CSI fuel system and 56-62 psi (4.0-4.4 kg/cm �� ) on SFI fuel system. If fuel pressure is as specified, go to step 16). If fuel pressure is not as specified, go to step 17).

15) Turn ignition off for 10 seconds with A/C off. Turn ignition on with engine off. Fuel pump should run for 2 seconds. Observe fuel pressure. If fuel pressure is less than 60 psi (4.2 kg/cm

�� ) on CSI fuel system or 56 psi (4.0 kg/cm �� ) on SFI fuel system, go to step 19). If fuel pressure is not less than specified, go to step 30).

(Continued below)

[GaryL]

Continued:

16) Locate and repair restriction in fuel return line. After repairs, go to step 30). If fuel return line is not restricted, go to next step.

17) Check for restriction in engine fuel return outlet pipe at point where fuel line was disconnected. If fuel return pipe is restricted, go to next step. If fuel return pipe is not restricted, go to step 22).

18) Replace engine fuel pipes. After replacing engine fuel pipes, go to step 30).

19) Inspect in-line fuel filter and fuel line for restriction. If restriction is found, go to next step. If restriction is not found, go to step 21).

20) Repair or replace in-line fuel filter and fuel line. After repairs, go to step 30).

21) Relieve fuel pressure. See FUEL SYSTEM PRESSURE RELIEF.


Disconnect fuel return pipe union located near fuel filter. Drain remaining fuel from fuel pipes into container. Install Fuel Line Shutoff Valve (J-42873-2) in place of fuel return pipe union. Open valve on shutoff valve. Turn ignition off for 10 seconds with A/C off. Turn ignition on with engine off. Bleed air out of fuel pressure gauge into container. Connect a fused jumper wire between battery voltage and fuel pump test terminal. DO NOT allow fuel pressure to exceed 75 psi (4.5 kg/cm

�� ). Excess pressure may damage fuel pressure regulator. Slowly close valve on shutoff valve installed on fuel return pipe. Fuel pressure should increase to greater than 66 psi (4.6 kg/cm �� ) on CSI fuel system or 62 psi (4.4 kg/cm �� ) on SFI fuel system. If fuel pressure increases as specified, go to next step. If fuel pressure does not increase as specified, go to step 23).

22) Replace fuel pressure regulator. After replacing fuel pressure regulator, go to step 30).

23) Check for the following conditions:
* Low fuel pump voltage due to high resistance connections.
* High fuel pump voltage due to internal pump binding.
* Poor fuel pump ground.
* Partially restricted fuel pump strainer.
* Incorrect or faulty fuel pump.
If any of the listed conditions are present, go to next step.
If none of the listed conditions are present, go to step 12).

24) Repair or replace as necessary. After repairs, go to step 30).

25) Replace fuel feed line. After repairs, go to step 30).

26) Start engine. Allow engine to idle until normal operating temperature is reached. Open throttle quickly. Observe fuel pressure. Fuel pressure should increase to near 66 psi (4.6 kg/cm

�� ) on CSI fuelsystem or 62 psi (4.4 kg/cm �� ) on SFI fuel system. If fuel pressure increases quickly, see H - TESTS W/O CODES - 5.7L article. If fuel pressure does not increase quickly, go to next step.

27) Check for the following conditions:
* In-line fuel filter for restriction.
* Fuel feed pipe for restriction.
* Mispositioned or damaged fuel pump strainer.
* Fuel pump flex pipe for leaks.
* Vehicle is equipped with correct fuel pump.
* Fuel pump electrical wiring for high resistance.
If any of the listed conditions are present, go to next step.
If none of the listed conditions are present, go to step 12).

28) Repair or replace as necessary. After repairs, go to step 30).

29) Locate and replace any leaking injector(s). After replacing leaking injector(s), go to next step. If all injectors are okay, go to FUEL INJECTOR BALANCE TEST under FUEL SYSTEM in I - SYSTEM/COMPONENT TESTS - 5.7L article.

30) Using scan tool, select CAPTURE INFO, REVIEW INFO
function. If additional DTC(s) is present, diagnose DTC(s). See G - TESTS W/CODES - 5.7L article. If DTC(s) is not present, system is

okay.

[ESKYMOPACK]

Continued:

16) Locate and repair restriction in fuel return line. After repairs, go to step 30). If fuel return line is not restricted, go to next step.

17) Check for restriction in engine fuel return outlet pipe at point where fuel line was disconnected. If fuel return pipe is restricted, go to next step. If fuel return pipe is not restricted, go to step 22).

18) Replace engine fuel pipes. After replacing engine fuel pipes, go to step 30).

19) Inspect in-line fuel filter and fuel line for restriction. If restriction is found, go to next step. If restriction is not found, go to step 21).

20) Repair or replace in-line fuel filter and fuel line. After repairs, go to step 30).

21) Relieve fuel pressure. See FUEL SYSTEM PRESSURE RELIEF.


Disconnect fuel return pipe union located near fuel filter. Drain remaining fuel from fuel pipes into container. Install Fuel Line Shutoff Valve (J-42873-2) in place of fuel return pipe union. Open valve on shutoff valve. Turn ignition off for 10 seconds with A/C off. Turn ignition on with engine off. Bleed air out of fuel pressure gauge into container. Connect a fused jumper wire between battery voltage and fuel pump test terminal. DO NOT allow fuel pressure to exceed 75 psi (4.5 kg/cm

�� ). Excess pressure may damage fuel pressure regulator. Slowly close valve on shutoff valve installed on fuel return pipe. Fuel pressure should increase to greater than 66 psi (4.6 kg/cm �� ) on CSI fuel system or 62 psi (4.4 kg/cm �� ) on SFI fuel system. If fuel pressure increases as specified, go to next step. If fuel pressure does not increase as specified, go to step 23).

22) Replace fuel pressure regulator. After replacing fuel pressure regulator, go to step 30).

23) Check for the following conditions:
* Low fuel pump voltage due to high resistance connections.
* High fuel pump voltage due to internal pump binding.
* Poor fuel pump ground.
* Partially restricted fuel pump strainer.
* Incorrect or faulty fuel pump.
If any of the listed conditions are present, go to next step.
If none of the listed conditions are present, go to step 12).

24) Repair or replace as necessary. After repairs, go to step 30).

25) Replace fuel feed line. After repairs, go to step 30).

26) Start engine. Allow engine to idle until normal operating temperature is reached. Open throttle quickly. Observe fuel pressure. Fuel pressure should increase to near 66 psi (4.6 kg/cm

�� ) on CSI fuelsystem or 62 psi (4.4 kg/cm �� ) on SFI fuel system. If fuel pressure increases quickly, see H - TESTS W/O CODES - 5.7L article. If fuel pressure does not increase quickly, go to next step.

27) Check for the following conditions:
* In-line fuel filter for restriction.
* Fuel feed pipe for restriction.
* Mispositioned or damaged fuel pump strainer.
* Fuel pump flex pipe for leaks.
* Vehicle is equipped with correct fuel pump.
* Fuel pump electrical wiring for high resistance.
If any of the listed conditions are present, go to next step.
If none of the listed conditions are present, go to step 12).

28) Repair or replace as necessary. After repairs, go to step 30).

29) Locate and replace any leaking injector(s). After replacing leaking injector(s), go to next step. If all injectors are okay, go to FUEL INJECTOR BALANCE TEST under FUEL SYSTEM in I - SYSTEM/COMPONENT TESTS - 5.7L article.

30) Using scan tool, select CAPTURE INFO, REVIEW INFO
function. If additional DTC(s) is present, diagnose DTC(s). See G - TESTS W/CODES - 5.7L article. If DTC(s) is not present, system is

okay.

THANKS GUYS. I'm copying this procedure for future reference. Sorry, I thought I had mentioned that the fuel filter was the first thing I repalced. It WAS the fuel pump! It would not hold pressure at the rail, everything is fine now! Thank You, ESKYMOPACK