Service Procedure

The following checks must be performed to qualify the engine support systems. A "Diagnostic Check Sheet" has been provided to assist in this process, and must be attached to the repair order.

1. Check PROM ID using Tech 1. See "Parts Information" of this bulletin for ordering replacement PROM. If new PROM is currently in truck, do not replace.
2. Check for diagnostic trouble codes (DTC's), both history and current. Use the 1994 Diesel Service Manual Supplement for diagnosis and correction. Clear all current and history DTCs before proceeding.

Attachment 2:

3. Check wiring connections at batteries, relay center, engine grounds and wiring grounds for secure and complete attachment.

4. Check air filter, clean or replace as necessary.
5. Check cold cranking RPM, spec: 100 RPM cold engine (see "Cranking Speed Check").
6. Check fuel supply system pressure, spec: 3 psi minimum at idle (See "Fuel Supply System Check").
7. Check glow plugs (See "Glow Plug System Check").

Once above procedures have been completed, install service kit which contains a visor label (engine starting procedure), electronic filter harness, and two stage housing pressure regulator (see "Electronic Filter Harness" and "Two Stage Housing Pressure Regulator" for installation procedure) . Install replacement PROM. Refer to the "Parts Information" section for determining proper replacement PROM.

8. Check for air in fuel system (see "Diagnosing Air In Fuel Lines") for procedure.
9. Relearn the TDC Offset. If the relearned value is between +0.75 and -1.75, continue to the next step. If the value is not between +0.75 and -1.75, reset pump timing following the procedure shown in "Timing Procedure".
10. Check fuel rate at idle using Tech 1 (maximum spec. 13 mm for manual transmission or 15 mm for automatic transmission). If out of specification, check fuel quality using a hydrometer (J34352). Refer to appropriate service manual for procedure and empty fuel system and refill, with known good fuel source if required.

NOTE:
IF OWNERS CONCERN WAS HOT START OR EXTENDED CRANK HOT OF MORE THAN 4 SECONDS BEFORE STARTING, CONTINUE WITH THE FOLLOWING DIAGNOSIS.

11. Block radiator and bumper holes, operate engine with A/C off at 3400 RPM in neutral/park until coolant temperature reaches 220 degrees Fahrenheit as indicated on Tech 1, or stabilizes at a lower number.
12. Shut off engine and let vehicle hot soak for 20-25 minutes.
13 Using a timer which accurately reads "seconds" record crank time.
14. If crank time exceeds 4 seconds check cranking speed, spec: 170-180 RPM (see "Cranking Speed Check").
15. If crank speed is within specification and crank time exceeds 4 seconds replace injection pump.

NOTE:
Injection pumps are to be exchanged through Stanadyne. DO NOT order form GMSPO.

Injection pumps are currently available through a Stanadyne Dealer (see GM Corporate Service Bulletin 376302, dated September 1993, for Stanadyne Dealer near you.)

16. Change engine oil, oil filter and lubricate chassis.
17. Install Campaign Identification Label.