Engine Performance - Cold Start Stall or Roughness
88cad04Bulletin No. T-88-117
File in Group: 6C
Number: 115 Corp. Ref. No.: 816302
Date: April '88
SUBJECT: ENGINE STALL, ROUGHNESS OR REDUCED DRIVEABILITY AFTER COLD START
MODEIS AFFECTED: 1988 DE VILLES, FLEETWOODS, ELDORADOS AND SEVILLES
Some 1988 DeVilles, Fleetwoods, Eldorados, and Sevilles may experience an engine stall, engine roughness or a reduced driveability condition following an engine start in cold ambient temperatures. This condition is not usually experienced during warm engine operation or in warm ambient temperatures and may be intermittent. Fuel pressure may drop to 4-8 psi (28-55 kPa) when the condition occurs.
FIGURE 1 - FUEL PUMP:
This condition may be caused by an oversized fuel pressure relief spring in the electric in-tank fuel pump. Fuel pumps built between December 3, 1987 (Julian Date 3377) and January 31, 1988 (Julian Date 0318) may be affected, refer to Figure 1, Item 2. The oversized pressure relief spring reduces the pressure limit at which fuel pump bypass occurs. If internal fuel pump pressure goes high, as during a cold start, the fuel pump may go into a full bypass mode and not return to normal operation. Fuel is discharged out of the fuel pump relief port directly back into the fuel tank. The corresponding drop in fuel pressure to the throttle body results in the driveability and/or stalling condition.
To diagnose and repair this condition, the following steps should be performed:
NOTE: This procedure may be performed with the engine warm or cold.
1. Install a 0-60 psi (0-400 kPa) pressure gauge to the Schrader valve on the fuel supply line at the throttle body.
2. Start the engine and note the fuel pressure. Normal fuel pressure should be 10-12 psi (69-83 kPa). If fuel pressure is at or below 9 psi (62 kPa), replace the fuel pump. If pressure is within the normal range, proceed to step 3.
FIGURE 2 - FUEL LINES:
3. Allow the engine to run for 30 seconds to stabilize fuel flow. Using smooth-jawed needle nose pliers, clamp the fuel return line at the flex hose near the fuel tank, refer to Figure 2, for approximately 15 seconds. Release the clamp and note fuel pressure. If fuel pressure is at or below 9 psi (62 kpa), replace the fuel pump. If fuel pressure is above 9 psi, (62 kPa), refer to Section 6E-A, "DFI System Diagnosis" in the appropriate Service Information Manual.
A new fuel pump has been released for service use. This pump contains a revised pressure relief spring and is available from GMSPO using the following part numbers:
Eldorado/Seville: 25116285 DeVille/Fleetwood: 25116286
For warranty purposes use Labor Operation T6313 at 1.2 hours.