PROM - Surge, Detonation or Code 32, EGR
Number: 89-263A-6ESection: 6E
Date: NOV. 1991
Corporate Bulletin No.: 136516
ASE No.: A1 & A8
Subject:
ENGINE DRIVEABILITY - SURGE HOT/COLD, DETONATION
Model and Year:
1987-89 C/K, R/V AND G/P TRUCKS WITH 7.4L ENGINE
THIS BULLETIN CANCELS AND SUPERSEDES DEALER SERVICE BULLETIN NUMBERS 88-162-6E, DATED AUGUST 1988; 88-195-6E, DATED MAY 1988; AND 89-263-6E, DATED OCTOBER 1989. ALL COPIES OF 88-162-6E, 88-195-6E AND 89-263-6E SHOULD BE DISCARDED.
Condition:
Some owners of 1987-89 C/K, R/V and G/P trucks with 7.4L engine may experience the following:
1. Surge on acceleration and/or at road load speeds
2. False Service Engine Soon Light - Code 32 (EGR)
3. Poor driveability during warm up
4. Detonation under load
Correction:
1. On 1987-89 models, check for vacuum leaks including:
A. TBI Base gasket to adapter
B. TBI Adapter to TBI
C. Re-torque intake manifold to 30 lbs.ft.
2. On 1987-89 models, check base timing (Spec. 4 degrees BTDC).
View A:
3. On 1987-88 models only, relocate Map Sensor to Air Cleaner.
A. Check Map Sensor operation using procedures on Page 3-122 and 3-123 of the 1991 Fuel and Emission Manual, replace sensor if necessary.
B. Disconnect vacuum tube assembly and electrical connection from Map Sensor.
View B:
C. Remove Map Sensor from upper plastic bracket (See Illustration, View B). CARE MUST BE TAKEN TO AVOID BREAKING BRACKET.
D. Remove sheet metal screw holding upper plastic bracket to lower metal bracket, and retain plastic bracket.
View C:
View D:
View E:
E. Add one additional 3/16" hole to plastic bracket and two 1/8" holes in Air Cleaner proper location using revised bracket as hole template (See View C and D).
F. Mount bracket so Map Sensor vacuum connection faces down toward engine, using two 8-3x1/2" sheet metal screws, P/N 447164.
G. Install vacuum hose harness, P/N 10129600 (See View D and E).
IMPORTANT:
On trucks not equipped with an accessory vacuum fitting in the manifold, install fitting, P/N 14088336 and use caps, P/N 343350 to plug any unused port.
H. Reinstall electrical.
4. On 1987-89 Check Control Idle Speed
A. On fully warm engine, Spec. is 750 RPM in Drive for Automatic Transmission and 800 RPM in Neutral for Manual Transmission.
B. IAC counts on both transmission should be between 5-30 counts.
If the control speed is not within the above specifications, a minimum idle speed adjustment must be made using procedure shown on Page 4-20 of the 1991 Fuel and Emission Manual.
5. Install latest PROM as shown on chart.
New New
PROM Broadcast New Scan
Transmission Axle Kit Code Tool I.D.
Auto (M-40) ALL 16169157 AZFT 9171
Man (M-20) 3.73 (GT4) 16169158 AZFU 9181
3.42 (GU6) " " "
Man (M-20) 4.10 (GT5) 16169159 AZFW 9191
4.56 (HC4) " " "
6. The Dealer should tell the customer that the Cold Start Procedure has been revised from that shown in his Owners Manual. After initial fire and run, the throttle should be cracked to about 1/4 to clean raw gas from the intake manifold.
Labor Operation Number: Labor Time
Relocating Map Sensor T7500 0.3 Hours
Replace PROM T0500 0.6 Hour C/K, R/V
0.7 Hour G/P