Engine - Driveability Conditions/Stored Codes
90chevy11Number: 88-440-6E
Secton: 6E
Date: May 1990
Corporate Bulletin No.: 936518
Subject: DRIVEABILITY CONDITIONS AND/OR STORED ENGINE CODES
Model and Year: 1987-88 A, J, L WITH 2.8L (VIN CODE W) ENGINE
TO: ALL CHEVROLET DEALERS
THIS BULLETIN CANCELS AND SUPERSEDES DEALER SERVICE BULLETIN NO. 88-435-6E, DATED FEBRUARY 1990. ADDITIONAL STEPS AND INFORMATION UNDER 3C AND 3I HAVE BEEN INCLUDED. ALL COPIES OF 88-435-6E SHOULD BE DISCARDED.
Some customers with an engine/vehicle combination listed below
1987 J-Car With a 2.8L Engine (Vin Code W)
1987-88 A and L Models With a 2.8L Engine (Vin Code W) may comment that they have experienced one or more of the following conditions:
A cold start stall or sag, A decel stall, A tip-in hesitation, A check engine light with stored Codes 23, 25, 33, 34, or
An engine speed flare during a declutch operation with a manual transmission equipped vehicle.
These conditions may be attributed to a number of components/interactions. In the interest of simplifying diagnosis and repair, the following procedure has been developed to reduce system sensitivity, thereby addressing a variety of potential causes simultaneously.
If a customer comment concerning an occasional engine stall or a drive hesitation is received, and/or a stored Code 33 or 34 is found, then complete the following procedure:
1. Perform diagnostic procedures per Section 6E of the Service Manual, and correct any faults except for Codes 33, 34, 23 or 25. If the diagnostics indicate the Mass Air Flow (MAF) is to be replaced or a Code 33 or 34 is present, DO NOT REPLACE THE MAF SENSOR! Proceed to Step # 3. If a Code 23 or 25 is present, go to Step # 2 below. PROCEED TO STEP # 3 ONLY IF NORMAL DIAGNOSTIC CHECKS DID NOT IDENTIFY A CAUSE FOR THE CUSTOMER CONCERN.
2. If a Code 23 or 25 is stored, perform the model year diagnostics for the Manifold Air Temperature Sensor (MAT). If the diagnostics indicate that the MAT is faulty and replacement is required, replace the combination MAT/MAF sensor. Proceed to Step # 3.
3. Install a new MEM-CAL into the Engine Control Module (ECM) per instructions below. The new MEM-CAL is available from GMSPO. See attached service part number chart. Install the identification label package to the ECM access door and to the left shock tower per label kit, P/N 10154725 instructions.
IMPORTANT: The new MEM-CAL to be installed does not need or use the existing MAF signal; however, it does need and use the MAT signal.
A.) Pull the underhood ECM continous power fuse or disconnect the battery and
leave it disconnected for at least 10 minutes.
B.) Remove MAF relay, if applicable, and discard. Tape up connector to prevent
water intrusion.
C.) Remove current MEM-CAL and install a new service MEM-CAL.
Clean throttle body I.D. bore in the area behind the throttle plate. Use a shop towel with GM Top Engine Cleaner, P/N 1052626, or AC-Delco Carburetor TuneUp Conditioner, P/N X66-A, or equivalent not containing Methyl Ethyl Ketone.
D.) Restore the baftery power and place air conditioning controls (if equipped) in the
"off" positon.
E.) Firmly apply the parking brake and block the drive wheels. Start the engine, and
shift the transaxle to "drive" for automatics or "neutral" for manuals.
F.) Allow the engine to run until the engine cooling fan has cycled once, or a
maximum of 10 minutes.
G.) Turn the ignition key to the "off" position for at least 5 seconds.
H.) Start the engine, and shift the transaxle to "drive" for automatics or "neutral" for
manuals.
I.) Allow engine to run for at least 5 minutes.
Install Tech 1 Scanner tool, CAMS or equivalent. Progam into Scan-Tool '89 model year.
With engine stabilized and in closed loop, the IAC motor position values should be between 9-20 counts for a desired RPM of 700 (Auto. Trans. and 850 Manual Trans.). If not, the adjustments may be tailored as follows, by adjusting the minimum air rate screw.
- More throttle valve opening = lower IAC valve counts
- Less throftle valve opening = higher IAC valve counts
IMPORTANT: Throttle angle must be equal to zero.
After a MEM-CAL replacement, the 1987-88 2.8L Speed Density Engine Driveability and Emissions Manual, ST399-87/88 SDM, must be used for Driveability and Emissions Diagnostics. To secure addiflonal publicabons use order forms available to all dealers through Helm, Inc., or dial (313) 865-5000 and ask for Customer Service.
Use applicable labor operations and times.
Labor Operation Number J5670 for MAF/MAT replacement.
T1492 for MEM-CAL change, as follows:
Labor Time: A-Car = 1.1 Hour
J-Car = 1.1 Hour
1987 L-Car = 1.0 Hour
1988 L-Car = 0.9 Hour
Add 0.1 hour to the above fimes to adjust minimum idle.
MEM-CAL - SELECTION CHART - SERVICE PART NUMBERS