POOR PERF/IDLE-CODE 32,33,34 ISOLATE/EMI/MAP SENSOR BRACKET

VEHICLES AFFECTED: Early Production 1984 Eldorados and Sevilles With DFI

A condition of poor performance, possibly accompanied by an intermittent 'Service Now' light on some 1984 DFI equipped Eldorados (before B.P. 602410) and Sevilles (before B.P. 801221), may be caused by an improper MAP sensor mounting.

Electromagnetic interference (EMI) may cause false MAP sensor input to the ECM causing rich engine operation. Poor vehicle performance due to over enrichment would be most noticeable at idle or deceleration, with detection at cruising speeds (55 MPH) being limited. Codcs 31, 33 and/or 34 may be set accompanied by an intermittent 'Service Now' light. The false input is a result of EMI in the 50 MHZ range (6 Meter Ham radio, TV or Navigation transmitters' conducted to the MAP sensor bracket which in turn acts as an antenna in close proximity to the MAP sensor electronics.

In order to correct this condition, the MAP sensor bracket must be electrically isolated from the I.P. mounting bracket. The following procedure should be followed when diagnosing and correcting this condition.

1. Verify condition and check for diagnostic, trouble codes. Diagnose and repair any codes other than 31, 33 and/or 34 following 1984 Cadillac Service Manual procedure.

2. Remove lower right side dash panel, below glove box, and gain access to the MAP sensor assembly

3. Refer to Figure 1. Check the MAP sensor assembly bracket (1) to determine if it is isolated from the IP mounting bracket (2). Using a digital multimeter (J-29125), set the meter on the OHM scale and probe between the MAP sensor assembly bracket and the IP mounting bracket as indicated in Figure 1.

If the reading is infinite (an open circuit), the bracket is isulated from the sensor assembly and the situation described above is not causing the condition and the 1984 Service Manual procedures should be followed.

If the reading shows continuity as is expected on most cars before the breakpoint ('E' car - 602410, 'K' car - 801221), proceed with the following service procedure.

4. Remove the MAP sensor assembly bracket (1) from the IP mounting bracket (2) and discard the C-clip (3) shown in Figure 1. Apply three to four wraps of DUCT tape on the IP mounting bracket at the point indicated in Figure 1.

Pierce the tape at the hole location and install the MAP sensor assembly bracket using a black plastic push fastener, GMWDD P/N 1605396.

5. Test the isolation of the mounting as described in Step 3. An infinite reading (open circuit) should be registered on the digital multimeter.

1984 Eldorados and Sevilles produced after the breakpoint have electrically isolated MAP sensor brackets. when servicing these vehicles, the MAP sensor bracket must remain isolated from the chassis.

Use most applicable labour operation from Canadian Labour Time Guide and claim .5 hour.

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.