INTERMITTENT MISS/SURGE/ CHUGGLE AT HIGHWAY SPEEDS

SUBJECT: INTERMITTENT MISS/SURGE/CHUGGLE AT HIGHWAY SPEEDS

MODELS AFFECTED: 1993 ELDORADOS, SEVILLES, AND ALLANTES EQUIPPED WITH NORTHSTAR ENGINES

Some 1993 Eldorados, Sevilles, and Allantes equipped with Northstar engines may experience an intermittent miss/surge/chuggle condition that is most apparent at highway speeds (1100 -- 1900 rpm) under a load or not. Condition could also occur at 20-40 mph speeds but under the same engine rpm as noted above. Condition typically occurs with no PCM codes set.

This condition may occur due to the ignition system resynchronizing under high spark loads because of noise induced into the sensor (crank/cam) circuits and/or the ignition control module (ICM). The noise may be transmitted from a bent or damaged terminal in the ICM or harness connectors. In addition, the noise may be occurring due to spark plug wire(s) contacting the ICM (particularly the number 1 wire). Refer to Figure 1.

To repair this condition use the following procedure:

1. Diagnose and repair all PCM trouble codes first.

2. Check (G102 for Eldorado and Seville) or (G104 for Allante), located on the engine block near the transaxle case extension, for being clean and tight. Refer to Service Information Manual Electrical Diagnosis - Section 8A-261 for an illustration of the area.

3. Disconnect all four ICM electrical connectors and inspect for bent or damaged terminals in the ICM or harness connectors.

4. Remove and reinstall the rear (RH) bank spark plug wire boots so that the wires exit the boot away from the ICM Assembly. This will prevent the wires from contacting the ICM Assembly (particularly the number 1 wire). Figure 1 illustrates the incorrect way for spark plug wire routing. Figure 2 illustrates the correct way for spark plug wire routing.

For warranty purposes use Labor Operation T6724 at .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.