Check engine light and misfiring in two cylinders

Hi,

Have you confirmed there is spark to those cylinders? Also, is there an injector pulse to the affected cylinders? Here are a couple links to help check:

https://www.2carpros.com/articles/how-to-test-a-fuel-injector

https://www.2carpros.com/articles/how-to-test-an-ignition-system

Also, I came across an old technical service bulleting (TSB) you may find of interest. Take a look through it and let me know if it helps in any way. The attached pics correlate with the TSB.

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1996 Chevrolet Corvette V8-350 5.7L VIN 5 SFI
Engine - Miss/Poor Drivability
Vehicle Powertrain Management Tune-up and Engine Performance Checks Technical Service Bulletins By Symptom Engine - Miss/Poor Drivability
ENGINE - MISS/POOR DRIVEABILITY
File In Section: 6E Engine Fuel & Emission

Bulletin No.: 87-65-27

Date: December, 1998

Subject:
Engine Miss/Poor Drivability Symptoms
(Install Opti-Spark (ABITS) Distributor Assembly Service Kit)

Models:
1994-96 Buick Roadmaster
1994-96 Cadillac Fleetwood
1992-96 Chevrolet Corvette
1993-97 Chevrolet Camaro
1994-96 Chevrolet Caprice
1993-97 Pontiac Firebird/Trans Am
with 4.3L or 5.7L Engine (VINs W, P, 5 - RPOs L99, LT1, LT4)

Condition

Some vehicles with the above engines and equipped with the Opti-Spark (ABITS) ignition system may exhibit an engine miss and/or poor drivability symptoms.

Cause

The (ABITS) cap and rotor may exhibit carbon tracking, cracking, or water intrusion which can cause an engine miss and/or poor drivability symptoms.

Correction

Perform strategy-based diagnosis. If it is determined that the ABITS cap and/or rotor is the source of the concern, then a service kit may be now implemented instead of a complete ABITS assembly.

Parts Information

There are two (2) variations of Opti-Spark Distributors. It will be mandatory to identify which type is to be serviced for proper parts procurement.

pic 1

1. Opti-Spark Distributor II (Pin Drive - WITH positive vent system) can be identified by the intake manifold vacuum hose connection (3), air intake duct hose connection (4), or non-splined pin drive (1). Refer to Figure 1.

pic 2

2. Opti-Spark Distributor I (Splined Drive - Without positive vent system) can be identified by the splined pin drive (1), or the lack of intake manifold vacuum hose connection and air intake duct hose connection. Refer to Figure 2.

pic 3

Important:
it is necessary to use tool J 39997 (or equivalent) for the Distributor Cap Screws and tool J 39998 (or equivalent) for the Rotor Screws. Parts are currently available from GMSPO.

Warranty Information

For vehicles repaired under warranty, use:

Labor Operation Labor Time J452O (B/D/F Cars) Use published labor J436O (Y Car) operation time

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Let me know.

Take care,
Joe

Hi,

Yes, that could be an issue. Lower compression, fuel pressure, a vacuum leak, and so on can cause it as well. What all have you checked so far? Also, if you have a live data scan tool, could you let me know what the short term fuel trims are? Have you checked for vacuum leaks or fuel pressure? Here are a couple of links you may find helpful:

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

Also, are there any other codes other than the misfire?

Let me know.

Joe