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Jerry Newton
Jerry Newton, Chevy Technician
Category: Chevy
Satisfied Customers: 4410
Experience:  ASE Master Technician, L1, Master GM Technician. Over 20 years of bumper to bumper GM experience.
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camaro: My 1994 backfiring out of the throttle body

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My 1994 z28 camaro is backfiring out of the throttle body when i try to start it. Would this be a problem with my optispark?
Probably. Those were known to take on water, and GM made a fancy ventilation system to try to keep the moisture out, but once you get moisture in there, they're hard/impossible to start, random misfire, etc. There is an optical sensor in there that does not play well with water.

Check the coil and the coil wire, they can also be problematic, but if they're OK, I would be getting into that distributor.
Customer: replied 5 years ago.
Ok, I've heard the 1994 has a problem with moisture building up. I just replaced my thermostat today and coolant leaked out onto whatever is around that area (right under where the throttle body connects to the intake). Could that have caused my problem
It should be sealed against dripping a little coolant on it, but after 15+ years in service, it's probably not sealed as tight as it used to be. I'd say yes, if it started running badly after you dripped coolant onto it, you probably need to go in there and try drying it out as best you can with compressed air or WD40, and sealing things back up.
Customer: replied 5 years ago.
Thank you! Could trying to start it and it backfiring be harmful to the car?
And I'm not too familiar with where all of the electrical on my car is, could you tell me a general area too look for the parts i need to make sure are dry?
Let me see what I've got for pictures......... here is a bulletin that talks about what you're experiencing and has a couple of drawings.....

File In Section: 6E Engine Fuel & Emission

Bulletin No.: 87-65-27

Date: December, 1998

Engine Miss/Poor Driveability 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)


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


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


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.

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.

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.

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

And here are some directions on how to take it off and put it back on again:

Remove or Disconnect:

  1. Disconnect negative battery cable
  2. Disconnect IAT sensor harness connector
  3. Remove air intake duct
  4. Remove serpentine drive belt
  5. Drain engine cooling system
  6. Disconnect three water pump hoses

Water Pump Removal

  1. Remove water pump assembly

Torsional Dampener Removal

  1. Remove crankshaft torsional damper
  2. Remove belt tensioner
  3. Remove spark plug secondary cables from distributor. Twist boot 1/2 turn and pull only on the boot to remove wire from distributor.
  4. Disconnect four terminal PCM connector from distributor.

IMPORTANT: The distributor shaft does not have any alignment marks and must be marked at time of removal. For complete engine replacement, set engine on Top Dead Center (TDC) number 1 firing position remove distributor and mark shaft and housing. Reinstall distributor with engine in the TDC number 1 firing position and align distributor marks.

Distributor Assembly Mounting

  1. Remove three distributor mounting bolts. Pull distributor forward until drive shaft disengages from engine. Mark the top surface of the shaft to denote location during reassembly.

Install or Connect:

  1. Install distributor shaft into distributor, if removed. Turn shaft until the mark is on top.
  2. Place distributor and shaft assembly into engine.
  3. Tighten three distributor bolts
Torque Value: 11 N-m (8 lb.ft.)
  1. Connect four terminal PCM connector to distributor
  2. Connect spark plug cables to distributor
  3. Install belt tensioner
  4. Install crankshaft torsional damper to engine
  5. Connect coolant temperature sensor connector
  6. Install water pump
  7. Connect three water hoses to water pump
  8. Fill engine with coolant

Serpentine Belt Routing

  1. Install serpentine drive belt
  2. Install air intake duct
  3. Connect intake air temperature (IAT) sensor connector
  4. Connect and tighten negative battery cable
Torque Value: 15 N-m (11 lb.ft.)

Jerry Newton, Chevy Technician
Category: Chevy
Satisfied Customers: 4410
Experience: ASE Master Technician, L1, Master GM Technician. Over 20 years of bumper to bumper GM experience.
Jerry Newton and 3 other Chevy Specialists are ready to help you
Customer: replied 5 years ago.
Thank you so much, best help i could get and on a saturday at that!

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