WILL A GM CAR IGN. SKIP OR CYCLE ON A CAR W/ CATTED (REMOVED CATALYTIC CONV. & 2ND OXYGEN SNSR)

ID Status Date Year Make Model Transmission Type A/C Controls Public/Private
#14879 In Progress 2000 Pontiac Firebird Base public

o Replaced ICM (used), 2 coil packs 3rd looks recent (tested OHM’s Prim/Sec.) replaced all 6 wires (tested all for Ohm’s of resistance). Coil pack new (serves 1 and 4 cylinder, early replacement for wires 1 and 4), 6 AC Delco spark plugs and an aftermarket Fuel Pump.

Sparky

Removed catalytic converters  and post converter O2 sensor will not cause a misfire. Do you have any codes? What do the misfire counters show?

Here is one of the code reader results.

Here is one of the code reader results.

Sparky

The P0140 code is being cause by the car being “catted” and will not cause a misfire condition.

The P0304 is obviously a misfire on cylinder number 4.  Now for the concerns. I am assuming  that you recently purchased the car and we have to wonder why it was “catted”? Was it done in an effort to fix the current problem?  The same question for why the 1-4 coil has already been replaced?  In theory if the 1-4 coil was faulty it should be affecting both cylinders but for the sake of argument I would suggest swapping it with one of the other two that is not involved n misfires. If a misfire follows the coil then the new coil is no good. It is a long shot but I have seen it many times before.

If swapping the coil changes nothing then we have to look elsewhere. From what I could understand you have already replaced the spark plugs and spark plug wires. If so and you are certain of the quality of the parts and the installation then you are looking at a control problem or a mechanical issue with the engine. These engines are prone to carbon build up on the backside of the valves that can prevent them from closing fully.

So my next steps would be to confirm:

Whether spark is present at number 4 spark plug or not.

There is computer control of the injector using a noid light.

The injector is actually clicking but using a listening device.

Inspect the spark plug for signs of over or under fueling.

Perform  compression tests (cold, warm and running) if needed.

The above testing requires some specialized tools and experience to interpret the results.

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