Mechanics

WHAT WOULD CAUSE MISFIRE OF #2 AND #3 CYLINDERS?

1999 Saturn SL2 • 190,000 miles

The car abruptly began to misfire, on the highway, with loss of power and vibration. It was turned off for refuelling, turned back on, and continued to misfire. After a five minute drive, it cleared itself for 5 minutes, was shut off, but resumed the same symptoms upon restarting. Codes P0300, P1599 and P1555 (previously registered, have not replaced EVO) registered. Followed advice to disconect plug wires, with engine running. Disconnection of #2 and #3 resulted in no change. Replaced O2 sensor for Bank 1 Jan 2011.
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1999sl2
January 28, 2012.



And the exhaust smells as if it has a lot of unburned fuel. Maybe the downstream O2 sensor has died, so the ECU is cutting spark to cylinders 2 and 3?

Tiny
1999sl2
Jan 28, 2012.
No a o2 sensor would not cut out two cylinders bad or not check for spark on number 2 and 3 cylinders. Let me know if you have spark on those two and we will go from there. If you have spark then we need to check compression. Only three things really tie those two cylinders together spark same compression stroke and fuel injectors firing. My money is on spark first then compresson issue.

Saturntech9
Jan 28, 2012.
I checked spark with the 3rd from left plug against the header. No spark. Are the coils the next thing to check? Is there an easy way to swap them?

Tiny
1999sl2
Jan 29, 2012.
Voltage on the battery when running is over 14.2, also.

Tiny
1999sl2
Jan 29, 2012.
You can swap the coils from left right to right you jut have to take the four bolts out see if the no. Spark follows the coil. Let me know what you find.

Saturntech9
Jan 29, 2012.
I swapped the coils, left to right, marking the original left, and the misfire still occurs on #2 and #3 cylinders, confirmed by disconnecting spark and injector wires. Still smells like gas. As you face it, the left coil feeds cylinders 1 and 4. The ignition control module didn't have anything visibly wrong with it.

Tiny
1999sl2
Jan 30, 2012.
Are you getting spark from the number 2 and 3 cylinders?If not then you have a bad ignition module. Let me know what you find.

Saturntech9
Jan 30, 2012.
Yesterday, I pulled the #3 spark wire and grounded it against the header: no visible spark, with the engine cranking.

Tiny
1999sl2
Jan 30, 2012.
If you have spark on the number 1 and 4 cylinders and not on the number 2 and 3 cylinders and its not the coil then the only other thing left is a bad ignition module.

Saturntech9
Jan 31, 2012.
Thank you!
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Tiny
1999sl2
Jan 31, 2012.
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