rough idle and backfires...

Post by **pierremcalpine** » 21 Mar 2018, 14:06

Looking for some opinions, I'm getting a rough idle and some misfires. The car starts out smooth but once the idle comes down to 650 (or thereabouts) it will sputter, sometimes dies, and regularly misfire and or backfire through the intake.

The misfire takes place across multiple cylinders.

I'm getting the following codes:
ECM-3503 Misfire, at least one cylinder - emission agitation
ECM-3513 Misfire cylinder 1 - catalyst damage
ECM-3523 Misfire cylinder 2 - emission agitation
ECM-3533 Misfire cylinder 3 - same
ECM-3543 Misfire cylinder 4 - same
ECM-3553 Misfire cylinder 5 - same
ECM-261A Long-term fuel trim, bank 1 - upper limit
ECM-262A Long-term fuel trim bank 1 - upper limit

Any suggestions on what to try first? My thought was to replace the upstream o2 sensor to start.
Of note, just finished fixing two exhaust leaks so I'm going to assume my exhaust is in decent shape.

Post by **pierremcalpine** » 22 Mar 2018, 11:43

yaaaahooo! New o2 sensor, car feels awwwwwwesome. Love it when educated guesses work out.

Well that's the good news...the bad news is that I broke one of the screws in half that holds the heat shield onto the motor...damn. I have no idea how I'm going to solve that.

Post by **jonesg** » 23 Mar 2018, 09:39

pierremcalpine wrote: ↑22 Mar 2018, 11:43 yaaaahooo! New o2 sensor, car feels awwwwwwesome. Love it when educated guesses work out.

Well that's the good news...the bad news is that I broke one of the screws in half that holds the heat shield onto the motor...damn. I have no idea how I'm going to solve that.

I broke one of those heat shield bolts too, they rust out and bind up. It rattles, eventually it will fatigue and break off.
What...eva.

Post by **RickHaleParker** » 23 Mar 2018, 10:04

Symptoms of a clogged exhaust system.

1. Hook a vacuum gage to a intake port.
2. Observe vacuum at idle.
3. Increase RPMs to 2000.

Vacuum should increase. If it decreases it is because the cylinders cannot push the exhaust out efficiently, creating back pressure on the intake side.

Clogged exhaust system can be Catalytic Converter, Resonator or Muffler. Before replacing an expensive Catalytic Converter, open the exhaust system downstream of the Catalytic Converter. If the back pressure goes away, the clog is downstream of the open. If it does not it is upstream of the open.

Post by **RickHaleParker** » 23 Mar 2018, 10:21

I broke one of the screws in half that holds the heat shield onto the motor...damn. I have no idea how I'm going to solve that.

I would give the bolt a long soak in penetrating oil. Then with a left hand drill bit next size smaller then the bolt shank, start drilling the bolt. If your lucky the left hand drill bit will bite and spin the broken bolt out. If not you can use a Tap to chase the threads or cut threads for a oversize bolt. Make sure you get the drill centered and drill true.

Post by **abscate** » 23 Mar 2018, 12:16

pierremcalpine wrote: ↑22 Mar 2018, 11:43 yaaaahooo! New o2 sensor, car feels awwwwwwesome. Love it when educated guesses work out.

Well that's the good news...the bad news is that I broke one of the screws in half that holds the heat shield onto the motor...damn. I have no idea how I'm going to solve that.

You can wire it into place, zipties, chewing gum - not too bad a thing to deal with.