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Misfires on warm start?

lambo

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Hey everybody, really been enjoying reading all the information here. I bought a lovely 2001 3.0L XLT with flare sides about a year ago and our relationship has been on the rocks for the past few weeks. I'm getting conflicting signals and not sure really what's going on.

I'm having rough idle, loss of power and severe misfires on 4, 5 and 6 after a warm engine start.

After sitting all night, or while I'm at work, I can start it up and roll like it's nothing. There's still a slight hint of misfire occasionally (noticeable only at idle), but nothing like what it does when I start it warm: shuddering and shaking like a mad man. I've also used the word puttering.

Over the last two weeks, I've only seen one code actually set: P0305 (cylinder 5 misfire). Pending codes I've noticed have been a P1152 (O2 sensor replaced), P1401 (DPFE replaced), P1504 (IAC replaced) and codes for cylinders 4 and 6 misfires.

Put all new plugs and all new wires on. Also, cleaned the MAF sensor with electronics cleaner (and cleaned the old IAC, probably screwing it up and causing the P1504).

The shuddering is not as severe since replacing the plugs and wires.

I've gone through a tank of premium fuel and some Prestone fuel system cleaner, then after filling up again with regular I added some Seafoam.

Tonight, after installing the new IAC and DPFE sensor I disconnected the battery and let it sit for two hours. I started it up, let it idle for 20 minutes, then took to the highway going out 10 miles, then back, each time running between 50-65 MPH. It ran satisfactorily the whole time, even with the A/C on for a few minutes. Couldn't have been more happy.

When I got home it idled fine for a few minutes before I shut it off. The capture below details what happened when I started it back up. It took a couple of tries to get started, and once it did the shuddering commenced.

Raw data:
https://spreadsheets.google.com/a/sparknewmedia.com/spreadsheet/pub?key=0AlRUitJDN1qBdHdhQmg2UWEydFpPX3AwSTNIQXBPSGc&gid=0

O2 sensor chart:
https://spreadsheets.google.com/a/sparknewmedia.com/spreadsheet/oimg?key=0AlRUitJDN1qBdHdhQmg2UWEydFpPX3AwSTNIQXBPSGc&oid=2&zx=ll3nf2uakvci

The Bank 2 Sensor 1 sensor is only a week old (it's the red one in the chart). That's the upstream sensor on the driver's side.

I guess my main question is this: is this new O2 sensor messed up now? The engine was behaving the exact same way with the old 02 sensor installed.

Could something malfunctioning with the EGR system foul the new O2 sensor in less than a week? Why does it run fine from a cold start?

Thanks in advance for any and all advice!
 


TimR

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check the coil pack
 

locovaca

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I'd check for some exhaust leaks on that side of the engine. Leak could be pulling in outside air which is messing up the O2 sensor. The O2 Sensor isn't used on a cold engine start up until the computer enters closed loop.
 

lambo

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I'm happy to report that a new ignition coil and some relearning on the computer's part solved the rest of the problems!

Thanks for your help Tim.
 

TimR

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