Mazda Ranger

[FFR6969]

290,000 kms later,... finally have a problem I can't solve ( yet).
Long time lurker. Happy to increase/ share knowledge.

 

[ekrampitzjr]

What is that problem?

 

[FFR6969]

2007/ 4.0/ Ford Ranger misfires cylinder 1,2&3 after warmup

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Drives fine when cold. Slight reduction in power. Misfires only at idle. RPMS at idle drop to 3-400.
Starts to smell like sulfur.
When cold, no smell, idles at 5-600 rpm.
All new plugs / wires / injectors/ MAF/ IAC Solenoid/ Fuel filter and bank 1 upstream O2 sensor. ( was reading stuck high- that code gone now. )
Only codes P300,301,302,303.
Totally fine at any speed except idle. Looking for most likely culprit based on someone similar experience

 

[FFR6969]

One theory I have is previous leaking injectors fouled O2 sensor and cat.
If cat clogged - maybe back pressure causing the misfires by Messing with air/ fuel mixtures.
There is a blank ( bung) ahead of bank 1 cat . If I remove that, should drop back pressure and possibly prove or disprove theory. I understand it will be loud when I do it.

 

[superj]

Welcome.

No idea on the theory but let us know what happens