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Discussion Starter · #1 ·
I've been trying to diagnose a misfire problem. Its behaves like the plugs are loading up. Temperature seems to have no effect. Its getting progressively worse and is now almost undriveable.
I scanned the data this morning and here's what I'm seeing:

Any suggestion? Thanks!

LT FTRM1 bouncing between -10% and -12%
ST FTRM1 bouncing between -4% and 0%
LT FTRM2 -10%
ST FTRM2 bouncing between -4% and 0%
ST FTRM11 -11.7%
ST FTRM21 -4% to -7%
O2S11 bouncing quickly between 0 and .8v
O2S12 steady at .8v
O2S21 bouncing from .1 to .6v
O2S22 steady at .9v
 

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I suppose the data were scanned at idling at normal engine temp.
Excessive fuel goes to the cylinder and the computer is trimming down the fuel delivery. Since you don't have a rich code, the trimming so far has been effective. But I think your engine is somewhat on the rich side. (-10 is a high number)

Your pre-cat sensor is switching between rich (near 1) and lean (near 0). It's normal. Post-cat sensors are not switching at all. I am not sure if they are not switching or your scanner (like mine, cheap, slow scanner) cannot detect a slow switching. A steady 1 V output I cannot explain. It has to switch. You need someone more knowledgeable to interpret it for you.

Is there a pending code?
 

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Discussion Starter · #5 ·
Thanks Paker,

There are no pending codes. In the past I have gotten a misfire code for cylinder 1 and later got a misfire code for cylinder 4.

So a negative fuel trim value means its rich. So the question is why is it so rich?

So far I've changed: plugs, wires, coil, pcv valve and its tubing(it was cracked).
 

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Post-cat sensors dont switch, that's normal. I don't know why it's running rich, but there were a lot of problems with flex fuel modules around that time.
 

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Negative fuel trims most often indicate fuel delivery problems. Since both banks are affected a similar amount, the most likely culprits are:

excessive fuel pressure due to either a faulty Fuel Pressure Regulator or a plugged return line where applicable (yours probably is a returnless system)

Ruptured fuel pressure regulator diaphram on conventional system (returnless systems have the regulator in the tank)

Faulty MAF sensor that isn't triggering codes on its own.

Multiple failed or leaky injectors (unlikely to affect both banks equally)
 
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