BotakBeng,
I'm seeing [about] the same fuel pressure ocilliation, with a rough (intermittant muffled misfiring) running engine at idle. I see your pressure ocillation wanders between 48 - 55 psi; my baseline pressure is 48 psi, and with the engine running it ocillates pretty consistantly between 46 -50 psi. The odd thing I'm seeing however is the ocillation will occasionally slowly move to between 47 and 49 psi, with a noticeable change in the engine running rough, then returning to the 46 - 50 psi spread with the engine resuming the rough(er) running .
I did check injectors using a stethoscope and found that #1 and #2 injectors have a 'louder' click than the rest of the injectors. #5 and #6 seem to be the quiter ones. Also checked the damper and it clicks away and [seems] to be doing its job.
Can't figure out why the ocillation would move to 47 to 49, then back to the 46 to 50 psi. Unless during the 46 - 50 psi ocillation one or more injectors are not functioning properly, then decide to jump in and smooth out the ocillation, then go back to not functioning properly and causing the wider ocillation.
In my case, I'm not convinced injectors are causing the problem; however I will check the resistance of each injector. I don't think I need to use a noid light in this case. I changed my injectors, and rail, about two years ago and the engine ran fine up until about six months ago
As a note: I changed my spark plugs (looked good) and wires (cap and rotor changed a few months ago). This had no affect on the engine running rough.
Could there be any engine (mal)function that would cause the fuel pressure to ocillate outside a normal range, and in my case, periodically move to a tighter ocillation range? Valve timing? Exhaust back pressure?
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BotakBeng,
How old are your injectors? Day one ('97)?
Have you listened to your injectors with a stethoscope?
Have your checked the resistance of your injector coils?