Rough idle, cylinder 3 misfire code

[xyzb]

1996 2.5 DOHC

 

The plug in 3 looked okay, a little darker color that the other 3- the engine uses a bit of oil.

New NGK plugs and plug wires - still rough idle and code set

Swapped fuel injectors from 1 to 3 - same issue

Swapped injector wires on 1 and 3 - same issue

 

I'm going to check the coil resistance - I doubt this is an issue.

 

I'm going to check compression on 3.

If the timing is off, how much effect would it have on compression and would this cause the misfire error?

 

Suggestions?

 

Thanks all!

[DaveT]

Ignition timing has no effect on compression.

[montana tom]

my 00 obw had the same symptoms, only on cly 4.  Car ran great as long as you were moving. At idle it would shake the engine. Did plugs, wires and the coil , car still idled and ran great just shook around at idle.  I finally did a compression test  ... sure enough 180 psi quickly in all but # 4 ... it had 120 psi after extra cranking. I had a rebuilt 2.5 engine that i had assembled for the wifes car...  its now in mine...  I'm currently disassembling the other.  Short diagnostic is one bad exhaust valve on # 4  I haven't pulled the valves yet to see exactly what was going on. 

[Fairtax4me]

Dohc engines burn valves because nobody ever checks the valve lash clearance. Compression or leak down test on number 3 will tell you what's going on.

 

Cam timing will not affect one cylinder. It will affect the two cylinders on the same side.

[xyzb]

Just checked #3 and there is no compression. So valve not seating I'm assuming?  Checked 1 and it is around 135, dry, cold engine, throttle closed.    I just checked #1 because I couldn't believe that #3 was 0.    I checked #3 twice now. 

[Fairtax4me]

Probably a burned exhaust valve.