Several tests done- whats causing my misfire? 2.3L

[cavity.]

1997 Ford ranger 2.3L w/ 100k miles
Slight misfire at idle (warm or cold), once every 300 miles or so I will get a P0302 code (misfire cylinder 2)

The car has:
New Plugs/Wires
New injector on cyl 2
Fresh oil, oil filter, air filter
New Catalytic converter

I've tried:
different spark plugs on cyl 2
Pulling either of the plug wires from cyl 2 makes idle rougher
both plugs at cyl 2 have spark
Vacuum test is unsteady -- points to ignition issue
Compression is a little low on cyl 2 (155 dry, 170 wet) (other cylinders have 168-175 dry), but im not sure this is enough to cause the steady misfire

So my two questions are:
Could this low compression be enough to give me a consistent misfire?
Could a coil pack be faulty if it is still giving visible spark (tested at idle)?

Thanks for any help, i really appreciate all the posts here.

 

[RonD]

While engine is running both spark plugs fire on compression stroke and exhaust stroke, so even with one coil failing engine wouldn't miss.

make sure spark plug wiring on coil packs is correct, easy to reverse these or the wires at the spark plugs.

There are 2 coils in each coil pack
1 and 4 spark at the same time, as do 2 and 3, they are "matched pairs" to balance the engine, so 1 and 4 share a coil, as do 2 and 3

So a coil issue on 2 should also effect 3

You could have a sticky valve on 2, won't show up on compression test well, jumpy vacuum also indicates that.

You can test for it at tailpipe using paper, video here: https://www.youtube.com/watch?v=PI5bBV0ZFek

 

[tomw]

I had thought that the spark plugs on the intake side of a dual plug head did not fire all the time. Meh.
If the plugs on the passenger side fail to fire, you will have misfire, as they are used 100% of the time the engine is running.
You have enough compression on #2 that the engine should fire. You may have valve(s) that are receding into the seats. That will cause intermittent misfire(I do not know why).
You can use a timing light on the offending cylinder to insure the plug is firing. Given that 1-4, and 2-3 fire together, a problem on one plug of the pair, might cause the other plug to either not fire, or fire poorly. The 'waste' fire(exhaust stroke) of one cylinder is an 'easy' fire for the coil, so the spark goes on through to the other plug(compression) which takes a bit more voltage and then does fire.
The plugs have their easiest time when an engine is running at idle, compared to being under load climbing a hill, for example.
If you have a steady miss, in general it is mechanical, where an intermittent will likely be fuel or ignition. The valve recession (receding) is the one exception to the rule that I have heard of, and it occurs in both the 3.0 and the 2.3.
I do not know which years were afflicted with the valve problem...
I would try swapping both plugs and wires between 2 and 3. Or even to a complete swap from the center two to the outer two to see if the problem follows.
You can also try swapping the coil packs, side to side. Be sure to get the wires installed properly, or you can create more problems. Check the wire position against a known correct installation, or a manual.
tom

 

[bruce102077]

While engine is running both spark plugs fire on compression stroke and exhaust stroke, so even with one coil failing engine wouldn't miss.

make sure spark plug wiring on coil packs is correct, easy to reverse these or the wires at the spark plugs.

There are 2 coils in each coil pack
1 and 4 spark at the same time, as do 2 and 3, they are "matched pairs" to balance the engine, so 1 and 4 share a coil, as do 2 and 3

So a coil issue on 2 should also effect 3

You could have a sticky valve on 2, won't show up on compression test well, jumpy vacuum also indicates that.

You can test for it at tailpipe using paper, video here:

96 ranger 2.3l p0320 code it comes and goes. Changed both crank and cam sensors. I believe I have a wiring issue. Could I bypass any inspection of that with a complete other wiring harness that I have?

 

[RonD]

In 1996 both the crank and cam sensors use AC Voltage that each generates for itself

Another part on the engine also generates AC Voltage for itself, the alternator, but it converts it to DC Voltage
Alternators can Leak AC Voltage, which would cause intermittent issues like P0320
So I would test for that first, since its a simple test

Google: AC Ripple Test video

4:50min video
Scroll forward to 2:30 when he uses a Volt Meter set to AC Volts, its a better way to test if you don't have a scope

0.05vAC is maximum you should ever see, if its more then alternator has a bad diode
Also REV engine to about 2,000 and hold it there


Here the things about Trouble codes, there are A LOT of them
If you go here: https://www.therangerstation.com/tech/obd-ii_trouble_codes/

Scroll down to P0335
These are just some of the crank and cam sensor codes computer can use
So if crank sensor signal/wiring was an issue you would get a different code
If it was Cam sensor same thing, different code specific to that sensor/wires

So looking at the codes the Computer DID NOT USE can be as important as the code it did use

Computer picked P0320 which is a general code not sensor specific
So could be leaking AC voltage issue or a computer internal circuit issue
I wouldn't think wiring harness issue since it is not sensor specific

 

[scotts90ranger]

I had an intermittent misfire issue at one point on my '97, turns out the plug wire on one cylinder had backed off for long enough to burn out the whole output connector on the coil... There's redundant spark plugs but no one had changed the drivers side plugs or wires in 160k or so miles whenever I addressed it...