#3 cyl does not fire

[hosshd2003]

I have a 1996 ranger that I have put in new plugs, wires, swapped coils and even replaced the computer and still have the same problem. I know it must be something simple but not sure. any ideas?

 

[Bachelor-house]

Do a compression test on the engine next.

 

[RonD]

V6 or 4cyl.

You said coils, with an S, so I assume 4cyl with dual plugs.
EDIT: sorry I see this is in the 4cyl forum...duh, senior moment.

You need 3 things for a cylinder to fire, spark, fuel and compression, remove one and cylinder will not fire.

4cyls have had issues with overhead cam and rocker failure, so exhaust or intake valves were not opening on one cylinder.

If you have had any recent "pinging" cylinder could have overheated and tuliped the intake valve or burnt the exhaust valve.

Either of the above cause low compression in the cylinder so it can not fire.

As Bachelor-house suggested a compression test would tell you a lot.

If you can't get a compression tester, then pull the valve cover off, have a look at the #3 valves.
Disconnect both coils so no spark/no start.
Disconnect air plenum from intake
Have some one turn over the engine with their foot on the gas pedal while you watch the cam and valves opening and closing and also listen at the intake opening for any hissing of air being pushed backwards into the intake from an open intake valve.

Renting a compression tester would be better, they only cost $30 new so it won't be much to rent.
Some auto parts store loan/rent tools like these as well.

 

[JC 97]

Does the OP mean no spark? Because what you described to do won't give you spark.While it is valid to check for compression on a dead cyl, If the problem is no spark he will be in the same boat. I think he must clarify a no spark condition, dead hole, or a miss.

 

[hosshd2003]

yes it is a 4cyl 2.3 with dual plugs. when the plug is pulled off the engine starts and runs the same. if you hold the wire away from the plug a little like you would normally do top check for spark you get nothing even if you swap wires. does this help any?

 

[RonD]

Use a timing light to check for spark on all the wires.
If you don't have one then get an extra spark plug and a jumper cable.
Clamp the base of the spark plug in the black jumper cable, clamp the other black end on the batteries negative/black post.
Spark plug is grounded.
Remove the exhaust side #3 spark plug cable and put it on the spare spark plug.
Start engine, watch to see if there is spark.

If it helps, the Exhaust side spark plugs are the ones that make the engine run, they fire on the compression stroke.
The intake side spark plugs fire on the cylinders exhaust stroke to burn any unburnt fuel, to provide better emission numbers.

So the 4 exhaust side spark plugs should be your only concern right now.

 

[hosshd2003]

checked compression and had 120psi at #2and 3cyls. have already tried the spark test and didn't have enough out of each coil to fire a plug. tried everything I was taught but am lost at this point

 

[Bachelor-house]

If it helps, the Exhaust side spark plugs are the ones that make the engine run, they fire on the compression stroke.
The intake side spark plugs fire on the cylinders exhaust stroke to burn any unburnt fuel, to provide better emission numbers.

So the 4 exhaust side spark plugs should be your only concern right now.

yes it is a 4cyl 2.3 with dual plugs. when the plug is pulled off the engine starts and runs the same.

It is a myth that the truck runs on only 4 plugs. Each plug fires on both the power and exhaust stroke. Removing one spark plug wire on #3 tells you nothing.
http://www.fordrangerforum.com/4-cylinder-tech/83785-dual-plug-myth.html

My truck will run with either the 4 intake, or exhaust side plug wires disconnected.

What was the compression in the other two cylinders?

 

[RonD]

120psi is very low, yes, what are the numbers for all 4 cylinders, maybe the compression meter is a little off.
160-180psi is what is expected.

When doing a compression test:
1 spark plug on each cylinder must be removed, so engine spins easily.
Pull both coil connectors
Pull fuel pump fuse or relay
Throttleplate should be open at least 1/2 way, to allow air in

 

[RonD]

Sorry missed that.

It's not a myth, maybe just misunderstood.

Ford has used a waste spark system for awhile now, as do most auto makers.
The Ford coil packs send spark to two cylinders at one time, both cylinders will be at TDC, one on the compression stroke, one on the exhaust stroke(the wasted spark).
The 2 spark plugs are wired in series in the coil, so +...-...+...-, this means one of the spark plugs will have a reverse polarity spark, not that important but it is slightly weaker.
On the 4 cylinders it did make a difference, so they added a second coil pack which gives the two cylinders getting the reverse spark on the primary coil a normal spark as well from the secondary coil, so yes both spark plugs fire on compression and exhaust.
Boring stuff.
So the engine will run on one coil, it will just run better and cleaner on two because all 4 cylinders are getting stronger spark, not just 2.
The exhaust side plugs are the primaries, intake the secondary, but does it really matter, no probably not.

If you are running a V6 with Ford coil pack then 3 of your cylinders have reverse spark, 3 have normal, mine runs fine that way

 

[hosshd2003]

I just want to know if anyone has any idea why all the other plugs, primary or secondary have good spark but #3 cyl on either coil does not causing a missfire

 

[RonD]

#1 and #4 fire at each of their TDCs from one coil in the coil pack
#2 and #3 fire at each of their TDCs from one coil in the coil pack

Same for the secondary coil pack.

So for only #3 to not have spark #2 would be lacking spark is well, since the spark comes from the same coil at the same time.

That's why we wanted to know the compression test numbers on all cylinders, because it's probably not a spark issue or both coil pack would have had to fail at the same time and if they did then #2 would also be missing.
If the PCM wasn't firing #3 on both coils the #2 would also be missing.

Only thing #2 and #3 don't have in common are the injectors and compression(and valves).
Compression is easiest to deal with so that was first, swapping #1 and #3 injector would be next.

 

[hosshd2003]

#2cyl spark is good so is 1 and 4. the coil is one pack connecting the four clys together for each side and one wire connector for each pack.

 

[RonD]

#2cyl spark is good so is 1 and 4. the coil is one pack connecting the four clys together for each side and one wire connector for each pack.

Yes, if you look at the connector for each coil pack you will see only 3 wires, one is 12v power.
The other two are to fire the cylinders/coils, so there are only two separate coils in that pack, not 4.
So when the computer fires one coil on the pack 2 spark plugs fire, not 1.

For this engine spark plugs in cylinders #1 and #4 fire at the same time, and spark plugs #2 and #3 fire at the same time.

I just reread your first post, I assume at least one new coil when you said you "swapped coils", what does that mean?
One new coil or you just changed their positions so still have the originals in?

If the latter I would get a new coil to try, one coil could have failed a while back and you were running #3 on just the one good coil, now it has failed so no spark at all on #3.
Because the coil sparks the plugs in series, #2 could still work from one coil, while #3 wouldn't work on either.

You can test coils with an OHM meter, pretty straight forward.
The center pin in each coil pack connector is the 12v power
The side pins are the individual coils ground.
Set OHM meter to 200 scale, or Auto should be fine.

Disconnect connector
Touch one probe to center pin on the coil and other probe to either side pin, should read .3 to 1.0 ohms.
Repeat for other side pin.
If either is not in this range replace coil.

Test second coil pack the same way.

Now the spark plug connections.
Put OHM meter on highest scale, or AUTO
Put one probe on a side connector pin(same as above), put other probe in spark hole on that side of the coil, should read 6,500-11,500 ohms, move probe to second spark hole on that side, if either is out of range that coil is bad.
Now do the same for the second coil in that pack, the other side pin.

And then for the second coil pack.

If the ranges are all OK it doesn't mean the coil is 100%, heat can change the OHMs, but if any are out of range, they are 100% bad.