I hope this isn't long winded but here's the way it went. 2 1/2 years ago i bought my 04 4x4 ranger 4.0l it had a code for the bank 1 rear 02 changed it in order to get it through the e test. It didn't clear the problem the mechanic said he's seen this many times the cat honey comb is burnt out and to install an extension on the sensor to pull it out of the exaust stream it worked happy guy. 2 years later its time for a retest a week before i took it in it set an b1 rear code again. I cleared it it stayed clear and it passed the test. A month or so later I was driving when the truck lost a lot of power and the cel was flashing then it picked up full power and the cell stayed solid lit a short time later it repeated and continued for the trip but never stalled. I took it to the mechanics it had po300,301,302,303 he felt that it must be the coil and changed it. Oops wrong answer But I drove it hoping it would give a better clue of what was happening but nothing changed drive loose power than it would clear and happen again. I used to do some build ups of street cars years back so i'm not without mechanical knowlege I felt it was a fuel issue he checked and found the fuel pressure low installed a pump and filter had full pressure but no change he pulled and cleaned the fuel rail and injectors still the same. I had parked the truck for a month or so the other day I decided to take it out (maybe it would die on the side of the road so I could get a reason to get rid of it) any way nothing changed except now even at an idol it will misfire than clear. Paul my mechanic thinks its a timing chain. I can't argue other than if it was the chain why is it intermittent. HELP
Ed

 

2004 4.0l SOHC was still within the poorly designed timing chains and cassettes(guides) years.
(New timing chain kits have the new design and last longer)

Misfire codes only on 1 bank, 301, 302, and 303 would indicate this, 300 is random misfire so would be the first code set.

I would do a compression test on all 6 cylinders, that should show Bank 1 as lower over all than bank 2 if it is a timing chain issue.

And yes it will come and go, from oil pressure changes(tensioners) and broken cassette movement.

4.0l SOHC is 9.7:1 compression ratio so you should expect 170-175psi per cylinder.

Only other thing that may cause one bank to misfire would be a clogged exhaust, but only on that one bank, and it would idle fine, misfires wouldn't start until rpms increased and back pressure built up.
So doesn't fit symptoms, only reason I mentioned it was because of that Clogged Cat work around, Cat should be replaced.

Lower intake leak would only effect 1 cylinder.

Misfire is caused by one of these 3 things:
Spark
Fuel
Compression

There are 3 coils inside the coil pack, and they are not per bank, so 1 failed coil would effect 2 cylinders one on each bank, or just 1 cylinder, not 3 on one side/bank

Fuel rail has all 6 fuel injectors on it, there are not 2 halves, one for each bank, they all share one rail.
So bad injector or low fuel pressure would effect 1 cylinder or all cylinders, not 1 bank

Compression, on the 4.0l SOHC there is a separate Cam to open the valves on the top of each head, so 1 per bank.
If a Cam gets out of time then valves on that bank open late so compression drops and misfires occur.
It can effect just one bank


And just as a "heads up", Flashing CEL means "Danger Will Robinson Danger"(Lost in space?), it means stop what ever you are doing and pull over, engine damage may occur.
Steady CEL on means there is a problem, check it when you can.
Flashing CEL is usual on misfires as that can cause engine damage if allowed to continue.

 

Thanks for the reply Don I understand the coil and fuel thing now however I cant quite under stand the timing chain thing. I use to play with cars when if you tossed a chain it would either misfire constantly or not run at all. Is the chain jumped or is it just flexing because the tensioner is worn. If it were an intake leak again why not a constant trouble I could understand it being temperature related (hot or cold engine) I sure miss the days when you could lift a dist. cap and see the timing was out.

 

Oops sorry Ron

 

On distributorless engines spark timing is done with Crank position(CKP) sensor, these will be a "tone ring" behind main pulley that has what looks like gear teeth and then a sensor that sends a pulse to computer each time a tooth passes by.

Since spark timing is based on Top Dead Center for a piston, the crank is more precise than Cam can be, old distributors ran off the Cam.
This is a better system and no user adjustment is needed, although you can have engine computers tuned, so spark timing is adjustable in that respect.

Yes, with single timing chain or belt a slip or skip would effect all cylinders and distributor if so equipped.

On the SOHC engine which should actually be called a DOHC the cams are each run by separate chains, so one bank/side can go "out of time" with crank and the other bank.
And the 4.0l SOHC is an interference engine so if it gets too far out of time valve damage will occur.
Yes, sloppy chain from loose tensioner or broken cassette/guide, can cause lower compression and misfires just on 1 side.

"Good ol' days" were not all that good as far as vehicles.
The reason you may know about timing a distributor, setting points or adjusting a carb is because you had to DO IT ALL THE TIME, lol.
People learned it by shear repetition.

I think most of the frustration with electronic controls is from it rarely breaking, it just keeps working without user adjustment.
And when there is a problem it is harder to find answers because there are not 1,000,000 people with the same problem, like in the "good ol' days", i.e. anyone with a car, lol.

90% of computer controlled engine problems are mechanical, not an electronic issue, vacuum leaks, fuel pressure, clogged exhaust, ect...........
And when the computer provides "codes" that usually means all the electronics are working, it is when there is a problem with no codes that you can suspect an electronic part.
And if there are codes you also have to look at what codes the computer DIDN'T use.
If you get a Lean code 171, but not a "slow switching or out of range O2 sensor" code then probably a vacuum leak.

 

Hey Ron as far as time being spent and repetitive practice on distributers you probably not to far wrong. But now you mentioned the lean code 171 I had forgotten that I did have it twice but not since the latest reset. At least not that I know of my mechanic checked the codes last time I will have to pull the codes myself someday and check for myself. I have a car to drive so im not driving the truck I took it out the other day because I felt like driving it. I assumed the lean code was to do with the ecm shutting down the fuel during misfire.
Ed.

 

ECM doesn't shut down fuel during misfires, it adds more fuel.

O2 sensors read Oxygen levels in the exhaust
Too much oxygen is Lean
Too little oxygen is Rich

But that's not exactly what code P0171 means
ECM gets the MAF data(weight of the air coming in)
It then calculates the weight of the fuel it needs to add to get the 14.7:1 air:fuel ratio
(It is a weight ratio, 14.7 pounds of air needs 1 pound of fuel added.)
This air/fuel mix is then burned in the cylinders

If the O2 sensor on one bank shows too much oxygen then ECM adds more fuel, and keeps adding fuel until O2 sensor reads correct oxygen level.
This only takes a second or 2, so at no time is engine actually running Lean.

If the ECM is adding more fuel than it thinks it should it will set the P0171 code for that bank, and turn on the CEL
It means the ECM thinks there is a problem with air/fuel mix ratio that the driver should look at.

When a cylinder misfires no oxygen is burned up with the fuel, and that oxygen is dumped into the exhaust and the O2 sensor reads it as too much oxygen.
So that can get you a Lean code, although the misfires would be the bigger concern.

 

Hey Ron my son and I are going to turn this issue into a project when the weather improves. My question now is whats the trick to removing #3 plug. Ive heard to many horror stories about guy's braking the plug off trying to remove it.
Ed

 

Have a look here: Changing spark plugs on a 4.0 SOHC - The Ranger Station Forums

I know,"pull the wheel and inner fender???, WTF!!"

But I have had older cars(Mustang V8s) that I had to drilled a large hole in inner fender to get to the rear spark plugs.

Ranger 4.0l SOHC is a snap, and the spark plugs last much longer now-a-days, lol