Hi folks, been here over a year and gleaned lots of good info. Thanks. Now I've got an issue I can't find any specific info on.... 1998 Ranger 4X4 3.0, 5 spd., 117,000 miles. She started running a little rough and "Check Engine" light came on. Local O'Reillys tested her and it showed a misfire on the #4 cylinder. I put a new plug in and the code cleared. Now it's back and seems worse. I put a new o2 sensor in yesterday (based on previous code) and no improvement. I'm short on $$ with the holidays so I'm hoping the expertise here can help me narrow the search field before spending unnecessary funds. Thanks in advance for any help. Geezer

 

Check the resistance of the spark plug wire.

 

If #4 is fouling perhaps a hotter plug might get you by until after the holidays.

 

Oddly, the plug is not fouled at all. It looks almost brand new.

 

Check compression,

 

Welcome to FTE.

We need more clues to make a more focused guess, so post All of the trouble code Numers you have.

We need 4 things to make em run, air, fuel, spark & compression.

At this point all of the above belong on your suspect list. Plugs, wires, coilpack, fuel injector, compression, maybe even an intake manafold vacum leak.

With the mileage you have on it, a whole host of scheduled maintenance is due, so where do you stand on All past & present due sheduled maintenence items?????

 

I've only had the truck about 18 months, so I don't know what has or has not been done maintenance wise. The only codes its shown were #4 misfire and 02 sensor on the passenger side exhaust manifold. When it first started about 3 weeks ago, I changed the plug, filled it up and added the appropriate amt. of Lucas injector cleaner. That seemed to have helped for a couple of weeks. Almost all my driving is to work and home, 12 miles total. Very little highway driving. Carbon in an injector maybe. But why the same injector. I can turn a wrench, but I'm no wizz bang mechanic. Your thoughts? Geezer

 

OK, good feedback.

What was the O2 sensor trouble code Number, that caused you to want to change the sensor out????

With the mileage, unknown maintenance history & the limited clues we have now, the #4 misfire could be caused by a number of things.

Plug wire resistance should be about 1K ohms/inch of length & steady, when both ends are wiggeled, 30K ohms max, no matter the length.

Injector resistance should be 12-16 ohms.
Listen to the #4 injector with a stethoscope, to determine if it's missing any clicks in time with the misfire, or if it's clicks sound different from the other injectors.

With the low % highway driving, Combustion Chamber Deposit Flaking (CCDF), could be a problem, if those deposit flakes get loose, lodge in & stick on the vlave seat, you'll loose compression on that cylinder.

SO, if you think this is a possibility, a 20oz dose of Techron Concentate Plus in a tank of Chevron, Texaco, CalTex, or maybe Shell, which now has PEA in it, would raise the treat rate 10x above pump gas alone & can tidy up fuel injectors, intake valves, piston crowns & combustion chambers in one tank.

Daily during the treated tank, perform the three mile above 3600 rpm blow it out part of Fords 4.0L decarbon TSB & run most of the teated tank out with spirited driving & see how it goes.

If you still have the miss, maybe you have a sticking valve, so maybe do a compression test & if it suggests you do, perhaps consider a temporary crank case lube top treat, like Auto-Rx, or maybe some Marvel Oil in the crankcase 1K miles before the next OCI, or maybe try one of the new SN recipe engine oils that claim to clean out deposits & see how it goes.

More thoughts for consideration, keep us posted.

 

Okay PawPaw, for your reading pleasure. You know what I've done so far... went out this morning, started the truck, no check engine light, no rough idle, OMG!!! ran like a new truck all day!!! WTF!! I'm knockin on wood but I'm wondering if the new 02 sensor had something to do with the computer or I blew a chunk of carbon. Anyway, I'm goin to p/u some of your additive and see what happens. I'll keep you posted. Geez

 

Kinda sounds like a case of CCDF, as that'll tend to clear itself, after the deposit flake moves on.

OR, maybe a sticking valve???
Were you hearing any louder than normal valve ticking around #4, when it was in one of it's missing fits???? If so, maybe suspect a sticking valve.

Use up most of the present Lucas treated tank of gas, so you don't have the additives fighting each other.
Then add the 20oz Techron at the pump, before filling up, so you get good mixing, then run most of the Techron treated tank out, with the above daily spirited driving, or accelerations & see how it goes.

If it's CCDF, or a dirty injector, the Techron treatment with some spirited driving should make a difference.

Once you get it cleaned up & running right, maybe consider using a Top Tier gasoline to keep the engines innards tidy.
Top Tier Gasoline

 

Hi there, I had a very similar problem that I was dealing for almost a full year replacing lil things here and there! I have a 2005 ranger V6 3.0, kept getting misfire 4, after a while was misfire 4,6 than misfires on rpm below 1000 etc.... bottom line is I tried everything every sensor etc.... the final fix was removing the head, problems with 4, 6 valve, compression was lower on those two cylinders. the machine shop said it is a very common problem with those ford engines. cost me 600 to get the head all redone... i did all the work myself.