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Bought a 2002 Ranger 4.0 back in August, 180k miles on it. As I do with all vehicles I purchase, I went to do a tune up on it. New plugs, wires, filters, etc. Had a few mishaps with getting the plugs in correctly, but they are all well seated now. Autolite Iridium plugs. I swapped out the plugs with Motorcraft basic plugs for a few weeks, and got no difference, misfires continued.
There are no codes being thrown, but I do get misfires at idle. Each time I pulled the plugs, they seemed to show a lean condition. The long term fuel trims at idle are consistently showing -10 to -13, indicating the computer is trying to lean things out. The O2 sensors are cycling as well, so those appear to be functioning normally. Misfires don't seem to happen off-idle.
Looking for some direction to go on this, as I am stumped. It seems to me that the computer is consistently trying to lean out the mixture, causing these misfires.
OK, good feedback, so lets think about this some more. The info about feeling the idle miss-fire in & out of gear After warm-up, but not when the engine is cold & at higher idle, along with the -10 to -13 LTFT & spark plug read of them looking lean, seems to me to be confirming your feeling about the air/fuel mixture trending lean is real, as on a cold start & run the ECM has fuel trim on the Rich side, to enable an easier cold start & smoother cold idle & its not missing then.
SO, with the mileage & unknown past maintenance history on this puppy, continue to get its Scheduled Maintenance up to date with OEM parts, or ones that say in writing they meet or exceed Fords specifications.
I'm not clear on this but was this warm idle miss there Before the scheduled maintenance parts replacement began???? If not, I have to ask if the new plug wires were Motorcraft, or just a house brand??? Our waste spark system works All of our ignition parts Twice as hard as the old distributor / coil system, as it fires the plugs on Every rotation of the crank shaft & the coil pack supplies half of the plugs & wires with a negative going spark that puts extra work on the plugs ground lug side wire, so All of our ignition system parts need to be designed for this unusual & double work load.
All that said just to try & cover all basic bases, so Murphy's Law has less of a chance to muck up this not so easy trouble shoot, because with the mileage & unknown maintenance history, so many things are up there on the suspect list, we have to consider All of them until we can move some lower down on, or off the suspect list.
SO, if all seems well with the ignition system, continue to look at, inspect & test things that can corrupt fuel trim in Both cylinder banks, like the PCV valve & its plumbing. As it's downstream of & not monitored by the MAF sensor, if its mucked up, worn out / weak spring, not sealing well, or its rubber hoses or grommet fitting are cracked, dry rotted, loose fitting & leaking vacuum, it is a non monitored vacuum leak that can corrupt fuel trim lean & this PCV valve if it's not been changed in 180K miles has lived about 2 lifetimes.
You didn't say what kind of air filter was in there when you replaced it, nor what you used but if it was a oiled cotton gauze type, put a dirty / slow to respond MAF sensor on the suspect list, as those filters are known to pass more dirt & if over oiled, it can migrate to & contaminate the MAF heated wire sensor, causing it to be slow to respond to air flow changes.
You say the O2 sensors seem to be switching ok, but with 180K miles / about 2 lifetimes, we need to know the voltage Range & Frequency of the switching, because with age they get wimpy, with less voltage switching Range & slow to respond, sorta like me!!!! lol
You could have the beginnings of a intake manifold gasket leak, so to check that you could rig a propane sniffer tester, using an unlit propane torch, some rubber tubing over the torch end & a sports needle in the hose loose end as a probe & pass it along the intake manifold gasket line & the PCV valve plumbing, with the vehicle at cold & warm idle & look / listen for a idle speed up tick when it gets a whiff of propane, which is sensor safe. The propane can get into a small leak & have the engine RPM have a more noticeable response, than using a solvent spray, which isn't a good idea around our plastic upper intake manifold, as many solvents aren't sensor safe & can be stress crack promoters for our plastic parts, so aren't wise for us to use.
Lastly measure fuel pressure & delivery rate over time, so you know the fuel pump, lines & new fuel filter are delivering as needed. The pressure should be 64 +/- 8psi & about 1/2pt per 15 seconds pump run time volume delivery rate.
A bunch of rambling beginning thoughts for consideration, keep us posted on your findings.
Fuel pump is brand new. The pump that was in the truck was losing pressure when I shut it off, so I replaced the entire assembly. Misfire was both before and after new pump. I verified pressure, and it was 60-65.
I did not notice problems before I replaced the plugs, but I didn't drive it much before then either. I put in Autolite Iridiums. After noticing problems, I swapped in Motorcraft coppers for a bit, with no change. Plug wires are new Motorcraft wires.
Air filter is a new standard Motorcraft.
PCV should probably be replaced. No idea how old it is, and it took me awhile to figure out where it is located. Since both the PCV and front O2 sensors are probably rather old, I'll start there. The O2 sensors are responding, but there are intermittent highs and lows where they don't continue the regular cycling up/down when idling.
Ok more good findings & feedback. Agreed the findings on the upstream O2 sensors unknown age & output has earned them a spot high up on the suspect list, along with the PCV valve. Also be sure to check the PCV valve rubber hose elbow, it likes to bake out & crack, out of sight on the outside bend. Also check the PCV valve cover grommet, it should be rubbery firm for a snug fit but not hard, or mushy soft..
The PCV valve can pass the rattle test & still be worn out internally, so sounds like its past time for Scheduled Maintenance replacement.
Ok, lets see if we can decipher a useful clue from the O2 sensor tracings. Since the O2 sensors seem to be switching ok, just not at full sensitivity range & are just reporting on what they find pumped downstream to them by the pistons from the combustion chamber & seeing the O2 sensors trace intermittently showing the mixture stuck rich / close to 1 volt, from time to time, seems to me to suggest maybe dirty, worn, runny nose fuel injectors, mucking up the air/fuel ratio???
SO, I'd maybe condider trying a 20oz dose of Techron Concentrate Plus in the tank, at the pump before filling, so to get good mixing.
If we''ll fill up with Chevron, Texaco, CalTex, or now Shell, all of which have some PEA in their fuel ad pack, along with the 1.0 oz / gallon addition of Techron, it'll bring the treat rate up to about 10X the pump gas level, so often we can get results in one treated tank. If you get an improvement but not fixed, run most of the treated tank out & consider repeating with another 20 oz Techron treatment & let us know how it goes. More thoughts for consideration.
Now that ur talking about gasoline additives..I've got something there..a really good experience with my 92 2.3L Ranger that suddenly started acting bad under
easy acceleration it would just go FLAT and barely run..haha..it was like only a couple cylinders were firing..and it would just continue for as long as it needed
to do it..usually a few miles.
Anyway I follow this Youtube show from residential New York State..whats the name?.Private Pro Garage.I forget but he's really good and one day he sheepishly admitted
that although it was against all his training he did have great success in a situation like mine when all else failed..and it was a gas additive named
Sea Foam..the usual snake oil promises haha.
Anyway I tried it and my Ranger hasn't done it since..and that's been almost a year now...So I'm a believer.
I pour a bottle in from time to time..and since then its never happened again.
Ok, lets see if we can decipher a useful clue from the O2 sensor tracings. Since the O2 sensors seem to be switching ok, just not at full sensitivity range & are just reporting on what they find pumped downstream to them by the pistons from the combustion chamber & seeing the O2 sensors trace intermittently showing the mixture stuck rich / close to 1 volt, from time to time, seems to me to suggest maybe dirty, worn, runny nose fuel injectors, mucking up the air/fuel ratio???
SO, I'd maybe condider trying a 20oz dose of Techron Concentrate Plus in the tank, at the pump before filling, so to get good mixing.
If we''ll fill up with Chevron, Texaco, CalTex, or now Shell, all of which have some PEA in their fuel ad pack, along with the 1.0 oz / gallon addition of Techron, it'll bring the treat rate up to about 10X the pump gas level, so often we can get results in one treated tank. If you get an improvement but not fixed, run most of the treated tank out & consider repeating with another 20 oz Techron treatment & let us know how it goes. More thoughts for consideration.
The only one of those stations near me is Shell, so I'll give that a shot with some Techron additive. The truck did sit for at about 6 months prior to me purchasing it.
I have not tested the coil yet, but certainly won't hurt to run the tests you posted.
Currently plugs are Autolite Iridium XP5144.
I also tested with the Motorcraft AGSF24N/SP-412, with no change. This is the basic, nickel/copper version of the plug.
The only one of those stations near me is Shell, so I'll give that a shot with some Techron additive. The truck did sit for at about 6 months prior to me purchasing it.
Ok let us know how the injector clean-up effort goes, as its one of the next least expensive things you can do to sorta move suspects lower down on, or off the suspect list. Yes you should also make sure the ignition system & the work you did on it & the parts replaced were actually good, so Murphy's Law has less of a chance of sneaking in & corrupting your Scheduled Maintenance parts replacement & idle misfire trouble shoot.
SO, if no joy with the Techron, fuel system, injector & engine intake valve & combustion chamber tidy-up, remember the unknown age O2 sensors are still up there on the suspect list, but because of cost replacement, can wait a bit until the fuel & ignition components goodness is verified. Just because parts are new, or OEM, doesn't automatically earn them a pass, make em prove themselves. Plugs can have cracked ceramics, bad gap, or damage from our mishandling during installation. Plug wires can have end to end continuity problems, or faulty insulation. I've heard of the plug end wire insulation being crimped to the boot end, but not stripped nor electrically fastened to the end metal contact that snaps onto the plug. The coil pack epoxy potting is known to crack, the case is too, out of sight underneath, or on one corner & intermittently break down. A "wet down test" after dark, with a spray bottle of water spritzed over each plug wire full length, the coil pack loosened & raised, so it can be spritzed top & bottom with the water, while looking for a arcs & sparks light show, is a quick way to spot faulty insulation. SO, if all that checks out, Then move the O2 sensors near the top of the suspect list. Seeing as how their the most expensive to replace, its money wise to eliminate as many other lower cost possibilities before having to pony up Big bucks to replace the O2 sensors, even though their well past / almost X2 their normal expected life span & are considered a 90-100K scheduled maintenance replacement item. More thoughts for pondering, let us know how it goes.
These are great tips, Paw! I just bought a 2000 4.0 OHV and have a high idle and misfire, but no codes. It runs smoothly at cold start, albeit with a high idle (as you said) and I went through last night and looked at the wires/air filter. I replaced the pre-cat bank 1 O2 (ordered the bank 2 pre-cat O2). I've got 95K on mine. Similar O2 cycling as the OP with my cheap scan tool. I've ordered a new coil pack, wires and plugs as I don't know the history.
I think the OP has the SOHC engine, but the same troubleshooting tips apply, and are much appreciated!
11-22-2020, 10:56 AM
