Good idea to check the plug wires resistance IMHO Joleford.
Well if they are ok or not, would depend on which multiplier you had the ohms scale set to.

Was it set on X1, X10, X100, X1000, x10,000, when you took the readings?????

To determine the resistance you read, you would multiply the numbers you got, by the scale multiplier you have the ohmmeter set to.

If it was on the x1000 ohms scale and was steady when you flexed the wires, your likey ok, as the rule of thumb, for resistance type spark plug wires its 1000 ohms per inch of length, 30,000 ohms max.

If you were on the X10,000 ohms scale, the resistance you got is too high, as they shouldn't measure more than 30,000 ohms, no matter what the length.

If the plug wires resistance is too high, it can make for a weak spark that can get blown out under stress & cause a miss or poor combustion, thus poor power & poor gas mileage.

I check ALL my new plugs & wires resistance right out of the box, before I install them.

I've seen & heard of plenty of bad parts right out of the box, so I never assume they're good, just because they're new!!!!

Fellow on the MotorWeek forum last year, bought & installed new wires & plugs for his truck, only to find it ran much worse.

Upon carefull checking, did he found one of the pug wires plug end contact wasn't even fastened to the wire. When he tugged on the boot a little, it pulled right off.

The conductor was stuck into the contact, but never crimped tight. So much for quality control!!!! LOL

Anyway I never trust anything new right out of the box, it's untested by time & thus unproven, as far a I'm concened, so it's gotta prove itself, thus I begin with testing them, or having them tested, if at all possible.

If I get another alternator, starter, relay, ect, ect, I have the store test em BEFORE I leave the premisis. LOL

 

Well this weekend I finally got around to replacing the #1 cylinder fuel injector that I thought was giving me the misfire. It did not change anything. Talk about being frustrated. I also checked the compression just to be safe. It checked out at 154lbs. of compression on #1 cylinder. That was within 1 lb. of the #2 cylinder. I also checked the primary and secondary resistance on the coil packs as it said in my manual. Everything seems to check out. The only other thing that I question is the plug wires still. I have a 20 inch wire that has 5.4 K of resistance and a 8 inch wire that has 2.3 K of resistance. Is this too low? Does anyone have any other suggestions?

 

Using the 1K ohm per inch of length rule of thumb, then yes those two plug wires resistance is well below what it should be.

Are these the #1 cylinder plug wires????

Are you certain the #1 plug is properly gapped????

 

Pawpaw,
Yes those are the #1 cylinder plug wires- that's where the misfire is according to the po301 code that it's giving. I have done EVERYTHING else that I can think of. They are new wires form autozone (cheapies) with a lifetime warranty. Should I take them back and have them replaced? I did not gap the plugs because I assumed they were pre-gapped (autolite double platinums). What should the gap be? Thanks.

 

I'm not very familiar with the 4-bangers, is it possible to swap any of the other cylinder plug wires with the #1 cylinder wires to see if that changes anything?

Also, FWIW, there is a wire harness that runs underneath the driver's side of your truck that can cause a variety of engine issues if it starts chafing against the undercarriage. It might be worthwhile to take a peek under there even if just to rule it out as a possible cause:

https://www.ford-trucks.com/forums/s...d.php?t=315257

 

Well I'd make shure the #1 cylinder plugs are gapped to spec, which I believe is 0.042-0.046". Then as I suggested earlier & as Rockledge has suggested I'd try swapping each #1 plug wire, one at a time, with one from the older set you removed, that wsn't used on either of the #1 plugs & see how that goes.

 

Ok boys, I checked the plug gaps, and switched the plug wires around. Then I again had the codes pulled- same thing #1 cylinder misfire. Can someone give me ALL the possibilites that can cause a #1 cylinder misfire. It seems I've tried everything and I'm beginning to lose my patience with this thing. It still bucks under load, and idles a little rougher than it used to. Should I start to look at things like the cam position sensor, egr valve, and o2 sensors, or won't they trigger this type of misfire?

 

I have seen weak valve springs give random 300 codes at higher rpm, and I have seen a broken spring give a 300 code for an individual cylinder. It is something associated with that cylinder, almost always electrical or fuel, but could be a leak on the intake side or like I said a valve problem. good luck.
Dave

 

Interesting stuff Dave, and I'm going to be keeping it in mind. Those 300 codes can really drive people nuts.

joelford, have you tried swapping the #1 injector with another cylinder?

 

rockledge,
I just this past weekend replaced the #1 injector. I just have a really hard time believing that it is something major like valves or internal engine. I have owned the truck since it was new, driven it very easy, and always been diligent about changing the oil. Furthermore, sometimes it runs nearly perfect. I drive this truck daily, and it never quits, it just has that slight miss usually. Lately it doesn't idle as smooth as it did and seems to ping more on hills and under hard acceleration if this helps at all.

 

I found this in the web maybe it will help..
Dave
I am having a problem with u 2000 Ford Explorer. It has a 4.0L engine and 200,000+ miles on the odometer. The vehicle originally came to our shop will the Check Engine light on and a DTC P0301 (cylinder No, 1 misfire) stored in the PCM's memory. The spark plug wires and spark plugs looked, pretty bad, so we recommend a major tuneup. We cleared the DTC and returned the vehicle to tlie customer.

The engine ran fine for a month or so before the customer returned because the Check Engine light was on again. This time a DTC P0304 (cylinder No. 4 misfire) was stored in memory. We suspected a defective ignition wire because the wire travels under the upper intake plenum to reach the No. 4 spark plug. After replacing the wire and clearing the DTC, we returned the vehicle to the customer. A couple of weeks later, he was back for the third lime, this time with a DTC P0301 in memory.

Inspection of the engine and related systems revealed a fuel pressure of 65 psi. Hot cranking cylinder compression ranged from a minimum of 130 psi to a maximum of 150 psi for the six cylinders. A relative (running) compression test also appeared normal. A smoke machine was used to check for vacuum leaks (none ware found).

We had installed a set of injectors during the vehicle's second visit because testing on a flow bench indicated the No. 1 injector wan weak. Scan data since then has never indicated an injector failure, but I've noticed that the injector pulse width seems wider than normal at times, at approximately 4.5mS. The oxygen sensor is switching normally from .2 to .9 volt, indicating the PCM is in control of the fuel mixture.

While consulting my service information, I found a Ford technical service bulletin that recommended valve spring replacement. A friend at a neighboring shop suggested that an intake manifold vacuum leak also might be to blame. There's supposed to be a TSB on that problem, too. What do you think?

Ignacio Gonzalez

Address not given

You've thrown a lot of information at me, Ignacio. Some of it may relate to the misfire problem and some may not. Let's start with the TSBs. Explorers, Rangers and Mercury Mountaineers of this vintage are equipped with one of three engines: a 5.0L V8 and two different 4.0L V6s. One of the V6s has overhead valves, while the other has single overhead cams (SOHC). It's important to know which engine your customer has before consulting the TSBs, because the bulletins may apply to one engine or the other, but probably not to both.

The TSB involving the intake and exhaust valves (Ford TSB No. 02-3-2) applies to the 4.0L SOHC engine only. Affected vehicles set a DTC P0300 or P0301. When die DTC is set is veiy important, which is why it's essential to consult the freeze frame data stored in the PCM before clearing any misfire DTCs. Once the freeze frame data is gone, there's no way to recover it until the next time the problem occurs.

In this case, the problem (misfire) must occur at an engine speed greater than 4800 rpm. This type of misfire (and the resulting DTC) occurs under heavy acceleration, due to higher-than-expected transient exhaust system backpressure, coupled with valve spring resonance points. In simpler terms: The exhaust valves may hang open slightly, causing the misfire. Install the updated parts to correct the problem, but bear in mind that this will correct an engine misfire problem above 4800 rpm only. If freeze frame data indicates your customers engine is misfiring at a lower rpm, look elsewhere.

Intake manifold gasket leaks were handled under a full-on Ford campaign (TSR No. 0OM12). Ford covered its 1997-2000 vehicles for six years or 72,000 miles, so your customers Explorer is unfortunately no longer covered. Once again, this TSB applies to the 4.0L SOHC engine only. Consult the TSB for information on updated gaskets and a camshaft chain tensioner, as well as installation instructions.

Leaking intake manifold gaskets on this engine often produce rough running complaints when the engine is cold. The leaking gaskets admit unmetered air, diluting the mixture and causing a misfire. As the engine warms, the gaskets may swell enough to seal a little better and the engine smoothes out. The symptoms won't return until the engine is allowed to cool.

If you don't have a smoke machine to check the intake manifold gaskets, simple carburetor cleaner will do the job. While watching the short-term fuel trim (STFT) for each bank with your scanner, try spraying the carb cleaner near the intake manifold gasket mating surfaces (upper and lower gaskets). Watch for big changes in STFT, as the PCM attempts to compensate for the sudden addition of uninvited fuel.

Them's one final thing you mentioned that may relate to die misfire DTCs: the abnormally long injector pulse width. You indicated that the injectors had been replaced, but not whether they were new. If the injectors are clogged or are receiving inadequate fuel pressure or volume, the PCM will respond the only way it knows how-by holding the injectors open longer. But this helps only if longer equals more. I only a trickle of fuel is making it through tho injectors, it won't matter how long they're held open. An inadequate fuel supply caused by clogged injectors, a clogged fuel filter or a weak fuel pump means a leaner-than-normal fuel mixture. And that can lead to what? Repeat alter me: misfire!

Copyright Hearst Business Publishing Dec 2004
Provided by ProQuest Information and Learning Company. All rights Reserved

 

Here are the Possible causes for a 301 from the 1998 ford manual.

-- Ignition system.

-- Fuel injectors.

-- Fuel pressure.

-- Evaporative Emission System.

-- EVAP canister purge valve.

-- Base engine.

-- Running out of fuel.
Dave

 

Well tonight my ranger finally just plain quit on me at a stop sign. After cranking it over quite a few times I got it fired back up but it did not seem to be running on all cylinders. I drove it directly to my garage and began to check things over again. Out of desperation, with the engine running, I began to pull the spark plug wires off of the coil packs. Low and behold 7 of the 8 were sparking and, what do you know, the one that wasn't was the number 1 cylinder- the same one that has been giving me such a headache. I took a quick run to the parts store and purchased a new coil pack. I installed it and FINALLY it runs the ranger I used to know. The problem is solved. I just wanted to take this opportunity to truly thank pawpaw, rockledge, and dave257 for sticking with me on this difficult problem. Your expertise helped me a great deal, and now, hopefully this thread will help someone else. Joelford.

 

Good deal !!
Dave

 

Good troubleshooting Joelford, with all the electrical checks we had you doing, it had boiled down to the coilpack. Question was going to be, how could we test it to be shure. Was nice of it to give up the ghost & make it easier to find. LOL

The clue you gave about it misfiring under load, is usally associated with plug or plug wire problems, so those had to be eliminated first.

Anyway good to hear it's finally put right. Makes you feel mighy good to win one once and a while, desn't it.