98 ranger 4.0L idles rough, when getting up to speed it lurches. Check engine light not lit. Replaced idle control motor, plugs and oxygen sensor. Checked plug wires at night for arching, found none. Disconnected battery overnight to reset computer. Still not running right

 

How long has it been since a tune up? Probably a good idea to pull the spark plugs and look them over.

 

I replaced them 6 or 7 months ago, with the fuel filter, serpentine belt and hoses around 73,000 miles

 

Good. So now when you pull the plugs they should all be in tip-top shape. A fouled plug or plugs might tell you which cylinder(s) - if any - are misfiring. From what you describe, I'm surprised you haven't gotten a CEL yet.

If the plugs that are currently installed are Bosch, replace them with Motorcraft or Autolite brand. Bosch spark plugs and Ford DIS/EDIS ignition systems do not get along very well.

P.S. Welcome to FTE.

 

Welcome to FTE.

Sure sounds like an ignition problem, but could be a number of other things.

Rockledge is right about the system being sensitive to plugs & a good idea to pull them for a "read".

Our "Waste Spark" ignition system works it's components TWICE as hard & in different ways, than the old single coil distributor ignition system, so it requires we use double platinum plugs, of the proper heat range & the Motorcraft or Autolite fine wire double platinum plugs are a good choice, along with a set of Motorcraft plug wires, that are designed to carry the double work load.

If your curious, check out the "Why double platinum plugs" link in the "Tech Info" thread atop this forums thread listing page. A wealth of other good info there too.

My random rough idle & underload miss was a cracked external insulator on #6 plug, that was found with a "wet down" test.
You can perform it with a water spray bottle.
Just do one ignition wire at a time, all the way from the coil pack to the spark plug, any change in idle & it's suspect.

The plug wires can look ok externally, but have internal problems , so do an end to end resistance check with your ohm meter. They should measure 1000 ohms per inch of length 30K ohms max, no matter the length.
Lightly flex the connectors on both ends when checking the resistance. It shouldn't change or jump around or open up when flexing.

Be sure the plug wires are routed as the factory had them & use ALL of the wire looms.

I suppose you could have a fuel injector problem, so try listening to them with a stethoscope to determine if any sound different.
If you find one that sounds like it may be acting out, plug a "Noid" light into it's harness & see if it blinks steady.

If all that checks out then maybe consider using a vacuum gauge to try & determine if the valves are seating properly & compression is ok.
If in doubt do a compression test, or a cylinder balance test with a scantool capable of performing this test, like an Actron CP9145, ect.

It'll disable the spark to each plug in sequence & measure rpm drop, any cyl that doesn't have much rpm drop is suspect & it'll flag that cyl, so you can go to it for a compression check, ect.

A bunch more trouble shooting thoughts for consideration, let us know what you do & find.

 

WOOPS, delete Double post.

 

After replacing the plug wires the CEL finally came on. I got it diagnosed as misfire-cylinder #4. Put a new plug in and she runs like brand new again. I want to thank you all for your time and assistance. Very much appreciated!! This forum rocks!

 

OK, good feedback & to hear you got it fixed & are "on the road again"!!!

 

hmm... you replaced all your plugs 6-7 months ago and now you need another one. I don't suppose you've lost any coolant have you?

 

I just checked, the reservoir was empty, added about a quart to the radiator. Why you ask? Should I be looking for some other problem?

 

My '98 4.0L developed a #4 misfire and mysteriously disappearing coolant. Turned out to be a failed lower intake manifold gasket.

https://www.ford-trucks.com/forums/2...ke-gasket.html

A few others with the 4.0L OHV who experienced similar symptoms ended up needing new head gaskets.

I recommend that you have UOA performed.

 

Change the engine oil NOW. Do a used oil analysis from Blackstone ($20). Refill the coolant resivor and monitor the level daily.

If the resivour is empty I would STRONGLY recommend having a friend/wife start the truck in the morning and standing/smelling the exhaust. If it's sweet or smokes an abnormal amount it's probably burning coolant. It pretty well guarantees either a cracked head or a blown head gasket.

The 4.0 OHV motor you have is a great one. There are very few weaknesses with it, but they are pretty bad about cracking heads. You are describing the exact same thing that happened to me with my 1999 4.0L. I pulled the heads myself, took them to a machine shop and found that one had cracked. Upon further review and searching on the ranger specific forums out there I found it's extremely common on the 4.0 OHV motors.

If you can turn a wrench you can get by relatively cheap (800-900). If not, it's going to get expensive. The "good" thing about a cracked head or blown head gasket is that theoretically you "can" drive on it so long as you constantly change the oil/add coolant/change the one plug. This shouldn't be done for too long, but it's possible to do in case you need to save up, or work out some plans for the downtime.

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Edit: I added something I typed a while ago for someone else on another ranger board. I figure it could help you here.

If you have a blown head gasket or a cracked head you will get rough idle when you first start the truck. Additionally you will probably have problems with fouling the same plug/s on a consistent basis. A cracked head or blown gasket usually won't have any externally visible leaks. If the head gasket is leaking externally it would most likely be coolant if anything.

If your truck has overheated recently than it's very likely that you have a cracked head or head gasket.

Ways to check for a blown head gasket/cracked head:
1. Slowly loosing coolant.
2. Smoke at start up.
3. Rough Idle.
4. Fouling spark plugs on a regular basis.
5. Inspect the block for coolant leaks around the heads, and pull the spark plugs after they have been sitting for a while to inspect for coolant.
6. Check for coolant for presence of oil.
7. Send your oil off for a used oil analysis. If it comes back with coolant contamination it's most likely a head/gasket.
8. Compression Test (good readings everywhere except the cylinder where you are burning coolant. Possibly the one next to it.

If you do end up tearing down the motor it would be a bad idea to just replace the head gasket. You will want to take the cylinder heads to a machine shop to have them magnifluxed to check for cracks and machined back into spec so they will go back on correctly without creating any new leaks. If you do not take the cylinder heads to a machine shop you run a very high risk of having to tear apart the motor again.

You're probably looking at $100 in labor to check for cracks and machine the heads flat. If the head is cracked they can repair them, but it's probably a better idea to get an aftermarket cylinder head from places like Alabama Cylinder Head or Ideal Cylinder Heads, or your local junk yard.

You will need to spend about $150 in gaskets alone. You will need to replace the intake gaskets, valve cover gaskets, head gaskets, and more. You will also have to replace the head bolts ($45)

You would be lucky if it's just a blown gasket. If that's the case you can probably get out of this for under $400 if you do it yourself. If it's a cracked head you're looking at around $600-$800. That cost quote will of course depend on if it's just one head or both heads that are cracked, and if you choose to repair or replace the heads.

If you take it to a shop you're looking at at least getting charged for 9-10 hours of shop labor to tear apart the motor which at $80 per hour rate is $720 minimum in just labor alone. Then you'll have to factor in parts cost, and machine shop charges. I would estimate that after it's all said and done you're looking at anywhere between $1500-$2500 depending on the shop you choose.

If you have some buddies who are mechanically inclined, can track down all the parts you are going to need, have access to an air compressor with an impact wrench and die grinder, quality torque wrench, and a breaker bar, and can afford to be without a car for 7-10 days you will save some SERIOUS cash, and learn a lot about working on cars.

If it makes any difference just about 3 years ago I was just learning how to change my own oil. I had all the symptoms that I listed above and used the forums to self diagnose the problem as a cracked head or blown head gasket. I learned so much about my truck, and cars in general. It's not hard if you just take your time and mark everything as you go. As long as you mark where every hose, cable, and wire connects when you are taking it apart you will be just fine. Just make good use of your digital camera and take pictures at every single step. With a digital camera, a Haynes shop manual, and the forums, you should be able to fix this yourself. It's easier than you think.

 

Thank you all for the info. I will be keeping a close eye on the radiator level. Hopefully it turns out to be nothing. Thanks again all!!!

 

Steamboat,

Please keep us updated on this. I'm interested because it's the exact same thing that I went through. Keep in mind that coolant will read different if the engine is hot or cold. If you notice a loss over the course of a couple weeks, and don't see any visible leaks, it's time to address the issue before it damages the bearings in the bottom end of the motor.

 

I will be watching the coolant level and will let you know.