This has been an ongoing issue for about a month.When I start the engine after it has been sitting and is cold it runs ruff for about a minute then smooths out and runs fine. I pulled a P0304 code (cyl.4 missfire) but I do not get a CEL.
I checked the plugs and they were ok but I changed them and the wires anyway as it just turned 50k and the plugs were original. I could live with a little cold ruff idle but the code throwing bothers me. The truck is a 2000 xlt 4x with auto trans. and 4.0 engine. This is my second 4.0 ranger but I have only had it for about 6 months.
Thanks Jeff

 

I would check the plug and wire on the number 4 cylinder, and then the coil pack. Running rough on start up and then getting smoother sounds like the IAC but the code does not agree with this.

 

Welcome to FTE
Good idea to have posted up your trouble code. Is that the only one you have, if not, post All code Numbers, as they can offer up good trouble shooting clues.

^+1 on checking the coilpack, plug & wires, even though the plugs & wires are new, as Murphys Law may be messing with you. Plug wires should measure end to end, about 1K ohms/inch of length, 30k ohms max, no matter the length.

The coilpack secondary winding should measure 13K-15K ohms & since we have a waste spark ignition, you'll have to measure secondary resistance between the coilpack #4 plug wire position & its companion #3, then #2 & #6, then #1 & #5, there is no spec for the primary windings resistance, but each primary winding should be less than 5 ohms, more like .5 ohms & be closely matched. Each primary windings should have 12 volts B+ at KOEO at the coilpack electrical connector.

If the plug wires & coils resistance checks out, maybe consider doing an after dark cold idle wet down test with a spray bottle of water, paying close attention to the #4 plug, plug wire & #4 coilpack position, as you wet down each one while watching for arcs & sparks, or listening for a change in idle.

If no joy, unbolt & lift the coilpack & spray under neath, as they are known to crack there & have electrical break down unseen underneath.

If still no joy, maybe take the coilpack to your favorite autoparts store for a no cost electrical output bench test & see how things go.

If still no joy, move on to the #4 fuel injector & using your stethoscope, listen to it when the engine is started cold & running rough, to determine if it sounds different than the others.
All of the fuel injectors should also have 12 volts B+ to their electrical connector at KOEO. Their resistance should be closely matched & fall between 12-16 ohms, so if #4 injector is the odd man out on resistance, or sounds different than the others on a cold start, or has less voltage, its earned a spot high up on your suspect list.

If no joy there, on a cold start, with your stethoscope, have a listen to the top end around the #4 cyl valves, to determine if things sound different there, like a sticking valve that'll tap louder on a cold start, that warms up & stops acting out.

More thoughts for consideration, let us know how your trouble shoot goes.

 

Thanks guys,
I have ruled out plugs and wires, I had checked the wires before I changed them and they checked out good I just replaced them because I was going to do the plugs anyway as they did look a little worn and the gap on the 2 that I checked was wide so I just replaced them (they were also original as per the different numbers on the left bank vs.the right)
I did clean the IAC but it didn't change anything.
I didn't know about the possible cracks on the bottom of the coil pack and will check that out. What is the process to check the resistance as where do you hook up the meter? the plug wire contact and ground or plug contact # 3 cyl. to Plug contact#4 ?
Thanks

 

Disconnect the #3 & #4 plug wire at the coilpack & measure that coils secondary continuity/resistance across those two contacts, as those two plugs share that coil in our waste spark ignition system. Same goes for the two other pairs of plug wires noted above, as the coil pack has three secondary windings & each winding powers two plugs.

Have a read on "why double platinum plugs" in this forums Tech Info thread, located atop the thread index page. So we hope you used the specified double platinum, or better yet the newer iridium enhanced fine wire center electrode, with platinum pad side wire design plugs, as they are needed so they'll last in the double workload our waste spark ignition system puts on them. Same for the plug wires, they need to be designed to take the double work load. Motorcraft, or Autolite plugs & wires are recommended as they are of high quality & designed to take that double work load.

Let us know how the wet down test goes.

 

OK, I just took readings on the secondary windings on the coil pack. They are as follows:
1-5 12.50
2-6 12.45
3-4 12.05 ( P0304 code pulled)

Given that does it look like the coil pack is on it's way south?
This issue ONLY happens when cold or when the truck hasn't been run for a few hours,it goes away and runs great after about 30 seconds.
Thanks

 

Seeing as how all secondary resistance readings seem low, at the same time all are about the same resistance, except the 3-4 secondary, so I'd keep that in mind & continue trouble shooting elsewhere as suggested above, like the wetdown, coil pack bench output & listen to fuel injector & valves tests, to see if something more difinitive turns up thats in time with the cold start rough running & let us know what you find.

 

Other than the cold start miss and the occasional P-0304 code the thing runs great. It only has 51k on the clock and is in near prefect condition. This is just irritating. The miss lasts such a short amount of time I can't even get out of the truck fast enough to use a stethoscope on it though there is no valve train ticking whatsoever. I think I am going to have to wait until it gets worse so as I have more to go on. I will keep you all posted.

 

Before you crank it for a cold start, cycle the ignition from off to run, say 3-4 times, pausing at run for a couple of seconds for the fuel pump to run & time out, Then go to Start to crank the engine & see if it helps the rough running start.

If it does, has the fuel filter ever been replaced???? If not, bring it up to date on scheduled maintenance & pour in a 20oz dose of Techron Concentrate Plus at the pump before filling, so you get good mixing & if you'll fill up with Chevron, Texaco, CalTex, or now Shell, all of which have some PEA in the fuel ad package, the added Techron will bring the treat rate 10X above pump gas alone & will usually tidy up the fuel system, fuel injectors, intake valves, piston crowns & combustion chamber deposits in one tank. Run most of the treated tank out with some daily rpms above 3500 for a couple of miles & let us know how it goes.

 

That was the 1st thing I did. I work at Chevron research and tech.
But you are right as I have done that on other vehicles and gotten good results. After doing just as you said I have gone through 3 tanks of Chevron in the hopes it would help. I might try another bottle of the Techron again.
On my last Ranger I was getting a irritating CEL on and off and the Techron cleared it right up and it never came back.