98 4.0 OHV MAF Mod, rough idle - Ranger-Forums - The Ultimate Ford Ranger Resource


4.0L OHV & SOHC V6 Tech General discussion of 4.0L OHV and SOHC V6 Ford Ranger engines.

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Old 11-20-2008
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98 4.0 OHV MAF Housing Mod, rough idle, Some clattering & Droning

Hi guys, I have at 98 ranger with the 4.0L OHV, auto, 4x4. 43K original miles. Fuel Filter just changed.

Several of the folks on this forum have done the Mas air flow sensor housing mod (port and polish)..

Well I was one of them and I cant tell if it is effecting my truck. Maybe you guys can help me out?

Let me give you a background, apparently myself and the previous owners of the rig did not know the thermostat wasnt working right. The truck never got warm so it always idles a tad high (1100-1200rpm). I ported and polished the MAF housing and then I fixed the thermostat. Now it seems to idle a little rough.

If I unplug the MAF the engine sputters a moment and then returns to a normal but slightly higher idle. It seems smoother than when it is plugged in though. The strange thing is that through this whole process of plugging and unplugging the check engine light never even came on? I even left it unplugged and restarted the engine.. No CEL.

So besides the annoyance of a rough idle and poor gas mileage, have any of you with this mod experienced this?? Should I be looking for a new housing? It was a royal pain to port and polish, it would be a shame to have to buy a new one.

The other thing is that this truck has the original plugs/wires/O2 sensors. It was suggested I change them to try and bump up the fuel economy, do you guys know where I can get quality replacements for a good price? I am also trying to find the small brackets to mount fog lights to the front of the truck (in front of the grill) do you know where I can pick those up?

Another crazy thought I had is when the engine was always running cold I would hear a clattering in the engine, someone was saying it is piston slap?? After the thermostat was fixed it still clatters.. Little less than usual when warm but its there. I wonder if there is something else wrong? Dont know about you guys but noises have always bothered me.. There is an odd droning noise at idle in park sometime too.. Very odd. But hey its a ford right?!

Thanks!
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Old 11-20-2008
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How long ago did you do this mod?

If memory serves me right, piston slap is normal on the OHC 4.0s.
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Old 11-20-2008
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have you tried cleaning the MAF sensor? and how about a tune up (plugs wires etc.) and the reason your light probably didn't come on was because you have to go through a "warm up cycle" in other words the truck has to be cold than warm up past a set temp. and it has to get like 40* above that temp. and you also have things called "drive cycles" which include the warm up cycle, and require you to hit a certain speed, and cruise above it for a while so the computer can run and test all of your sensors. and then this will have to happen twice and the sensor will have to fail both times before the DOOM light comes on. you might also have a vacuum leak. i would hook a vacuum gauge to it and see how much vacuum your engine makes. could suggest a problem with the readings that you get
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Old 11-20-2008
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Christian: I did this mod about 6 months ago. As for the noise I guess you guys have some clattering too? The droning is wierd, sounds like its comming from the transmission area (at idle). The clattering is comming from the bottom of the engine somewheres. The top sounds good.

Carson: Yes, when I did the port and polish I used MAF Sensor cleaner. I have not done plugs/wires or O2's mostly since the truck only has 43K on it. I was hoping to do that soon but i wanted to know if you guys had any recommendations and where to buy for the most reasonable price. Is it true these engines use two different kinds of plugs on each side? I was thinking Autolite double plats personally, would you use the thin or thick conductor types?

I dont know what a vacume gauge is, but I can check the hoses, I think we are good in that department though. When I first bought the truck (2yrs ago) I cleaned the IAC but I would imagine it might be due again.

To test the IAC all I need to do is uplug it at idle right? And if it idles exactly the same then its probably fine? Or was that for jeeps...
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Old 11-21-2008
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If it was me i go to napa to get parts here because the people at "shucks i got the wrong part again" are morons. your O2 sensor should be fine still. i have the SOHC 4.0L so i don't have/hear piston slap. I would start with new plugs and testing your pulg wires. they should be about 7k ohms per foot, and check for little white pin holes in the wires to indicate one thats been arcing. and all a vacuum gauge does is show you how hard the engine is sucking in air. at WOT you'll have 0 in of vac. and i'm trying to remember but it should be around 17 at idle and 14 at cruiz. (those numbers i would almost guarantee they are wrong) and if you watch the needle on the gauge at idle it should be steady. if its flickering then you probably have valve problems. another thing i did to my ranger was i had the engine cleaned. they call it a motor vac and the solution they use is about 10 times stronger than any of that stuff you can buy off the shelf for cleaning the engine. and it will clean the carbon off the valves and make it run like brand new. you probably wont notice much seeing how low of miles you have. i did it to a few cars and a jeep that could barely idle, once it was done that jeep ran like a raped ape lol
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Old 11-21-2008
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I'd first and foremost clear the KAM and put the motor through a idle learn process. (search here at RF for the idle learn)

Lets see what that does first.

Rich
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