Misfiring under hard acceleration - 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 04-17-2007
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Misfiring under hard acceleration

I recently purchased a used 2000 Ranger 4x4 w/ 4.0 OHV. It's got a rebuilt engine in it (15k miles) but 145k on the truck. Since I bought the truck, it's had this misfiring/surging problem under hard acceleration. Anytime I'd accelerate in higher gears or just when there was a lot of load on the engine, the truck would surge. I couldn't tell if it was a drivetrain or an engine problem.

Initially, I thought it might have been clutch slippage since the clutch hadn't been replaced since the truck was new and didn't engage until the pedal was nearly all the way out. I had that replaced (it definitely needed it anyway) but didn't solve the problem.

I drove the truck more and paid close attention to what was happening when the truck surged. The Tach didn't jump and the engine didn't seem to rev at all when the surges occurred, so I concluded (hoped!) that the engine misfiring was the problem.

A little research online led me to the common problem this engine has with the MAF sensor getting dirty and causing the air/fuel mixture to get thrown off. A common symptom of this is surging due to misfire and rough idle. I didn't have the rough idle problem, but the surging was definitely there.

I carefully cleaned the MAF sensor (these things are really delicate) with a can of electrical contact cleaner and canned air, checked the air filter (good), and reassembled the air intake. I also pulled a spark plug to check the condition. The first one I checked had a small crack in the insulator and was also showing some wear to the electrodes, so I ran to the store and picked up a set of Bosch Platinum2 plugs.

A short time later, all problems were gone and the truck runs like a champ. Just figured I'd pass on the news for anyone having similar problems with their Ranger.

~Adam~
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Old 04-17-2007
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Good job and good post. MAF problems are very common especially and cleaning does help in most cases.
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Old 04-17-2007
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Just curious, what exactly are you refering to "MAF" and where do I find it? I am wondering if it may have something to do with my problems (See Tread 93 4.0 into 94 swap help) I do have new plugs in mine and have tried both the original air box and the box and tube from the donor vehicle. but it definately has a definate miss under load. Differance is mine seems to go away if I mash the pedal completely?
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Old 04-17-2007
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MAF = Mass Air Flow Sensor. It sits atop the aluminum bracket that attaches the air intake hose to the air filter housing. The F-150 page linked below has a photo of the sensor.

Follow the instructions closely and be VERY CAREFUL with the sensor. DO NOT touch any of the sensor components - you'll break them and it will cost you $150+ to replace the part. Spray the thermistors carefully with electronic component cleaner, then canned air (it's much cleaner than air from a compressor). Wipe any dirt you see off the housing being careful not to get any into the intake. When you reinstall the sensor, don't overtighten the screws. They don't need to be torqued very tightly.

http://www.therangerstation.com/tech.../CleanMAF.html

http://www.fordf150.net/howto/clean-...low-sensor.php

Good luck. Hope this solves your trouble. Let us know!
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Old 04-17-2007
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You can also have a bad oxygen sensor. Generally, the engines run open loop when you mash the pedal. If the miss goes away, it could be that you have fuel ratio control problems when the engine runs open loop.

Does it miss when it's both cold and warmed up? If it runs okay cold then that could be it.

The MAF wires are quite delicate, so you just use spray to clean them, by the way.
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Old 04-26-2007
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My 2001 4.0 edge seems to be doing similar things. When I really get on it, it is fine until it starts to shift into OD. It will start to studder and will not accelerate past 90mph. I don't do this all the time because it's never good to push the truck to hard, but occasionally I get the urge to just get up and go. Is it governed at 90? Or is this a misfiring problem? Please help me with this issue.
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Old 04-26-2007
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That's the speed limiter and not a problem as such. There is a 92 mph speed limiter and at that speed fuel is cut off and on to limit the speed.

If you want it removed do two things:

1. Get tires rated for the speed you think you'll want.

2. Contact Bamachips, JusnesModified, or RoguePerformance (all .com's with members here) to get a tuner so you can remove the speed limiter.
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Old 04-26-2007
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Thanks for the information, and I am happy to hear it isn't a problem with my truck.
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