'99 4.0 OHV 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 04-15-2011
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'99 4.0 OHV rough idle

OK my 99 4.0 has been idling rough lately. When i first crank it up it acts like it wants to shut off and sometimes does. But if i turn the key off and crank it again it fires and idles fine until the rpm's drop back down to around 700 then the idle goes to around 500rpm and it tries to die again. When accellerating it acts a little sluggish but otherwise no problems there. The other problem is when cruising at say 60 mph i can feel like a little bump or misfire every now and then. But after the truck has warmed up it idles fine and doesnt try to die but you can tell something is wrong. Within the last 10-15k miles I have changed plugs, wires, all O2 sensors, fuel filter and the IAC valve. There are no mods to the motor other than a K&N drop in filter. Any ideas???
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Old 04-19-2011
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Update: It's throwing codes P0171 and P0174 Systems too lean (Banks 1 & 2) Any ideas as to what this could be?
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Old 04-19-2011
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good luck finding out, im curious too, as i have been hunting this problem down since i got the truck. too lean means too much air not enough fuel so look for gasket leaks and that kind of thing, or not enough fuel pressure.
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Old 04-19-2011
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to lean most likely start with O2 sensors that should fix the lean, as for idle I would go with IAC.

it still misfires you might have the common cyl #4 and cyl #3 cracked head problem.
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Old 04-22-2011
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Changed the upper intake manifold gaskets this morning and she's idling like a champ! No more lean codes! Although it does still feel like it has a little "miss" in it i'm thinking it may be a bad plug due to it running lean for an extended period of time.
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Old 04-22-2011
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good 4 u, least it fixed ur prob. i did that too and lowers and didnt help
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Old 05-23-2011
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My truck has just become sick with this issue, still researching but here is ford's first round of checks.



Quote:
H41 DTCs P0171, P0172, P0174 AND P0175: FUEL SYSTEM AT THE CORRECTED FUEL TRIM

NOTE:
It is necessary to address all Continuous Memory Ignition and Misfire DTCs, if received during Continuous Memory testing, before addressing any Fuel Trim DTCs.

DTCs HO2S Reference list:

-- HO2S-11 = DTCs P0171 and P0172

-- HO2S-21 = DTCs P0174 and P0175

l Check intake air system for leaks, obstructions and damage.

l Check air cleaner element, air cleaner housing for blockage.

l Verify integrity of the PCV system.

l Check for vacuum leaks.

l Are any of the above concerns present?

Yes
REPAIR as necessary. COMPLETE KAM Reset.

No
GO to Pinpoint Test Step DC25. If MAF reading is within specification, return to Pinpoint Test Step H42.
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Old 05-27-2011
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Swapped the brake booster no CEL for 2 days now after the reset.

The booster was about half working, first half of travel had boost second half massive vacuum leak.
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