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  #1  
Old 09-26-2012, 06:12 AM
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Default Rough Idle, hesitation on acceleration, loss of power

I have a 94 4.0 XLT and let me just say I've tried what I could think of and luck just hasn't been on my side. When I start the engine its starts up right away with no issues. As its idleing however, the rpms fluctuate up and down erratically and then it'll smooth out for a few min and then it will begin again. When I take it for a test drive its worse. If I accelerate it will hesitate big time and I can a feel a noticeably loss of power. If I floor the gas pedal it'll hesitate, then take off full power for about 3 seconds and then completely loose power as if though the motor was shut off but if I let off the gas it will idle between 500 and 700 sometimes wanted to shut off. At first I was told it was the MAF so I swapped that out, it didn't work. Then I was told it was possible the TPS, I swapped that out it didn't work. I'm being told that there is a possible vaccum leak but I've looked everywhere I could see a vaccum leak anywhere so no luck there. I was then told to take a look at the fuel pressure reg by checking the vaccum line for any evidene of gas in the line, no gas in the vaccum line so I'm assuming its ok. I haven't check yet but will a lil later to verfiy the lower intake manifold is on tight because I could have a leak there. Please if anyone has any ideas that would be great. Oh yes one more thing obviously gas economy is herendous, and I can smell the gas coming out of the tail pipe. So much so my eyes start to hurt.
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Last edited by tchachee; 09-26-2012 at 06:15 AM.
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  #2  
Old 09-26-2012, 06:30 AM
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Default Re: Rough Idle, hesitation on acceleration, loss of power

  • cracked spark plug
  • bad wires
  • bad coil
  • bad TPS
  • vacuum leak
  • blown heads
  • no compression
  • blown head gasket

list goes on start simple
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2000 Ford Ranger XLT 4x4 Offroad, 4.0L ext cab, Converted to Manual M5OD-R1HD.
_____________
33x13.50 Toyo M/T, 15x10, Body Lift, Rebuilt OHV, JBA headers, Hurst shifter, Warn VR10000-s, Class 1 bars, Belltech Shackles, Mustang GT rear disc, Level II hooks, Modded rear hitch, Custom front hitch, Level II Blue seats and black console, Explorer IRS rear cover, Extang fulltilt, Leer Cap Yakima Roof Rack, Cobra 29 with firestik stake mount, Scangauge II
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  #3  
Old 09-26-2012, 06:38 AM
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Default Re: Rough Idle, hesitation on acceleration, loss of power

cracked spark plug
bad wires
bad coil
bad TPS
vacuum leak

Thanks for the reply, checked all of these I have two coils changed wires and plugs and both the TPS and MAF were swapped out. The engine was actually removed from the truck so new gaskets were installed througout. The heads were inspected, no signs of cracks of any sort, it is possible that the head gasket may have blown already if so I'll check the coolant resevior for traces of that and I'll run a compression check because haven't done that yet. Thanks, any other suggestions from anyone would be great.
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  #4  
Old 09-26-2012, 07:13 AM
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Default Re: Rough Idle, hesitation on acceleration, loss of power

I had this exact same problem, I replaced all the plugs and plug wires and it fixed it. I used motorcraft plugs and wires.
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  #5  
Old 09-26-2012, 07:17 AM
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Default Re: Rough Idle, hesitation on acceleration, loss of power

I have new wires and plugs, plugs are motorcraft but wires are duralast. But did cover that base.
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  #6  
Old 09-26-2012, 09:24 AM
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Default Re: Rough Idle, hesitation on acceleration, loss of power

Ok I took a really long and close look at the engine compartment looking for any loose lines that may produce some sort of vacuum leak and couldn't find one. What I did find was a connector coming off the wire harness with no home. Its located behind the engine at the two top bolts where the transmission and engine bolt up. There are three other connectors two go to the O2 sensors and one have no idea but has a home but there is another just lingering around I couldn't find a home to. If anyone can help does anyone know what connector that might be? I thought maybe the cam position sensor but couldn't find that on this engine either. If that connector does indeed go somewhere that could be my issue if it doesn't go anywhere, well I guess I'm stuck again.
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  #7  
Old 09-26-2012, 12:27 PM
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Default Re: Rough Idle, hesitation on acceleration, loss of power

The cam sensor lives near the firewall hiddent by the upper intake.

The 4.0 OHV is known to have intake gasket problems and they need to be replaced. These gaskets get degrade over time and begin to leak causing bad idle. Also gives you a chance to inspect vacuum lines.
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  #8  
Old 09-26-2012, 07:07 PM
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Default Re: Rough Idle, hesitation on acceleration, loss of power

Ok, checked fuel pressure had about 32psi at idle and about 40 at full throttle. At idle I removed the vaccum for the FPR and it shot up to 40 psi so I'm sure the FPR is good to go. Spark Plugs are new but are completely black. I gave it full throttle in neutral (standard) and it reved to about 4500 then bogged down to about 1500 spitting and sputtering with the pedal all the way down. Let it idle for about 2 min then attempted again and got same result, I capped of vaccums to trouble shoot, sprayed carb cleaner around intake and no fluctuation that would indicate that there was a leak. The only think I can think of is either the cats are clogged, the pcm is crap.....someone please help give me more ideas!!
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  #9  
Old 09-26-2012, 08:46 PM
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Default Re: Rough Idle, hesitation on acceleration, loss of power

Check your EGR valve. Carbon build up will cause your symptoms.
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  #10  
Old 09-26-2012, 09:25 PM
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Default Re: Rough Idle, hesitation on acceleration, loss of power

Or dpfe sensor
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2000 Ford Ranger XLT 4x4 Offroad, 4.0L ext cab, Converted to Manual M5OD-R1HD.
_____________
33x13.50 Toyo M/T, 15x10, Body Lift, Rebuilt OHV, JBA headers, Hurst shifter, Warn VR10000-s, Class 1 bars, Belltech Shackles, Mustang GT rear disc, Level II hooks, Modded rear hitch, Custom front hitch, Level II Blue seats and black console, Explorer IRS rear cover, Extang fulltilt, Leer Cap Yakima Roof Rack, Cobra 29 with firestik stake mount, Scangauge II
Few mods
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  #11  
Old 09-27-2012, 06:17 AM
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Default Re: Rough Idle, hesitation on acceleration, loss of power

Alright, I must be completey dumb or blind or something because I don't see an EGR valve or DPFE sensor anywhere in my engine compartment. I have a 1992 4.0 X Vin engine in my 94 ranger. The only thing that was swapped out was the engine block itself, all other components, brackets, lower and upper and lower intake, exhaust manifolds, ect remain the same not sure that that would make a difference but in terms of an EGR or the DPFE.....nada. I'll keep looking but anyone can reference that that would be outstanding. Thanks for the replies, I'm definately learning a whole lot but unfortunetly I still can't find the source of my issue but I'm sure we all will, thank for the help. Any new ideas? Please post.

----------

Sorry I wasn't clear about the engine swap. I put in a 4.0 from a 1992 Explorer. Again only block and heads, everything else remained the same.
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  #12  
Old 09-27-2012, 06:41 AM
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Default Re: Rough Idle, hesitation on acceleration, loss of power

Checked spark plugs, they are new, and they are carbon fouled (dry black carbon powder like stuff on it) assuming rich mixture.....just updating what I find
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  #13  
Old 09-27-2012, 03:58 PM
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Default Re: Rough Idle, hesitation on acceleration, loss of power

Here are some photos of the DPFE sensor (it has two hoses connected from below) and the EGR valve (it's round and has one hose on top, one pipe below and connected to the intake manifold). Good luck!
Attached Images
File Type: jpg egr sensor.jpg (41.9 KB, 59 views)
File Type: jpg egr valve.jpg (2.0 KB, 48 views)
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2001 Ford Ranger with the flare sides. 4x4 with a 4.0 engine. The only thing I did so far is: F/R Brakes, rotors, drums, F/R shocks, tires, bed cap, cone filter, hanger/shackles, F/P wheel bearing, upper control arm, lower ball joint, filler neck, fuel filter and DPFE sensor, muffler, sway bar links and spark plugs!
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  #14  
Old 09-28-2012, 09:08 AM
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Default Re: Rough Idle, hesitation on acceleration, loss of power

Well it turns out my truck was not equipped with and EGR system. After looking everywhere for it I finally took it to the ford dealership and my vin was ran and this truck was never equipped with an EGR. So I'm back at square one again, I'm going to remove the oxygen sensors and have them tested because that may explain my rich fuel mixture "if" they have failed I will keep everyone posted. As always though, always open for suggestions.
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Last edited by tchachee; 10-01-2012 at 05:45 AM.
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  #15  
Old 10-08-2012, 01:20 PM
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Default Re: Rough Idle, hesitation on acceleration, loss of power

Well what can I say I've tried just about everything and cannot figure this out. I've changed out the fuel pump, catalytic converter, O2 sensors, TPS, swapped out he MAF with another, spark plugs wires and coil and can't seem to find a solution at all. I still have rough idle when at operating temperature, and when I attempt to accelerate the truck completely gives up as if though the fuel was disconnected from it. If I floor it, it backfires in the intake and bucks. When I let off the accelerator there is a point where it'll get some power so I have to feather it back home when I'm out testing. Its not overheating, oil pressure is good, fuel pressure was tested. Put a vacuum tester on it and when I stepped on the gas most of the vaccum disappears so I assumed a clogged cat but new cat proved that to be wrong. Had it scanned got code 111 and 159 (MAF) cleaned the MAF with cleaner and no luck. Please someone with same issue or similar resolved share your knowledge.
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