unusual problem
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unusual problem
I posted this over in the TRS and as of yet have not had a response. While driving my 2000, 4.o, auto ranger, when I let off the gas the vehicle will slow down as usual till it get to around 1500 rpms and then it just drops like a rock to around 1000 or 900 rpms. If I watch the tach there will be a little spike in the rpms then it returns to normal. When it drops you can really feel the truck slow down almost like braking. Then I will press on the gas and everything will go back to normal till I let off again and it gets to 1500rpms. I have replaced IAC, TPS, MAF, and one of the O2 sensers. Oh, and I do not have a CEL. It does not matter if it is in overdrive or just drive. I talked with the mechanic that owns the service station I go to and he told me that both of his wreckers (fords) will do this but not all the time. He said it must be a ford thing!!! What does anyone think?
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Joined: Jan 2004
Posts: 13,851
Likes: 111
From: SW Va
Could be a number of things, like an acting out speed sensor, EGR system, vapor recovery purge valve, sticking PCV valve, acting out, torque converter or tranny control innards ect, ect, but my 99 4.0L doesn't do it.
I'd have the computer scanned for any "Pending" trouble codes, which may not have occured enough times to have turned the CEL on yet, as they could help narrow down your trouble shoot.
If your autoparts store won't do the scan it unless the CEL is lit, just unloosen the gas cap on the drive over there & that'll turn it on so they'll scan it, but you'll know why you have the loose gas cap code!!!! Post any Pending code Numbers found.
Did this problem begin suddenly after some event????
Are you up to date on All past & present due scheduled maintenance????
Why did you only change the one O2 sensor????
Were the parts you replaced testing bad????
I'd have the computer scanned for any "Pending" trouble codes, which may not have occured enough times to have turned the CEL on yet, as they could help narrow down your trouble shoot.
If your autoparts store won't do the scan it unless the CEL is lit, just unloosen the gas cap on the drive over there & that'll turn it on so they'll scan it, but you'll know why you have the loose gas cap code!!!! Post any Pending code Numbers found.
Did this problem begin suddenly after some event????
Are you up to date on All past & present due scheduled maintenance????
Why did you only change the one O2 sensor????
Were the parts you replaced testing bad????
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New User
Joined: Nov 2009
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Well, I dont have an egr valve, not sure where the vapor recovery purge valve is, checked the pcv vlave and it rattles so guess its good. Just had it scanned and there is no active codes right now. I just bought this truck and it was a one owner and he was a rather old gentleman and he bought it new and just drove it. Since I had it I changed the o2 sensor, tps, iac, and cleaned the maf. Changed the o2 because the cel came on and thats the fix my service station told me. The cel went out after replacing it. I had to change the timing chain cover gasket. Leaked in and not out thank god. Oh and I changed the fuel filter and it was an original !! The truck has 88000 on it now.
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Joined: Jan 2004
Posts: 13,851
Likes: 111
From: SW Va
Ok, well you don't have any pending codes stored, so you don't likely have any ptoblems with the vapor recovery system.
Seeing as how you have 88K miles on this ride, do you know if the tranny fluid has ever been changed???
So I take it that the parts you've replaced were likely ok, except the O2 sensor????
What was the trouble code Number, that caused the gararge to suspect the O2 sensor was bad????
Have you pulled the battery B- cable, to wipe the computers memory, after you replaced the above parts & cleaned the MAF sensor????
If so, did you go through the cold & warm idle relearn sequence, so the computer could relearn it's cold & warm idle strategy & begin to build new fuel trim tables???? If not you might begin with that.
Then if you can come by a scantool that'll read PID's, hook it up & monitor things when it acts out & see if any of the PID's look abnormal.
That might offer up a good clue as to which system might have a problem.
No need to throw parts at the problem, unless you have tested them & know they are faulty.
You can down load an owners & scheduled maintenance manual here, if you didn't get one with the vehicle.
http://www.fleet.ford.com/maintenanc...ls/default.asp
Seeing as how you have 88K miles on this ride, do you know if the tranny fluid has ever been changed???
So I take it that the parts you've replaced were likely ok, except the O2 sensor????
What was the trouble code Number, that caused the gararge to suspect the O2 sensor was bad????
Have you pulled the battery B- cable, to wipe the computers memory, after you replaced the above parts & cleaned the MAF sensor????
If so, did you go through the cold & warm idle relearn sequence, so the computer could relearn it's cold & warm idle strategy & begin to build new fuel trim tables???? If not you might begin with that.
Then if you can come by a scantool that'll read PID's, hook it up & monitor things when it acts out & see if any of the PID's look abnormal.
That might offer up a good clue as to which system might have a problem.
No need to throw parts at the problem, unless you have tested them & know they are faulty.
You can down load an owners & scheduled maintenance manual here, if you didn't get one with the vehicle.
http://www.fleet.ford.com/maintenanc...ls/default.asp
