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1500 rpm miss, sluggish and bad MPG

Ross-N-Chicago

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'91 XLT 2wd
OK,

The X idles fine but has noticeable hesitation when cold for the first half dozen accelerations from stops until warmed up. Then, on the highway while crusing if I slow down to the 50-55 MPH range and about 1500 RPMs she will definitely hesitate until the RPMs get back up there. Mileage is down a bit too which leads me to the FPR, which was replaced at the stealer in 2000. Is it time for a new one and O2 sensor?

Other than that everything is normal...
 


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EliteConcept

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how new are the plugs?

i had one plug on my 92 on the passenger side complete corrode. i was going to work one day and the truck starting shaking really bad and missing and wouldn't go past like 45. I just vouched to go cheap and have the spark plugs replaced instead of thinking it was something bigger..... turns out one plug was soo corroed it couldn't have been firing at all....

i'd maybe just pull and check teh quality of your plug and gap
 




DaHeinah

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What's your mileage? Also, since the velocity you mentioned is 50-55 mph and your RPMs are in the vicinity of 1500, I'm assuming that you were in OD. Sometimes it can be a bit hesitant to down shift in OD, or that is the problem in mine. Has it always done that?
 




Ross-N-Chicago

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Haven't checked the plugs but put Motorcraft Plat and Jacobs wires on around Xmas of 2001. I'll pull and check them since it's painless.

I am in OD when the hesitation happens on the highway, it just kind of stumbles unitl speed/rpms are back up. It has not always done this.

I believe it is either plug, wire or fuel related. Duh.
 




Ross-N-Chicago

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Plugs and wires tested fine. Vacuum good all around as well. However, mileage came back around 11 mpg and lots of black smoke on the tailpipe. This is the infamous FPR, is it not?
 




Rhett

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Sounds like there is a chance it could be the FPR; have you pulled the vacuum line off the FPR and checked for fuel in that line?
 




Ross-N-Chicago

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Yes, but the line was dry. The truck had been sitting for a couple hours. Is there a correct time to check the line?
 




iceplorer

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Hey Guys.
My ´93 Explorer acts like that too but not that smoke. I´ve checked the plugs and they are fine. Could the fuel-filter be a factor in this problem? Is "FPR" the Fuel pressure regulator? I think he could be a probable cause for the hesitation or the MAF sensor not metering the low speed air accurately at that low 1500-1800rpm? I´m checking my Ex.step by step and I´ll let you know if I find anything.
 




Ross-N-Chicago

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iceplorer,

that should read black soot on tailpipe. it doesn't smoke.
 




Rhett

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Ross I just can't remember the best way to test the FPR. I thought that info was on here somewhere though in the past. I know that I've seen FPR's with the vac tube dry while the truck is sitting and yet still be malfunctioning in operation. You could also have a bad O2 like you said; even without a CEL they can start throwing snake-eyes on you with poor acceleration spots. How about the MAF sensor, is it clean?
 




Sallad420

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Have you tried the "Cleaning the MAF" trick yet?

I took mine apart and wiped it down with some Q-Tips and carb cleaner, and now it runs perfect, doesn't studder or chug at all. I was actually amazed that cleaning it would actually make that much of a difference.

Mine used to "studder" at around 1500-2000 RPM as wel.
 




Ross-N-Chicago

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OK,

The cat from Summit that I installed last week is definitely the right one. However, since I just replaced the FPR tonight thinking it may solve my problem and didn't, I am leaning toward the O2 sensor as bad. This would explain my crappy mileage as of late as well. I am going to replace it tomorrow and see if that doesn't solve it.
 




Nate1

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I personally think you should clean your maf and reset your computer before you go spend any more. Its basically free and could be the cause of your problem.
-----Nate
 




Ross-N-Chicago

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Nate

I cleaned it last week so that shouldn't be it. However, I will do it again to see what's going on.
 




iceplorer

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Hey Ross.
I cleaned my MAF yesterday and it did not change anything so I´m gonna look at the O2 sensor and the fuel-filter next.
I also think checking wires, vacum hoses an fuel-lines is worth it.
 




Ross-N-Chicago

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I've checked all vacuum and fuel lines. Replaced fuel filter a month ago. I'm OK on those. I've searched tons of posts and I am quite sure that I fouled my O2 sensor. I will replace this afternoon after some family stuff. I'll let you know if it helps...
 




Ross-N-Chicago

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Finally Found It!!

Nate, you were close. Codes came back 157, MAF voltage too low. So I checked the connection and sure enough it had come loose and was barely seated (I broke the top connecting pin awhile ago). So I ziptied the connector as tight as I could get it around the MAF housing and took it for a spin. WOW, what a difference!!

Even though I probably didn't need to replace the FPR or O2 sensor I can rationalize that I don't have to do that for some time. And since I am getting a ProFLow MAF from Exp Express this summer and KKM new air tube (whenever they come out) I will probably see even better gains considering my MAF is 12 years old now.
 




Sallad420

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Great to hear!:D
 




Rhett

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KKM air tube? Are they going to make one? I have not heard this!
 


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Ross-N-Chicago

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Rhett, check this out

http://explorerforum.com/forums/showthread.php?s=&threadid=63430

My X still misses on the highway in the 1500 rpm range but it is better than before. I think I am either losing my OD or I've got a fron or rear U Joint that is about to go. Or, my MAF is just shot and I've heard of a few people that have replaced them and solved a problem or two.
 




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