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Rough ideal at Low RPM and a miss at Low RPM

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Rough ideal at Low RPM and a miss at Low RPM

 
  #1  
Old 03-27-2004, 11:29 AM
Stampede
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Rough ideal at Low RPM and a miss at Low RPM

I have a 97 F 150 4.2, 4x4, 5-speed, with a 130,000 miles. My problem is, I'll be sitting at a light and the RPM will drop to about 550 or so, when the light turns green and I start to go, the truck acts like it has a miss, not enough power, kind of like a two step, but when I hit about 2500 or higher RPM, it comes a live, runs normal. I do get a check engine light, but it's when driving the truck, have not had it checked. What do you think?

And does any one know how the dealer ships get the engine compartments clean?

Thanks Stampede.
 
  #2  
Old 03-28-2004, 01:10 PM
horizonhuskies
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I think they use a heavy duty degreaser....they pay someone minimum wage to go through out the compartment and tape off any electronics...then they pay someone else to spray a crapload of degreaser in it...thats when the next guy/monkey (whichever is cheaper at the time) to scrub...and thats when the foreman gets to spray it down....just a guess though.

Have you pulled your plugs yet? Double check to make sure nothing came unseated, like a plug boot or something. Good luck.

Garrett
 
  #3  
Old 03-28-2004, 05:52 PM
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my 2000 has done that exact thing, it even died at a stop sign.....I drove it like that for a couple days, then I got a good tank of 93 with some octane boost to and it never happened again, just bad gas I guess.....
 
  #4  
Old 03-29-2004, 09:32 AM
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The dealers sometimes spray that Vaseline type junk all over your motor, which makes it look shinny at first but is impossible to take off and it attracts all kinds of dirt.

I don't tape off any of my electronics. First, I spray the entire motor down with Silicone spray, then I just use a light pressure washer to take off the gunk, then I spray the motor down again with Silicone spray.

The silicone spray will keep dirt from sticking to anything on your motor. So the next time you clean it, all you have to do is rinse it with water. I spray everything but the fan belt.

Tom
 
  #5  
Old 07-26-2004, 12:38 PM
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New guy, same question

I am new to the forum.

I have a 98 F-150 with the 4.2 and 75000 miles. I have owned since nearly new (16000 miles). In the last six months it has started to run rough.

I have had the injectors cleaned on a Snap On machine. That helped for awhile. About a month and a half ago, I performed the Sea-Foam treatment.

The truck is back to it's rough idle. It works fine with some throttle. At an idle it acts like a really hard miss.

Plugs are new. Wires are good. No leaks in vacuum hoses can be found. I did have a code for a miss in #3. After having the injectors cleaned, that went away. Any other ideas? It doesn't seem to be the EGR valve. Sometimes, after running it hard, the engine idles silky smooth. Can the #3 injector be changed without removing the upper air plenum?
 
  #6  
Old 07-26-2004, 12:51 PM
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How do you know the wires are good? Have you run your truck at night and looked for arcing while varying the throttle?
 
  #7  
Old 07-26-2004, 12:55 PM
tiller2pu
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Plug wires

I was running it in a dark shed. No indication of any arching was seen. I did not very the rpm. I let the truck idle, as that is where the problem tends to be.
 
  #8  
Old 07-26-2004, 01:06 PM
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Hm, man. A rough idle can be so many things that the process of elimination can be enormous. If you threw a code for a miss on 3 and you think you may have a problem with 3, perhaps you can pop the plug wire off while it's idling rough and see if there is any change in the way your truck is idling. If there is no change than that narrows the problem down quite a bit. Have you tried that?
 
  #9  
Old 07-26-2004, 01:29 PM
tiller2pu
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rough idle

I appreciate your help.

At the time the truck was running it's worst, before putting on the motor vac. Unplugging the spark plug wire made no difference. Afterwords, it would be a noticeable drop in performance.

I plan on talking with a mechanic about the possibility of installing an injector without removing the upper air plenum. Per our last correspondence, I might order a new set up plug wires to rule out the chance of internal resistance creating the problem.
 
  #10  
Old 07-26-2004, 01:32 PM
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I didn't realize that it was that difficult to replace an injector?
 
  #11  
Old 07-26-2004, 02:22 PM
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Per my Haynes manual, the upper air plenum needs to be removed before you can get the injector out. I would rather just swap it out. I am also working in a less than perfect garage and some limited tools. Weekend mechanic, if you know what I mean.
 
 


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