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'91 Ex, intermittant low power, ignition retarded?-thoughts on HP boosting chips

Discussion in 'Under the Hood' started by Az_NavajoRob, December 23, 2004.

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    1. Az_NavajoRob

      Az_NavajoRob Member

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      Okay guys, here's the deal. I rescently bought a '91 Navajo that needed cyl heads (and radiator, heater core, starter, battery, altinator, etc.). After doing all this work, it generally runs great. I say generally because sometimes it feels like it's down on power, like it's dragging an anchor. Other times it feels fine and has plenty of power. Also, I get pretty crappy mileage (12-13 mpg). It passed emissions fine and there is no fuel leak so my thought is that the computer is retarding the ignition, like in response to poor fuel or engine knocking and that's what is causeing the loss in power. I run 87 octane (the cheap stuff) and have never had a hint of pinging.

      My question is this-is there a knock sensor that could be bad telling the computer to retard the ignition timing? Would this show up if I pull codes? If there is no knock sensor then how does the computer know how to alter the timing? Does it use the air intake temp sensor for this purpose? If so, would one of those $10.00 "chips" (you know, the little resistor that plugs into the harness instead of the temp sensor to fool the comp into thinking the air being drawn into the engine is at 0 degrees) keep the computer from retarding the ignition?

      Any advice or thoughts on this subject would be appreciated, including any experience with those "cheater chips" that fool the computer as described above.
       
      Last edited: December 23, 2004
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    3. MrShorty

      MrShorty Explorer Addict

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      The '91 doesn't have a knock sensor. I would pull codes and see if the computer can see a problem. As part of the KOER test, you can verify the computer's timing advance (see ignition timing tests at www.dalidesign.com/hbook/eectest.html). If everything is working as it should, there's very little to be gained by "fooling" with the computer.

      In addition to pulling codes, some other basic diagnostic stuff (fuel pressure test, vacuum test) might be in order.
       
    4. Az_NavajoRob

      Az_NavajoRob Member

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      Any other thoughts? I'm going to pull codes this weekend so hopefully I'll find an "untied shoelace".
       
    5. adale

      adale New Member

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      Just my .02 worth. Have you checked your tranny?
       
    6. Az_NavajoRob

      Az_NavajoRob Member

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      Checked the tranny for what? It's an auto and it seems fine. When I got it I changed the filter and purged all the fluid out of the system and it has worked fine since. I do have 3.55's in it with 30.5 inch tires so I know it's not going to be a neck-snapper, even on its best day. But it runs so good sometimes and other times it feels a little sluggish, kinda like the timing got retarded to like 5 degrees BTDC. I'm thinking it has to be something eletrical but where should I start?
       
    7. adale

      adale New Member

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      I've seen trannys slip and make the vehicle seem like it was under powered. Also have seen brakes drag and cause the same feeling. I suggested it, since a motor having to have all that repair makes me wonder how the rest of the vehicle was maintained. No offense intended.
       
    8. Az_NavajoRob

      Az_NavajoRob Member

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      No offense taken. Any suggestion is appreciated, especially those I've been quick to dismiss.

      When it feels low on power the engine isn't reving high like a slipping tranny. Also, when I got the rig I had to do a mini restoration job as it was neglected pretty bad. I had to basically redo the whole rear brake system, including e-brake cables and brake lines due to rusted/broken/MISSING components. For the fronts, new pads were all that was needed. The only thing I have left to do is to replace a u-joint that clunks a little when going into reverse.
       

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