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Need help with acceleration problem...

Discussion in 'Dakota, 1998-2013 Durango and Aspen' started by Peymack91, May 2, 2017.

  1. Peymack91

    Peymack91 Member

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    OK. 1991 Dakota, V6. 215,000 miles.
    First- New cap, rotor, plugs, wires. All correct items. Champion plugs are clean and gapped correctly. New fuel pump and TPS. New PCV valve. All the vacuum hoses are new and tight. Cleaned tank with Sea Foam as well as throttle body with TB cleaner. Timing is correct and no noise from chain tensioner (may have already been changed out). Oil is clean with no sign of head gasket issues.

    The problem - Truck is incredibly sluggish. Floor the pedal and it gets moving...just barely. At partial throttle, it will cut out and "misfire" (not sure it actually misfires, but it will backfire slightly). Poor fuel economy all the way around. To really get up to speed, you have to floor it. It will downshift but not stay in the lower gear. It upshifts again too quickly for the lower gear to be any use.

    Does this sound like a plugged cat? With 215,000 miles it could be. Not long before this started, the truck backfired big time after a cold start in about 32 degree temps. Would that have blown out the cat and plugged it up? It idles fairly well at the correct RPM, but not strongly.

    Any ideas or suggestions.
     
  2. Doug D

    Doug D Virginia Gentleman

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    Sure sounds like a plugged cat.
     
  3. Peymack91

    Peymack91 Member

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    I'm leaning that direction and it's an easy (and cheap) fix. I no longer need to be emissions-compliant, so I can gut it (or cut it out completely).
     
  4. AllanC

    AllanC Well-Known Member

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    Here is a short video on how to test for a plugged catalytic converter.


    View: https://www.youtube.com/watch?v=9TlygJMxTps


    A quick, easy way to check if you do not have the appropriate scan tool to check engine data parameters is to disconnect the oxygen sensor and physically remove it from the exhaust pipe. This will provide an escape for exhaust gas before reaching the catalyst. Since a 1991 vehicle would be OBD I emissions compliant, it will have only one sensor before the catalytic converter. Drive the vehicle. If performance is more normal as you would expect, then the catalytic converter is probably restricted.
     
  5. Peymack91

    Peymack91 Member

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    I can do that.

    EDIT: I just went out to crank the engine and feel the exhaust by hand. It seems as if there is PLENTY of exhaust coming out of the tailpipe. Could this be misleading and I do, in fact, have a restriction?
     
    #5 Peymack91, May 2, 2017
    Last edited: May 2, 2017
  6. valiant67

    valiant67 Rich Corinthian Leather
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    I would not suspect the cat converter based on your description. The backfire and missing are pointing more to ignition or fuel. A plugged cat will make it sluggish, but generally not a backfire or a misfire.
     
  7. Doug D

    Doug D Virginia Gentleman

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    Not to be a curmudgeon, but even if the vehicle no longer needs to pass emission tests, the converter is required by law if the vehicle had one from the factory and there are applicable fines if caught. Plus the tuning of the engine takes into account the presence of the converter.

    Yes, some of gutted them so it appeared to have a converter, but they usually had tuning issues. Not worth it my opinion.
     
    Bob Lincoln likes this.
  8. Peymack91

    Peymack91 Member

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    The plugs, cap, rotor and wires are all new. I just checked the cap and rotor...normal wear. The plugs are not sooty or oily, with correct gap. One of the wires has a small cut at the cap boot, but no wire is exposed. Don't know when it happened.
    The fuel pump is brand-new and the tank is clean of any debris. The throttle body is clean as well.
    Would the misfire be due to too much or too little fuel?

    This is a daily driver, so I need to figure something out pretty quick. I just hate to take it somewhere for someone to throw parts at it.

    BTW, thanks for all the information so far!
     
  9. AllanC

    AllanC Well-Known Member

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    Yes, too much fuel can cause driveability problems just as too little fuel that starves the engine. Before you remove the oxygen sensor to create an exhaust escape path, disconnect the wiring at the oxygen sensor. Drive the vehicle. How does it perform? If it drives better with more normal response then the issue is an oxygen sensor sending incorrect signals to the PCM (powertrain control module).

    The CHECK ENGINE lamp will illuminate and an oxygen sensor signal code will be set. But driving with the oxygen sensor disconnected forces the PCM to go into OPEN LOOP mode (oxygen sensor signals not used). The PCM uses fixed parameters to set the fuel trim. If the engine runs better you know that the oxygen sensor is the culprit. But that needs to be backed up with a scan tool that looks at the signal from the oxygen sensor. It should vary between a lean condition (sensor voltage < 0.45 volts) and a rich condition (sensor voltage > 0.45 volts). An oxygen sensor stuck in a lean condition will be interpreted by the PCM to add more fuel (overly rich). This can cause dirveability issues.
     
  10. Bob Lincoln

    Bob Lincoln "CHECK FAULT CODES"
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    You could still be getting a misfire from that wire shorting out. These are not stranded copper cables, you won't see exposed wire. Try changing out that wire. Even if it isn't the cause, it will get worse with time and complicate any diagnosis, now or later.
     
  11. Peymack91

    Peymack91 Member

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    Ding, ding, ding. I think we have a winner. I unplugged the o2 harness and she ran like a scalded dog. No check engine light yet, but I'm sure it will pop up soon.
    Normally, I would have checked this item, but I'm used to a CEL when the o2 sensor goes bad. Truthfully, when a CEL gets thrown, most folks just assume a bad 02 sensor right off the bat.
    I'm gonna replace it and keep an eye on things. I'll report back when I'm confident in the solution.

    Thanks, guys.

    Chuck
     
  12. Peymack91

    Peymack91 Member

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    Just saw this. I plan on replacing it, absolutely. I'd like to find an individual plug wire instead of paying for an entire new set. I'll see what NAPA has to offer.
    Thanks.
     
  13. Bob Lincoln

    Bob Lincoln "CHECK FAULT CODES"
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    Can't buy them separately. You could try a junkyard if you've already tossed the old set. I keep mine for about a month to be sure I won't need them.
     
    Doug D likes this.
  14. Locodave

    Locodave Member

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    Sounds good on might need a new O2?
     
    #14 Locodave, May 2, 2017
    Last edited: May 2, 2017
  15. Peymack91

    Peymack91 Member

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    I spoke too quickly. Truck started with the same old symptoms and, rather than waste a day doing diagnostics, I dropped it off with my wrench-turner. Something is seriously wrong with the valve train and I have a dead cylinder. I trust this guy and what he tells me.
    I am going to cut my losses and get out of the truck. I hate to see another dead Dakota, but the cost to get her right is going to be higher than I am willing to spend.
    Thanks to everyone who has chimed in to try to get this truck over the hump.
     
  16. ImperialCrown

    Level III Supporter

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    Was it replaced with an OEM O2 sensor?
     

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