Question about 1987 Jeep Comanche

1 Answer

2.5 liter no power

Compression check shows 125 on each cylinder. New fuel filter. Plugs and fuel pump less than 1 year old. Idles fine and drives fine. Not enough power to climb hills on normal asphalt road. Drops from 55 mph to about 30 mph even with downshifting. Waiting on a new TPS to arrive to see if that helps. Running straight gasoline with no ethanol. Any other ideas?

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  • 3 more comments 
  • Bryan S
    Bryan S Feb 07, 2012

    Also have removed the catalytic converter and found a previous owner had gutted it. We just had that issue with our '93 Lumina APV.

  • Bryan S
    Bryan S Feb 07, 2012

    Transmission is 4 speed manual and truck is 2 wheel drive. Manual steering and no A/C.

  • Bryan S
    Bryan S Feb 09, 2012

    Excellent tip. As soon as someone gets home I will try it.

  • Bryan S
    Bryan S Feb 09, 2012

    I checked the ignition coil resistance as outlined in my Haynes manual. The first 2 checks look fine but the 3rd may not be. The book says on high resistance scale connect negative meter lead to negative terminal on coil, positive lead to high voltage terminal, resistance should be infinite. Mine reads 6.7k ohms. I am guessing that is too low to be considered infinite.

  • Bryan S
    Bryan S Apr 30, 2012

    I got busy and forgot to post the results of dropping the fuel tank. I found about a teaspoon of very fine dirt in the sock on the fuel pump. I cleaned that out and tried to clean the fibrous filter in the bottom of the pump. With this done the truck would run about 10-15 minutes before losing power. I just pushed in the clutch, turn off the key, coast about 5 seconds, turn on the key and pop the clutch. Over time it seems to have cleared more of the dirt as I rarely have to do that now. Thank you folks for all the troubleshooting help.

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  • Jeep Master
  • 5,332 Answers

Check for back pressure in the exhaust. A plugged cat will cause the exact symptom you have described.

Posted on Feb 07, 2012

  • 8 more comments 
  • Bryan S
    Bryan S Feb 07, 2012

    Thank you for the suggestion. I forgot to mention that in my original question. I tried that first due to the recent problem with our van.

  • Jeremy W.
    Jeremy W. Feb 07, 2012

    and your sure it's not a timing issue?

  • Bryan S
    Bryan S Feb 07, 2012

    Not positive but it does start and run just as it did prior to starting this. I have not mucked around with the distributor or anything other than a new cap and rotor last year. I do not recall it ever backfiring or anything else that would make me think it may have jumped time. It is possible though as it has roughly 230k miles on it.

  • Jeremy W.
    Jeremy W. Feb 07, 2012

    is it boggy when you power brake it?

    My gut says week spark or fuel pressure. Have you checked to see what you have for fuel pressure. Have you checked spark output with a variable spark tester?

  • Bryan S
    Bryan S Feb 07, 2012

    I have not tried power braking. I do not have a fuel pressure test gauge or spark tester. I did replace the coil and ignition module last year soon after replacing the spark plugs. I plan on replacing the plugs again in the next couple days to be sure about the condition. I will try the power braking as soon as I can and post what happens.

  • Bryan S
    Bryan S Feb 09, 2012

    Installed the new TPS yesterday but no change. Power braking it seemed to do ok until more pedal pressure is applied then it starts bogging. Timing is not adjustable according to Haynes manual. Distributor is still tight and does not turn. I did not try loosening to adjust it. I am going to check the coil today as per the manual and possibly swap it with an old one that works fine until it gets hot to see if there is a difference in performance. If not then I plan on dropping the tank to check the sock on fuel pump.

  • Jeremy W.
    Jeremy W. Feb 09, 2012

    When it starts to bog have somebody give it a shot of carb spray. If performance is restored its a fuel issue. If it stays the same it is spark/ignition issue.

  • Jeremy W.
    Jeremy W. Feb 09, 2012

    sounds like you may be on to something!

  • Bryan S
    Bryan S Feb 09, 2012

    I am hoping so. Just contacted the parts store to make sure warranty is good and part is in stock. Yes on both counts so I may have good news in a few hours. Installed the coil just under a year ago.

  • Bryan S
    Bryan S Feb 10, 2012

    Got the new coil and plugs. The suspect reading on the old coil was the same on the new one but resistance across the primary winding was about 3 ohms lower on new one. After installing coil and plugs I tried the power braking again and it pulled well against the brakes. Went to the bottom of a hill next to the house and it climbed well. Drove out to the asphalt road and it did not even want to take off. Looks like dropping the tank is next but we got a good rain so I will have to wait for a couple days or lay in the mud.

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