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High Rpms But Low Power. 74 Cj-fif

Discussion in 'Intermediate CJ-5/6/7/8' started by Douglas Wolcott, May 27, 2021.

  1. May 27, 2021
    Douglas Wolcott

    Douglas Wolcott New Member

    Maine
    Joined:
    Dec 13, 2020
    Messages:
    8
    Hi everyone. First time poster, long time lurker. Bought a 74 CJ5 232 back in sept 2019. Finally got it out on the road but wondering if this is just how these run or if my Jeep needs some work.

    Shifting into second and third gear seem to take a lot of acceleration to get moving. Almost like a dump truck. It sounds like the engine is doing a lot of work but the output to the rear wheels seems low. (I’m in 2h)

    Tcase looked like chocolate milk when I changed the gear oil. Transmission had like 10 oz of oil before flushing that.


    When I bought the jeep it wasn’t running so I have no baseline to compare against. Do these CJs just sound like jet engines as the mph climbs or do I have more work to do?

    Thanks
     
  2. May 28, 2021
    Jw60

    Jw60 Sitting up n buckled down. 2024 Sponsor 2023 Sponsor 2022 Sponsor

    Sedalia MO.
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    Apr 8, 2008
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    My first thought is to do a round of tests.
    Compression on each cylinder then again with a little oil in the cylinders.
    Check the valves all move the same distance and none of the cam lobes are flat.
    Check base timing and mechanical advance.
    Vacuum leaks

    When you get out feel the wheels for heat from dragging brakes or bad bearings.
    Check Transmission and transfercase for excess heat.
    Inflate the tires appropriately.

    I highly recommend an infrared thermometer for chasing dead cylinders and driveline issues.
    I was flat towing my jeep and the truck was down from 15 to 12 mpg and I found a caliper n the jeep was dragging. I'd gone 30 miles at 75mph and that wheel was HOT. Normally the ir temp is 80 to 100deg it was over 300deg that time.
     
  3. May 28, 2021
    bigjohn

    bigjohn Active Member

    Kelso Wa
    Joined:
    Mar 18, 2010
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    1,054
    That era of straight 6 should not be a rocket but plenty quick. Even my junk pushing 100-120psi on the compression checks still seems peppy enough. I’d be suspect of the ignition system. Think point and condenser or hie/, electronic ignition
     
  4. May 28, 2021
    PeteL

    PeteL If it wasn't for physics, and law enforcement... 2024 Sponsor 2023 Sponsor 2022 Sponsor

    Hills of NH
    Joined:
    Aug 3, 2003
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    9,754
    The above points are good ones.

    But it is true that if you have never driven a jeep, it may be a shock to find it is nothing at all like a modern passenger vehicle.

    Even after many years, when I switch from my f-350 to my '88 YJ at first it almost seems like something is "wrong."
     
    AKjeff likes this.
  5. May 28, 2021
    Douglas Wolcott

    Douglas Wolcott New Member

    Maine
    Joined:
    Dec 13, 2020
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    8
    Camshaft is new. The old one had a flat lobe on cyl 5 causing backfiring through the carb.

    Brakes are new and there no noticeable drag as I can push the jeep in neutral with ease. I don’t hear any drag when doing this.

    I have purchased an hei but didn’t want to introduce too many factors at once. So the coil is still in play.

    Compression for each cylinder was around 115 (+/- 10) I’ll have to see where I put my results when I did it last. I thought I saved them on my phone but can’t find them.

    Vacuum gauge shows “normal operation” at idle but closer to the “late timing” reading. To get it like right in the middle of “normal operation” I can adjust the distributor to a timing mark around 20 as opposed to the 8-12 range where it is now.
     
    Jw60 likes this.
  6. May 28, 2021
    Douglas Wolcott

    Douglas Wolcott New Member

    Maine
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    Dec 13, 2020
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    8
    I’ll recheck the compression after work and post those results.
     
  7. May 28, 2021
    dane71

    dane71 Member

    USA
    Joined:
    May 11, 2017
    Messages:
    195
    Check that the timing is advancing with revs. Mine was being really slow yet it ran so smooth, I thought it was low compression but it turned out that the mechanical advance mechanism in the distributor was gummed up.
     
    Fireball likes this.
  8. May 28, 2021
    Douglas Wolcott

    Douglas Wolcott New Member

    Maine
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    Dec 13, 2020
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    Thanks I’ll check that too. The advance is new, the cap is new, the dist is still the same one that came with it. So maybe I messed up the new advance install, though it seemed pretty straight forward when replacing. All good suggestions, thanks.
     
  9. May 28, 2021
    Douglas Wolcott

    Douglas Wolcott New Member

    Maine
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    Dec 13, 2020
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    How far advanced would the timing be with the mechanical and vacuum advance working as expected? I see it advance an extra 10-12 degrees when revving. This is the same when the vacuum line is unplugged.
     
  10. May 28, 2021
    PeteL

    PeteL If it wasn't for physics, and law enforcement... 2024 Sponsor 2023 Sponsor 2022 Sponsor

    Hills of NH
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    I heard of a case like this once. Owner of a Jaguar complained the "performance is way down...." Turned out to be too strong a return spring on the gas pedal. :lol:
     
  11. May 28, 2021
    Jw60

    Jw60 Sitting up n buckled down. 2024 Sponsor 2023 Sponsor 2022 Sponsor

    Sedalia MO.
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    When I bought My cj5 with the f-head it had only plowed snow for the past decade and the floors had been repaired. The pedal hit the floor at half throttle.
     
  12. May 28, 2021
    Douglas Wolcott

    Douglas Wolcott New Member

    Maine
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    I don’t know if this fixed the issue, but I know it fixed an issue...


    After work i decided to re-check the compression as mentioned by jw60. I expected the readings that I’ve seen before around 110 or 120. The last time I checked is when I replaces the camshaft a few months ago. Anyway, well I got to cylinder five the compression was around 30.


    So I was confused by this because I know that I checked the compression before and literally nothing has really changed between when I changed the camshaft in now. I decided to take the valve cover off and check the valves and make sure nothing was stuck. I checked the compression of cylinder five again and at this point it was back up to 120!


    Well to my surprise I look inside the valve cover and there’s marks from the valve where I assume it got stuck against the cover on the exhaust stroke. The valve cover is aftermarket but I think it’s just a little tapered toward the top than the original cover.


    So I put the old valve cover back on which I happen to have and haven’t thrown out yet. And now the engine is running smoother than I’ve ever heard it run. I’m getting good compression on all cylinders and the vacuum gauge is almost right in the middle of the green for “normal operation”.


    I won’t know if this fixed the high rpm low power issue until tomorrow as it’s raining but it seems very promising. See the attached picture for where the valves got stuck.
     

    Attached Files:

    FinoCJ and Jw60 like this.
  13. May 29, 2021
    dane71

    dane71 Member

    USA
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    That sounds about right.

    Also its good to hear like you might have it solved! Fingers crossed!
     
  14. May 29, 2021
    Douglas Wolcott

    Douglas Wolcott New Member

    Maine
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    Dec 13, 2020
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    Took it for a ride today and while it seems to be running a little better there’s still a high amount of rpms needed to get it going.

    One of the exhaust header plugs popped off (prob wasn’t screwed in that well from the factory) while I was driving and I just figured I blew something since it got reallly loud but I think it was a happy accident because I can see some backfiring coming out of the exhaust manifold through the plug hole. I adjusted the timing and it’s pretty far advanced at the moment but the backfiring through the manifold has subsided a bit. It doesn’t sound so hot roddy. It was probably losing a lot of power by the gas igniting in the exhaust manifold.

    I can still hear it backfiring a bit so I’m thinking there’s some additional work to be done. oh I also put the HEI in and it seems like it’s running a little better at idle.

    I’ll take it out tomorrow to see if there are any improvements in power.

    Is the backfiring in the exhaust manifold because the mixture is too lean?
     
  15. May 31, 2021
    johneyboy03

    johneyboy03 The green beast

    Quebec, Canada
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    For a 3 speed transmission its normal, long gear and a torquer engine will make speed change a lot longer thank a 5-6 speed modern transmission.
     
  16. Oct 8, 2021
    Douglas Wolcott

    Douglas Wolcott New Member

    Maine
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    I know it’s been a few months but it just needed a new clutch. I’m in business now

    thanks again.
     
    crewrest, FinoCJ, Fireball and 2 others like this.
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