Forum Discussion

jjrowan's avatar
jjrowan
Explorer
Apr 09, 2014

Lacking Power

I purchased a 1998 Gulf Stream Sun Voyager today. It has a 5.9 liter Cummins Diesel with Allison 4 speed transmission. The test drive the owner took me on was about 20 miles, since I didn't drive I couldn't tell whether it was being floored or just cruising. After purchasing it I got it onto the highway and was disappointed that it lacks power. I made frequent use of the four way flashers going uphills. I didn't try shifting from 4 to 3 as I wasn't comfortable downshifting something I wasn't familiar with. Pressing the accelerator pedal all the way to the floor didn't cause a downshift. The prior owner said they'd replaced the "kick-down cable". The air filter was just replaced so it shouldn't be a factor. I had planned on towing my 2007 Trailblazer from New Jersey to Maine but the lack of power makes me think it won't handle the tow. I'm looking for anything to get more power out of the 5.9.
Class A
  • wirenutz's avatar
    wirenutz
    Explorer
    Apr 09, 2014
    I had a 5.9 in my old first gen. Dodge, it was rated at 180HP to get a few more ponys out of it I straight piped it, it helped some, it sounded cool as well
  • RFCN2's avatar
    RFCN2
    Explorer
    Apr 09, 2014
    Take it to cummins and have them put it on their computer before you do anything else.
  • crasster's avatar
    crasster
    Explorer II
    Apr 09, 2014
    RFCN2 wrote:
    Take it to cummins and have them put it on their computer before you do anything else.


    I agree. They'll be able to tell what is going on with that diesel.
  • jjrowan's avatar
    jjrowan
    Explorer
    Apr 09, 2014
    I guess I just Google for a Cummins service center near New Jersey?
  • OhhWell's avatar
    OhhWell
    Explorer
    Apr 09, 2014
    1998 was when the 5.9 switched from 12 valves to 24 and both were produced that year. It sounds like you probably have the 12v version which topped out at a little over 200hp I believe when in perfect condition. The 24v would have been at a little over 230hp in 1998. The 12v were known to be extremely reliable engines. What were the RPMs when you were chugging up the hills? It may have been in the power band in 4th and didn't need to downshift. Diesels don't rev to produce max power like Gassers do.

    It would be a great Idea to take it by a Cummins authorized service center for a checkup and they may be able to suggest upgrades for more HP.

    There is always:

    Banks Power
  • jjrowan's avatar
    jjrowan
    Explorer
    Apr 09, 2014
    The RPMS were around 2000 from what I remember, have to go out and pay more attention to that. Just took several pictures of engine compartment trying to obtain the engine serial number to no avail. I was surprised to see how small the turbo unit is on it. No option to post picture in replies.
  • John_S_'s avatar
    John_S_
    Explorer II
    Apr 09, 2014
    Heck my ISM has to down shift on steep hills. I had an 8.3 ISC that would get down to 45 to 50 on steep hills too. Depends on what you think is low and the grades steepness.
  • jjrowan's avatar
    jjrowan
    Explorer
    Apr 09, 2014
    John, I'm not talking about 6% grades, these are somewhere around 3% and it struggles.
  • OhhWell's avatar
    OhhWell
    Explorer
    Apr 09, 2014
    jjrowan wrote:
    The RPMS were around 2000 from what I remember, have to go out and pay more attention to that. Just took several pictures of engine compartment trying to obtain the engine serial number to no avail. I was surprised to see how small the turbo unit is on it. No option to post picture in replies.


    2000 rpms sounds about right, especially for a 4 speed transmission.

    Power Curves

    You likely just need more horsepower or a little longer to get to your destination if you will be climbing hills. You have found out the difference between HP and Torque!
  • Pass42's avatar
    Pass42
    Explorer
    Apr 09, 2014
    I had a 1988 Xplorer DP with the 12v Cummins 5.9, 180hp.....hills were an issue! the engine ran great, had decent fuel mileage, needed a running start on most grades....70+ coming into the hill, 40-50 at the top, depending on the incline & length... before you "boost" the HP, make sure your Allison Tranny can handle it.... the one in mine was only rated for about 230hp max, so I could have increased engine hp, and taken out the tranny!!!

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