Lacking Power

[jjrowan]

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.

[jjrowan]

A pleasant surprise. Today, with less traffic on the highway, I figured I'd see how the cruise control worked. Accelerated to 60, turned on cruise button and pressed "set". The 5.9 did a great job maintaining speed. I guess I wasn't mashing the throttle pedal enough. A little longer test drive tomorrow, 120 miles to mother-in-law's for her 88th birthday. Garden State Parkway with EZ-Pass should be nice ride.

[Old-Biscuit]

Downshift.........keep RPMs under 3200

[discovery4us]

The 5.9 is good on fuel and reliable and you can definitely get more power out of it but I think your weak link is going to be the 4 speed Allison. Having a Cummins center take a look is a good idea and you might also check into a Banks kit although I don't think Banks will install a kit using anything less than a 6 speed tranny.
I have the 24 Valve 5.9 mated to a 6 speed Allison and while I can't compete with the big boys as long as I watch my weight I'm not far behind.

[Gjac]

Power in a MH is very subjective. Most folks say they have "a lot of power" or it "feels under powered on hills" . I would post what your HP rating is and its weight. Also if you do a 40-60 mph test at WOT and post results you can see if there is something wrong with the MH or if it is just what that MH is capable of doing based on HP to weight ratio. As a data point my friend had a 5.9 diesel bounder 34 ft and it took 22 secs to go from 40-60 mpg. I felt it was under powered but it was brand new and that was the best it could do. I just tested a 2002 40 ft CC for a friend it had 370 hp and weighed around 34,000 lbs or so (the owner did not know the weights) it took 20 secs to go from 40-60 mph on a flat slab. If you post your HP, Wt. and 40-60 time folks could give you a more accurate answer if something is wrong or not.

[DougE]

Welcome to the motorhome world. Getting the engine checked out is a great idea, but you'll need to learn that finding the gear, rpm and speed the vehicle is happy with in any situation is just another aspect of the RVing experience. Patience, brother, patience!

[noteven]

Hi jjrowan - what does the motorhome weigh?

Our 5.9 powered pickup is rated at 300 hp / 660 torques and hauls truck/5th wheel combined weight of 22,999lbs at 45mph at part throttle up 8% grades.

A quick look at the Google suggests your engine may be rated in the 210 hp range at the moment. There should be a placard attached high on engine opposite to the exhaust side that states to original power rating and serial number.

First I would replace the fuel filters and check the air filter to makes sure fuel and air is not wanting.

The 5.9 can be modified to produce 600+ hp and 1300 torques reliably if you have the cooling system & transmission to handle it. Travelling over hill and dale at a mile a minute like a passenger car with a heavy vehicle only takes $$$'s nowadays.

If you choose to make modifications for power an idea might be to sit down and make a plan with a shop with a proven track record in towing / hauling / marine engine mods - conditions where engines operate reliably at full power for extended periods - that will give you reliable results for your money.

There will be lots of power options between what you have and the limit of the engine's capability.

[YC_1]

I agree on the service center check. You may not be getting the turbo boost you need due to something as simple as a leaky coupling hose.

In any case I suspect it would not be a speed demon. I bet your mileage is good though,.

[Pass42]

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!!!

[OhhWell]

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!

[jjrowan]

John, I'm not talking about 6% grades, these are somewhere around 3% and it struggles.

[John_S_]

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]

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.

[OhhWell]

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]

I guess I just Google for a Cummins service center near New Jersey?