No power climbing a hill from dead stop

[daldelta]

Current Situation
I have a 98 HR Imperial 40' motorhome with a Cummins mechanical 6CTA8.3 @ 325hp. My problem is no power on a hill from a dead stop. --I live in Tennessee in the hills, and do to property constraints when I back my motorhome out of my pole building I have to crank the coach hard to the left once my front end clears the building, I am also going downhill as I back out. After I have backed up as far as I can, to get out of my driveway onto the main road my wheels need to be cranked hard the opposite direction and climb uphill from a dead stop. I hold my breath every time because now when I bury the throttle the motorhome does not want to move. The engine is flat and I have no boost. After a few tries and much anxiety, it usually very slowly starts to move and I am able to get out of my driveway onto the main road. Once I am on the road I climb hills with no issues and seem to have plenty of power, my only issue with power is in the position stated above.

History- The engine has 48K miles and the only engine repair has been replacing the turbo charger. I do my own maintenance (not a professional) and changed the turbo myself after I was told by a Cummins dealership that it needed replaced. I had to be towed from my driveway to Cummings because on that occasion I could not get the motorhome to go up the hill. Cummings changed the waste gate and said it is a temp fix to get me home. After I changed the turbo it did not seem to help much, but now slowly the motorhome climbs the hill. It’s probably only a matter of time before I will need to be towed again. What can I do to get the power needed to get up the hill from a dead stop? What should I check, waste gate adjustment, fuel pump etc.? I do have a slight exhaust manifold leak, and I have adjusted the valves a couple of times, maybe I did something wrong there. When I changed the turbo I added a boost gage, and recently have seen as much as 20 pounds going uphill moving down the road. From my first observation it seems the crossovers and hoses/fittings are Ok and do not seem to be the problem.

Thank you for your responses and help
Dave

[sc3283]

Dald, did you have this issue last year? If not...retrace ALL your repairs made this spring

Any chance you changed filter brands?

Any chance your fuel got full of algae over the winter and plugged your new fuel filter?

Mechanical 8.3s do seem to have times when a take off from dead stop is less powerful than other times. I have been told this is a normal thing and to eliminate this..adjust the star wheel as stated previously. Cummins has the pump set very lean to make the EPA happy. The adjustment causes no adverse effects or long range problems...What is does is supply fuel faster...which causes the turbo to spool faster. Turbos can not spool if engine is not getting fuel.

[daldelta]

lfeather wrote:
It may sound dumb, but have you ever changed your fuel filters during the time frame you have had this problem?

Larry

Yes, every year I change the filters. Changed this spring and used the motorhome twice. Both times same issue leaving driveway.

[daldelta]

daldelta wrote:

havasu wrote:
Have you done a stall test on the transmission?

How many revs does it give you?

No I have not, how do you go about doing this--leave the air brake on and block the tires? Can I do this on the flat surface inside my pole building? How do you analize the results?

Yes, every year I change all filters. Changed all this spring and used motorhome twice. Both times same issue getting up the hill.

[daldelta]

havasu wrote:
Have you done a stall test on the transmission?

How many revs does it give you?

No I have not, how do you go about doing this--leave the air brake on and block the tires? Can I do this on the flat surface inside my pole building? How do you analize the results?

[lfeather]

It may sound dumb, but have you ever changed your fuel filters during the time frame you have had this problem?

Larry

[JetAonly]

havasu wrote:
Have you done a stall test on the transmission?

How many revs does it give you?

I was thinking of this, too. Stall speed is like 900rpm? A drag racer might have a stall speed of 5k to get max HP at launch. The RV is much lower in order to prevent overheating the fluid.
So at 900 rpm you aren't going to build much boost anyway, even with a new gasket.

You simply need to figure out a way to keep some momentum, like keep some speed, or change your drive way.

[time2roll]

If you are sure you are in low gear then I would have that mechanic come test drive it out of your driveway.

[havasu]

Have you done a stall test on the transmission?

How many revs does it give you?

[daldelta]

adondo wrote:
I think we might be getting to the problem.

The cold transmission doesn't help matters at all. I've stayed in a nice little campsite in Klickitat Canyon near Glenwood WA a few times. It's a fish camp, better suited for campers on trucks. I have about 4" clearance on each side (trees) to get in there. :B It's the kind of place where a 40' coach just doesn't look like it belongs. 🙂

The place is on the river, and there's a climb of about 6% either direction when heading out, and it's in the middle of a curve too. (The entrance is pretty much the bottom of a V notch) It's also a busy road for log trucks, and many's the cold morning when I'm patting the dashboard saying "COME ON, BABY, COME ON BABY, PLEASE, LET'S GO!!" as I'm looking in the mirror for the grill of a Peterbilt pulling 80,000 lbs. of logs that could be rounding the corner any second. When she's fully warm, she rockets away from the same kind of place. (Relatively speaking)

The manifold leak is a BIG issue, even if a small one. A turbocharger is a centrifugal compressor driven by a turbine. (compressor and turbine are directly coupled together) You'd be surprised at how a tiny leak can really effect the turbine's speed, and if there's no boost, it ain't makin' enough torque.

A stuck shut flapper (exhaust brake) will usually kill the engine, and it won't rev unloaded, so I doubt that's it. If it's all the way shut, it shouldn't even idle. But, an exhaust manifold leak will keep it from making boost until the RPM comes up. And, as mentioned, a cold transmission will keep the RPM from coming up enough in the first place, and when everything's warm on the road, the higher from-dead-stop RPM can compensate for the low boost and/or turbine speed.

Adondo, thank you for your response. I am sure not looking forward to it,but it looks as though I need to remove the turbo and replace the manifold gasket once again just to start a process of elimination. I am still a little unsure if that will fix the problem though since after I changed the turbo my situation of getting up the hill was still the same-slighly improved at least I have made it up the hill without a tow. Looks like I may have fixed one issue and started another, if the turbo was bad I made an improvemnet changing it out but now face a manifold leak that mght have cancelled out the turbo improvement. Before I changed out the turbo i did not have a exhaust manifold leak. I may try to seal the leak once again, I did buy some very high temp pressure pipe caulk to patch but it did work loose.

I will try all the good ideas from everyone who posted and see if I can get through the summer before changing out the exhaust gasket this winter. Hopefully the fix will be one of the suggestions. Going to start next week implementing a couple. Dave

[Airstreamer67]

I have a rig that I can manually activate the exhaust brake because it is designed as a rapid warm-up device. If I try to move with it activated, I don't think I could climb out of a molehill.

[adondo]

I think we might be getting to the problem.

The cold transmission doesn't help matters at all. I've stayed in a nice little campsite in Klickitat Canyon near Glenwood WA a few times. It's a fish camp, better suited for campers on trucks. I have about 4" clearance on each side (trees) to get in there. :B It's the kind of place where a 40' coach just doesn't look like it belongs. 🙂

The place is on the river, and there's a climb of about 6% either direction when heading out, and it's in the middle of a curve too. (The entrance is pretty much the bottom of a V notch) It's also a busy road for log trucks, and many's the cold morning when I'm patting the dashboard saying "COME ON, BABY, COME ON BABY, PLEASE, LET'S GO!!" as I'm looking in the mirror for the grill of a Peterbilt pulling 80,000 lbs. of logs that could be rounding the corner any second. When she's fully warm, she rockets away from the same kind of place. (Relatively speaking)

The manifold leak is a BIG issue, even if a small one. A turbocharger is a centrifugal compressor driven by a turbine. (compressor and turbine are directly coupled together) You'd be surprised at how a tiny leak can really effect the turbine's speed, and if there's no boost, it ain't makin' enough torque.

A stuck shut flapper (exhaust brake) will usually kill the engine, and it won't rev unloaded, so I doubt that's it. If it's all the way shut, it shouldn't even idle. But, an exhaust manifold leak will keep it from making boost until the RPM comes up. And, as mentioned, a cold transmission will keep the RPM from coming up enough in the first place, and when everything's warm on the road, the higher from-dead-stop RPM can compensate for the low boost and/or turbine speed.

[Ivylog]

Daldelta, do a google search "cummins p7100 injection pump pictures" and the fourth one on the first line is what I stole. If you right click on a picture it will sometimes give you the option "copy image url".
If you do a search for p7100 #10 fuel plate you should be able to find all kinds of info on boosting the 5.9/8.3 HP. Here's a long video as it's hard to get to the pump on a 5.9's star wheel. I have a crew cab FL 70 (for sale):W with the 8.3 and yes I've done this and I cut my fuel plate so it looks more like a #10.
Here is a better picture, scroll down a little.

[daldelta]

Ivylog wrote:
Dave, as you stated, you do not have an electronic engine... something pulls on the black lever in the picture I posted above. There is no derating on your engine. How many RPMs do you get and how much boost pressure when you try and go up the hill? If you are getting 1500+ RPMs and 10 psi boost then I'd say your tranny is low on oil and it is slipping. Econo mode raises the shift points, not lowers... but in first gear it makes no difference.

Ivylog can you please send that picture to my email, I cannot get it to open up and I don't see where I cange my prefrences on this site. daldelta@aol.com Thanks

[daldelta]

loghauler191 wrote:
check the oil in the tranny when was the last time it was changed

Changed the tranny fluid and 3 filters inside the tranny at 32K.