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

[daldelta]

eHoefler wrote:
Check your air filter, is it dirty?? Has a critter built a nest in the duck work to the air filter?? When was the last time you changed your fuel filters??

If you are not a proficient mechanic on diesel engines, you may have not adjusted your valves correctly. 48k is very early for a valve adjustment, normally done around a 100,000 miles or later.

I am very particular about service, I keep the unit inside as well. Change every filter fuel/oil every year regardless of mileage. I did change the air filter as well it had 30K on the engine. I may have adjusted the valves wrong but I have done this in the past on car engines and if I was off i don't think it would have been enough to reduce my power. Owners manual says to adjust valve lash at 24K. Engine sounds very healthy (everyone says so anyway) and runs great on open roads. Thanks any other thoughts?

[daldelta]

Ivylog wrote:
Remove the plug at the top/back of the injection pump. Turn the star wheel inside CW (looking from the back of the engine) two turns. This will put more fuel to the engine sooner with less boost pressure. Are you sure your tranny is in first gear. How many RPMs are you getting?
...........................................................................................................The plug is about here in picture below.
Another option to try is to let your engine run with the tranny in gear for 10+ minutes to heat the oil up so the torque slips more before trying to go up the hill.

Thanks I will try the get the tranny warm. Never thought about leaving it in gear to get it hot.good suggestion. I have heard about the injection pump suggestion , have you done this, any issues to worry about doing this?

[loghauler191]

check the oil in the tranny when was the last time it was changed

[bluebirdPT36]

First I will say that I am not familiar with the throttle on your coach. If it is drive by wire, with the aid of an assistant, can you watch the throttle lever at the injection pump and see if it is going wide open when assistant mashes foot throttle? You may be able to do this with the switch on and the engine not running. If it doesn't move, try test with engine running and trans in neutral. CAUTION; make sure it is in neutral and the assistant is someone you can trust not to do anything stupid.

[havasu]

I am no expert but from what I read, low boost at takeoff with a mechanical engine means that there are no revs to generate the boost.

I assume that it revs just fine in neutral?

So that points at a transmission issue - the torque converter isn't slipping enough to allow the engine to rev to generate the boost.

When underway, the engine is revving well enough to give you the 20# of boost that you need.

I may be off the mark, but it's just a thought.

[Ivylog]

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.

[paulcardoza]

Again --- If in your driveway you are seeing NO TURBO BOOST as you state, the de-rating is probably the issue. Obviously, the engine doesn't "know" you are in your driveway, so not being warmed up and de-rating is the likely answer.

daldelta wrote:

paulcardoza wrote:
OP ----

This is the key statement "The engine is flat and I have no boost." Only when in your driveway?

A few other folks have mentioned that the engine may de-rate until warm. If you have no boost when in your driveway, but it works fine when you are out on the road, this may well be your problem. I assume there are no issues from a dead stop, when out and about on the road?

No issues from a dead stop at least on flat land, takes off well from stop lights etc. When leaving from a stop light in 1st gear it is a little slow but when it hits 2nd I surge and it really takes off. What controls the de-rating is it the ECM? Is there any way to change or work around this? Maybe this is why after changing the turbo it really did not help getting up the hill.

[WILDEBILL308]

I think the problem is/as someone else posted your engine de rates in first and second to protect the driveline. This sounds wild but have you tried to ease into the throttle instead of flooring it maybe 1/4 to 1/2 till it starts to go? Do you have it in econ mode? I wouldn’t use the econ mode when starting out in your circumstance.
Bill

[eHoefler]

Check your air filter, is it dirty?? Has a critter built a nest in the duck work to the air filter?? When was the last time you changed your fuel filters??

If you are not a proficient mechanic on diesel engines, you may have not adjusted your valves correctly. 48k is very early for a valve adjustment, normally done around a 100,000 miles or later.

[daldelta]

paulcardoza wrote:
OP ----

This is the key statement "The engine is flat and I have no boost." Only when in your driveway?

A few other folks have mentioned that the engine may de-rate until warm. If you have no boost when in your driveway, but it works fine when you are out on the road, this may well be your problem. I assume there are no issues from a dead stop, when out and about on the road?

No issues from a dead stop at least on flat land, takes off well from stop lights etc. When leaving from a stop light in 1st gear it is a little slow but when it hits 2nd I surge and it really takes off. What controls the de-rating is it the ECM? Is there any way to change or work around this? Maybe this is why after changing the turbo it really did not help getting up the hill.

[daldelta]

DutchmenSport wrote:
This may sound stupid, but have you checked your transmission fluid lately? If it's low, this could be the reason you're not moving, especially when it's still cold and you're on a hill.

I am starting to wonder, I have recently done the check(Allison auto check) and it said it was OK when I was at a road side rest. I have changed the fluid and filters in the past and the Allison 6 speed auto check feature has told me I was low "X" quarts of fluid after I changed it so I think it is working. Since I am on a hill and the fluid would be cold(I do not believe the fluid gets warm until you drive it not while its idling) maybe it is too low. As mentioned in another post maybe I am not in 1st gear? Any suggestions? Thanks Dave

[paulcardoza]

OP ----

This is the key statement "The engine is flat and I have no boost." Only when in your driveway?

A few other folks have mentioned that the engine may de-rate until warm. If you have no boost when in your driveway, but it works fine when you are out on the road, this may well be your problem. I assume there are no issues from a dead stop, when out and about on the road?

[daldelta]

WILDEBILL308 wrote:
What boost pressure are you getting when you are trying to get out of your driveway?
Bill

. Bill, I am not sure,I do not believe I am getting any boost. Currently my boost gage is mounted down behind my stearing wheel and is not easy to lean forward to view when the motorhome is pointed up hill. With all the emotions of not getting up the hill I try everything else but I foget to look at the gage. I will have the throttle floored and the motorhome just sits there so I do not believe I have boost Sometimes I shut off the engine and restart and slowly it starts rolling. Any ideas--Thanks Dave

[JetAonly]

A couple of thoughts. It is normal to derate the motor in first gear, sometimes second to save the driveline. It does this even when warm. If my brakes stick, from rusting to the drums, the MH will not move. I have to rock it. If you put a chock in front of your tire, I don't think you will be able to drive over it.

Keep your momentum up or rock it to get going.

[DutchmenSport]

This may sound stupid, but have you checked your transmission fluid lately? If it's low, this could be the reason you're not moving, especially when it's still cold and you're on a hill.