Sign in to follow this  

Cummins 8.3 Mechanical- Power Issue

Recommended Posts


Hello FMCA:

Current Situation-- I have a 98 HR Imperial 40' motorhome with a Cummins mechanical 8.3 @ 325hp.

My problem is no power on a hill from a dead stop. I live in Tennessee in the hills, and due 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 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.

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 Cummins 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. I changed the turbo when I got home, still did not help much, but now slowly the motorhome climbs. It’s 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? 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. Hard to tell when the problem started since I lived in Indiana (very flat ground) when I adjusted the valves and did not have any dead stop hills to climb with the wheels cranked.

When I changed the turbo I added a boost gauge, and have seen as much as 20 pounds going uphill moving down the
road. All crossovers and hoses/fittings are OK and do not seem to be the problem.

Thank you for your responses and help.

Sincerely Dave

Share this post

Link to post
Share on other sites

Hi Dave,

Like DD mentioned, check for leaks in the exhaust manifold area and all the hoses and connections between the turbo output and the intake manifold. One can use kids soap bubbles in a spray bottle the check for leaks in the air intake system.

Also check the air input hose for the Air Compressor for a leak, they expand like a radiator hose and burst.

Also check the output pressure of the fuel lift pump, you should read around 15lbs. if the pressure is less then 5 to 8 lbs. Change the lift pump, starving the engine for fuel and the low fuel rate can damage the injector pump !!!!

Should your engine response be good, then you might have a torque convertor issue.

At around 1700 rpm you should notice a definite increase in engine power as the turbo spools up.

The exhaust leak could be a real issue, just how big is it ? and any leak would limit performance.

The valves should not need adjustment on you model engine until after 150,000 miles. from the information published in their engine information. There is a TDC setting and an after TDC setting point to adjust the valve train.

Do you have any hard starting issues?


Additional information regarding the Cummings 8.3 engines.

Beginning in 1998, Cummins
introduced the ISC based off the earlier mechanical 8.3 C-series engine. The
original ISC engine featured a Cummins Accumulator Pump System (CAPS). This
CAPS pump was a computer controlled injection pump, with individual fuel lines
to each injector. Prior to 1998 they where Mechanical / Post 1998 they incorporated the CAPS system. Engine serial number will list the fuel delivery system used.

In 2003, Cummins released the
updated ISC engine. Among other differences, the most significant was the
change to the High Pressure Common Rail (HPCR) fuel system. The new fuel system
eliminated the CAPS injection pump, relying on electronic controlled injectors
to actuate fuel.

Share this post

Link to post
Share on other sites

Thanks DD and Rich for your help:

My exhaust manifold leak is at the #1 or #6 cylinder, the cylinder furthest away from the back of the motorhome. The leak is at the gasket where the exhaust header bolts to the manifold. I over torqued it when I changed the turbo. The way I noticed the leak was seeing some black residue in that area around the gasket. I did a bubble leak test back when I changed the turbo around 2 years ago and the leak did not seem that bad, that was at idle speed and may have gotten worse. It was very disappointed to see after all the work it took to change the turbo, I could not check for leaks until everything was back together. I did buy a very expensive and very high temp sealant and applied the best I could around the leak. I do not believe it really helped. Not sure the exhaust leak is only problem, since I had the same climbing problem before I changed the turbo? The lack of power was the reason I changed the turbo and Cummins told me it was bad. I do not believe there was an exhaust leak when the old turbo was on.

I have checked all the hose clamp fittings, I have not checked the hoses themselves for leaks, so I will make sure to do that. How do I check to see if the turbo is free to spin? I assumed it was working since I had boost going down the road.

I have not checked the air compressor hose; will the water leak test be adequate to check for the leak? I will do some research to figure out how to check the output pressure of the fuel lift pump. Any good web sites I should check out for how-to info?

With the anxiety of the motorhome not moving up the hill I failed to notice what the engine RPM is reading, I am thinking the engine does not even rev up; it just sits there and then slowly starts to roll forward. It is really is like nothing happens when I press the throttle. Sure hope it’s not the torque converter, I have not noticed any kind of slippage. Any checks to verify this? I have changed the filters and fluid in the tranny--Allison 6 speed. It has a fluid level check and it does read OK and seems to shift fine on the road. Should I look into a potential throttle issue? It has the Electronic throttle control.

FYI- I did have another issue once where I had no power and found the exhaust brake was sticking closed. It released with a couple of sprays of WD-40 on the plunger shaft. I always check it now before I leave to insure it is not stuck closed. I was on the road from a campground when that happened not at my home on the hill.(As I mentioned, I do make sure the exhaust brake is not stuck shut before I back out of my pole building so I don’t believe it has anything to do with my power issue.)

Thanks you again, all help is greatly appreciated.


Share this post

Link to post
Share on other sites


Regarding the hose between the intake manifold and the Air Compressor, if its still OEM just replace it, they dry out over time and its is not that pricy. For its size it might be a little over priced, but if it does fail you will have an issue again with power and not many shops stock it !!!

Fuel pressure is measured by placing a pressure gauge in the line(made for that purpose). There are two ways to check it. Opening the output side of the lift between the pump and the filter by connecting the gauge directly to the pump output line, or by installing a "T" connector in line and then connecting the gauge to the "T" output.

I prefer this method because you can run the engine and watch the pressure level relative to engine load.

When you open the fuel line you could loose system priming.

Do you have a friend that works on there Diesel engines that might have the gauge and knowledge using it.

I'm concerned about the exhaust leak, that is number 1 on the list, A Leak has a profound effect on your turbo boost pressure. Then check your fuel pressure.

Turbo link LUBE.--- WD-40 evaporates / burns off quickly.

PacBrake has a special high-temp lube for their exhaust brakes ( is also a product called Super Lube, you can look it up on line by just typing it into the search engine. Ace and True Value hardware stores carry it, but often do not stock it. They can special order it. Now it is a little pricy, but it works very well to keep the turbo link working freely and for other areas that need lubrication that tend to run hot because it has a high temperature rating. This is the recommended Lubrication from Cummins / Freightliner. They sell it in liquid form, not in a spray can.

Hope this helps, Rich.

Share this post

Link to post
Share on other sites


I had a older 5.9 Mechanical and had pretty much the same power issues as you. I believe the set up for the two engines is very close. There should be an "air tube" extending from the waste gate valve. On the 5.9 it carries on up the inside of engine, where it is/was attached to the second manifold bolt. This air tube then continues over top of the engine, and connects into the Fuel Pump. On my engine the Air Tube had severed at the clamp. This tube carries air under pressure to your fuel pump. In orther words the pump wasn't getting enough air. No air, no power. I jury rigged a piece of fuel line hose in place and the power returned to normal. Upon my return home, I purchased the air tube from a Cummins dealer. This tube on the 5.9 was very hard to see and find. But the focal point was the waste gate valve, behind the turbo.

Hope this helps.


Share this post

Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this