Loss of speed/power on any grade

[LisaRandy]

Help! I apologize in advance for long winded post! We have a 2006 National Dolphin. W22 Workhorse 8.1 Chevy Engine. Allison transmission. Currently in the shop for 3 months ( waiting on parts, Covid delays etc.), with the shop unable to figure out why we lose all speed going up any grades. Truck runs fine until you try to drive up a highway on-ramp, hill or even up some wood in my driveway to level rig! Started last year on a trip to New foundland, Going uphill in Buffalo New York, Truck lost all power halfway up, stopped, wouldn't go any further. Towed to local shop, replaced catalytic converter & new pipes. Seemed to work, went on our way, we could then go uphill but still would lose RPMs. Made it to New foundland got worse on the grades over there getting down to 25 mph on some of the hills. Found a shop back in Nova Scotia, waited 4 days for parts and repairs , replaced 2 sensors. Hit the road, again same thing, after much cursing on my husbands part, decided to get back home to the states to handle it here. We have now replaced all spark plugs, wires, coils, then fuel injector, Then the shop says its our torque converter, Then the decision is made the whole transmission needs to be replaced. $7000! Still the same on I-95 on ramps! Then we waited for a (specialist) to reprogram the computer..That's not it either! At Wits End! Anyone have any idea? Everything runs great on the truck, truck starts right up, runs smooth. It just will not go uphill! Thank you for any input!

[Arch Hoagland]

Are you getting a check engine light?

[Skip426]

No mention of fuel filter replacement or fuel pressure testing .

Was the fuel filter replaced and fuel pump pressure tested?

[edgray]

Originally Posted by LisaRandy

Help! I apologize in advance for long winded post! We have a 2006 National Dolphin. W22 Workhorse 8.1 Chevy Engine. Allison transmission. Currently in the shop for 3 months ( waiting on parts, Covid delays etc.), with the shop unable to figure out why we lose all speed going up any grades. Truck runs fine until you try to drive up a highway on-ramp, hill or even up some wood in my driveway to level rig! Started last year on a trip to New foundland, Going uphill in Buffalo New York, Truck lost all power halfway up, stopped, wouldn't go any further. Towed to local shop, replaced catalytic converter & new pipes. Seemed to work, went on our way, we could then go uphill but still would lose RPMs. Made it to New foundland got worse on the grades over there getting down to 25 mph on some of the hills. Found a shop back in Nova Scotia, waited 4 days for parts and repairs , replaced 2 sensors. Hit the road, again same thing, after much cursing on my husbands part, decided to get back home to the states to handle it here. We have now replaced all spark plugs, wires, coils, then fuel injector, Then the shop says its our torque converter, Then the decision is made the whole transmission needs to be replaced. $7000! Still the same on I-95 on ramps! Then we waited for a (specialist) to reprogram the computer..That's not it either! At Wits End! Anyone have any idea? Everything runs great on the truck, truck starts right up, runs smooth. It just will not go uphill! Thank you for any input!

I am assuming you have a W-series chassis because you said "Allison".

I have to say your problems are about the strangest things I've heard (NOT doubting you) and I find it incredible that you don't have enough power to even climb onto some leveling boards in your driveway, especially after throwing all those parts and $$ at this problem.

Since you said its in a shop for 3 months waiting on parts, I have to ask if this is the same shop that changed all these engine parts and recommended a new Allison? Is this a WCC / Navistar Authorized Service Center (ASC)? It sounds like everybody you have been to is just throwing parts, and your money, hoping to "fix" the problem without any real diagnosis.

Please know we hope to help you find an actual solution, and I hope you can provide answers to our questions without thinking we are picking on you. The more precise info you provide, the better the chance of figuring out this mystery. Ed

[pointrow]

If it were me I would find a shop with a dyno and actually diagnose the problem not throw your money at it.
When you experience loss of power are you losing rpms or just forward motion/ speed?

Good luck and keep us posted.

[Full-Timers]

You say, "the shop says its our torque converter, Then the decision is made the whole transmission needed." Was the torque converter replaced or just the transmission? You could still need a torque converter if it wasn't replaced.

[LisaRandy]

No check engine light.

[LisaRandy]

So the sensors, catalytic converters were different shops on the road. We did the plugs, wires, coils ourselves. Then made the decision to put it in the shop. And after too many $$$. Still no fix, even though they assured us each time it was definitely this or that. Pretty fed up at this point!

[LisaRandy]

Torque converter replaced as well as whole rebuilt transmission installed!

[Arch Hoagland]

Several months ago I had the same thing happen.

Extreme loss of power...took almost three minutes to get up to 55 on a level highway.

Engine ran smooth and no check engine light. Just absolutely no power.

It first occurred as I pulled onto highway 40 in Newberry Springs CA. It's in the Mojave desert and I ran for about 40 miles that way until I got to a roadside rest where I could turn it off and if it didn't start at least I was in a place it could be worked on.

Turned it off and then restarted....ran fine the next two days until we got home.

Took it to my Workhorse dealer and then the check engine light came on. They replaced both O2 sensors and the fuel filter.

Was headed out on a trip then to test it but Covid broke out and we cancelled the trip. So tomorrow we are finally going on a 300 mile trip and I'll know if the problem is solved.

I'll check back in here tomorrow and update you.

[Prontix]

I’ve experienced some of the same symptoms. I purchased a Bluedriver to monitor the sensors and fuel flow. My symptoms started after plugs, wires and air filter was changed. I have seen some improvement since I cleaned the MAF. I just hit 58K so I’m ready to change trans fluid.

I’m very interested to find a final solution.

[Xmcdog]

Printed, you may have hit on it. Air filter.
The entire problem sounds like either a blocked air filter or a blocked exhaust system. I had a similar problem many years ago and even had the engine rebuilt. Turned out to be the muffler. A baffle came loose and partly blocked the flow.

Low fuel pressure or fuel flow could also be the cause.
Good luck.

[Arch Hoagland]

Originally Posted by Arch Hoagland

Several months ago I had the same thing happen.

Extreme loss of power...took almost three minutes to get up to 55 on a level highway.

Engine ran smooth and no check engine light. Just absolutely no power.

It first occurred as I pulled onto highway 40 in Newberry Springs CA. It's in the Mojave desert and I ran for about 40 miles that way until I got to a roadside rest where I could turn it off and if it didn't start at least I was in a place it could be worked on.

Turned it off and then restarted....ran fine the next two days until we got home.

Took it to my Workhorse dealer and then the check engine light came on. They replaced both O2 sensors and the fuel filter.

Was headed out on a trip then to test it but Covid broke out and we cancelled the trip. So tomorrow we are finally going on a 300 mile trip and I'll know if the problem is solved.

I'll check back in here tomorrow and update you.

Today I ran 150 miles and crossed over a very steep mountain with no problems. Seemed to have a bit more power than I used to going over that steep pass.

So far...so good.

[LisaRandy]

No check engine light.