Extreme drop in horsepower

[Mark Antony Wray]

Greetings All,

Strange thing, can't figure it. Cummins Injected Turbo Diesel with Allison 4sp Auto/Tranny was running perfect, running like a bat out of ****, pulling hills and running 80mph without breathing hard. Today it can't pull a hill at 35mph, and takes a few minutes to get up to hiway speed. No odd sounds, no indication something is wrong other than...now umph, no pulling power.

All fluid levels are good, all gauges look good....I'm stumped.

Any ideas??

Thanks...Mark

 

[opus-SKO]

Brakes on? Any smoke? Shifting correctly? Whats it do in neutral when you pin the throttle?

 

[dond]

Start with cheap stuff first:

Air filter


Fuel filter

 

[Mark Antony Wray]

Brakes on? Any smoke? Shifting correctly? Whats it do in neutral when you pin the throttle?

No....No smoke, brakes are fine. No strange smells, however yesterday I did notice a "slightly" stronger diesel smell from the exhaust than usual - but nothing drastic. As I mentioned - I do not perceive any "weirdness".

 

[Mark Antony Wray]

Start with cheap stuff first:

Air filter


Fuel filter

I sort of wondered about "airflow"? Yeah, come to think of it it could be filters. How do you know if the turbo is engaging properly?

 

[opus-SKO]

I'm thinking turbo but you'd hear a different noise and most the time see smoke. Will it run to full rpm? Is this a 5.9?

 

[Mark Antony Wray]

I'm thinking turbo but you'd hear a different noise and most the time see smoke. Will it run to full rpm? Is this a 5.9?

Honestly...I am a newbie to the bus world, but have a decent amount of mechanical experience. I too wondered about the turbo, but I am not sure what I am listening for? As far as smoke is concerned, no - no radical increase in smoke, but there is an increase in diesel smell - not drastic though. I attributed this to the fact that the church I bought this bus from let it sit for a couple of years, and although I put fuel additive and filled with fresh diesel there may be some diesel algae, gelling, etc fouling the fuel filter.

I just topped everything off once again, and she broke loose and ran like a champ - then after a shut down and restart began to act like constipation again....LOL!

 

[opus-SKO]

I'd go with a filter for now. Get some Power Service and prime the filter with it then put the as much a bunch in the tank. If you are really thinking algae, you can get Bio-Kleen from Power Service, as well.

 

[Mark Antony Wray]

I'd go with a filter for now. Get some Power Service and prime the filter with it then put the as much a bunch in the tank. If you are really thinking algae, you can get Bio-Kleen from Power Service, as well.

Now I am stumped! Darned thing broke loose, and ran like a scalded dog, then while out test driving it i had trouble pulling a hill - darned near didn't get up it. When I got back to my neighborhood I couldn't even pull the hill. Just no power to the drive train. Does not shift hard or loose, revs fine when revving through throttle linkage - just no power to the wheels...

 

[Mark Antony Wray]

Does anyone know how to troubleshoot whether or not a turbo is working or not?

My lack of power may be related to the turbo, or possibly nasty algae packed fuel filter....have not checked the air filter yet - not even sure where this stuff is. Guess it's time to seek out a manual.

 

[opus-SKO]

Do you hear the transmission shift all gears properly? Can you try manually shifting it and see if that makes a difference? I think you have eliminated it being the turbo.

I need you to tell me what engine it is...and if you know, what transmission. Front engine, rear engine??

The manual wont help with this.

 

[dond]

After a filter check, you did check the AF right?

Could be shut off solenoid. From an online forum:
"Hey marine one : White lightning wins the money, I wired the solenoid up in the on position and it ran just fine, I also found out why they call it a fuel shut off. To my surprise when I shut the key off the truck just sat there running Ha Ha. I had to get out and loosen the wire then push the shutoff bracket to shut the engine down, then after startup had to push the solenoid up until it stuck and the truck ran fine. I have driven this truck for 3 yrs. now with this intermittent power problem and am very pleased from all the input and soon to be fixed problem. Thanks guys. dog 94

Read more: http://forums.dieselpowermag.com/70/811 ... z3GXi0baZT"

 

[Mark Antony Wray]

Do you hear the transmission shift all gears properly? Can you try manually shifting it and see if that makes a difference? I think you have eliminated it being the turbo.

I need you to tell me what engine it is...and if you know, what transmission. Front engine, rear engine??

The manual wont help with this.

Greetings...I will pull the paperwork out of the bus tomorrow to confirm tranny and engine. I know it does have an Allison 4 speed automatic, and a friend of mine said he thinks the engine is a Cummins 8.3, or maybe an 8.9??? Oh yeah, and it is in the front.

I never noticed ANY problems with the shifting, no lag, no jumping, no whining....it just bogged down, and wouldn't get up a hill in my neighborhood. I barely made it home today. Strange...this is completely a new development with no prelude of symptoms that I could recognize.

 

[opus-SKO]

Well if its bogging down, it may not be downshifting....which could be the throttle control module....or whatever the right name is for it. Thats why I asked you if you could manually shift it and replicate the same issue.

Its either a 5.9 or an 8.3

 

[Mark Antony Wray]

After a filter check, you did check the AF right?

Could be shut off solenoid. From an online forum:
"Hey marine one : White lightning wins the money, I wired the solenoid up in the on position and it ran just fine, I also found out why they call it a fuel shut off. To my surprise when I shut the key off the truck just sat there running Ha Ha. I had to get out and loosen the wire then push the shutoff bracket to shut the engine down, then after startup had to push the solenoid up until it stuck and the truck ran fine. I have driven this truck for 3 yrs. now with this intermittent power problem and am very pleased from all the input and soon to be fixed problem. Thanks guys. dog 94

Read more: http://forums.dieselpowermag.com/70/811 ... z3GXi0baZT"

Greetings...By AF do you mean air filter? If so - no, I have not. In fact I have not yet check any of the filters yet - ****, I don't even know where most of them live yet. I am trying to determine the best starting place - besides the common stuff like all the gauges reading correctly, all the fluid levels being right, cranks up and runs immediately, shifts through all gears smoothly while sitting. Up until today it was like trying to hold back wild horses...this bus wants to ruuuun like Kunta Kinte!....LOL!

As I mentioned previously...I am new to buses - don't know much about this one. I bout it about two months ago, started the strip out for rebuild, then almost immediately found out I had to go through some chemo treatment, so all my fun got put on hold. I'm just now getting back to it.

I do appreciate any help or advice.

Thanks!

 

[Mark Antony Wray]

Well if its bogging down, it may not be downshifting....which could be the throttle control module....or whatever the right name is for it. Thats why I asked you if you could manually shift it and replicate the same issue.

Its either a 5.9 or an 8.3

Yes...even if I manually shift down I get the same result. Like I mentioned, there was no precursor to a problem...just happened.

 

[Mark Antony Wray]

Oh yeah - forgot to mention: When I turn the key off to shut down the bus engine keeps running. I have to lift the cowling cover inside, reach into the engine compartment to manually pull a switch on the drivers side of the engine to shut it down.

 

[Mark Antony Wray]

Well if its bogging down, it may not be downshifting....which could be the throttle control module....or whatever the right name is for it. Thats why I asked you if you could manually shift it and replicate the same issue.

Its either a 5.9 or an 8.3

OK...Just confirmed: It's got a 8.3L L6 Cummins, and an Allison 4spd Automatic trans.

 

[Mark Antony Wray]

I am going to have to rent a steam cleaner for a day to clean the entire drive train area. It's got 2 1/2 decades of crap down there. Any recommendations from anyone before I do it?....anything to be very cautious to NOT steam. I don't wish to compound this current problem. I appreciate the advice....Mark

 

[Booyah45828]

I would check and make sure the brakes aren't dragging first, because it is extremely simple to do so. Then I would check for any fuel issues.

I wouldn't completely rule out the transmission, but if you dropped it in manual 1st and it still wouldn't accelerate, I doubt the transmission is at fault.

Start with the filters, check the fuel to make sure it hasn't turned bad. Then you start troubleshooting.

Seeing how it is an 89, it would be mechanical injection.
I would check that the shutoff lever operates and releases correctly, then I would check to see lift pump pressure is adaquate.

After that I would check if it has a smoke limiter on the injection pump. What they do is limit rack travel in the pump with a diaphragm until it receives boost pressure from the manifold. If that checks ok then I would check the turbo wastegate that it isn't frozen and works correctly.