Detroit 8v92t no power

[dieselgiant]

Our Schools 1989 MCI bus just got back from the shop from working on the trany, but it still has a problem. It has no power when you go from a dead stop. My dad's the driver and I'm about to get my CDLany way when you floor it it takes about 3 to 5 seconds for any reaction and when it does go it so slow and it seams to surge but it has new fuel filters and where talking dangerously slow. Also the trany waits to shift when the the motor is maxed in RPM but its especially bad when its in 3rd. When you let off the throttle to let it shift it does so no problem, but you have to get on it pretty hard to accelerate and then it just shifts up again, and your back to square one. Any suggestions on getting more power. It doesn't smoke at all Which is odd for a Detroit, not even a little blue smoke only on start up of course.

 

[geonc]

How does it idle after starting? Is it easy to start...or does it chug,spit,sputter?

Check the simple stuffs first....The easiest takes 2 people--one in the drivers seat and the second at the throttle linkage on top of the govenor...switch key on in run position {if equipped with elec/air shut down} and mash the throttle pedal down to the floor and see if the throttle linkage on the gov is going all the way open to full fuel [ you may have to disconnect linkage to verify]
If not adj as nesc.

Also check the stop lever and make sure when released to the run position, it does in fact release fully---if not when trying to accelerate, it is trying to pull the racks out of fueling position.

Did this all of a sudden happen or was any internal {under the valve covers} work done?

Sluggish acceleration from a dead start --along with no smoke at all--may be due to improper throttle modulator adj, valve covers interfering with the rack movement....does the coach have Jake brakes?---indicated by very tall valve covers.....they are known to interefer as well if installed incorrectly.

 

[dieselgiant]

When it starts it idles just fine. I haven't paid much attention to the valve covers, but the bus is not equipped with a retarder of any sort. The bus was slow before but it would give a instant reaction to any throttle input, but it was never this bad. As far as I know it was just trany work.

 

[DeepRoots]

takes thirty seconds to pop off the valve covers and see if you are going full fuel.
otherwise listen to George.

 

[geonc]

takes thirty seconds to pop off the valve covers and see if you are going full fuel.
otherwise listen to George.

A bit longer in an older MCI coach And by checking full fuel...I meant at the gov to throttle cable linkage and stop solenoid....trying the KISS principal first!

I'm kinda surprised the lack of Jake brakes on the engine [many MCI coaches had them] {evident by very tall valve covers}...and you mentioned no retarder in the tranny either?

You "should" have cast alloy valve covers as opposed to the older stamped steel ones and the alloy ones really only need the crank vent hoses {if equipped} removed and a 3/8" 12 point socket....the right side turbo inlet from exh manifold will need to be removed "if" fully removing....my suggestion would first be to just loosen them and slide "down" the head ---or towards the exh mnfld, then re-tighten. Reason for doing this is there is a chance the injector control racks will interfere with the valve cover casting.

As far as I know it was just trany work.

....removed or just either serviced or.....

 

[dieselgiant]

Thanks guys for all the help, but finally found out what the cause is. The guy who gave us the bus, yes gave as in Zero Dollars to are school, had the trany serviced AND HAD THE FUEL TURNED DOWN, OMG WTH why would you turn the fuel down. The reason was is to get better fuel eco. On a Detroit???? The crazy thing gets 5.5 - 6 mpg all ready and thats good right, and that was on the way through Missouri with a full load of Students and I mean jam packed. If he wants better eco Modify the 60 foot muffler its so loud any way just put resonator on it even then your not going to get much better no matter what you do right. I would think your mpg would go down if the motor has less power and you hold it wide open all the time to go any were. oh boy I'm going crazy over this, but when you need to cross a large busy 4 lane hwy with a bus that's full of people and it don't accelerate. Safety over Fuel economy, I would pick safety. But ya'll give me some feedback. Fuel economy or a bus that can't hit 65 MPH. If you choose safety how can I modify this thing back to stock or little over Under the radar.

 

[geonc]

Thanks guys for all the help, but finally found out what the cause is. The guy who gave us the bus, yes gave as in Zero Dollars to are school, had the trany serviced AND HAD THE FUEL TURNED DOWN,

First off... score on the bus!

Now on to "turned the fuel down"

Unless you have one of Detroits "Fuel Pincher" 92 series [with bellville washers on the high speed spring pack]---unlikely but ...... there is no real way to turn down the fuel without changing injectors .....unless it is one of those fuel pinchers and that would require removing the high speed spring cover and loosening up the bellvile washers and completely re-adjusting the injector racks......

I would still bet based on your lack of any acceleration smoke that whoever did the "adjustment" took the easy way and simply adjusted the fuel modulator --throttle delay--- tighter than normal.

Depending on weather yours was a rebuilt or a complete swing engine was installed, you could have either...

A "modulator" is a device that attaches to the left bank ---cyl L3---injector control rack [tube] and operates off of turbo boost [ or air box pressure] and is adjusted after the inj racks are set with a gauge tool that is sleeved to set on one individual inj control rack [I believe it is .485 but don't hold me to it ] and spaces an arm on the tube to the modulator piston....delaying any further fueling till boost [air box] pressure is adequate for fuel being delivered....

A throttle delay is a simplier version that attaches to the right bank ---cyl R2-- and is merley a small piston in a bore that is fed with oil pressure from the rocker arms....adjustment is similiar to the modulator...only 2 setting tools are used---a pin gauge and a sleeved gauge--- the pin sets in the top of the piston bore , limiting th episton travel, and the sleeve gauge determines the rack travel....

Alot to comprehend but
clear as mudd

 

[dieselgiant]

So I need special tools to adjust every thing correctly or??? Thank you for your help by the way. From what I have been told (I'm told a lot of things) that the engine was rebuilt. To what extent I don't know if it was refreshed or fully reworked. It has 30000 miles on the rebuild. I will have to look at the motor, but our local volunteer fire department has a engine with a 8v92T and it's easy to look at so I will have to study on it, and that thing flies, you mash on the gas and it goes, now the weight difference is a lot but its instant reaction to throttle in put. It used to puff blue but now its a nice thin black when you floor it. Thats what I'm after for this bus.

 

[geonc]

So I need special tools to adjust every thing correctly or??? Thank you for your help by the way.

Your welcome on what help I can offer

And yes...tooling is the key but there are many things you CAN do without them...such as verifyng the throttle linkage is indeed allowing the govenor linkage to travel to full fuel, as well as that the stop lever is in the run position and not under tension by the shut off mechanisim..regardless of cable or solenoid...

You have already covered fuel filters ---BOTH...correct?

Throttle delay/modulator adjustments can be done without those pesky special tools

My coach memory is a tad foggy so I ask ...is your engine straight in from the rear or mounted sideways [with a slight angle off flat to the rear] with an angled tranny????

 

[dieselgiant]

Both filters are new, and the engine is mounted straight back and a nice panel in the couch to get to the top of the engine. So I will let you know what if find on the linkages.