Compete and utter newbie here. Recently bought a 1982 MC9 w/ an 8v71 i believe (so I was told). It is an auto (not sure which, used to be a manual). I am losing power going up small hills. I have it floored and I slow right down. I was given two recommendations:
1. Change Fuel Filters
2. Check Throttle Linkage.
Figures the fuel filter part out, have not changed them yet. How do I go about checking, fixing the throttle linkage? ANy other opinions on possible causes?
Thanks,
Jason
Jason,
All 8v71 engines lose power going up hills. As they get old they, just like us, they lose power for several reasons. It all depends how you define "small hills". A hill with a 4% grade if it is long, can cause my bus with the same engine will cause me to drop down to 35 MPH. The key to it is to be sure to shift down so you keep the rev's up an keep the temp under 180. Otherwise keep downshifting until the temp gets down below 180.
A plugged Air Filter will cause a loss of power too. It can be cleaned and blown out but if it is really bad, it is better to install a new one.
Or you could have a leak in your fuel line or a fitting could be sucking air, or the fuel line could be plugged.
If the bus hasn't run for a while, it is a good idea to pour some fuel stabilizer in the fuel tank and that may break up some of the crud and water if there is any.
You can also install larger fuel injectors to put more fuel in the system, but that will also lower your fuel mileage. Some folks think the trade-off is worth it for close to $1000.
Down shift to a lower gear a 8v71 faints if it see a small hill,seriously get a run at or down shift don't wait for the transmission to shift down, do it manually.Changing the filters and being sure the governor is opening is a good start but a 8v71 is not much in the hills
What are you talking about Cliff. My 8V71 can top 85 MPH easily going down the Grapevine. ;D
Gary he is probably set on around 260 hp and 775 ft lbs of torque to keep the heat down for a MCI lol a 8v71 does like down hill
Heck, Inline 6-71 loves down hills!
All of the advice about the air cleaner and fuel filters is quite true, particularly the fuel filters. One bad load of fuel, or old fuel with contamination can really put a crimp on power fast in any diesel. The engine might also need a tune (running the rack). Assuming the engine is as good as it will be, you then have to not be afraid to take command of the engine and downshift when necessary and run it up to the governor limit. Then sit back and wait while watching the temperature gauge while the everybody else goes shooting by. Appreciate the sound of the 2 cycle while it is spinning its heart out for you, because it will get you to the top.
I am downshifting. A small hill is a few hundred feet at a 5% grade. Flats I am doing 55 (if I am lucky) and floored.
Quote from: DoubleEagle on April 27, 2016, 07:16:15 PM
The engine might also need a tune (running the rack).
Will that include fuel filters, or is it separate?
Quote from: jasong71 on April 27, 2016, 07:18:43 PM
I am downshifting. A small hill is a few hundred feet at a 5% grade. Flats I am doing 55 (if I am lucky) and floored.
It should do better than that are you getting any black smoke ? change the filter then check the shutdown cylinder on top of the governor housing and be sure it is retracting all the way and you have a small gap between the lever and cylinder rod
That is substandard, a 8V71 will do better than that. Change both fuel filters (they need to be filled with fuel to the top). Running the rack is done by a mechanic with skill. It is adjusting the timing of the fuel injectors and involves taking the valve covers off. You can do the filters yourself. The old ones should have numbers on them, and NAPA, at least, can get you the right ones. You might have to crank the engine for a while to re-prime the system. If you are lucky, the filters will make a big difference.
Where are you located ?
Hello, and welcome to the madness!
Please, do not touch your fuel filters unless you KNOW how to do it without losing prime.
And have the tools necessary to RE-PRIME on hand.
You have a coach that will run right now.
Lose prime, and you have a coach that will not start, and you will kill the batteries trying fruitlessly.
Do not use starting fluid as any part of this process, do it properly.
Simple check for the throttle, see if all the parts in the back on the top of the engine move their full travel when someone pushes the pedal to the floor. You can do this with engine off. Take pictures and post them here.
After that, it gets complicated.
happy coaching!
buswarrior
Shop vac primes them right up. Vinyl tubing. Jug of some sorts. Make sure it didn't have volatile liquid in it. Set it up vac to jug, jug with vinyl hose to the fuel line comming from the filter to the pump. Turn it on and wait til there is about a quart or so of fuel in the jug. Hook the line back up and start it. I've done this a lot. Works great.
Quote from: Gary Hatt - Publisher BCM on April 27, 2016, 07:01:33 PM
What are you talking about Cliff. My 8V71 can top 85 MPH easily going down the Grapevine. ;D
Yes, no point burning those crappy old drum brakes up unnecessarily
I can remember when I was in 9th grade (1971) the school ski club chartered a Continental Trailways bus for the trip from L.A. to Mammoth Lakes and back. It was an Eagle 1. Course just a 8V-71 and 4spd manual. The bus was full, and the under cargo compartments were full too. I'm guessing grossing around 45,000lbs. What I remember most is pulling the long hill on highway 395 going north out of Bishop, Ca and doing it in 2nd gear against the governor for a speed of around 25mph. I knew the driver was a good one since on the way back down, before the down hill, he slowed down to 25mph again and down shifted to 2nd and went down the hill at that same speed since the bus didn't have a Jake brake.
My bus with 8V-71 and V730 pulls the same hill in 1st gear (converter locked up) at 32mph. After turboing the engine I pull that hill in 2nd at 45 mph. Good Luck, TomC
Curious as to what transmission was put into your bus. If it was swapped out to an automatic from a transit bus that would keep you from going over 55. The guys here would know better.
2nd - Is it going into 4th gear on the flats? (Assuming a 4 speed auto) Check your transmission fluid. If its short it may not be shifting into 4th gear.
3rd - My bus with a 6v92 and Allison 740 Ill notice that I start losing power/speed on very small grades/hills when in 4th gear unless I have pretty good momentum. So if Im driving over a bridge or overpass in 4th and Im only doing 60 I wont be able to accelerate and if the grades long enough will have to drop to 3rd to keep it above 55 on those small hills. If Im barreling at 70 mph Ill cruise over those hills and my speed will only drop to 68 - 65 mph.
Like the guys said - watch your tach and temp. Let us know what your tach is at when you start to lose power. If the tach is full on and you are losing power it will be torque/tranny. If you are not getting full tach then its power/fuel from the engine.
Let us know what happens. These guys are a great resource and you wont find a better collection of humans more willing to help then on this website. (Although they will dish out the trash talk from time to time which makes for goos entertainment)
-Sean
Quote from: buswarrior on April 27, 2016, 08:40:26 PM
Hello, and welcome to the madness!
Please, do not touch your fuel filters unless you KNOW how to do it without losing prime.
And have the tools necessary to RE-PRIME on hand.
You have a coach that will run right now.
Lose prime, and you have a coach that will not start, and you will kill the batteries trying fruitlessly.
Do not use starting fluid as any part of this process, do it properly.
Simple check for the throttle, see if all the parts in the back on the top of the engine move their full travel when someone pushes the pedal to the floor. You can do this with engine off. Take pictures and post them here.
After that, it gets complicated.
happy coaching!
buswarrior
I think we scared off the Newbie with all the possibilities. Yes, it would be wise to be ready to re-prime if necessary, but I have successfully changed both filters by filling completely with fuel without any big problem. Maybe I was lucky, but after the hassles of the old filters (not knowing what was going on with them), I switched to the single fuel processor back in the nineties, and that has never been a prime problem.
there is no fluffy way to say this... priming a Detroit is not that hard...anyone who says it is would last about an hour working for a dealer...
And it seems like 86% of the people think that it requires way to much extra stuff to accomplish.Priming a Detroit is a pretty basic beginner deal.
ok, 8 more people can ignore me now. ;D
ps... there is no way you can remove the filters without losing prime.
Quote from: eagle19952 on April 28, 2016, 06:55:26 PM
there is no fluffy way to say this... priming a Detroit is not that hard...anyone who says it is would last about an hour working for a dealer...
And it seems like 86% of the people think that it requires way to much extra stuff to accomplish.Priming a Detroit is a pretty basic beginner deal.
ok, 8 more people can ignore me now. ;D
ps... there is no way you can remove the filters without losing prime.
Lol they are fairly easy to prime ( I cheat), I recall Sean's ordeal at a dealer in MT it took them 2 days to prime his 6v92 wonder if those guys still work for Interstate ;D
Quote from: luvrbus on April 28, 2016, 07:20:20 PM
Lol they are fairly easy to prime ( I cheat), I recall Sean's ordeal at a dealer in MT it took them 2 days to prime his 6v92 wonder if those guys still work for Interstate ;D
let's put it this way... they'd have a lot of explaining to do... if they worked for me..
were i in Sean's shoes and he was me... me and the service manager would have had a long talk too...
there should have been a bill with a 0 and a line thru it...
Donald all kidding aside some of these old buses like a MCI with the fuel tank up front can be bitch to prime using only the filters and fuel
Quote from: luvrbus on April 28, 2016, 08:20:53 PM
Donald all kidding aside some of these old buses like a MCI with the fuel tank up front can be bitch to prime using only the filters and fuel
i know this but it's kinda like being a KungFu'y... you gotta wanna be one with your motor... so, take your filters off 4 times in one day and deal with it... you will then be one with the agony and the ecstasy, grasshoppers..
or lower your filters :)
When changing the fuel filters, warm up the engine first. Then change the filters filling the new filters with fuel before putting them back on. Never have had a priming problem. The engine will stumble a bit but if you raise the rpm up right away (the main reason for warming the engine first) then you shouldn't loose prime.
My Cat 3406B is extremely easy to prime. Take off the fuel line and return line from the tank. Attach a 5psi fuel pump to the feed line with the pumps pickup in the fuel tank. Run the fuel pump till you see fuel come out of the return line. Reattach the fuel lines to the tank and start the engine. Can do the same thing with a Detroit with a fuel pump T'd into the feed fuel line. Good Luck, TomC
I used one of those cheap harbor freight orange colored hand oil/fuel pumps and a 2 liter bottle and tapped into an access hole on the fuel pump on my 671, piece of cake to prime
Quote from: eagle19952 on April 28, 2016, 06:55:26 PM
there is no fluffy way to say this... priming a Detroit is not that hard...anyone who says it is would last about an hour working for a dealer...
And it seems like 86% of the people think that it requires way to much extra stuff to accomplish.Priming a Detroit is a pretty basic beginner deal.
ok, 8 more people can ignore me now. ;D
ps... there is no way you can remove the filters without losing prime.
Nope, you will not be ignored (I think they should do away with that button). I submit the following freak of nature: Back in the nineties, I was on the New York State Thruway headed toward Buffalo in my Model 05 Eagle (8V71) when I began losing power and the engine was running rough, and I dropped below 40 mph, so I pulled over and shut down. I suspected bad fuel as I had put in some Thruway fuel stop fuel about two hundred miles earlier. I noticed that the truckers were not fueling there, but I was low. I had both filters on hand and a can of diesel and a few tools, but no pumps or hoses. I filled the filters to overflowing, put them on quickly, cranked the engine a little bit, it caught, ran rough for a little while, but kept going and got smooth. I technically might have lost prime, but because it was warm, it was not incapacitating. I also did this at home when doing maintenance with the same results, but after I switched to the fuel processor, I never had any close calls with losing prime again.
Now guys DD has always offered the electric priming pump or the mechanical hand type ever since I can remember.The OEM just never installed 1 till MCI did with the C.I have owned my electric priming pump from DD since the 70's and a hand type made in the 50's
Quote from: luvrbus on April 29, 2016, 08:05:45 AM
Now guys DD has always offered the electric priming pump or the mechanical hand type ever since I can remember.The OEM just never installed 1 till MCI did with the C.I have owned my electric priming pump from DD since the 70's and a hand type made in the 50's
worked on Detroits for Uncle Sam in 1970.. spent 3 years doing that..
i started working at a TEREX/DD dealer in 1973... never saw an electric pump on anything...
we started swiping/finding/getting Cummins/KW primer pumps soon after... that little pencil pump is all we ever used... that and a pour can..
Has anyone suggested the OP pull a valve cover and have a look inside? See if the rack goes to full fuel on both sides, see what injectors are in it? Could be as easy as a tune up and new injectors and off to the races.
Brian
If the guy posted his location I may know of someone in his area that could help a rookie
Quote from: luvrbus on April 27, 2016, 07:40:26 PM
Where are you located ?
I am in central New Hampshire
Quote from: luvrbus on April 29, 2016, 12:14:18 PM
If the guy posted his location I may know of someone in his area that could help a rookie
Not scared off, just overwhelmed. I am a learning by watching kind of guy. Trying to figure this all out. Trying to find where everything is. Just a lot.
Jason
back on track...i seriously doubt this will be solved with filters alone. my bet goes to a linkage or tune solution. probably linkage.
Quote from: jasong71 on April 29, 2016, 12:45:42 PM
I am in central New Hampshire
I could have helped you when I lived in Littleton, but that was many years ago. You will have to get your bus fixed if you want to make it up through the Franconia Notch. If you are new to diesels and 2 cycles there is a lot to learn. Take pictures of the top and back of the engine, that might help us guide you.