Smoking 8V92TA DDEC II

[robertglines1]

Didn't chime in earlier. In feb my 8v92 blew a exhaust gasket . but symptoms were a little differant with only loss of power and fuel economy. That's why I did not say anything sooner. $16 dollar gasket and all was well. Sounds like you had a minor problem that led to fixing some other problems for you.  Sort of a blessing in the long run. sad the high dollar guy couldn't hear it from the seat? I heard mine. I was around heavy equipment all my life and can detect changes--funny I can not hear my wife sometimes.  Bob  

[Sam 4106]

Rick, There was only one injector that was quite loose, the others were near spec and the valves needed minor adjustment. Curt thinks that the new ECM program is what is causing the remaining smoke because the throttle delay is different than the old ECM. I may send the ECM to Hard Headed Ken this winter to see if the throttle delay from the 111 version ECM can be put into the 154 version. It will be a while before I know if the fuel consumption returns to pre-ECM change levels. Thanks for your interest in this issue and your recommendation for Central Truck.

JC, thanks for the suggestion of using the former A/C pipe to route the boost line toward the front of the bus. If that line still goes to the former A/C compartment the rest of the way will be a piece of cake. There is an electrical conduit that runs to the front electrical panel from the A/C compartment. One way or another I will get the job done.

Bob, I wish you had suggested the possibility of a blown manifold gasket. That would have gotten me to looking in that direction. I welcome all ideas when I have problems with the bus. Hope your recovery is going well and you can return to your bus project soon.

Thanks, Sam

[robertglines1]

Sorry :;When mine blew there was no doubt. top speed dropped 7 mph and fuel mpg dropped right away. Did not fit your case problems  Will throw out there no matter how far out there it is.  Made temp road repair till I could get to place to fix and replaced that whole side.   Bob

[luvrbus]

Sam,you should have noticed a drop in power with a exhaust leak a fine 8v92 you have there if it didn't lose power with a exhaust leak most drop like a rock lol

[Sam 4106]

Hi luvrbus,

The exhaust leak was probably too small to cause a big drop in power or maybe I was just not aware of it because we don't have big hills or mountains in Minnesota and North Dakota. The leak was on only one cylinder and just on the bottom of the manifold. I can see why it was missed at Fargo because the mechanic there didn't give as thorough of inspection as Curt did. I was really impressed with his attention to detail. I think I do have a good 8V92 since it has 96,000 miles since new. I am surprised I am having the problems because of the low milage, but maybe part of it is that the engine was built in 1990. I learned that from reading the information on the valve covers when they were off. I wish I had written all that information down when I had the opportunity.

Curt has a rebuilt 8V92 MTU engine in an MCI cradle if you know of anyone looking for one.

Thanks for all your help, Sam

[Sam 4106]

I got the boost pressure gauge hooked up today. The test drive up the steepest hill in the area, 3rd gear (HT740), engine at 2100 RPM, 22 pounds of boost. Air temp was 70 degrees F. with no wind. The air filter minder is showing 9. I think I will install the new air filter, that came in today, and test again tomorrow. Hard headed Ken called me yesterday and advised me to be sure I don't have another mechanical issue before sending him my ECM to check the fuel maps. Is 22 pounds boost enough to rule out other mechanical issues? He also mentioned the blower bypass and I am not sure how to check that or exactly where it is located. Will someone please help on that question? I found a 1 1/2" cylinder, with a flange and two bolts holding it on top of the blower housing in front (flywheel end of engine)of the turbo horn , with a 1/2" or so hose going from the side of the cylinder to the side of the blower housing above the blower rotors. Is that the blower bypass valve? If so, can I just unbolt the flange and check its operation? It should be fairly easy to reach with the air cleaner out of the way. Are there any special cautions I need to be aware of and what should I be checking when I get the cylinder off?

I hope with these questions answered I can relax and stop worrying about the black smoke on acceleration.

Thanks gain for all the help that has already been given, you people are the best. Sam

[luvrbus]

Yep 22 lbs is enough for a 8v92 on level ground no hard pull around 8 to 10 lbs and what you are describing is the bypass valve check the hose those are supposed to be a silicone hose not regular rubber I hope you have the serviceable type by pass (has a 1/2 or 1/4 in square head in the top cap) if not it will cost you about 75 bucks

Post some photos so we can see if yours is a full bypass or a mini bypass valve ok check for wear on the plunger if signs of excess wear replace it  

good luck

[Sam 4106]

Hi Clifford,

I have the bypass valve out and it doesn't have the square head on top. The top is flat with two pins on opposite sides that hold the top plug in. So, I believe I have the non serviceable type. When I talked to Ken, he described his bypass valve to be about 3" in diameter and mine is a little less than 1 1/2" in diameter so I guess I have a mini bypass valve. The plunger is smooth and doesn't appear to be worn. It seems that the plunger is normally extended by the internal spring, so I am not understanding how the valve is supposed to work. How do I tell if it needs to be replaced? I guess I could replace the O-ring and reinstall the valve and see if it has made a difference with the black smoke, but I would like to only put things back together once.

Thanks, Sam

[Hard Headed Ken]

Sam here's a link to that part of the service manual. Take a look at section 3.4.1 page 3 it explains the operation.

Clifford if the bypass valve is not working how would that affect boost pressure or would it?  I tend to think is would be higher because the pressure can't get around the blower.

I'd don't think the manual said this, but  I used a hand vacuum pump to see if vacuum would pull the plunger up.  

Is that correct Clifford?

Maybe about 2 inches in diameter.

http://www.mediafire.com/view/?qveq05rys244dj8

[Sam 4106]

Hi Ken,

Thanks for your phone call and your continued help. I don't know how to open the information in the link you sent since I'm not very computer literate. Could you email that page to me? If not I will try to get my wife to make the link work when she gets home. The part number on the bypass valve is 8927187 if that is helpful. I would like to post a picture, as Clifford asked, but I don't know how to take a picture or post one, sorry. The bypass valve was a little hard to remove. It seemed like maybe something was stuck. Without knowing how the valve works, I don't know for sure. With all the help I am getting I think I am getting closer to eliminating the black smoke and I am learning something about my engine. I still enjoy learning even if I will never use the new knowledge.

Thanks, Sam

[Hard Headed Ken]

Sam,
The file is too large to email. Click on the link, then in the upper left corner there should be a small green down load button, click that and another window should come up with a larger green down load button near the bottom. Click that and the file should down load to you computer. If it the asks where to save it choose desktop(the page your computer opens to when it starts). If it doesn't ask it will most likely be saved to your down loads folder. Then just go the down loaded file and click it. It's a PDF file, most any computer will open it.

Ken

[Sam 4106]

Hi Ken,

My wife got the link downloaded for me and I read the page. Now I understand how the mini bypass valve works and know that there is nothing wrong with it. Do I need to clean the passage on the engine that the plunger slides in, and if so, how would I do that?  If the plunger was stuck would it likely have been in the closed, open, or partially open position? My thought is that it would have been open or partially open and allowing the blower pressure to recirculate. Therefore causing black smoke at lower RPM, I hope this solves the problem.

Thanks, Sam

[Sam 4106]

I visited friends with my wife yesterday so I didn't test drive the bus. So, I took the bus for a test drive this morning, with new air filter and cleaned mini bypass valve, and still have heavy black smoke on pedal to the floor acceleration but with light pedal acceleration, only a small puff of smoke at the shifts. I still have 22 pounds of boost on the hill so I don't think the old air filter was dirty enough to cause a problem. I do think the bypass valve was stuck open or partially open. I could be wrong! Anyway, I think I will call it good enough until winter when I will ask Ken to compare fuel maps between my ECM and his '88 8V92TA DDEC II ECM. How often do I need to check the mini bypass valve, or do I just watch for black smoking again?

Thanks Ken and everyone else for guiding me through this ordeal, Sam