Turbo Boost?

[gmcbuffalo]

Will didn't the resealing of the turbo pipe from the exhaust manifold solve or reduce the descrepency in the two turbo readings?

[Jon Wehrenberg]

There is a lot of potential confusion here.

If I am interpreting Will's post he defined his problem as a failure to get full turbo boost, but it was in fact what sounds like a fuel flow problem preventing full turbo boost.

The two gauges I think Will refers to were the pyros which are measuring exhaust gas temperatures and he was NOT getting temeprature readings as high as 2000 to 2500 difference. It was likely there was a 200 to 250 degree temperature spread.

He was losing boost going up a hill because he was losing fuel flow. The critical lesson here is to not make assumptions about a problem until all questions which must be asked to isolate the problem have been answered. Since Will has a DDEC engine he could have been losing engine power or turbo boost for a variety of reasons, including reduced fuel flow. Sooting would have been a clear indication of a leak in the exhaust leading to the turbo, but without leaving the dirver's seat he could have done a good job of analysis.

Looking in his mirror at the exhaust would have revealed blacker than normal exhaust if his turbo problem was the issue. But he would have gotten some codes if he had a turbo boost problem or a throttle position sensor problem so superficially I would suggest the problem with the turbo would be less likely.

Losing power climbing a hill is certainly an indication that something is preventing the engine from performing to its maximum potential. Our engines need air (little or no air means black smoke) and fuel. Starve it of fuel and it will not perform. Usually fuel starvation is accompanied by some jerking and pulling. It will start to die out, and as you let off the gas, and step back on it it may actually recover for a bit before again dying out. Sometimes just shutting the engine off for a little while temporarily cures the loss of power. When turbo systems puke they are usually not intermittent.

Will, help folks out be describing the symptoms a little more.

[Will Garner]

Tom,

I thought I recalled seeing a small units identifier on the face of the Pyro gauge. If I did it said 1,000's of degrees. If I didn't see it then I must have made a typo!

No I'm not consuming any North Carolina Mountain Spring Water today - maybe tomorrow!

Finally got a poop chute that would work. My original was 5' too short, not good for those downhill from us! The ten foot extension I bought at the campground would not go onto my fittings. I bought their fittings and could not get it to go on them either. At least I could not force them on and I did not have any KY to help out. I just thought, I should have checked with Acme Products before going back and buying the 15 foot new poop chute! After all, they were right next door. I am sure with all their sheep they must have something that would be slippery enough to get the new chute on the new fittings. By the way, the new hose and fittings did spring a small leak but only when dumping the gray water. I guess the black water was too viscous to get out that pin hole!

We knew we had a long day ahead of us with the boost issue unresolved or would have been there until later Thursday. I tried to sneak out but obviously failed. Glad you got to hear me go even though I am sure the sound was a little weak.

Hope all is well with you guys.

[gmcbuffalo]

Jon the reason I bring up the exhaust leak is that I also had a 500 deg diff in left and right pyro temp. I thought I got it solve with readjusting the clamps on the pipes to the turbo. I still had sooting and could not get the clamps or pipe seal and better. I then found that I had a bad manifold gasket on one side and as it turned out a flaw in the manifold casing causing the leak. So I thought Will would see a change in Pyro temp with the fix on the leaks.
GregM

[Jon Wehrenberg]

Greg,

The 8V92 exhaust manifold castings are notorious for cracking, but also they all seem to have failed gaskets after a while also. Obviously that affects the pyro readings because the exhaust gases are not all going past the thermocouple. If I had to guess the fuel filters were the primary issue, but Will may also have some exhaust gas leaks.

Unless the engine is clean and the silver paint is maintained it gets hard to spot the black spots where the gasket has failed or the manifold has cracked.

[Will Garner]

Jon,

Twin Pyros reading different, off by 2-2.5 units of temperature. When they were reading off the turbo struggled to get 8-10 pounds of boost. My gauge pegs at 15. The engine usually scoots right to max turbo when placed under a loaded condition. At times the Twin Pyros read the same as they went up and back down. During this condition the engine was able to get between 13 and 15 pounds of boost.

Ok, now I don't polish my slack adjusters but I try to keep the grunge off the engine. I stuck my nose pretty deep onto both sides and the top of the engine specifically looking for sooted or burnt areas around all exhaust gas piping, pipe clamps, exhaust manifolds, the hot side of the turbo, and the cool side from the air filter to the intake manifold. I did not find any indication of a plumbing failure. I did trust the Service Technician since there had been previous POG posts about the pipe cracks, no not crack pipes!

Their work did not fix the problem and never having had a diesel engine before, and having changed both filters at the begining of this year I thought the filters were good to go. If only I, or perhaps the Service Technician, at 0200 hours had taken the time to look through the glass housing on the primary filter the real problem could have been fixed in 30 minutes instead of not being fixed in five hours!

Again, moral of the story, check the simple things first then move on to the more exotic possibilities. When it is pronounced fixed, take the Service Technician on a check ride with you doing the driving!

[Jon Wehrenberg]

When fuel filters start to plug the indication is subtle. Correct me if this does not describe your situation Will.

At first there will be a loss of power on the hills. As Will points out he sees a loss of turbo boost. Since only the 8V92 coaches have pyros not all owners will be able to see a difference there. At some point the loss of power will not be a smooth reduction in speed or ability to pull a hill, but the bus may actually jerk a little.

When going down the back side of the hill, the dirt plugging the filters may actually fall away since there is less demand for fuel and it may appear when cruising on the level that the problem is gone. But it will return, and at some point there is more than a loss of power, there may actually be a stumbling of the engine or rough running or a misfire.

The thing to remember is that if the turbo is not getting enough exhaust gas due to a broken or cracked manifold or inlet pipes, you will see the loss of boost, but the bus engine will run smoothly and it will put out lots of black smoke, proportional to the size of the crack or break in the turbo inlets.

It will not correct itself, and there will be no jerking or misfire.

With a reduction of fuel flow, initially it will feel like a loss of power, the engine may continue to run smooth, the boost will be down, but the exhaust as seen in your mirror will be clean. If you have a fuel filter with a clear sediment bowl as Will points out you will see evidence of the problem.

[truk4u]

And to add to that, if you have a secondary spin on fuel filter, that one will give you fits as well.

[Will Garner]

Jon,

Yes we experienced some jerkiness as well as some unusual transmission shifts. I did not or could not see any increase in black smoke and believe me I looked often and hard to see what the exhaust looked like. I guess not getting enough fuel it could not produce much smoke.

Tom,

Change one, change the other. I change both filters at the same time irregardless of the secondary spin off needing it or not. I can't see inside the tin can so it comes of too.

Thanks for all the feed back on this experience. I needed that!

[Jon Wehrenberg]

Will, thank you for the thread on this. I think a lot of owners would be hard pressed to discern the difference between a compromised turbo system affecting boost and fuel starvation affecting the ability to create boost.

I think this thread will help folks understand within a few seconds how to decide what kind of issue they are faced with. The key is looking for the clues that differentiate one from another.

When DDEC is involved it can get a little more complex because of the throttle position sensor and the turbo boost sensor, but narrowing down causes is merely a process of elimination.