Turbo Boost?

[rfoster]

This is only a drill. Information derived from this thread can save time and money if applied correctly:

What causes turbo boost or better yet what causes the loss of turbo boost?

There is no prize for the correct answer till you are on the road in the middle of the interstate - then you will appreciate the answer.

Find out tommorrow or the next day.

Answer Away

[Jon Wehrenberg]

Failed turbo boost sensor.

To check for turbo operation (especially on 8V92) make sure the exhaust system going into the turbo is leak free. Look for sooting.

If the exhaust to the turbo is tight, remove the air side or exhaust side, whichever is easiest to access and verify the turbo fan spins freely, and does not bind, have missing blades or wobble.

I had one sensor fail on my 8V92 and the bus couldn't hardly get past idle.

[hobobimmer]

Failed turbo boost sensor.

To check for turbo operation (especially on 8V92) make sure the exhaust system going into the turbo is leak free. Look for sooting.

If the exhaust to the turbo is tight, remove the air side or exhaust side, whichever is easiest to access and verify the turbo fan spins freely, and does not bind, have missing blades or wobble.

I had one sensor fail on my 8V92 and the bus couldn't hardly get past idle.

Word for word, that was going to be my answer, also. Jon just got to the keyboard before I did. Just kidding, Jon. I was going to guess leaky hub seals.

Eric Faires
Huntsville, TN

[JIM CHALOUPKA]

It's SHEEP, if you get SHEEP in the turbo the wool packs in and around the spool and binds it up. Simple as that, that's it for sure, NO!, maybe its BULL:eek:


JIM;):D

[Mark3101]

This is only a drill. Information derived from this thread can save time and money if applied correctly:

What causes turbo boost or better yet what causes the loss of turbo boost?

There is no prize for the correct answer till you are on the road in the middle of the interstate - then you will appreciate the answer.

Find out tommorrow or the next day.

Answer Away

A loose or broken spring clamp on the intake tubing, usually between the turbo and the charge air cooler on a 60 series would do that. (this would apply on any engine, DD, Cat, Cummins etc.) Could also be a sensor, but those are more rare of a failure than clamps are....

[JIM KELLER]

Does altitude have an effect on Turbo Boost ? If it decreases boost is there a way to compensate.

[Kenneth Brewer]

Does altitude have an effect on Turbo Boost ? If it decreases boost is there a way to compensate.

Generally speaking, most turbo diesel truck engines have waste gates (internal or external to the turbo) to prevent excessive boost. I would not think you should be affected by altitude (less need for the wastegate to relieve) until you get to around 6 to 8 thousand feet. Our engine wasn't affected on our recent trip into the Rockies, but others may have a different story. Our Cat 3208 turbo started to fall off boost rather early and severely. Similarly, higher temperatures (lower air density) affect boost to an extent. But again, our series 60 doesn't seem to notice, which I attribute to excess capacity, but there seems to be slightly more boost pressure when it is colder. The BB was noticeably affected.

[Jon Wehrenberg]

If I remember Jack recently had a cracked intercooler on his Liberty that cost him boost and performance.

A failed turbo boost sensor is not uncommon, but is less common than broken turbo inlet pipes (on 8V92 engines).

[Gary & Peggy Stevens]

On my D60 I was having intermittent Turbo Boost Failure.

While driving I would notice the Turbo Boost Gauge would go to 0 and a light on the dash would come on. I took the bus to Stewart & Stevenson, and they determined I needed a New Style Barrometric Pressure Sensor. and ReProgram the ECM to the correct software level.

$700 later I haven't had any problems with the Turbo Boost.

Gary S.

[Jon Wehrenberg]

If my understanding is correct the turbo boost sensor works to determine how much charge air is available to the engine, and then DDEC via the injectors (which are solenoid controlled) introduces fuel in the proper ratio to air for combustion.

In the bad old days when stuff was mechanical you would see black clouds of exhaust from a diesel when the driver rapidly pressed the throttle or the engine was lugging under load. That was because the mechanical injectors introduced fuel relative to the position of the driver's foot on the pedal rather than how much air was available for combustion.

Since soot is on the EPA hit list, if the sensor fails in a manner in which it cannot measure boost or air pressure it only allows for the introduction of small amounts of fuel. If it fails in a manner in which it senses lots of boost pressure when there is none or very little there will be all kinds of black exhaust.

On 8V92 engines it is on the RH side, top of the engine looking forward. On the Series 60 it is on the RH side of the engine on the intake manifold, easily seen through the RH door looking over the batteries. It is a black plastic device about as big as a small cell phone.

[Jerry Winchester]

The hoses on the intercooler will also keep you on the sideline.

I think Jim's sheep answer is the best one yet. I'd start there and make sure there wasn't plastic sheep parts melted to the turbo inlet.

[chtree]

We replaced 3 sensors and then finally found a short right next to a connection. Once we removed that section of harness it worked fine.

Chris

[JIM CHALOUPKA]

Also look for Locusts or Grasshoppers, they have been known to eat through a filter and jamb an orifice.

I bet if you lost oil to the turbo that would kill it too.


:eek:JIM

[gmcbuffalo]

I was told by a ford dealership service writer that the reason I was having problems with my turbo in my Excursion was that I tow it behind my motorhome and the road debris from the bus junks up the turbo.
GregM

[Jon Wehrenberg]

I'm pretty sure you can tell that service writer he is full of sheep $hit.

Don't you just love it when you bring your vehicles in to be serviced by idiots.

[jimblu]

No doubt he is full of it about the turbo, but funny things do happen. When I towed a VW Jetta over 12 hours on hot days without starting it the hydraulic lifters would bleed down, perhaps from the heat and vibration, and the engine would have a death rattle with flat lifters for several minutes on the first start.

[JIM KELLER]

It's all about Air, Fuel and Exhaust. You can tell alot about your engine and what it needs, by watching the turbo boost guage. I witnessed the performance of Roger's bus go downhill. But when he tried to go uphill as we were climbing the grade we compared readings. While my boost was 25 to 30 PSI. Roger's readings were 19 to 24. It was fun having two buses side by side comparing readings while climbing 10,000 to 11,000 feet. Roger obtained 2 new fuel filters and his boost imediately went to 30 PSI.
Further on our trip took us across Utah and New Mexico where we encountered a 50 MPH dust storm for the entire day. Although he was only two or three bus length ahead of me and we were down to 30 MPH, I could barely see the back of his tow. The dust clogged the air filters and choked down our engines. I loss engine performance because my turbo boost fell to 24 PSI on a hard pull. We install new air filters, and I imediately had 30 PSI back on exceleration. Although both of us started with new filters, It was a good example how fast they can deteriorate.

[jack14r]

Jim that is great to know,our gauge shows about 30 PSI but my Silverleaf digital gauge which agrees with the Prevost analog gauge up to 30 actually will show 46 PSI on a hill in 5th gear at about 1600 RPM.The Prevost gauge has a stop on it so it doesn't appear pegged,if you were down to 24 PSI you were really down much more than you thought.You were really only making about 50% boost.

[Will Garner]

I promise to try and not have this post go to the lengths of a Jeff Bayley one. On our way to OKC I had my first encounter with loss of turbo boost. My mind went racing back over the previous POG Forum posts for a possible cause. There was the infamous on 8V92's cracked manifold or manifold pipe that feeds the turbo inlet hot side, all sorts of sensor issues, clogged air filters, ad nausium. Well when I got to OKC and found our coach parked beside Tom Chilcote I thought we might find the source of the problem by using Ray Davis's DDECII code reader sold to Tom. If nothing else it would be a learning experience for Tom to get acquainted with his new diagnostic tool.

Well we read the codes. No active but lots of old codes. The old codes did not have a date so they were essentially useless. We fired the engine and reread the codes with the engine running. Same result, no active codes. Man was I frustrated.

Thursday morning comes, departure day from OKC and the issue has not been resolved. On the first leg of the trip, OKC to Nashville, the engine ran fine until just east of Memphis. I even caught up with Ray Davis, who left OKC about five minutes earlier than we did. We caravaned almost to Memphis when traffic separated us. East of Memphis the turbo again started losing boost. No problem, Nashville and a well known service shop is only 3 hours ahead.

We got there around 8:15 PM and were in the service bay by 9:45 PM. Wow, what great service and the shop is open 24/7 Monday through 3:30 PM on Friday. Well I described the symptoms to the service tech. They were the Twin Pyros were not rising and falling together like they had for the 2 1/2 years I had owned the coach; the right pyro was some 2,000 - 2,500 degrees hotter than the left pyro; the turbo was struggling to make 8-10 pounds of boost instead of going to the instrument peg at 15 pounds; and going up hill I doubted the coach could pull a greasy string out of a .. well you know that expression. So contrary to previous posts the Twin Pyros gave me my first indication that something was amiss in the power generation source.

The service tech pulled the exhaust pipe from the right cylinder bank and pronounced it not to be cracked but that it was only in contact with about 20% of its circumference with the exhaust manifold. He made adjustments, installed a new fan belt for one that was cracking and also changed bulbs in two dash panel gauges - Twin Pyro and Speedometer.

The coach was then driven by the service tech and pronounced as running "very well." Upon arriving back at the shop the coach was placed in a space with power and we went to bed.

The next morning we unhooked and went to stay overnight at Jellystone so we could visit our daughter. My driving the bus getting on I-65 southbound said the problem was not fixed and in frustration, and not wanting to alienate the shop, I decide to just limp home and make what ever repair was necessary myself. We were able to limp home. I also got to experience the low speed hill climbing that was a routine part of truckers travels until the turbo was added to truck diesel engines - 30 mph flat out uphill is a real pain.

I got home and called a person who shall remain nameless in order to protect my membership in this group. We spoke for almost an hour about possible causes. That was on a Tuesday and I did not get to try the easiest fix until Friday that week. OK, here it is, I changed out both fuel filters with new ones I had carried all the way to OKC as spares. I did not get to do a road test until yesterday. Well, I am tickled pink with the results. The 8V92 was up and growling again, ready to rip up the pavement and get on down the road. By the way, I had changed both fuel filters in January 09 and the air filter in July 08. I am going to get a new air filter and change it too.

So the moral of this story is, try the simple solution before chasing the exotic one. Oh by the way, when a turbo fails it is usually a catastrophe (did I spell that one right Lew?) and you won't be going any further - lots of white smoke. Ever watch the Indy 500? They experience turbo failure and that will ruin a good day.

Gee, this does resemble a Jeff Bayley post. I've got to go on a word diet for sure!

[truk4u]

Will,

You where my wake up call on Thursday morning, didn't even get a chance to say goodbye to you and Carole. Nothing like the sound of an 8V firing up in the morning.;)

Glad you sorted it all out, but I'm real concerned about your Pyro's being in the 2000 - 2500 degree range!:eek: You didn't think I would let that one go did you?:D

I didn't think fuel filters would cause a difference in left and right EGT, my experience has been a degrade in all over performance and loss of boost would be right on target. I guess I missed that while we were talking at OKC, I thought you just had a Pyro discrepancy.

By the way, nice sewer hose!:p

[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.

[Will Garner]

Jon,

You are welcome. I finally got to contribute something to the technical knowledge of the group. I did not do it alone, I did have help from others. It was a long trip home but we made it and learned something in the process - now if I could just remember where I put those slippers!

Greg,

There was no change in the differential pyro readings after the Service Tehcnician polished the exhaust pipe. I did notice something strange to me. That was he smacked the clamps serveal times in several different places. After a couple smacks he retightened the clamps. There were about three rounds of pipe banging then clamp tightening.

[Jon Wehrenberg]

Uh, this was the wizard that thought your problem was related to the turbo?

My guess is he is not the example to follow.

Black smoke equals turbo, also detected by sooting around the exhaust.

Clean exhaust equals fuel starvation, also proven by no visible sooting around exhaust and irregular performance (jerking in drivetrain).