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Turbo Problem?
Guys,
On my way to Prevost in TN today… about 6 miles out coach started lurching a bit on acceleration then got worse… Lots of black smoke…. then check engine light…. never told me to stop and given I was less than 5 miles away at that point I nursed it into service to avoid a tow. I have never experienced anything like this before. When it lurched, dash turbo was fluctuating significantly in sync with the lurching…. Anyone have this issue before… How bad could this be?
My appt is for 7:30 so I guess I will find out soon enough…
Bill
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15 Replies
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On my Legendary (2006 chassis XL2) the VPOD failed giving similar issues to yours. The DD shop replaced it with a reman, but that also failed…in only 35 miles. Had to get another one ordered in and that fixed it.
They thought it was a boost sensor first, but that was not it. The mechanic said they had lots of VPOD failures in that vintage engine FWIW.
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Mark can correct me if I am saying this wrong, but the VPOD is controlling the turbo speed, which is variable depending on a number of factors including power called for or if the EGR is functioning.
When it fails to adequately regulate the turbo it is like the turbo is kicking on, kicking off or performing at the right speed. It is way more complex than a wastegate which has been traditionally used to regulate turbo output by allowing more or less exhaust to pass through the turbo, or out the exhaust pipe.
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Prevost says the pin popped out so the turbo isn’t engaging. They have ordered the part and it shouldn’t be a big deal. So that is the good news. bad news 19 bad boots… UGGH
Bill
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Expand on “19 bad boots”. Thanks!
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Upper a Arm grease boots and the like around the bus…I think… they showed me one on the ground where it’s just a ball of grease… they are going to do a front end alignment as well….
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Bill’s comment about the dust boots requires a bit of thread drift.
For a long time we have had comments posted about the failed boots around fittings that are greased such as at tie rod ends. In my 30 years of ownership I have never had a failed dust boot. The reason is simple and it relates to how the chassis is lubed.
First, understand that if you pay someone to lube the chassis you are likely not getting a master mechanic. Not only that, he likely has never been given a chance to understand the quality of a lube job is not related to how much grease he pumps.
When a joint is greased the grease enters the fitting and goes directly to the space between the two mating surfaces that rely on the grease to prevent wear. After the grease passes that area, the excess goes into the rubber dust cover. The moment any indication grease has entered the dust boot or cover is seen, that is the time to stop pumping and move on. But instead the grease jockey will keep pumping until the dust boot or cover expands to the point where grease starts coming out. That is like blowing up a balloon until air comes out.
The rubber dust covers do expand and eventually grease comes out because there is so much pressure. That’s not going to cause a new dust cover to fail, but over time as that over filling is repeated the cover gets a crack and with each subsequent lube job the crack increases in size until the dust cover has torn and failed.
As owners we either have to watch the grease jockey and make sure he does not over grease the fitting or make sure whoever is going to do the work understands the concept. (Good luck with that).
Replacing dust covers is time consuming and expensive and completely unnecessary. As the name suggests the rubber boot is intended to keep dust and dirt from getting between two moving parts. There is nothing in the use of the coach that will make it fail. But over greasing and the associated inflation of a part never intended to be inflated will ruin them.
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VPOD controls the vanes, not the speed. It moves the vanes to add or remove boost as needed. No VPOD, no boost. There is a speed sensor on the turbo that is in the mix of sensors needed to run, but the VPOD is electric over air and moves the vanes.
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Jon, Thanks for the explanation. Sorry I didn’t see your post prior to emailing you. All that makes sense. If you were me and you had a bunch of them that needed to replace would you or would you just continue to let them over grease them and roll with it. They are saying about 20 hours and 5k for parts and labor plus a front end alignment which I don’t feel I need. She tracks great as is…
THank you
Bill
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Thanks Mark. My brain was locked on a waste gate which pushes more or less exhaust through the turbo, which in turn controls how much boost. The VPOD adjusts boost by making the turbo vane’s position determine boost.
For those with Series 60 EGR engines max normal boost is about 30 PSI. What is not seen is when the EGR is working boost increases to 50 PSI, something not displayed on the gauge, but is seen if the engine is hooked to a reader. The VPOD controls this.
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Actually the VPOD does control turbo speed as one of its functions. It controls boost as called for by the ECM and limits speed thru blade angle. The turbo speed sensor sends information the the ECM to help determine the VPODs response and control of the turbo.
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Bill wrote: they are going to do a front end alignment as well….
I’ve been told a number of times that we should be getting a three axle alignment, not just a single axle alignment. Is Prevost telling you something different? Dick
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Dick,
I not good with the details… I can confirm tomorrow. Jon talks very highly of what they do here in Nashville so I am sure it’s what you described. They finished up putting on all the new parts and I am first on the rack tomorrow. I saw them working on the bus before me and they had stuff on the front wheels as well as the Tag I think on the one they were doing today…
Bill
1984 96" with 8V92TA
(remodeled Liberty Coach)
Greenwood, MO -
Prevost will do a three axle alignment because to get it right everything has to be correct relative to everything else.
Because of their expertise with conversions in Nashville they have developed specifications for conversion alignments that differ from the alignments in the service manuals. When a seated coach is aligned it is significantly lighter than a conversion and the specifications in the service manual are based on that lighter chassis weight. Ours can easily be many tons more weight so Nashville uses different correct values based on our weights and all three axles are involved.
I do not know what other shops use as the alignment values, and I do know the alignment machine structure that Nashville has is designed to handle the weight of our coaches without flexing and whoever does alignments needs an equally strong machine otherwise the flexing throws off the readings.
My point is if Prevost Nashville is doing an alignment they are going to do it right.
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When we had a three axle alignment at Prevost Jacksonville on the suggestion of the late Peter Campbell, the tech who did it (can’t remember his name, was from Quebec) had the same conversation with me that Jon just shared above. Made a WORLD of difference in how the coach drove. He also replaced the tie rod ends.
So … how often should we have the three axle alignment done?
Mike Harper
2004 Marathon XLII -
My clue was my fingers and hands. Part of my pre-trip or 5000 mile service is to run my hands around the tire treads. Apart from looking for cuts or stuff stuck in the tire, I am feeling the treads and it is incredible how the slightest uneven wear can be sensed by your fingers and hands.
Normally there is no indication of any unusual wear, visually or be touch, but in my case I could feel the wear was unusual compared to other axles and when I looked very close I could see some feathering on the tread.
If it is bad enough to feel bad, like poor tracking, or wandering, or pulling to one side you really, really need an alignment.
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