Power Problem with FM260

[JRhetts]

Summary Nov. 5, 2013

Three days ago, in post #100, gait wrote:

from first principles (not experience of wastegates)

His phrase about "first principles" echoed in my brain all last weekend – all the while I focused [narrowly] on imagining and designing a volume/pressure reducing ‘thingie’ [technical term]. The thought kept niggling at me: was I perhaps too much absorbed in the learning and design process – might I be missing a more important point?

So, reflecting for the umpteenth time on “first principles”, I decided I needed to back off and review the big picture. What follows does NOT represent the sequence of how I got here, but it is what I take to be an orderly assembly of what I did and what I think I “know” at the moment.

I’d welcome and appreciate any comments or suggestions!

SYMPTOMS
Excessive loss of speed when climbing moderate grades
Excessive times accelerating to pass
Low boost pressure at Intake Manifold as measured by hard-wired gauge on dash: 18 psi actual compared to spec 22 psi
Relatively poor fuel economy – 6.5-7.5 mpg typical
Very high Temperature Gauge readings when climbing long, steep grades in high ambient temperature [assumption: would expect higher temp if relatively high fuel in F:A mix due to lower boost pressure]

QUESTION #1: Is this engine objectively producing specified HP and Torque?
Rx: Chassis dynamometer test to quantify output HP and Torque

QUESTION #2: Are the performance symptoms due to an air supply problem or to a fuel supply problem?

HYPOTHESIS #1: The power shortage is due to an air supply problem

EVIDENCE Low turbo boost at Intake Manifold [IM] High Coolant temp when climbing steep grades in high ambient temps [>95°F] – pyrometer reading would be preferable to Temp Gauge, but I don't have one

Question #3: Where to look for air supply problems?

air intake path [restricted?]
turbocharger output [sufficient?]
air supply path from turbo via Intercooler [IC] to IM [leaks?]
Waste Gate [WG] [proper “dump”?]

WGValve
WGActuator​

INFERENCES /“CONCLUSIONS”	EVIDENCE
boost gauge is reasonably accurate; 4 psi observed shortage is real	Verified accuracy of dashboard boost gauge; – 0.5 psi in range 15 psi to 25 psi compared to high quality, oil-filled gauge
air intake path is open; turbo receiving full air input	Inspected air intake path, cleaned air filter, verified no obstructions
turbo is capable of developing sufficient boost necessary for engine to perform at full specs	disabled WG; turbo pressure at IM reached ~24 psi before ECU set #54 code & activated ‘limp’ mode [disabled both WGActuator and WGValve
turbo-to-IM piping shows no observable boost pressure loss	observed simultaneous pressure at both turbo outlet and at Intake Manifold; within 0.5 psi [gauge measurement error ]; tested both with WGActuator operative [18 psi max] and disabled [up to approx. ~24 psi max] Further tests (?): – remove Intercooler and perform water test at 22 psi – test turbo-to-Intake-Manifold piping and connections for leaks
WGValve operates freely – not restricted or sticky	disconnected WGValve arm from WGActuator rod; manually manipulated WGValve arm
WGValve seals reasonably well – WGActuator ‘backside’ spring can hold up to 24 psi	disabled WGActuator, maintained connection to WGV; drove under load [up grade]; gauge reached ~24 psi at Intake Manifold when ECU set overboost fault code
in static conditions, WGActuator appears to operate at approx. 21-22 psi; however, under operational conditions WGValve may prematurely open due to the exhaust ‘backpressure’ in the turbo turbine chamber preloading against WGActuator spring	attached regulated air pressure to AGActuator input; operation/movement appeared to initiate at 21-22 psi [imprecise!!] [this static test differs from operational conditions when exhaust ‘backpressure’ could lower the pressure required by WGActuator by pressure on the input side of the WGValve– i.e., lowering pressure required at WGActuator to open WGValve
Hypothesis #2: Air Supply Problem is created by WGActuator operating at 4-psi-too-low pressure relative to actual input pressure at Intake Manifold [IM] Rx: adjust WGActuator so as to open at relative pressure to deliver 22 psi at IM	Inspected WGActuator for physical adjustability – none found; tried rotating WGActuator arm to test if threaded on end of rod inside housing; no difference

Question #4: How can achieve WGActuator operation at appropriate pressure relative to boost pressure at IM?
1. replace existing with new WGActuator [OEM unit and replacement 11/2/2011 unit have not been correct]
2. add shims to WGA mounting bracket, shift WGA farther away from WGV; equivalent to shortening WGA rod; delays movement of WGV arm
3. modify WGA rod to add threaded adjustment; adjust so as to shorten rod length, delays movement of WGV arm
4. change leverage point on WGV arm, to reduce WGV movement relative to WGA rod; delays movement of WGV arm
5. insert calibrated pressure relief port in WGA boost pressure line to supply lower relative pressure to WGA diaphragm compared to IM pressure

QUESTION #5: Is there a fuel-side component in the power loss problem?
Can I get Mitsu to measure the actual Fuel:Air Ratio?

Again, my deep appreciation to all who have read and commented on this thread. You have been very helpful.

John

 

[gait]

nice summary John.

Silly question ... did the test on the steep grade with wastegate disconnected have an effect on engine temperature (usually high on that grade if I've read correctly)? Possibly difficult to determine due to overboost error switching to limp.

I don't know enough but accelerator position / rpm and thus fuel input would presumably be different. Gets me way out of depth into ECU mapping.

 

[JRhetts]

... did the test on the steep grade with wastegate disconnected have an effect on engine temperature (usually high on that grade if I've read correctly)? Possibly difficult to determine due to overboost error switching to limp.

gait

the wastegate-disconnected test and the high temp observations were more than 2 months apart. High temp occurred at end of our summer [August], while waste gate-disconnected data were observed last week. Also, the wastegate-disconnected data were done in the span of less than one minute climbing a much less steep grade than the grade in August, so the over boost error occurred way before I could have observed a temp rise on the dash temp gauge.

John

 

[nick disjunkt]

after reading about your problems and the lengths that you are going to to resolve them I am surprised at your reported cruising speeds! In Europe any vehicle heavier than 3.5 metric tonnes is limited to 56 mph, it's worth remembering to keep things in perspective! Perhaps you'll have the joy of overtaking me on a hill, I should get to Oregon in late summer next year, travelling in my heavy 10 year old speed limited Mercedes.

 

[SkiFreak]

travelling in my heavy 10 year old speed limited Mercedes.

Maybe you can disable the speed limiter when you get to the US...

 

[JRhetts]

...it's worth remembering to keep things in perspective!

Point very well made. … With a psychological attitude adjustment, perhaps I can just cruise, climb hills slowly and not chafe at queuing in traffic rather than needing to pass. :rally_guys:

...Perhaps you'll have the joy of overtaking me on a hill, I should get to Oregon in late summer next year, travelling in my heavy 10 year old speed limited Mercedes.

If you are going to show up here I sincerely hope you will take to opportunity to contact me. I am sending you my personal contact info by PM. I'd much rather hoist a pint with you than pass you by!!

John

 

[mog]

I typically cruise at 62-68 mph, with my foot NOT on the floor; the max speed I recall taking notice of was in the 78-80 mph range, tho I have the impression of having been in the low 80's on a relative flat at some point; and I frequently pass other vehicles (tho not on moderate+ grades, and my pass times can be uncomfortably long on 2-lane roads.)

Excessive loss of speed when climbing moderate grades
Excessive times accelerating to pass
Relatively poor fuel economy – 6.5-7.5 mpg typical

You have a 23,300 pound BRICK that can cruise at 62-68 mph with 78-80+ mph possible, you are already not obeying the law of physics. :Wow1:
I'd say 6.5-7.5 mpg running those speeds is in the ball park. My F-250 (V10 gas) can get 15-16 mpg at a cruising speed of 50-55 mpg and it goes down to 11-12 mpg at 60-65 mph.
I'd bet if you cruised at 50-55 mpg you see 11+ mpg
I did the 'horsepower used to overcome aerodynamic drag' calculations for my Fuso, and it takes 120% more horsepower to go 65mph instead of 50mpg (a 30% increase in speed).
--Using frontal area of 64.57 sq ft and a Drag Coefficient (Cd) of 0.7 {0.7 is very generous, 0.9-1.1 is probably more realistic, so the numbers would be higher}--
It sounds to me your 'performance' is better then I would expect for your FM's Weight-HP/TQ-Drag, so I would venture to guess that knowing your boost pressure is low and hearing the 'other RUF-FM' performs better, is biasing your view on performance.

Low boost pressure at Intake Manifold as measured by hard-wired gauge on dash: 18 psi actual compared to spec 22 psi

As I've said in our conversations, I would follow-up and get the boost were is should be, just to be at a 'correct starting point'. Having it on the dyno at the dealer will be a great baseline also.

 

[Amesz00]

Originally Posted by JRhetts
Excessive loss of speed when climbing moderate grades
Excessive times accelerating to pass
Relatively poor fuel economy – 6.5-7.5 mpg typical

I'd say 6.5-7.5 mpg running those speeds is in the ball park.

by my (google, blame them if its wrong. but if its right its all me ) calcs to change from mpg to km/L should be 0.425. ie 7mpg should be 2.98km/L
that is a relatively fast cruise for an expedition rig, but is basically identical to what my dad runs in his 10t MAN. i would say frontal area and drag coefficient would be almost identical, tho the MAN is shorter and a bit lighter @ 8t tare. wouldnt make much difference to flat ground cruising though. he gets roughly 4km/L at 100km/h. thats 9.4mpg. anything below 3km/L is almost getting into semi-trailer territory..

also, in all honesty the dyno graph and AFR meter may not tell you much, unless you have something similar to compare it to. unless of course, mitsu knows what it should be...

 

[Aussie Iron]

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[TD]in static conditions, WGActuator appears to operate at approx. 21-22 psi;



however, under operational conditions WGValve may prematurely open due to the exhaust ‘backpressure’ in the turbo turbine chamber preloading against WGActuator spring[/TD]
[TD]attached regulated air pressure to AGActuator input; operation/movement appeared to initiate at 21-22 psi [imprecise!!]


[this static test differs from operational conditions when exhaust ‘backpressure’ could lower the pressure required by WGActuator by pressure on the input side of the WGValve– i.e., lowering pressure required at WGActuator to open WGValve[/TD]
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John

Ok , I don't know what I'm talking about - but is it not back pressure in the exhaust (that you would expect) but exhaust flow creating sucking on the WG opening it.

Like I said I know little about it, but it is an interesting thread.

Dan.

 

[nick disjunkt]

If you are going to show up here I sincerely hope you will take to opportunity to contact me. I am sending you my personal contact info by PM. I'd much rather hoist a pint with you than pass you by!!

John

An offer I wont turn down, hopefully you can show me where to get some real ale, the British stereotype of American beer is all low strength watery lagers!

Maybe you can disable the speed limiter when you get to the US...

At 56mph I'm towards the end of the 'green' rev range, any faster and I reckon fuel economy will take a nose dive. I'm in no rush and I'll elect to leave the limiter engaged unless I feel that I'm posing a danger on the interstates.

 

[JRhetts]

... - but is it not back pressure in the exhaust (that you would expect) but exhaust flow creating sucking on the WG opening it. Dan.

Dan

You may well be correct.

My choice of the word 'back pressure' came from looking at the diagrams in the Fuso Shop Manual. I took the open and closed pictures to imply that exhaust gas into the turbine would be under pressure and thereby would spin up the turbine-side blades; if so, that looked to me like it would also put pressure on the inlet (or escape) side of the waste gate valve, making it "want" to open. Perhaps it is the case that there is a vacuum on the other side of the valve which would also cause it to "want" to open. I really don't know, and so my choice of words may indeed be incorrect.

Am I correct in thinking that – in either event, by pressure or by vacuum – the exhaust gas passage through the turbine side of the turbocharger will, as it were, pre-load the waste gate valve to open? That this will lower the pressure needed on the diaphragm to cause it to move under operational vs.static conditions?

John

 

[JRhetts]

...hopefully you can show me where to get some real ale, the British stereotype of American beer is all low strength watery lagers!

de gustibus non desputandum est and all that, but the NW [Oregon and Washington states] and Bend in particular have nurtured a large number of local microbreweries doing everything from stouts to IPAs. I can almost guarantee you a good brew!

PS I got your confirmation. Do call!

 

[kerry]

At 56mph you don't want to be on interstates in the western US where trucks routinely drive at 80+ mph. Stick to the 2 lane highways.

 

[JRhetts]

…It sounds to me your 'performance' is better then I would expect for your FM's Weight-HP/TQ-Drag, so I would venture to guess that knowing your boost pressure is low and hearing the 'other RUF-FM' performs better, is biasing your view on performance.

mog, as always you raise good points.

While I have objective data on boost pressure, I have no objective measure that I am actually lacking power from my engine. All my "data" are impressionistic.

Regarding power output or performance, I really only have seat-of-the-pants impressions from 3 people: the builder of this and its sister vehicle; myself; and a Mitsu shop manager who has driven a bunch of FM260s over the same terrain we tested mine on.
While I was admittedly being facetious in my exchange with kerry above, I really do KNOW that the final solution may be a psychological attitude adjustment on my part.

I, too, would absolutely venture to guess that [what I've heard] is biasing my view on performance. Back in 2009 when I bought the rig, the builder primed me with his disclaimer that he thought the sister rig seemed to perform better. After 2 years of desiring to climb and pass better, I mentally circled back to the builder's comments and decided to pursue the possibility of improvement. That's why I'm trying for some objective measures like the dyno test. I really don't want to torture myself if I am in LaLa land.

… I'd say 6.5-7.5 mpg running those speeds is in the ball park. My F-250 (V10 gas) can get 15-16 mpg at a cruising speed of 50-55 mpg and it goes down to 11-12 mpg at 60-65 mph.
I'd bet if you cruised at 50-55 mpg you see 11+ mpg

Let me reframe my numbers in order to be more accurate. While I CAN cruise quite well at 62-68, that is NOT where I CHOOSE to drive. When I am on 2- and 4-lane roads, I typically set the cruise control at 58-62, but of course I cannot hold those speeds for very long periods due to other traffic, towns, and hills.

I drive with a GPS for speedo and odometer readings [differential and tire mods make the OEM speedo inaccurate]. My GPS calculates my average speed while moving. Over roughly 400+ days of driving to date, my ‘moving' daily averages on paved roads are tightly clustered around 45mph. I am only VERY occasionally on 4-lane or interstate highways for any length of time; on them I may have a 55-60 mph average for a day or for a chunk thereof. But my 6.5-7.5 mpg fuel consumption number is based on a roughly 45 mph day, not higher average speed. I have actually tried several intentional 50-55 max speed days, and on those I can get up to 8.0 mpg if the terrain is not too hilly – nowhere near 11+.

by my calcs … 7mpg should be 2.98km/L…[my dad] gets roughly 4km/L at 100km/h. thats 9.4mpg. anything below 3km/L is almost getting into semi-trailer territory…

Amesz00 If anything, your numbers suggest my fuel economy is on the low side. Thanks for the perspective.


Back to the psychological aspect: as mog suggested, I want to get the boost to where it should be – as much for mental relief as performance increase. For me, given my prolonged forays into remote places, I'd “feel better” with an engine I think is at 100%. And if I can get better fuel economy and/or better driving performance as well, I'm all for it.

 

[Overland Hadley]

Is the 22psi number for the turbo a normal operating figure, or a max output figure? It makes me wonder if they normally operate at that figure if the limp home mode kicks in at 23. (I am thinking of it like engine hp, during normal operation you never see max hp as that is only reached at near red line.)

This is a most interesting discussion, thank you for facilitating it. I am learning a lot.