I hope at this point – 183 posts and counting – that the hard core is not getting bored. The lurkers are as always: on their own.
This has been a really great experience for me, in part for the final outcome, but VERY MUCH MORE SO for the perspective and assistance I have received from so many knowledgeable people in so many disbursed places. I could never have known where to find nor could I have afforded to assemble the talent that has contributed to this “Power Problem with FM260” thread. I think this has been a paradigm example of how the ‘net' can work at its best.
My last attempt to summarize my understanding of things was 4 days ago, which of course seems like an eternity in internet-time.
I am one lucky sob. Over the last week I have managed to corral tens(!) of hours of (gratis) expert attention: two extremely knowledgeable aviation mechanics who have worked extensively on turbocharged engines, both diesel and gasoline, and an expert diesel truck engine mechanic. In all honesty I could not have engaged their attention so fully without the help I got here to prepare me.
Lots of conversation, discussion of the modest quantitative data I have, and their(!) educated opinion has led me to conclude: Going into this whole thing,
my impression that I lacked power was off-base. [OK, call it ‘erroneous' or ‘wrong', but not in public and not to my face.]
Really, it has not been so very hard to convince me of this. I DID think that –
from the original builder's comments,
from the seemingly slow passing and hill climbing, and
from the 2011 Mitsu shop manager's statement that I “ought to be getting 22 psig”
– my engine was underperforming.
In addition to the typical masculine desire for more power, I actually have been more concerned about the integrity [longevity] of my engine. But now I think there is actually NO INDICATION of a likely problem, and some knowledgeable drivers have persuaded me that this rig goes along very well compared to others they have driven.
Whether you compare it to the ratios
mog computed [post #28], or to the performance of a brand new FG truck with a camper body on the back [which
mog and I drove two nights ago], my truck is actually not a dog. It does not blow Ferraris away on hills, but it also does not really lag “that much.”
MOST IMPORTANT, the mechanically-knowledgeable guys do not think any of the objective or subjective data suggests that I have a problem cooking in the engine that is just waiting to do a Murphy's Law number on me. [I am only threatened by the normal dose of that *&#@ing Law.]
I have eliminated [at least temporarily] the ‘adjustment' valve that allowed me to raise the boost to 22psig. [I got no performance improvement from raising boost 22% – 4psig.]
I have also re-evaluated the actual 22psig number I originally got from the Mitsu shop. Given the lack of performance improvement, and given the fact the engine can be seen as running just fine at 18 psig on a new turbocharger and waste gate, I doubt the accuracy of this number. I cannot find any support for any specific running boost number in all the technical information in the Shop Manual. And as
mog pointed out to me, there is no place in the Manual where ‘lack of boost pressure' is cited as a criterion for any remedial action.
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INSERT LATER: After repeated scrutiny of the Service Manual, I have found nothing resembling a value given for something like “max. actual operating boost under load.” So, either the Mitsu mechanic who gave me the number got it from his previous experience with FMs he had worked on, or it came from some source not so far discoverable by me, or……..
How I picture things now is: the ECU sets a max boost limit based on the boost pressure sensor. I think of this as a max-safe-for-the-engine limit the engineers designed in. I would not be surprised if the voltage value from the boost pressure sensor were corrected for density altitude, incl. temperature [as there is an atmospheric pressure sensor and an intake air temperature sensor which the ECU's programming could easily use.] So the boost level at which the ECU will set a fault code may vary according to local operational conditions. But it seems to average around 23.5psig.
The waste gate, on the other hand, is a purely mechanical device. It receives no feedback control, though it exerts feedback control on the intake manifold pressure. Its diaphragm and spring combination open and close the butterfly valve so as to create a set point at a particular psig value: 18psig under the operational conditions I have observed. I have seen as much as 19psig for literally a moment, but the additional pound seems to be a function of the mechanical response time of the waste gate system, momentary overshoot if you will.
So, although I was able to create a stable operational situation in which the intake manifold was getting 22psig rather than 18psig, there was no performance difference. In my simple reasoning, the overall engine, combining both fuel and air sides of the equation, is designed to operate at 18psig. Maybe it would put out more power at 22psig if more fuel could be put in. But there does not seem to be a straightforward way to do that.
Perhaps operating at 18psig is one of the ways the engineers “de-tuned” the engine for reliability and longevity. I can live with a reliable engine that gets me where I want to go and back.
Parenthetically, since the turbo is capable [according to the Service Manual] of 73kPa or 10.59psia of boost, then at sea level this would equate to a maximum of 25.3 psig. Since it is regulated at 18 psig, the turbo in effect has 7.5 psia ‘in reserve' to compensate for changes in pressure-density; so, I should be able to get my 18psig of boost up to as high as 10,000 feet. Think so? Sounds logical, but I'm not sure. I will say: I have driven at 10,000 feet and do not recall noticing a performance drop. If my line of reasoning here is correct, then that would again seem to indicate how much the engineers designed for reliability/longevity.
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I am reminded of a lesson I know well but 'occasionally' forget: you really should not continue to trust/accept values even from 'authorized' sources when over enough time they don't make sense on the ground.
In general, I think the numbers from the dyno test are worthless. The range of rpm values that were collected is way too limited; the shape of the Hp and the torque curves are so far off from the norms Mitsu publishes that they just don't look like my generally well-running engine. Considering the specific peak Hp number of 188 [77% of the 243 rated Hp], this is well within the net-net-net efficiency loss numbers Mitsu publishes. [Air intake loss: 5%. Mechanical 4x4 drivetrain: 13%. My additional transfer case, driven axle and hubs 10% easily. Combined, these would estimate a 75% efficiency.]
I am pursuing how I might attach an EGT probe with minimal work and intrusion into the engine. [Surface bolt-on is my leading contender.] Then I plan to drive for a few thousand miles gathering some normative EGT data, at which point I will decide whether to try for more fuel or not. So far, I do not see a clear path to that goal.
From being engaged with this thread, I have developed a vastly better understanding of diesel engines in general and mine in particular. I am much better equipped to deal with engine issue down the road when [not ‘if'] they happen. I can even describe coherently how the entire fuel and air sides of the engine work and to some degree [don't know the ECU code] what variables control or limit them. [Wow! Am I also “a better person?”]
“Thanks” does not seem like quite a strong enough word, but it really is how I feel. Thanks!
Comments still welcome.
