Power Problem with FM260

[JRhetts]

Those intercooler numbers are weird.

My thoughts exactly. But I got them right out of the e-manuals for FG and FM models respectively - I purchased disk contained manuals for FE-FG-FK-FM models from Mitsu several years ago as I began to have to dive deeper and deeper into this truck.

John

 

[JRhetts]

More Tests, Conjectures, 4 [apparent] options



I performed four tests:
a) I verified that the Actuator delivers a max of 18 psi boost when climbing a modest local hill;
b) I re-verified that if I get an overboost condition: up to 23-24 psi on my gauge, then a “Check Engine” fault light on the dash, and a diagnostic code #54 recorded in ECU memory.
c) on the possibility [hope springs eternal] that the Actuator rod was adjustable, I disconnected the arm from the waste gate valve pin, I measured the length of the arm, I rotated the arm both clockwise and anticlockwise measuring again in each position [no difference detected]; reconnected everything and drove my test hill with the arm still rotated one turn clockwise [to see if there was a change in boost]; my gauge showed the same old 18 psi max
d) I drove out to a longer steeper hill several miles away. On the way out there I started throwing codes on flat stretches of highway as I was accelerating only enough to reach and hold highway speeds. Each time I could reset by ignition-off and then ignition-on again. I got 5-6 ‘limp mode' events in 7-8 miles.


As I see it, I have 4 options at this point:
— Live with 18 psi boost; it hasn't been all bad so far.
— Install another Actuator if I can get Mitsu to provide one under warranty.
— Purchase a commercial adjustable boost compensator and run its plumbing up to the cab.
— Trial and error my way to a fixed, in-line, no-moving-parts device that gets me to 22 psi under most conditions and does not cause overboost fault codes.

The first option is getting more and more acceptable; realistically, I can go anywhere I want ,I just get there a few seconds to minutes later than I might if I had lots more acceleration and hill-climbing power. The engine is completely reliable and that is more important than a few seconds, frankly.

 

[gait]

seems like good logic to me John.

Pity about the non adjustable arm.

 

[JRhetts]

Pity about the non adjustable arm.

WELCOME HOME!!

Yeah, adjusting the arm length was too much to hope for. Many other manufacturers seems to provide this, but not Mitsu.

 

[kerry]

WELCOME HOME!!

Yeah, adjusting the arm length was too much to hope for. Every other manufacturer seems to provide this, but not Mitsu.

That arm on my 93 GMC 6.5 diesel wastegate actuator is not adjustable either.

 

[JRhetts]

Analysis of Vent "Solution"

After reflecting a bit, I am getting more and more comfortable with "acceptance" of a completely reliable truck that is not a hot rod.

 

[westyss]

John,

By the sounds of things you seem pretty convinced that the problem is the WGA, barring a problem with the WGA line. So it seems that the solution would be to get a new OEM actuator or one that can replace that, perhaps one that is adjustable?? I seem to remember seeing one that has an adjustment on it or the ability to swap the spring out in it to adjust pressures that way, and the one I mentioned before I think had that but I am not too sure. Obviously the difficulty is in finding an actuator that can replace the OEM one, might be worth the effort to seek one out.

By the way, this thread has been awesome and well produced even though it was started by your troubles, thanks for openly sharing your efforts, it enlightens everyone with one of these trucks.

 

[JRhetts]

John,
By the sounds of things you seem pretty convinced that the problem is the WGA, barring a problem with the WGA line. So it seems that the solution would be to get a new OEM actuator or one that can replace that, perhaps one that is adjustable?? I seem to remember seeing one that has an adjustment on it or the ability to swap the spring out in it to adjust pressures that way, and the one I mentioned before I think had that but I am not too sure. Obviously the difficulty is in finding an actuator that can replace the OEM one, might be worth the effort to seek one out.

Yes, I have a request into Mitsu for a replacement WGA. I don't know how that will turn out, even tho my truck is still under warranty. In the mean time I am pursuing how I might solve the problem with the current WGA. It may be a waste of time in the end, but it keeps me out of the bars ;>)

By the way, this thread has been awesome and well produced even though it was started by your troubles, thanks for openly sharing your efforts, it enlightens everyone with one of these trucks.

Thanks for the positive feedback. I have benefitted enormously by all the contributions and suggestions and speculations. I have frequently wondered privately if I have gone a bit overboard with the length or details of my posts. On the other hand, I have been especially pleased by the international mix of input. I think it's fantastic that I and we can benefit from the vast experience of our brothers [? any sisters] down under.

I believe in karma - what goes around comes around. John

 

[gait]

from first principles (not experience of wastegates)

I think the control relies on pushing the wastegate to a fixed position to achieve the set point boost. Which means its a very limited control scheme. Probably why in more advanced vehicles wastegate control may be from the ECU.

The actuator normally is driven by the absolute boost pressure. Introducing the orifice to atmosphere introduces an element of relative pressure which may need adjustment at sea level or mountains.

Introducing the first orifice to limit overall flow will damp the response a bit. Probably will be hidden by the even slower response of turbo speed. The slow turbo speed response is important as it probably limits the movements the actuator has to make to maintain control.

Apart from that its workable (as suggested by the commercially available versions).

 

[JRhetts]

…My conclusion was that I wouldn't buy an FM given the lower hp/torq #'s per pound. I am happy with my FG but it is right on the edge. I've probably only passed a couple of vehicles on the highway in my years of ownership. I almost always drive it with my foot near the floor. What's the top speed on your FM? I top out around 68mph.

kerry

I meant to respond to this part of your 10-23-13 post long since, but I have been sidetracked by all the minutia of trying to diagnose and remedy my turbo issues.

I found the ratios mog put together quite interesting, and they have made me rethink several times the fact that so far that I have no objective measure of an actual shortage of power. While I do have a measurable 4 psi boost pressure shortage, I may not be experiencing an actual power shortage; it may indeed be the case that my subjective impressions are off base, they may be based on too high expectations.

On the other hand, I can respond to your query about overall performance: 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.]

My complaints are not about cruise or top speed; they arise from potential low fuel economy along with poor performance during acceleration and speed maintenance on grades. Setting aside the boost shortage, I have [silently] wondered if my performance complaints arise from the combination of the final gear ratios in my diff's, my 41" tires, and the engine's power curve?

John

 

[kerry]

That's a higher top speed than my FG. My guess is that the higher top speed would result in slower acceleration overall. The dynamometer results should be interesting. The psychological solution may simply be to find the couple touring the US in an MB 911 whom I met in Chaco last spring. Driving their truck for a few days would change the FM into a speedster.

 

[JRhetts]

...The psychological solution may simply be to find the couple touring the US in an MB 911 whom I met in Chaco last spring. Driving their truck for a few days would change the FM into a speedster.

kerry

It may be time for me to reveal that I am a :Wow1: psychologist (retired). Given that, it would not be surprising that the solution to my 'problem' will have to be "psychological." I certainly cannot rule out my needing an attitude adjustment more than a turbo waste gate adjustment. :exclaim:

 

[kerry]

Well, I'm a retired (almost) philosopher. So, with us two thinking about the problem it may guarantee it will never be resolved.

 

[JRhetts]

...I think the control relies on pushing the wastegate to a fixed position to achieve the set point boost. Which means its a very limited control scheme. Probably why in more advanced vehicles wastegate control may be from the ECU.

gait

If I have doped things out correctly, my actuator does not push the waste gate to a fixed position. It has a range of response proportional to the pressure applied to the diaphragm. Thus the waste gate will be constantly adjusting its opening to the amount of turbo pressure on the actuator diaphragm. But lack of precision and adjustment would certainly be reasons to use a more sophisticated controller from the ECU.

...Introducing the orifice to atmosphere introduces an element of relative pressure which may need adjustment at sea level or mountains.

Indeed, temperature/altitude factors will affect air density and therefore effective boost. I had thought to settle for something that works to full [but without fault codes] effect at sea level at cool temp, and let the turbo compensate as much as it can for higher altitudes and temps. I don't prefer to drive around thinking about whether I can distract myself to adjust things to get another psi or two out of the system and then forget to reset it before I go lower or cooler. [I gave that up when I quit flying.] I am REALLY into simple is better as much as I can [KISS].

John

 

[JRhetts]

Well, I'm a retired (almost) philosopher. So, with us two thinking about the problem it may guarantee it will never be resolved.

I nearly pissed my pants laughing. ALL TOO TRUE!!