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M35A2 military conversion to diesel only?

Mrmag1

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I have a 1971 M35 that was last overhauled by the Army in 89 (the work order was for seatbelt upgrades looks like). A few retired Army maintenance friends of mine seem to think that there was a point where alot of the A2s where converted to diesel only (not the full A3 conversion). Now if this did happen how would one tell? I would love it if my truck was a true multifuel not just a straight diesel. Anyone aware of this happening???
 
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Scar59

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Post up a picture of the engine data plate, located on the right side of the engine block. Bypassing the fuel density compensator (FDC) would lend the engine to diesel only. Other than that, your truck should be equiped with a multi-fuel engine.
 
Fatalid

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Scar59 said:
Post up a picture of the engine data plate, located on the right side of the engine block. Bypassing the fuel density compensator (FDC) would lend the engine to diesel only. Other than that, your truck should be equiped with a multi-fuel engine.
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Wait... From my understanding, as long as it still has the LDT engine, then even if the FDC was bypassed, it is still a multifuel engine. Having the FDC bypassed simply removes it's automatic adjustment of fuel, so you will notice a power difference between diesel and gasoline, etc.

Am I wrong? I don't want bad information floating around, and I want to make sure my understanding is correct...
 
Mrmag1

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From what I can find is that if it was converted it will have the FDC bypassed and diesel only stenciled everywhere. There is not one single stencil of that, however it was a fire truck before I got it and it was all red before I made it green.
 
E

eric67camino

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My 5 ton has the multifuel and it has a big yellow sticker on one of the fuel filters stating something about "diesel only, fdc has been bypassed". Some brakleen took some of the wording off so you can't read it, or I would have gotten you a picture.
 
Scar59

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eric67camino said:
My 5 ton has the multifuel and it has a big yellow sticker on one of the fuel filters stating something about "diesel only, fdc has been bypassed". Some brakleen took some of the wording off so you can't read it, or I would have gotten you a picture.
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Yes, if the FDC has been bypassed, diesel only is the recommendation. It will run on other fuels, however it may lead to detrimental consequences. Remember, this engine was designed to operate reliably under combat conditions, hopefully you are not being shot at. Run diesel.
 
Mrmag1

Mrmag1

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I don't want it to be multifuel for the purpose of throwing anything in it any time I want, I want it multifuel so if I need it I can. A good adage to live by is "that it's better to have and not need than need and not have".
 
Scar59

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Mrmag1 said:
I don't want it to be multifuel for the purpose of throwing anything in it any time I want, I want it multifuel so if I need it I can. A good adage to live by is "that it's better to have and not need than need and not have".
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Yep, I live by that adage. Do a little research on your vehicle. You may what to ensure the FDC is operational. My trucks are all stock and nothing is bypassed, turned up, or modified. Keep them stock, they'll last forever.
 
Mrmag1

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Scar59 said:
Yep, I live by that adage. Do a little research on your vehicle. You may what to ensure the FDC is operational. My trucks are all stock and nothing is bypassed, turned up, or modified. Keep them stock, they'll last forever.
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That's the plan, I'm upgrading filters and other things around the truck but the engine is staying as is for the most part. I want it to out last me.
 
searls84

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Scar59 said:
Yes, if the FDC has been bypassed, diesel only is the recommendation. It will run on other fuels, however it may lead to detrimental consequences. Remember, this engine was designed to operate reliably under combat conditions, hopefully you are not being shot at. Run diesel.
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Detrimental consequences, no. The FDC only regulates the fuel delivery based on the viscosity of the fuel. The LDT/LDS multifuels will burn and run on most anything because of two main features; the hypercycle design and high compression ratio ( there are more than two, but these are the most notable.) The purpose of the FDC is to keep the engine power output the same across a variety and quality of fuels.

When there are markings that say “diesel fuel only” means that the FDC has been bypassed and that the preferred fuel is diesel because the engine performs as close to output spec as originally designed with that fuel. If you run another fuel type, gas, WMO, or mixtures etc. there wil be power differences between the different fuels. The FDC compensates to keep the motor at the same power output regardless of the fuel being used.
 
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rustystud

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searls84 said:
Detrimental consequences, no. The FDC only regulates the fuel delivery based on the viscosity of the fuel. The LDT/LDS multifuels will burn and run on most anything because of two main features; the hypercycle design and high compression ratio ( there are more than two, but these are the most notable.) The purpose of the FDC is to keep the engine power output the same across a variety and quality of fuels.

When there are markings that say “diesel fuel only” means that the FDC has been bypassed and that the preferred fuel is diesel because the engine performs as close to output spec as originally designed with that fuel. If you run another fuel type, gas, WMO, or mixtures etc. there wil be power differences between the different fuels. The FDC compensates to keep the motor at the same power output regardless of the fuel being used.
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That is correct. You can compensate for the differences in fuel by using your right lower appendage (ie: your foot) .
The reason the FDC was installed was to keep the same "feel" or power curve to the engine so any driver could just jump in and go. That way no damage would be done to the engine due to over heating. Whenever you disconnect the FDC you need to install a "Pyrometer" to keep tabs on the exhaust temperature. You will feel a power increase using straight diesel once the FDC is disconnected that is why the Pyrometer needs installing first. Either that or you need to "detune" the injection pumps power output.
Basically the FDC just sets all the major four fuel types to the highest "common" denominator. That means diesel fuel must be lowered to match gasoline and kerosene and JP fuel.
 
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Floridianson

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Just a reminder the sticker diesel fuel only FDC bypassed does not mean a thing. I have seen a truck with the sticker and the FDC was not bypassed. You have to know what you are looking for to see if FDC is bypassed. If the fuel line coming off the final fuel filter goes to the FDC it is not bypassed. If it goes from the final fuel filter to the Head unit on the IP it is bypassed. If you can take a picture of the IP if you have trouble deciding if it is bypassed. Also you need to bypass the FDC if it is not and install a Pyro so you can get the most out of you motor without going to high on the exhaust temps. The FDC can leak fuel into the crankcase so we that know the problem bypass it and not hard to do.
 

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Keith_J

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The FDC decreases fuel based on increasing viscosity as energy content per volume increases with viscosity. A gallon of gasoline has fewer BTU than diesel.

The AMBAC injection pump is a volume injection device, diesel has more energy per injection stroke than gasoline.

You can still run gasoline, it will only produce less power.
 
Floridianson

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Nope not bypassed. You might get lucky and the line from the final fuel filter might be long enough to reach the Head unit. Then it is just a inverted flair plug and two NPT plugs.
 
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Floridianson

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Then you better keep a eye on you dip stick and if you see it gaining level then you are getting fuel into the crank case.
It really is a simple thing to do and adding a pyro is not that hard. The performance will surprise you.
 
searls84

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Mrmag1 said:
I don't know if I want to bypass it honestly.
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Bypass it. You’ll save your self a headache and maybe a wallet-ache down the rd. It’s easy to do and you’ll n ever know the difference.... unless you’re filling up straight from an oil well on the Permian basin.
 
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