12h-t Sucks Off-road??

[dogboy2]

Forgive me, I'm a complete diesel newbie (but learning more each day) and in searching this forum for info on the 12H-T, I've come across a few posts that claim this particular diesel motor is awful to drive off-road. Although I waded through 9 pages of threads on this engine, I wasn't able to get a clear understanding of why this may be so.

Would someone be so kind as to help educate me on this issue? I'm seriously considering following Mountain Goat's conversion path with my '87 FJ-60 and despite the 2F's shortcomings, I've been very pleased with it's performance off-road.

Not anxious to spend a bunch of $$$$ on a motor conversion to only trade shortcomings in the end. From everything I've been able to gather, the 12H-T sounds like the ideal diesel to drop into this rig.

Thanks in advance for your input,
-dogboy- '87 FJ60

[roscoFJ73]

The 12HT is a great engine offroad and I dont think anyone who has driven one would disagree.
However,the throttle on manual transmissions makes it very difficult to maintain a steady rate of power as the the bumps cause your foot to bounce which cause the vehicle to lurch forward and make it even harder to keep a steady rate of progress.
I think Greg B has a fix
I havent driven the auto but it is apparently more manageable.

Dont let it turn you off as you can get use to it and if you had a hand throttle fitted that would also negate the problem

[dogboy2]

Originally Posted by roscoFJ73

The 12HT is a great engine offroad and I dont think anyone who has driven one would disagree.
However,the throttle on manual transmissions makes it very difficult to maintain a steady rate of power as the the bumps cause your foot to bounce which cause the vehicle to lurch forward and make it even harder to keep a steady rate of progress.
I think Greg B has a fix
I havent driven the auto but it is apparently more manageable.

Dont let it turn you off as you can get use to it and if you had a hand throttle fitted that would also negate the problem

Thanks Rosco... doesn't sound like the accidental throttle bumping is really any more of an issue than it is with the 2F. Can't tell you how many times I've done this when things get bumpy.

One nice thing about the 2F is that it can crawl along at idle speed (terrain depending) without having to place your foot on the pedal -- is the 12H-T any different?

-dogboy- '87 FJ60

[BlueHZT60]

I've bounced off the roof more times than I'd like to admit. Never a throttle issue. That's 2f and the hz-t plants. I actually think my HZ is incredible offroad. The low end grunt-when wanted, no downhill braking (H55) when in proper gear, no drowning while sitting window deep waiting for help. I'm not too sure a 12ht would be a whole lot different, especially with the low range gears that offer instant action. Heck, I'd have to push it off on driver issues, not power plant issues. Bob

[bigbrowndog]

Originally Posted by roscoFJ73

The 12HT is a great engine offroad and I dont think anyone who has driven one would disagree.
However,the throttle on manual transmissions makes it very difficult to maintain a steady rate of power as the the bumps cause your foot to bounce which cause the vehicle to lurch forward and make it even harder to keep a steady rate of progress.
I think Greg B has a fix
I havent driven the auto but it is apparently more manageable.

Dont let it turn you off as you can get use to it and if you had a hand throttle fitted that would also negate the problem

X2, The 12HT throttle is a lot more touchy than your 2F or a 2H the way it is set up.A lot of it can be corrected , a small draw back for nearly double the fuel economy off road, less maintenance,better reliability and driveability etc.cheers

[roscoFJ73]

Originally Posted by dogboy2

Thanks Rosco... doesn't sound like the accidental throttle bumping is really any more of an issue than it is with the 2F. Can't tell you how many times I've done this when things get bumpy.

One nice thing about the 2F is that it can crawl along at idle speed (terrain depending) without having to place your foot on the pedal -- is the 12H-T any different?

-dogboy- '87 FJ60

I have 2X 1HZs and I also had 3F in the FJ73 and I also had a HJ61 for a short while and believe me there is a big difference in sensitivity with the 12HT
The 12HT can crawl along with the best but when you need to blip the throttle on rough ground it gets more blip than you want

Thats why I was hoping Greg B would come along as I never really got to investigate why.

[cody c]

if the only issue is that the throttle is too touchy, why not extend the throttle arm moving where the throttle cable connects outwards. This would decrease sensitivity although it may stop you from getting full throttle.

Maybe you would have to increase the range of motion for the gas pedal as well.

[roscoFJ73]

Originally Posted by cody c

if the only issue is that the throttle is too touchy, why not extend the throttle arm moving where the throttle cable connects outwards. This would decrease sensitivity although it may stop you from getting full throttle.

Maybe you would have to increase the range of motion for the gas pedal as well.

Maybe but you would have to be careful not to limt the throttle travel.
Another way maybe to try some different springs.

[Greg_B]

Originally Posted by roscoFJ73

Thats why I was hoping Greg B would come along as I never really got to investigate why.

Three potential fixes I've heard about but never investigated myself...

1) There is space on the return linkage at the injection pump for a second spring.

2) Move the pivot point behind the pedal to a higher spot on the pedal.

3) Place a shock behind the fuel pedal ala some high end European cars.

And do not drive with your foot in the air. Support your foot as best you can: (tranny tunnel in LHD, or drivers kickpanel in RHD).

hth's

gb

[dogboy2]

Thanks Greg, that does help.

So with a little re-engineering and some saddle time with the "new" motor, it's sounds as though with a bit of practice this isn't really an issue at all but rather one of driving technique.

-dogboy- '87 FJ60

[dogboy2]

Originally Posted by bigbrowndog

X2, The 12HT....nearly double the fuel economy off road, less maintenance,better reliability and driveability etc.cheers

I like the sounds of all this... a lot

Less maintenance? Better reliability? How does the 12H-T differ in these regards as compared to the 2F?

-dogboy- '87 FJ60

[goldchaser]

dont sweat it dogboy,i found mine a bit touchy when i first got it but after a few weeks you adjust.
cheers goldchaser

[goldchaser]

oh just seen your last post dogboy,i had a 60 series 3f before the 12ht,big difference in power,3f would die on hills,12ht just keeps pulling,i wouldnt compare them too much.
cheers goldchaser

[BURGER]

The hand throttle works great in those lower speed situations. I have the m/t 12 ht combo and they are all right the throttle is touchy at low RPM but if you install a hand throttle all is well.
Allows me to use the clutch and brake without having to switch over to the gas pedal as well.


No BOUNCY BOUNCY

[Garry]

A heavier return spring worked for me Now I can rest my boot on the accelerator no matter what terrain, and keep it constant

[Mountain Goat]

In the short time that I've owned a 12H-T I've found it unstopable off road. The torque well exceeds traction (open diffs).

I have also experienced the throttle issue. I added another spring and it didn't fix the problem, but maybe it wasn't heavy enough.

Love the engine though. I'll never go back.

[Garry]

Yeh, the difference is I don't run a turbo. I can see that running a turbo would be similar to riding a two stroke motocross bike, twitchy

[dogboy2]

Originally Posted by Mountain Goat

In the short time that I've owned a 12H-T I've found it unstopable off road. The torque well exceeds traction (open diffs).

I have also experienced the throttle issue. I added another spring and it didn't fix the problem, but maybe it wasn't heavy enough.

Love the engine though. I'll never go back.

Oh yes, don't I know it, deliverer of my destruction....ruined for life I am, ruined for life.....

Until I find the right deal on a good 12H-T that is!! MUUHAHAHAHAHAHAHAHAHAHA!!!!

-db-

[Mountain Goat]

Yeah, I posted on your thread before I realized who the owner is.

If you want confirmation of off-road performance, we should take it out some time soon.

How's the search going? You mentioned you have a couple of leads.

Good luck, my friend!

[Tapage]

Originally Posted by Greg_B

And do not drive with your foot in the air. Support your foot as best you can: (tranny tunnel in LHD, or drivers kickpanel in RHD).

pretty easy to me .. and I never be in this issue .. in my 2H-T

[Greg_B]

Originally Posted by Tapage

pretty easy to me .. and I never be in this issue .. in my 2H-T

Ya it seems to be one of two things, or a combination of both: one setting the other off.

From the top the 12HT where the throttle cable transitions to hard linkage, there are a lot of linkage points to the final connection spot at the fuel lever.

The DI engines seem to have a lot of snot right from the bottom. There does not seem to be as much turbo lag as with their turbo IDI brethren...power is smooth all the way up.

Put a lot of snot from the get go together with multiple linkages...bouncing/jerky/harmonics have creation potential. I’ve not tried to see if all those linkages can be firmed up.

The 12HT loves to bounce off the bottom governor too, it seems. Adjusting the idle up juuuust a tad can assist if this is part it.

Anyway...as many have said...nothing that can not be learned about and worked with..as the engine is nothing but stellar imo.

hth's

gb

[dogboy2]

Originally Posted by Greg_B

Ya it seems to be one of two things, or a combination of both: one setting the other off.

From the top the 12HT where the throttle cable transitions to hard linkage, there are a lot of linkage points to the final connection spot at the fuel lever.

The DI engines seem to have a lot of snot right from the bottom. There does not seem to be as much turbo lag as with their turbo IDI brethren...power is smooth all the way up.

Put a lot of snot from the get go together with multiple linkages...bouncing/jerky/harmonics have creation potential. I’ve not tried to see if all those linkages can be firmed up.

The 12HT loves to bounce off the bottom governor too, it seems. Adjusting the idle up juuuust a tad can assist if this is part it.

Anyway...as many have said...nothing that can not be learned about and worked with..as the engine is nothing but stellar imo.

hth's

gb

More good info Greg -- thanks! You guys are sealing my fate, I can see it now

-dogboy- '87 FJ60