96 HDJ81 HDFT car runs smooth when cold shutters between 1800 and 2000 rpm when warm.

[80SeriesNomads]

Hey guys, I hope you can bring a bit of light into the darkness.

I've got a 1996 HDJ81 HD-FT automatic, and it drives super smoothly when cold. But as soon as it warms up, it "shudders" between 1800 and 2000 rpm, as well as when shifting to second and first to use the engine brake.

All fluids have been flushed and changed, and it's been fully serviced. It doesn't happen if I shift to neutral and rev the engine; it only happens under load. Both driveshafts are firm, no play.

It's constant when going uphill and holding it between the said rpm.

Anyone have an idea?

 

[SciroccoDamonte]

Hey guys, I hope you can bring a bit of light into the darkness.

I've got a 1996 HDJ81 HD-FT automatic, and it drives super smoothly when cold. But as soon as it warms up, it "shudders" between 1800 and 2000 rpm, as well as when shifting to second and first to use the engine brake.

All fluids have been flushed and changed, and it's been fully serviced. It doesn't happen if I shift to neutral and rev the engine; it only happens under load.

It's constant when going uphill and holding it between the said rpm.

Anyone have an idea?

Try grabbing the rear and front drive shaft and wiggling them up and down, left and right. It only occurring when the engine is under load makes it seem likely its driveline.

 

[80SeriesNomads]

Try grabbing the rear and front drive shaft and wiggling them up and down, left and right. It only occurring when the engine is under load makes it seem likely its driveline.

Thanks, mate. Sorry, I forgot to mention that I tried to wiggle the driveshafts. They're firm, no play at all. And if one of the driveshafts were the culprit, why doesn't it happen when the car is cold and only starts after a few kilometers?

 

[SciroccoDamonte]

Thanks, mate. Sorry, I forgot to mention that I tried to wiggle the driveshafts. They're firm, no play at all. And if one of the driveshafts were the culprit, why doesn't it happen when the car is cold and only starts after a few kilometers?

True. My only other idea would be that if its an lsd in the rear, the clutches have warn out. Which would track for temps and even rpm.

 

[Squash]

You can have a sticky caliper.
If your brake pedal is stiff when shuddering, and/or you feel shakes on the brake pedal.
Of course this assumes that everything else is in order.
Check your drive shafts with tires in the air, great time to also test wheel bearing preload by manhandling the tires while feeling for play.
My 95Hdj80 with a 5speed does this once in a blue moon, and I suspect that I will have to adjust the master cylinder.

 

[mudgudgeon]

Have you done any recent maintenance?

Does it feel like there's a loss of power?
Any white smoke out the tail pipe?

It's really common for the diesels to have air getting into the fuel lines through a loose hose connection or a cracked hose.

Old hard rubber hoses don't like to be disconnected and reconnected. They don't squish back down tight on hose barbs.
Swapping to acworm drive clamp is common, but IMO is a bandaid and can deform the hose and make the issue worse.
Air can be getting sucked in with no visible fuel leaks.

Its really simple to test for this.

 

[80SeriesNomads]

You can have a sticky caliper.
If your brake pedal is stiff when shuddering, and/or you feel shakes on the brake pedal.
Of course this assumes that everything else is in order.
Check your drive shafts with tires in the air, great time to also test wheel bearing preload by manhandling the tires while feeling for play.
My 95Hdj80 with a 5speed does this once in a blue moon, and I suspect that I will have to adjust the master cylinder.

Thanks Squash, I'll give this a go

 

[80SeriesNomads]

Have you done any recent maintenance?

Does it feel like there's a loss of power?
Any white smoke out the tail pipe?

It's really common for the diesels to have air getting into the fuel lines through a loose hose connection or a cracked hose.

Old hard rubber hoses don't like to be disconnected and reconnected. They don't squish back down tight on hose barbs.
Swapping to acworm drive clamp is common, but IMO is a bandaid and can deform the hose and make the issue worse.
Air can be getting sucked in with no visible fuel leaks.

Its really simple to test for this.

Cheers mate,
The car gets regularly maintained.

It's hard to say if it feels like a loss of power. I know it sounds weird, but it actually runs alright, though at the same time it feels like it's not getting enough fuel. But then, as soon as I hit 2000 revs, it runs super smooth without any issues.

The problem is more noticeable when starting from a complete stop or when downshifting to use the engine brake.

How would you test for air being sucked in? Would you replace the entire fuel line?

 

[Squash]

Swap out the hose from the fuel filter to injection pump with a clear fuel line.
Clear hose should be free of air bubbles indicating good vaccum.
A steady stream of air bubbles indicates a poor connection or hose.
Other than that your turbo really doesn't kick in until higher rpms.
Do you have a boost gauge and egt?

 

[mudgudgeon]

Sounds odd. The downshifting for engine braking thing has thrown me

If it feels like its starving for fuel, definitely do the clear hose test as @Squash said.

$10 piece of hose from the hardware, and 10 minutes to swap one bit of hose, you'll either know you have air in the fuel, or you can tick that off the list.

I literaly did this in the hardware parking lot on my way home from work.

Search in the diesel tech section for more details.

Boost gauge could be relevant too. You should be seeing decent boost by 1800rpm.

Do you have the stock turbo? Or an upgrade?

 

[80SeriesNomads]

Swap out the hose from the fuel filter to injection pump with a clear fuel line.
Clear hose should be free of air bubbles indicating good vaccum.
A steady stream of air bubbles indicates a poor connection or hose.
Other than that your turbo really doesn't kick in until higher rpms.
Do you have a boost gauge and egt?

Ok, great, will give this ago as well in about two weeks time when I'm back home. Yeah, turbo kicks in around 2100 revs

 

[80SeriesNomads]

Sounds odd. The downshifting for engine braking thing has thrown me

If it feels like its starving for fuel, definitely do the clear hose test as @Squash said.

$10 piece of hose from the hardware, and 10 minutes to swap one bit of hose, you'll either know you have air in the fuel, or you can tick that off the list.

I literaly did this in the hardware parking lot on my way home from work.

Search in the diesel tech section for more details.

Boost gauge could be relevant too. You should be seeing decent boost by 1800rpm.

Do you have the stock turbo? Or an upgrade?

Nope, everything standard and turbo kicks in around 2100rpm. Is it supposed to start by 1800rpm?

 

[mudgudgeon]

Nope, everything standard and turbo kicks in around 2100rpm. Is it supposed to start by 1800rpm?

Do you have a boost gauge?

1hd-ft makes peak torque at around 1800rpm. The turbo should be starting to work well before 1800rpm.
You should be seeing around 9-10psi boost and climbing by 1800rpm with stock turbo if you are accelerating.
Boost will drop off if you are coasting. But should stay up if the engine is still under load.

 

[mudgudgeon]

Is yours definitely a HDJ81?

HDJ81 is the Japanese market designation, so in Australia they are grey market used imports from Japan, and rare. Australian government shut down the importation of v them in about 2004.

 

[80SeriesNomads]

Do you have a boost gauge?

1hd-ft makes peak torque at around 1800rpm. The turbo should be starting to work well before 1800rpm.
You should be seeing around 9-10psi boost and climbing by 1800rpm with stock turbo if you are accelerating.
Boost will drop off if you are coasting. But should stay up if the engine is still under load.

Are you serious? The car picks up around 1200rpm but I can definitely feel a boost at 2100rpm. Maybe I should get this checked.

 

[80SeriesNomads]

Is yours definitely a HDJ81?

HDJ81 is the Japanese market designation, so in Australia they are grey market used imports from Japan, and rare. Australian government shut down the importation of v them in about 2004.

Yep, imported it last year in November.

 

[mudgudgeon]

Are you serious? The car picks up around 1200rpm but I can definitely feel a boost at 2100rpm. Maybe I should get this checked.

Yeah, I don't remember exact numbers.

You may just be underfueled. It could explain what you're feeling from 1800 -2000rpm, but it doesn't explain what you experience when down shifting.

Tuning from the factory varied a lot.
Lots of these cruisers were very conservatively tuned, and some minor tuning can make a big difference in power delivery.

I know there's a couple of diesel specialist shops around Brisbane/ Sunshine Coast that used to get mentioned in forums regularly. (Can't think of any names right now). Might be worth getting it looked at.

@AussieHJCruza got any thoughts?

 

[AussieHJCruza]

Yeah, I don't remember exact numbers.

You may just be underfueled. It could explain what you're feeling from 1800 -2000rpm, but it doesn't explain what you experience when down shifting.

Tuning from the factory varied a lot.
Lots of these cruisers were very conservatively tuned, and some minor tuning can make a big difference in power delivery.

I know there's a couple of diesel specialist shops around Brisbane/ Sunshine Coast that used to get mentioned in forums regularly. (Can't think of any names right now). Might be worth getting it looked at.

@AussieHJCruza got any thoughts?

Thanks @mudgudgeon
1) Sorry, I haven't read the whole thread so my apologies if I've missed something, or stating the obvious here. How long ago were the fuel filter and air filter replaced? Have you checked the transmission cable for adjustment as per the FSM?
2) Have a quick check and make sure the vacuum line setup is correct, especially boost compensator etc.
3) First mod you should do after basic maintenance is a 3" exhaust from turbo back; don't keep the factory dump pipe to save a few $$$. It doesn't have to be loud but will get you positive manifold pressure at least 200 rpm sooner.
4) JDM 1HD-FT would have EGR IIRC, would suggest you move this on - Aussie trucks didn't have it. While you're doing this, put a Pyrometer/EGT gauge in the block off plate you install on the exhaust manifold, pre turbo, and same deal with a boost gauge in the intake crossover block-off plate.
5) JDM (and other emissions restricted markets) trucks often have a very conservative setup on the boost compensator, you can make it a lot more snappy with some adjustments here. GTurbo have a good tuning guide for mechanical diesels, but you'll need boost/egt before you do anything here.
6) I've never used them, but heard good reports of HD Automotive in Rocklea, they're a GTurbo + UFI + PDI dealer as well for when you decide to make serious power!
Hopefully this is somewhat relevant...
EDIT: what brand fuel filter if it's recently changed? Have had fuel starvation issues with some aftermarket filters occasionally.

 

[80SeriesNomads]

Yeah, I don't remember exact numbers.

You may just be underfueled. It could explain what you're feeling from 1800 -2000rpm, but it doesn't explain what you experience when down shifting.

Tuning from the factory varied a lot.
Lots of these cruisers were very conservatively tuned, and some minor tuning can make a big difference in power delivery.

I know there's a couple of diesel specialist shops around Brisbane/ Sunshine Coast that used to get mentioned in forums regularly. (Can't think of any names right now). Might be worth getting it looked at.

@AussieHJCruza got any thoughts?

Sry, been away.

Entire car was imported stock standard. It even came with the factory bed/kitchen .

I'll bring it to Cornell Diesel Systems North Brissi and see what they say. Thanks Mate, really appreciated your help

 

[80SeriesNomads]

Thanks @mudgudgeon
1) Sorry, I haven't read the whole thread so my apologies if I've missed something, or stating the obvious here. How long ago were the fuel filter and air filter replaced? Have you checked the transmission cable for adjustment as per the FSM?
2) Have a quick check and make sure the vacuum line setup is correct, especially boost compensator etc.
3) First mod you should do after basic maintenance is a 3" exhaust from turbo back; don't keep the factory dump pipe to save a few $$$. It doesn't have to be loud but will get you positive manifold pressure at least 200 rpm sooner.
4) JDM 1HD-FT would have EGR IIRC, would suggest you move this on - Aussie trucks didn't have it. While you're doing this, put a Pyrometer/EGT gauge in the block off plate you install on the exhaust manifold, pre turbo, and same deal with a boost gauge in the intake crossover block-off plate.
5) JDM (and other emissions restricted markets) trucks often have a very conservative setup on the boost compensator, you can make it a lot more snappy with some adjustments here. GTurbo have a good tuning guide for mechanical diesels, but you'll need boost/egt before you do anything here.
6) I've never used them, but heard good reports of HD Automotive in Rocklea, they're a GTurbo + UFI + PDI dealer as well for when you decide to make serious power!
Hopefully this is somewhat relevant...
EDIT: what brand fuel filter if it's recently changed? Have had fuel starvation issues with some aftermarket filters occasionally.

Hey mate,
Thanks for jumping in.

The entire service, including flushing the oil and transmission, was done about 8000 km ago. I'll check the transmission cable next—thanks for the hint.

I've added that to my list as well.

I'm still running the stock exhaust since it's in near-perfect condition. Do you really think I should get rid of it already?

It doesn't have an EGR.

Cheers, I'll look into that as well.

I don’t want to mess with the engine at all. I just want it to run smoothly. It has enough power for my needs. With the current setup, it weighs 3.3 tonnes and had no problem getting up Big Sandy in Byfield NP. Otherwise, I'm just cruising at 80 km/h on the road anyway.

Thanks for taking the time to write this list, mate—much appreciated!