1HZ to 1HD-T swap on 105

[rngkll]

I recently acquired a 1999 HZJ105 that now has a 1HD‑T engine taken from an 80‑series truck. The previous owner owned both vehicles and performed the swap.

I have a few questions:

1. Is this a true 1‑to‑1 replacement?
   • Are there any mounting, wiring, or ECU differences I need to be aware of?
2. What specific checks should I run after the swap?
   • Any particular bolts, hoses, or sensor alignments that are commonly missed?
3. Diagnostics:
   • Should I be able to use the diagnostic port with an adapter from toyota 22 pin to OBD-II 16 pin?
   • What baseline tests should I perform to verify the swap is sound?
4. Idle‑speed problem:
   • The engine idles at ~650 rpm when cold, but after about an hour of driving the idle drops to ~500 rpm.
   • I’ve tried adjusting the idle speed using the procedures from the Toyota service manual (see HOME | LC100 Factory Service Manual - https://lc100e.github.io/).
   • Any ideas on what could be causing the drop—e.g., idle air control valve, throttle position sensor, vacuum leaks, or ECU mapping?

Any advice, checklists, or diagnostic steps would be greatly appreciated. Thanks in advance!

 

[Eurasiaoverland]

Both the 1HZ and 1HD-T have the same block dimensions, so there should be no changes to the engine mount brackets, or gearbox crossmember etc.

Both engines are mechanically controlled, so I assume any ECU is for an automatic gearbox, not for the engine itself.

Idle air control valve on a diesel? Have you found it? Does it have a TPS? Are you sure it's a 1HD-T?

The 1HD-T injection pump may have a cold start device which increases idle speed when the engine is cold. If you have followed a factory manual to set the idle speed, you should have deactivated the cold-start to set the idle speed.

 

[rngkll]

Both the 1HZ and 1HD-T have the same block dimensions, so there should be no changes to the engine mount brackets, or gearbox crossmember etc.

Both engines are mechanically controlled, so I assume any ECU is for an automatic gearbox, not for the engine itself.

Idle air control valve on a diesel? Have you found it? Does it have a TPS? Are you sure it's a 1HD-T?

The 1HD-T injection pump may have a cold start device which increases idle speed when the engine is cold. If you have followed a factory manual to set the idle speed, you should have deactivated the cold-start to set the idle speed.

Thanks for you answer, I'm new to this so I asked generic questions, maybe some might be wrong, I hope not much misleading.

I'm sure it is an 1HD-T, I have tested the Vacuums Switching valve and it is working as expected from the functional point of view, but I'm reading 36ohms between terminal, not the 143.5 ohms as explained here: https://lc100e.github.io/pdf/rm/rm616e/m_ac_0174.pdf, not sure if this is a big problem.

for adjusting the IDLE speed, it says, "(a) Engine at normal operating temperature" I drove it for around 30 min, according to the dashboard it reached temperature. then I did the following steps.

How long it takes the driving in a city to get reach "normal operating temperature"?

Thanks to your message I'm researching on the ACSD

https://lc100e.github.io/pdf/rm/rm617e/m_fu_0070.pdf

 

[John Young]

I did the same swap on Mister Blue, my daily driver here in Dubai, and near as I can remember it was just a drop in. Discussion of the swap starts on post #77. Re diagnostics, there are none given that my truck is a manual transmission. I'm now deep into the rebuild of a really rough 1HD-T and I have to replace the pump, but I decided to experiment with a Chinese replacement pump.

Re your pump, if your engine came from an auto or standard transmission, it will make a difference. Make note of the part number on the pump and then do a search on the usual suspects (Amayama seems easiest) and with some hunting around it will tell you whether it came from an automatic or a manual.

This is the pump that came off the late 1991 1HD-T I am rebuilding:

How different the two types of pump are, I can't tell you. I can say they are different part numbers. When I did some research I found that although my engine came with a manual transmission the pump was from an automatic transmission vehicle and HDJ81, specifically.

And similarly on my manual 80 I have a 1HD-FT that came from a donor truck with an automatic transmission. Low end torque is kinda crappy, but that kinda makes sense because automatic transmission have a torque multiplying effect at low RPMs so the pump would be set to produce less torque at low RPM. Again, not sure how real any of this is, but it was annoying enough to me that I ended up buying a new Chinese 1HD-FT pump corresponding to the part number for a manual transmission pump just to see if it materially improves things. Worse comes to worse I have a spare pump on hand.

These are 30 year old engines at this point. God only knows what they've gone through in that period, especially a few years ago when the were just another old vehicle. The good news is that the 1HD-FT is a really nice engine and IMHO worth putting effort into.

 

[Eurasiaoverland]

The differences on an injection pump between manual and auto transmission applications are mostly external in my experience, as the auto version needs to accomodate a kick-down cable. So the governor/accelerator crank on the pump is different, as is the AC idle-up bracket and parts of the ACSD. Internally, I've only ever seen a difference in the governor link spring, with a two-piece spring on the autos, possibly to dampen rapid accelerator input to get a slushbox to down-shift.

 

[John Young]

The differences on an injection pump between manual and auto transmission applications are mostly external in my experience, as the auto version needs to accomodate a kick-down cable. So the governor/accelerator crank on the pump is different, as is the AC idle-up bracket and parts of the ACSD. Internally, I've only ever seen a difference in the governor link spring, with a two-piece spring on the autos, possibly to dampen rapid accelerator input to get a slushbox to down-shift.

Thank you EAO, I defer to your greater knowledge. I'm just beginning to learn about these Toyota diesels. From my reading I had understood that low-RPM fuel flow was lower on the auto-tranny pumps.

I am planning on installing the manual part number pump from China on the 1HD-FT and see if I can tell the difference.

 

[Eurasiaoverland]

Thank you EAO, I defer to your greater knowledge. I'm just beginning to learn about these Toyota diesels. From my reading I had understood that low-RPM fuel flow was lower on the auto-tranny pumps.

I am planning on installing the manual part number pump from China on the 1HD-FT and see if I can tell the difference.

I'm no authority but have recently exorcised any ATM-specific parts from my 15B-T injection pump. However, I'm only familiar with the four-cylinder diesels. That led me just now to compare MTM and ATM injection pump part lists side by side for a JDM 1995 1HD-T and indeed there is a different governor sleeve in each version, though the length (which I believe is the key characteristic of the sleeve) is the same. So I'm not really sure how much, if any difference this would make to the fuel map.

I think if you notice any difference between a Made in China and a proper ND pump, the difference will not be anything to do with MTM/ATM application, but rather a difference in setup, component quality, dimension etc.

Also, if you are comparing a 1HD-FT to a 1HD-T I would expect the 2 valve engine to have more low-down torque compared to the 4-valve version.

 

[John Young]

I'm no authority but have recently exorcised any ATM-specific parts from my 15B-T injection pump. However, I'm only familiar with the four-cylinder diesels. That led me just now to compare MTM and ATM injection pump part lists side by side for a JDM 1995 1HD-T and indeed there is a different governor sleeve in each version, though the length (which I believe is the key characteristic of the sleeve) is the same. So I'm not really sure how much, if any difference this would make to the fuel map.

I think if you notice any difference between a Made in China and a proper ND pump, the difference will not be anything to do with MTM/ATM application, but rather a difference in setup, component quality, dimension etc.

Also, if you are comparing a 1HD-FT to a 1HD-T I would expect the 2 valve engine to have more low-down torque compared to the 4-valve version.

Thank you UOL, you are certainly much more knowledgeable than me, and this was quite interesting.

I actually have two Chinese pumps I will be trying out, one for an FT and the other for a T. In fact today we are trying to wrestle out the pump for the FT. The FT's current pump is probably good--the engine only had less than 200K km on the clock. What happened was that I was shopping for replacement pump for the 1HD-T and decided to go ahead and also get one for the FT because the price point just a little too attractive, and I had been very impressed by the Chinese CT26 turbo quality that recently arrived. I also figured that these are 30 year old mechanical designs and at least here in Dubai everyone tells me that when they get a pump rebuilt Chinese internals are what typically is used. But I have really no idea and I thought it would be an interesting exercise. Hope to be able to share what happens in the next few days.

if you are interested, here are some photos of the OEM CT26 next to the Chinese replacement.

 

[AussieHJCruza]

The 1HD-FT is generally a dog down low due to lack of fuel off boost for emissions reasons. Play with the star wheel on the boost compensator and easily can make them much snappier.