1HZ to 1HD-T swap on 105

[rngkll]

Hello folks,

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!

 

[Kamran Khan]

Post this question in Diesel /24 volt section of this forum, you will get plenty of advises. In this thread many people are owners petrol version of 100 series land cruiser. Very less people have diesel experience in this section.

 

[rngkll]

Post this question in Diesel /24 volt section of this forum, you will get plenty of advises. In this thread many people are owners petrol version of 100 series land cruiser. Very less people have diesel experience in this section.

Thanks for this recommendation

 

[John Young]

I did the swap on Mister Blue, my 2003 105 and have had no issues.

Regarding diagnostics, both the 1HZ and 1HD-T are 1-wire diesels. Well actually three wires if you count the tach sensor on the back of the diesel pump. There are NO diagnostics related to the engine, which is just the way I like it.

You have not said anything about the condition of the donor or its mileage. You are talking about a 30 year old engine and a 30 year old diesel pump. Have you done the basics? Checked compression? If it were me I would consider pulling the pump and having it overhauled at a place that knows these particular pumps or alternatively buy the fixture that allows you to measure fuel flow and check what you are getting out of the pump. Have you changed the fuel filter canister?

I will say that I love the 1HD-T in the 105. Peppy enough so I don't feel uncomfortable merging into traffic. I'm working on one now.

The 1HD-T has several material improvements over the 1HZ, namely higher pressure pump, bigger diameter fuel lines, bog standard low stress turbo, redesigned head. It is now my favorite engine. The 1HD-FT just got a little too complicated for me and the extra 12 valves don't seem worth the bother.

I'd love to hear more of how thing are going with your transplant.