1HD-T variants: what are the differences between older and newer versions? (1 Viewer)

Aug 5, 2014
Orange, CA
In the next couple of months, i'll be swapping in a later model year 1HD-T to replace my older 1991 1HD-T. I know there are some differences between the two, but im really struggling with determining if I should replace certain parts I had initially planned to swap over from the original engine.

1. Injectors
I know the part numbers are different, though 90% of the injector components are identical. I believe only the top capsule and the two small copper washers at the top are different. Of course, the seats are also different. Are there any actual, noticeable, and worthwhile changes between a pre-92 set of injectors and a post-92 set? Is the spray pattern unique to accommodate the updated piston design on post-92 engines?

2. Injection Pump
The pre-92 pumps and post-92 pumps are also different part numbers (with different color ID plates), but it's not clear what the actual difference is. Can a pre-92 pump work efficiently and appropriately with a post-92 block / pistons? I know timing is different on the newer 1HD-Ts... Can you rebuild a pre-92 pump to post-92 spec?

3. General Engine Changes
There appears to be a number of 1HD-T variants over the years. Some appear to be as new as 1998 - 2004. Is there any documentation on the changes? Aside from the piston update and some small differences in the injection system post-92, what else was changed?

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