1KZ-TE heat specific power loss - KZJ78 95 Prado JDM

[LostLTinJP]

Hello IH8Mud,

I’m in Denver, CO running a 1995 KZJ78 JDM import. I’ve owned this Prado for 5 years and it’s been a great rig, but I make regular trips up mountain passes here in Colorado and lately it’s been struggling. Diesel expertise in the US is basically nonexistent for this platform so figured IH8MUD is my best resource. Hope someone can help me nail down a frustrating diagnostic. Please see below, thanks in advance!

Engine: 1KZ-TE Vehicle: 1995 KZJ78 Land Cruiser Prado JDM import Mileage: 310,000 km

Symptom: Heat specific power loss and sluggish RPM build, particularly from a standstill. Fine when cold, deteriorates after 5-10 minutes of driving in heat. Black smoke under load on hill climbs. Intermittent — sometimes power comes back.

What’s been done recently:

• Full head and head gasket replacement last year
• Timing belt replaced 10,000 km ago — confirmed tight
• AC and alternator belts just replaced — no improvement
• Motor mounts replaced
• ECU reset — minor improvement initially
• Fuel filter replaced a few months ago
• Diesel shop previously richened fuel baseline adjustment

What’s been ruled out:

• Head gasket
• Timing belt
• Belts
• Cooling system — temps normalize but sluggishness remains

Leading suspects:

• Spill control valve 096600-0033
• Weak original turbo never replaced
• Fuel baseline adjustment off from previous shop work

Any help appreciated — hard to find 1KZ-TE expertise in the US.

 

[AVL KZJ78]

Hello IH8Mud,

I’m in Denver, CO running a 1995 KZJ78 JDM import. I’ve owned this Prado for 5 years and it’s been a great rig, but I make regular trips up mountain passes here in Colorado and lately it’s been struggling. Diesel expertise in the US is basically nonexistent for this platform so figured IH8MUD is my best resource. Hope someone can help me nail down a frustrating diagnostic. Please see below, thanks in advance!

Engine: 1KZ-TE Vehicle: 1995 KZJ78 Land Cruiser Prado JDM import Mileage: 310,000 km

Symptom: Heat specific power loss and sluggish RPM build, particularly from a standstill. Fine when cold, deteriorates after 5-10 minutes of driving in heat. Black smoke under load on hill climbs. Intermittent — sometimes power comes back.

What’s been done recently:

• Full head and head gasket replacement last year
• Timing belt replaced 10,000 km ago — confirmed tight
• AC and alternator belts just replaced — no improvement
• Motor mounts replaced
• ECU reset — minor improvement initially
• Fuel filter replaced a few months ago
• Diesel shop previously richened fuel baseline adjustment

What’s been ruled out:

• Head gasket
• Timing belt
• Belts
• Cooling system — temps normalize but sluggishness remains

Leading suspects:

• Spill control valve 096600-0033
• Weak original turbo never replaced
• Fuel baseline adjustment off from previous shop work

Any help appreciated — hard to find 1KZ-TE expertise in the US.

The intermittent nature of your symptoms suggest electronics to me. Spill control valve sounds like something to check. You might consider opening up the ECU and carefully examining the board for evidence of leaking capacitors and damaged traces. Mine were fine on my 1996, but I replaced them as a preventative measure. User Tigris here has a good tutorial.

Also, I personally would be wary of turning up the fuel on the stock 1KZTE. I could easily get EGTs of 1400+ under prolonged acceleration, and I personally think that these motors are fueled pretty aggressively in stock form. I added a FMIC, increased boost to 16psi with a manual controller and a bleed valve on the manifold pressure sensor (to lean out on boost mixture and prevent the 1 bar fuel cut) with the intent to lower EGT and thereby prolong head life. I have not really noticed the potential decreased power with my driving style, and full throttle EGT are around 1000.