80 Series Stalling issues

Jun 7, 2018
1994 FZJ80R - 1 FZFE

Hey All,

Recently replaced the head and since then things have gone a bit pear-shaped.

She runs beautifully with a very consistent idle, however, since changing the head over I am getting a Code 25. At the same time, while driving the engine will simply cut out. At high revs it is more like a hiccup, however, at low revs it completely stalls. Often it will start up straight away, however, at other times I need to wait for things to cool down a bit.

Code 25 suggests a bad oxygen sensor, however, as stated earlier the idle is smooth and consistent. Albeit, the code comes up when the engine starts to warm up, and when it comes on it becomes a bit sluggish... no power!

A colleague of mine suggested a bad MAF sensor, which could potentially spit out a code, however, once again, the idle is smooth and consistent so I have my doubts.

Yet another colleague suggested that the fuel pump could be the issue, and although this makes sense with regard to the stalling, it has nothing to do with the code 25.

I have also heard that it could be the ECU, so now I am completely lost with regard to how to go about finding the issue. Changing all of these things will be an expensive process!

Any ideas? Could the MAF sensor be responsible for all of these things?


Nov 9, 2012
Olathe, KS, USA
It's probably a bad O2 sensor or connection.

When these get up to temp they switch to clean loop and the fuel pump speed will change and the injector timing will change.

Fix the code first and properly diagnose it. Don't just start throwing parts and guessing.

Tools R Us

Jul 20, 2004
Chandler, AZ
If it's the same setup that we get, the first thing I would check is the fuel pump relay. Depending on load, it switches from going through the resister (low speed) to direct (high Speed). Have had a couple of them die and do what you are describing.
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