The Isuzu is an inline 4-cylinder diesel engine, not a 6-cylinder engine. The "4" in the engine designation explicitly refers to its 4-cylinder configuration. If you are looking for a 6-cylinder Isuzu workshop manual, you may be thinking of the 6HE1 or 6HH1 models.
The Isuzu 4HF1 is part of Isuzu’s ‘H’ series of engines, known for their robustness in medium-duty trucks like the NPR, NQR, and early-model F-series. However, unlike its 4-cylinder cousin (4HG1) or the larger 6HE1, the : a 6.0-liter+ displacement with a compact, Japanese-designed overhead valve (OHV) configuration. isuzu 4hf1 workshop manual 6 cylinder pdf