Our engine is running rough we have a 1999 Isuzu wizard 4jx1 - we think we have an injector problem - how can I check this fault - I need to establish if it needs a replacement injector or is it an electronic problem. cheers

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Diesel misfiring...
4jx1 in what country?
fueling issues are complex.
and varies by type of injection system used.
that varies by countries laws. (smog)
Injection pumps, or EFI injection. no common rail then so..
the injection types can vary by country. ....and if turbo....


remove them and take them to a pro injector cleaning shop.
they use ultrasonic cleaner and they will tell you if one is non serviceable (flow rate ,pattern or dead coil)
no location stated so who'd we ever guess that and point out good places to go... are you in Canada?

are you sure its a 4jx1? (below is wiki, quote)
The 4JX1 is a 3.0L direct injection diesel engine, turbo, some intercooled,

and
European and Asian buyers could opt for the diesel engine option of the 4JG2 3.1 L (later superseded by the more problematic 4JX1 3.0 L of 159 PS or 117 kW).

so , welcome to the WWW, the world wide web
where are you, in Asia?

Buy a can of throttle body cleaner take off the air filter box, follow the tube and then spray the throttle body and wipe it out first before condemning the injectors