Engine cranks but won’t start after engine swap

[handofthesly]

Hi there Isuzu fam, first time poster here so bare with me!

The vehicle in question is a 1998 Isuzu Mu 3L 4JX1 Diesel automatic, the new body style.

The backstory: a coolant pipe split and the engine overheated causing a cracked head. My partner and I decided that it was cheaper to buy a new secondhand 4JX1 and swap it out. The replacement engine had been pre-tested and was running mint.

The situation now: the new engine was installed and everything seemed to be connected back up properly. We changed out as many of the rubber pipes as possible. Unfortunately the engine will crank but won’t start unless we’ve got a rag of petrol up the air intake. Once it has fired up the first time, afterwards it usually will start up fine once it’s warmed up. We’re thinking a fuel feed issue or dodgy glow plugs but aren’t 100%. What can we do to test either of these theories? The check engine and oil lights on the dash come on as well as the ABS light for some reason.

The other concern is whilst driving, the car lurches at upshifts, the tacho drops in revs briefly. I’m not sure if it is the transmission or if it’s the engine doing something funny. It feels like it briefly loses drive resulting in a sharp but brief deceleration before it returns to normal speed. It seems to get better after a while of driving before mostly disappearing.

Any help would be appreciated so much. I know it’s not a lot to go on and there could be potentially so many things causing an issue electronically. We are scratching our heads and feeling defeated. All of the mechanics we have called don’t want to touch it.

Cheers!
Hannah

[geeves]

First thing that comes to mind is too thick oil but with current summer temps that is unlikely. The sensors might be off but also has the ecu been programmed to the new engines injectors?

[handofthesly]

Thanks for the feedback geeves!
The oil is 5w30 synthetic, if anything it could be almost too thin.
I never thought the ecu would need to be recalibrated for the diesel injectors. I’m guessing this is something a mechanic with the right tools or a specialist engine tuner would need to do?

[geeves]

You need to be able to talk to the computer