Cedric, I am truly sorry to hear of your bad luck, but I am equally impressed by
the fact that you're already focused on getting your truck up & going again
Frans has covered pretty much everything you need to know. All I can add is that you should not blame
the turbo for your misfortunes...
Even though diesel engines have nearly
the same optimum stoichiometric ratio (14:6:1 vs. petrol's 14.7:1), their mixture tends to vary all
the time (depending on your revs and right foot!). They also top out leaner than
in a petrol engine because diesel is slow to ignite, so it cannot burn quick enough at its optimal 14.6:1 mix and just produces black smoke. This slow burning gives diesels their lower rev-limit, but because
the diesel burns for so long it also gives them their characteristic torque.
A diesel engine's air intake is not throttled and is therefore a function of engine revs - higher revs sucks
in more air.
In a petrol engine there's a butterfly that restricts air-flow. To speed a diesel's engine up, you add more diesel to
the unrestricted air that's being sucked into
the engine, with a petrol engine you'll remove
the air restriction to allow revs to increase while adding more fuel/air
in the proper mixture.
With a modern multi-point fuel-injected petrol engine you may think that you're only injecting fuel into an air mix, but your engine's ECU is working overtime to ensure that this mix stays close to 14:7:1 so that not does not contaminate your car's catalytic converter. On your 4.2 diesel motor there is no ECU, no throttle body to limit airflow into
the motor, no lambda sensor to monitor for optimal stoichiometry
in the exhaust, no airflow meter to tell
the ECU how much air is going into
the motor so that can adjust its fueling, etc. All we have is a diesel pump that's calibrated to squirt "X" amount of fuel into
the engine when
the position of
the accelerator is "Y" and
the engine revs is "Z".
But... if your pump is not calibrated correctly, you'll add more diesel than can be
burnt and end up with over-fueling. And over-fueling increases combustion temperatures
in diesels.
In a petrol-engined car, a lean mixture will end up burning holes
in your pistons,
in a diesel you'll just go slower.
Upping
the boost on your diesel lowers
the EGT pressures because you're forcing more air into
the mix whilst retaining
the same amount of diesel, effectively causing
the engine to under-fuel again. There's a limit to
the amount of boost you can add, but it's usually decided by how much extra torque your engine & drive-train can handle, and how much extra combustion heat (cause you'll be turning up
the fueling to utilise
the extra air) your engine's cooling system can cope with.
The crunch is: if you over-fuel a non-turbo diesel engine it will self-destruct just as nicely as an over-fueled turbo diesel.
The key is NOT to over-fuel, and that's why we monitor our EGT's. And if you see black smoke under acceleration, reduce your fueling...
PS: Sorry for delivering episode 2 of "War & Peace", but I know you're new to
the wonderful world of diesel!s
PPS:
The 3.0 Patrol diesels have added ECU's, airflow meters, EGR, etc. to
the mix. There's another book to be written about them...
..)so I had to use my cell phone cam which is not as good as hers.
