| BUYERS GUIDE
ISUZU FSS and FTS 4X4 RANGE
Heavy Isuzu 4x4s now come with a choice of engines
The Australian 4WD truck market leader has extended the appeal of its 8-9-tonnes-payload capacity 4x4 truck models with the addition of two new diesel engine variants. A new, powerful four complements a variant of the proved six that's purpose-designed for off-road operation.
Isuzu Trucks Australia gave its market-leading F Series mechanical and cosmetic changes for 2016. The company is targetting a 28th year of market leadership Down Under and the new Fs will certainly help.
“The new Isuzu F Series range represents change on a level we haven’t seen in the medium-duty market for quite some time,” said Phil Taylor, IAL director
and chief operating officer.
The mechanical changes are headed by a new four-cylinder, turbocharged diesel and a significantly revised six-cylinder engine, aimed mainly at vocational
The new 5.2-litre four-cylinder retains the same bore and stroke dimensions as its predecessor, but the 2016 4HK1-TC engine has new cylinder head, camshaft,
block, main-bearing ladder frame, combustion zone components, higher-pressure injection system and injectors, and a two-stage turbocharger.
Two-stage turbocharging improves torque at low engine speeds, to the extent that the 240hp four has more torque than the six formerly used in 12-tonnes-GVM
F Series trucks.
The 4HK1-TC has two output levels: 154kW (210hp) and 726Nm, and 177kW (240hp) and 765Nm.
Increased performance from this engine has allowed Isuzu to increase its application in the F Series, so now the 4HK1-TC powers FSS 4x4, 11-tonnes-GVM
models. The 13.9-tonnes-GVM FTS retains its six, but with significant differences.
Task-specific emissions strategy
On the 4HK1-TC engine cooled exhaust gas recirculation (EGR) and diesel particulate ‘diffusion’ - filtration - (DPD) are used for emissions
control to Japanese ‘post new long term’ (PNLT) standards that are expected to be accepted as part of ADR80/04 (Euro VI) when it’s eventually adopted
Unlike most other engine makers Isuzu is confident it won’t need selective catalytic reduction (SCR) with urea (AdBlue) injection on the 4HK1-TC to meet
Part of this emissions package is a DPD unit with its own ‘regeneration’ injector. This a departure from existing Isuzu practice that sometimes uses post-combustion injection in each engine cylinder to increase exhaust gas temperature, to burn off soot and particulate matter from the DPD.
On-highway trucks normally don’t require post-combustion injection, because exhaust gas temperatures are high enough to clean the DPD continuously, but
slow-running 4WD truck engines sometimes need to be actively regenerated.
Active regeneration requires the driver to park the vehicle and let the engine’s electronic control unit run through a regeneration cycle.
Another issue with post-combustion injection is the possibility that some unburnt fuel can find its way past the piston rings and into the engine sump.
Part of Isuzu’s existing DPD-equipped engine maintenance is regular checking for a rising dipstick oil level.
Although the new 4HK1-TC retains a DPD unit it now has its own regeneration injector, so post-combustion injection is carried out in the DPD, not in the
engine cylinders. Sump oil fuel dilution from DPD regeneration is no longer a possibility, but active regeneration may still be needed in some low-speed
and stop-start truck applications.
Two-stage turbocharging and improved DPD should make the new 4HK1-TC a very popular engine, but there are some 4WD applications where even this combination won’t be optimum.
Isuzu is hoping that a revised version of the proved six-cylinder diesel 6HK1 will be the answer for these vocations and this is the new
powerplant for the FTS. This development uses new injectors and combustion zone components, has no DPD and, hence, no need for DPD regeneration.
The 6HK1-TCC 191kW (260hp)/761Nm Euro V engine meets current emissions regulations by using cooled EGR in conjunction with a diesel oxidation catalyst
(DOC). It is the only medium-duty diesel engine in the market not to have DPD or SCR, but as Isuzu points out, it’s not a Euro VI engine like the 4HK1-TC.
Transmisson offerings remain similar: six-speed manual with two-speed transfer box (2.09:1 reduction) in the FSS and either a six-speed manual or Allison LCT2500 automatic - now a six-speed - combined with a two-speed transfer box (1.91:1 reduction) in the FTS.
Other changes in a nutshell
The 4HK1-TC-powered FSS has a ‘start assist’ function, to allow easier, faster clutch engagement.
A revised multi-information display, with a larger screen and incorporating satellite navigation, is now standard across the entire F Series range. Off-road models get the big screen but not navigation, which seems odd for vehicles that are likely to get lost!
Given that daily checks aren’t always done daily, the addition of a low-coolant-level sensor to all models is timely.
A fuel-line cooler has been introduced with the new 4HK1-TC and 6HK1 DOC engines.
An upgraded anti-lock braking system (ABS) module and ABS 8 software is now fitted to FSS and FTS models.
The rear seats in crew-cab models have been given additional padding in the seat bases and realignment of the back rests, for greater support.
A much-needed passenger ISRI 6860 air suspension seat is standard in the FTS 4x4 single and crew cab models.
A 90-amp alternator has been fitted to all new F Series models.
There’s an extension of oil change intervals from 15,000 km to 20,000 km for those models powered by the new 4HK1-TC or 6HKI DOC engines. The entire F
Series range now has 20,000 km service intervals.
Previous models - FTS800 Auto
Isuzu’s 4x4 F-Series is the preferred
vehicle of choice by many rural fire authorities and is also popular with councils and those who have to work off the beaten track.
The original FTS 800 had conventional leaf springs and a part-time 4WD system and so wasn’t driver and crew friendly, but progressive upgrades saw the
2012 model with taper-leaf front springs and full-time 4WD. Ride quality was still firm, but not as jarring as before and driveability was eased by
a full-time 4x4 system.
Other improvements to the FTS 800 included driver airbag and seatbelt pre-tensioner, an ISRI 6860 driver’s seat and cruise control.
Like the manual-transmission model the FTS 800 Auto was available with a short-sleeper cab or a crew cab. The automatic transmission was an Allison LCT 2500, five-ratio box that linked electronically to a proved Isuzu 7.8-litre turbo-diesel, with outputs of 176kW (235hp) and 706Nm.
The standard manual transmission was an Isuzu six-speed manual (five ratios synchronised) with a tall overdrive top gear (0.72:1) and a constant-mesh first
gear with 6.6:1 gearing. The manual-box FTS 800 had excellent crawl capability, thanks to a low-range reduction of 1.9:1 and final drive ratios of
5.57:1. Overall crawl gearing was 70:1, allowing walking pace progress up and down steep grades.
To show off its automatic-transmission 4WD truck Isuzu put on a drive day at Victoria’s Australian Automotive Research Centre, near Anglesea in Victoria. The weather was drizzly rain that turned clay slopes into skating rinks.
The test truck was a single-cab tray model, loaded to 12.9 tonnes.
When venturing off-road in the FTS 800 the truck needs no 4WD selection, but the driver could lock the centre differential for additional traction and
then choose low range for stump-pulling toque and crawl capability. The standard rear axle differential was a self-locking ‘No-Spin’ that required
no driver intervention.
The manual box FTS 800s we’ve driven in the past were easy enough to operate, with the only possible difficulty for novice drivers being the need to double
declutch and match revs to pick up first gear on the move.
The automatic box shifted superbly on this test, but there’s no such thing as a free lunch: in exchange for hands-free and foot-free shifting the automatic
transmission sacrificed some low-speed capability.
With a torque converter stall ratio of approximately 1.8-2:1 the auto model had overall gearing reduction that was almost identical to the manual’s, so
uphill climbing ability was about the same. We found it possible to idle the loaded auto FTS 800 up slopes that were too steep to stand on, but it
was a different story when descending those grades.
Torque converter stall doesn’t apply when running downhill, so the effective gear reduction changed to only half that of the manual vehicle’s and so it
tried to run away on downgrades that would see the manual creeping down in low gear. In the auto it was necessary to use the service brakes to control
OTA reckons that operators who work in very steep conditions – like the Victorian High Country – would be best served by the manual-transmission FTS, but those who don’t need powerful downhill gearing have the choice of both boxes.
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