Understanding the P38

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P38_technical_understanding Electronics and diagnostics are what makes this power plant tick : credit: © Ed Evans
If buying a P38A, or already enjoying one, knowing what makes this machine tick will enhance the experience. Ed Evans offers some insights . . .

If you’ve read our P38 Buying Guide you’ll know there’s a broad price range covering all examples from rough to resplendent. If buying a cheap and tired example for restoration, you really do need to understand electronics and diagnostics, and enjoy fettling the beast without worrying too much about budget. Further up the scale, mid-priced examples represent bargains that may run nicely for a long while – if fully serviced.

This supplement to our buying guide explores some of P38’s systems, and gives tips on checking a prospective purchase and monitoring a car’s condition.

 

Electrical

Nerve centre: The BeCm is mounted under driver’s seat. It can suffer printed circuit failures (dry joints). Specialists can test and repair the unit.

The heart of the electrical systems is the Body electrical Control Module (BeCM), a multi-purpose unit with its own fusebox, powering multiple ECUs around the vehicle, and providing dashboard messages to the driver – it was revolutionary and it works. But it didn’t always. In the early days, insufficient understanding of the systems and diagnostic procedures introduced latent faults that caused breakdowns later. Unexpected malfunction of P38’s security systems caused by radio interference from external sources further damaged its reputation. As the cars aged, earthing faults caused by dampness and corrosion added to the confusion, and even a failing battery could cause spurious faults and indications. Because the BeCM interacts with so many functions, the ability to resolve problems with such disparate systems as air suspension, security, airbags, air conditioning, lighting, door locking, windows, transmission, ABS and engine cranking needed a deep understanding of the vehicle and the necessary diagnostic equipment. Of course, this kind of multi-system interaction, which was revolutionary on P38, is now commonplace on modern vehicles where it works fine because it’s fully understood and respected, as it now is on P38.

So, if viewing a prospective purchase, it’s essential to check every electrical function works correctly, including seat motors and heating elements, locks and windows (clunky windows suggest a worn regulator), aircon and heating. P38 needs a healthy and correctly spec’d battery: a minimum 72 amp/hour battery on petrol models and a 107 amp/hour for diesels. If all that is good, then you’re starting with a clean slate and the chances of faults developing is no more likely than for any other top end car of the era.

 

V8 petrol engines

The 4.0-litre is a revised 3.9, having the same cubic capacity but improved smoothness and performance via improved inlet and exhaust flow, new pistons, a stiffer cylinder block and larger crankshaft main bearings. Both the 4.0 and the longer stroke 4.6-litre share the same engine/fuelling management: initially a Sagem-Lucas GEMS hot-wire system, then from 1999 model year the Bosch Motronic system (as on Discovery 2 V8).

Hot wired: GEMS V8 is distinguishable by its rectangular plenum chamber (this is actually a non-standard 4.8-litre built by ACR).

The GEMS systems was said to be less reliable than the Bosch but, over the
years, both have proved dependable. The GEMS’ reputation may have been influenced by the car’s early teething troubles, and the fact that more GEMS models were produced.

Maintenance of the V8 cooling and lubrication systems is vital. An oil and filter change is advised every 6000 miles. Neglecting this accelerates wear on camshaft lobes, followers and tappets, resulting  in engine noise and a deterioration of performance and emissions. Clean oil, a quiet engine, a smoke-free exhaust and good genuine service records give peace of mind here. Good servicing includes condition checks and preventative maintenance, and covers often forgotten items such as renewing Lambda sensors at 84,000 miles – a simple task which can prevent a catalogue of running problems.

Looking the business:  The later Bosch Motronic V8s are recognised by their rather tasty curved ‘tubular’ air inlet system

P38’s cooling system is particularly sensitive to coolant loss, so the level needs regular checking. Original leak issues were rectified by Land Rover, but heater matrix O-seals still leak (see later).

The major cooling concern is caused by cracking in the aluminium cylinder block between the internal coolant passages and the steel cylinder liners. Coolant passes along the crack and seeps up the side of the liner and into the combustion chamber. It can also seep downward, into the sump so, if there’s water-emulsified oil on the dipstick, expect more than just a head gasket leak. Upward leakage into the combustion chamber is difficult to identify because the coolant is vaporised without trace (though white smoke can be a giveaway), and the crack cannot be detected by a pressure test because it’s hidden behind the cylinder liner. Traces of combustion gas in the coolant tank doesn’t confirm a crack – that might also be a head gasket leak. If the heads are removed and a combustion chamber and piston crown are found to be washed clean, that is confirmation. The only cure is a replacement engine block. However, if there are no signs of coolant issues or excessive topping up, and the engine temperature is steady, then there is probably nothing to be concerned about or, quite likely, the block has already been replaced with a modified unit that won’t let the condition recur (see pic below).

The cracking is common, though doesn’t necessarily result in a leak, and can be influenced by high engine loading, overheat from reduced coolant flow and possibly design/production issues.

Crack solution: Even if the cylinder block cracks, this liner being fitted by ACR to a remanufactured V8 has an upper flange and lower seal that effectively blocks any coolant leak path

Sparking system: V8s do not use a distributor, ignition being provided by four individual coil packs positioned at the back of the engine near the bulkhead

V8s are thirsty, so LPG conversions are common. A well installed and proven system is fine for the engine, and the cheaper fuel will give diesel economy. But check the installation paperwork and up to date inspection certificate, without which, insurance may be a problem.

Lubrication: The V8 camshaft and associated valve operating gear is the first engine system to suffer when oil changes are neglected

Tuning option: Diesel and petrol engines can be electronically tuned, in addition to mechanical improvements. This GEMS engine ECU from a 4.0-litre V8 is receiving a performance chip

 

Diesel engines

Fuel feed: Diesel starting problems with a cold engine are often due to air ingress through pipe joints and perforations, such as these fuel pump pipes

The BMW turbo diesel is a solid and dependable chunk, given decent maintenance. Check it starts okay when cold and hot. Cold start issues suggest heater plug or other electrical problems, pipework air ingress, possibly a weak fuel pump. A worn distributor pump will hamper hot starting, but this can be got around by fitting a simple kit that causes the ECM to activate the heater plugs and increase the fuel to the cylinders. Be aware the pump is still worn, though, and if the engine becomes smokey or fails an emission test, the pump may need a rebuild.

As with V8s, diesels need a check for oil and coolant leaks. Poor output from the interior heater in a diesel may be caused by a failing coolant pump, in which case you’d expect to see trouble on the temperature gauge.

 

Transmission and running gear

Transfer box: Knocking could be chain drive wear (blue). Heavy handling can be a seized viscous coupling (red) which can damage other transmission parts (viewed from front – propshafts run on left side on P38)

This was the last Range Rover available with a manual gearbox (4.0-litre only), and the first with a chain-driven transfer box. When testing the transmission ensure the autobox pulls away cleanly from a standstill and changes quickly without any over-revving. Check it in sport and manual modes. Listen for knocking from a worn transfer box drive chain when setting off, and when accelerating – the chain is jumping the teeth and the unit needs a rebuild. Test the transfer box range change which is electrically operated on this model. A seized internal viscous coupling has the effect of driving in difflock: heavy steering and tyre scrub. Slow speed creaking from the front is a sign of wheel bearing failure.

Multi selector: On automatic models, electrically operated transfer box range change is selected using the H-gate. Manual models have a facia-mounted switch

Later 4.6 V8s benefitted from a higher rated transmission system, though the 4.0 and diesel transmission is perfectly up to the task. Supplementing the transmission, Electronic Traction Control (operated via the ABS system) on the rear axle only was initially an optional extra, becoming standard on all four wheels from the 1999 model year.

 

Heating and air conditioning

Mixing hot and cold: Replacement of the three climate control blend motors is simple enough, but reaching them is a time-consuming affair

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During a test drive confirm the heating and cooling is working correctly. That means trying all settings, noticing the rate of temperature change and that directional airflow systems work correctly and, of course, checking no warning message show on the dash. Check that hot or cold air can be directed to each side of the car. Problems with air/temperature flow are likely to be caused by one or more of three blend motors. They are sold as a pack of three and replacement is a lengthy job needing removal of dash and console trim sections.

 

Steering

Ball joint steering: Front axle ball joints can be replaced three times before a new axle casing needs to be fitted but, as they can last up to 150,000 miles, the expense of a new axle probably won’t arise

The P38 should be responsive and fairly taut. Heavy steering on a neglected vehicle may be due to low fluid level or a slack steering pump drive belt, whereas directional vagueness can be down to loose front or rear Panhard rod bushes.

Although P38 rides on beam axles, it has no steering swivels, instead using a hub knuckle turning on upper and lower ball joints (shared with Discovery 2) – replacement requires an inexpensive special tool, but can be a difficult job. The MoT test should ensure these joints never become sufficiently worn to affect the steering movement, though excessive wear can cause juddering, especially when braking, but that can also be caused by warped brake discs and wheel imbalance. Steering wheel shake or vibration when hitting a pothole is usually due to wear in the steering ball joints.

 

Suspension and handling

Suspension power: The air suspension compressor is handily mounted under the bonnet with its row of solenoid actuating valves behind. Rebuild kits are available

Although many P38s have been converted to coil suspension, this is usually a matter of avoiding issues and expense related to the original electronic air suspension. As with everything P38, the standard suspension is superior and reliable if properly maintained. The vehicle should always sit straight and level, and remain at normal road height when parked up. If it doesn’t, there are likely to be air leaks in the rubber springs (not difficult to replace) or the connecting pipework and seals. Unattended leakage causes the compressor to run continuously when the car is driving, wearing it out prematurely. With all doors closed, check the suspension moves to all its selectable heights within a few seconds.

Flexible friends: Air suspension springs cost from around £60 and are not difficult to replace, but safety in relation to pressure release and vehicle support is important

Worn suspension bushes and dampers will adversely affect handling and braking stability, but checks and issues are no different from any other late beam-axled Land Rover, despite rear radius arm design being unique to P38. Uneven tyre wear suggests suspension bush issues, as does a recently fitted set of budget tyres on a vehicle for sale. Matching edge wear on both front wheels is probably only a tracking issue.

Apparent over-reaction to road undulations might be noticed on cars with 18-inch wheels. This is due to reduced compliance in the lower profile tyres. For general driving, 16-inch wheels give more comfortable and predictable handling.

 

Brakes

Braking power: The ABS power unit comprises a pump and an accumulator vessel mounted separately from, but close to, the ABS modulator

The braking system employs a pump forcing fluid into an accumulator vessel which is pre-charged with nitrogen (behind a diaphragm), providing an instant charge of hydraulic energy for when the brakes are next applied. Poor braking performance and a soft pedal may require a replacement pump and/or (more commonly) an accumulator vessel, collectively known as the ABS power unit. It’s a simple enough job, but components are expensive. Don’t expect to necessarily get away with a brake bleed.

 

Body

Body bother: Despite good corrosion protection by Solihull, aluminium body parts are now corroding under the paint. Check minutely for pinprick signs that will worsen

Bodies are beginning to suffer. Look for corrosion around the sills, and check for signs of the clear lacquer peeling from paintwork. Be especially alert for signs of white-spot corrosion developing on aluminium panels, especially the wheel arches and tailgate – it’s difficult to repair and really needs panel replacement.

Open the tailgate to check for water in the spare wheel well, suggesting problems with the tailgate seals and/or rear side window seals. Corrosion may be a concern at the inside bottom of the tailgate. Also check the undersides of the doors.

Cracked bumpers are common and, while they can be repaired or are easily replaced, the cost of repainting should be factored in.

 

Underside

Fuel saver: The worst rust to be found on the underside is usually on the fuel tank support cradle – reasonably easy and cheap to replace with an aftermarket unit

Before checking the underside, a word of warning. It is dangerous to go underneath a vehicle that has air suspension without first securely supporting the chassis. Vehicle height can settle automatically without warning, perhaps dropping one corner, or the complete vehicle if there is a component failure. Unless you have the use of a garage lift, set the vehicle to its maximum height to see more, then look underneath from around the vehicle without going under it. Off road impact damage is always possible, but these are tough machines, correctly designed to handle off-road hazards. The chassis structure is one of the best, but still needs careful inspection, especially around the rear. Look for corrosion under the wheel arches and under the sills.

At the front, inspect the drive shaft gaiters for splits and fluid leakage with the steering turned outward for each side. Check for oil leaks from the crankshaft seals, the transmission and from axle differential pinion seals.

It’s difficult to assess the condition of air springs as they inevitably develop harmless surface cracking where they flex, but anything serious will be obvious. Inspect the dampers for leakage and corrosion, and cast an eye over the brake pipes, especially at the rear over the axle – they’re not all visible, but those that are will give a general impression.

 

Interior

Turn the ignition to position 2 and check all the instrument panel warning lamps illuminate and then extinguish (ETC may stay on until you drive away). There should be no issues showing on the dashboard message centre (unless you get an appropriate discount on the price), the idea should be to buy a car with zero existing faults. Ensure the message centre is fully legible with no fading digits.

The interior is of good quality (despite BMW’s original reservations) and it’s not surprising to find it almost like new on the best examples. Even the plastic parts are good. Replacement interior trim is available, but expensive. So check condition carefully, bearing in mind future deterioration of existing defects.

The main concerns include cracked and dirt-stained leather, burst stitching and sagging headlining. Also check the facia for sunlight distortion, and the wood trim for peeling lacquer.

Feel the footwell carpets for dampness which may be coolant, especially in the right hand side (LHD and RHD) and the side of the centre console there. Leakage could be from the heater core or, more usually, from two O-seals that connect the heater to the pipes from the engine. The seals are cheap, but might take a day to replace; the heater core is an even longer job. Leakage onto the passenger side front carpet is likely due to a blocked air con condensate drain, which is an easy fix.

Water leaks from the heater system should be slightly sticky to the touch and will smell of antifreeze – remember, you don’t want any cooling system problems on a P38. Moisture from rain water leaking into the front via deteriorated screen seals or the cabin air inlet port can cause corrosion of electrical connections behind the facia, resulting in future problems.

 

Running reality

In reality the truck is no more complex or troublesome than any other of its type and era. To be a fine machine, all P38 needs is understanding and competent maintenance by owners who accept their limits and specialist garages that really know the vehicle.

 

See more technical advice from our experts here.