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[ V8 Engine Fitting Information ] [ Rover 3.5, 3.9, 4.2 to 4.6 Conversion ] [ LPG Conversion details ] [ Fuel Injection Section ]
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boxer Gems 4.0 and 4.6 essential upgrades
Gems Supercharging, not a good idea!
Why do I need to Re-chip my 3.9, or 4.2 ECU?
TVR 4.0, 4.3 and 5.0 upgrade issues, chipping & more
How do I change a 14 CU to 14 CUX (US only)
What problems will I have converting to Injection?
How do I get best fuel economy from my V8 EFi?
How can I improve the fuel mixture of my EFi?
What is the Tornado chip for?
What is 'Twin plenum'
What Tune resistor should I be using?
I have chipped my car but its still not right?
Re-chipping Optimax FAQ section
And More
Hot Wire injection (chipping).'questions answers'
Hot Wire injection upgrading 3.9 to 4.6 airflow meter
Hot Wire ECU pin outs

Gems, 4.0 and 4.6 ECU essential upgrades

From 1995, Range Rovers and NAS Discos.
'Gems Engine Management, long since unlocked!

(See my own 'Gems 4.0 Litre' Range Rover (upgraded to 5.2 with massive torque & LPG economy)

GEMS upgrades are actually quite complex. The ECU has two chips which are both in sockets. In addition, the ECU is also keyed to the vehicle it belongs to. Therefore, the upgrade process has to be performed on the vehicle's own ECU. Two warnings, when working with GEMS vehicles, never try to locate a misfire by pulling plug leads off, pull the injector connector instead. Otherwise you can blow up the ECU. Second, never swap ECUs between vehicles to test them because both vehicles and ECUs will stop working, and you'll have to have them all reset by a franchised LR dealer (ouch!). There are no known emissions problems with this conversion. The only major difference between this and the North American spec. version is that NAS vehicles have four Lambda sensors, whereas European vehicles only have two.

Chipping the Gems at our level is something that cannot be done anywhere else in the world, in fact it is so difficult that a well known UK company had to work around it on their supercharge kit to get 60bhp from them at £15,750.00 that's what I call expensive.
We have now, long since supplied our own 4.8, 4.9 and 5.2 Gems Upgrades achieving
up to 360bhp from up to £10,000.00 less than others.
Our conversion will idle from 600rpm, yet bring up 90mph in 15-17 seconds on a HSE Range Rover, and faster still on a D90, and, unlike the destructive tendencies of a Supercharger, these engine upgrades use Forged Pistons, Arrow Rods and are fully blueprinted, heat treated and balanced to ensure your engine is not only smooth, powerful and economical, but almost bullet proof.

Chipping (fuel & ignition map re-calibration) alone will give smoother running and better throttle response, it will also improve mid-range torque to make gear shifts stronger, and will also improve economy by about 7%.

>What are the gains from a chip install only
(No cams or other)? up to 10-15BHP all models, 10-15% better gas mileage, huge increase in mid-load torque. Chip is compatible with selected cam upgrades also without modification.

>Does it change exhaust gas?
(Nearly all US states have exhaust gas tests). Not on cruise or idle. The mixture is slightly weaker around there, which produces slightly more Oxygen in the exhaust and a slight increase in NOX before the cat. The cat eliminates the NOX, and the extra Oxygen improves CO values. No effect on Cat life.

>Will it work with all North American models?
4.0 Defender 90, Range Rover 4.0 and 4.6, and Discovery 4.0? without problem, have not yet found one we can't do (up to latest version - '1999').

>Will it allow me to run on LPG
The ECU upgrade is essential for all LPG conversions.

>What is the install time? It's no more than 15mins under the bonnet and the simple 'Plug and Play' installation of two management chips.

>What other advantages can you offer?
We can easily remove the road speed limiter and refine other parameters in the Gems ECU, but this would mean you would need to send the whole ECU to us.

Where can I find out more on your web site?
(more details and associated upgrades here)

>Why not Supercharge
Supercharging a Stock Engine is going to be destructive to your engine for the following reasons

Supercharging does it offer the results?

. More info on Why not to Supercharge from a good and trusted friend of mine.

Why (we) won't touch anything with a (certain type of) supercharger. We could easily do a chip for the (certain type of) supercharger, but there are a lot of good reasons for us not to sell you one! This is just another good reason why. I had a 4.6HSE (GEMS) melt a piston on the Dyno. This cost me a lot to sort out, but I learned a lot from it and hopefully I can prevent my friends from making the same mistakes.

The wreckage of the engine was analyzed by (a certain company) Europe's leading supercharger specialist. His summary was that the system 'could never be set up properly in its present form' and is 'unsuitable for the purpose for which it is sold'.
Perhaps now is a good time to look here!! (you will find Pics and info here)
All of these seven major failure modes were exhibited in the engine, which had had the system fitted for 9000 Miles:

1. Extremely poor air distribution within the inlet manifold, leading to major mixture errors between cylinders (this also confuses the GEMS adaptive engine management system).

2. Cylinder bore washing on rich cylinders.

3. Trapping of piston rings and gudgeon pins in some cylinders caused by piston collapse under chronic long-term detonation.

This would have led to a small end seizure and a rod through the block within another 2000 Miles.

4. Early stages of head gasket failure on most cylinders, possibly influenced by item 3 above.

5. Severe camshaft wear, which is probably largely responsible for oil loss by crankcase pressurization. This has been observed in other supercharged engines, although the connection (if any) is unclear.

6. Insufficient engine breather capacity, leading to oil entering the bores past the piston rings and lowering the Octane rating of the fuel, hence exacerbating the detonation problem.

7. Large quantity of oil leaving the breather system. Because of the breather arrangement this almost exclusively went down the number two cylinder inlet runner, causing detonation problem.

Simply rebuilding the engine could not cure items 1-3. Over seven years working with several hundred Rover V8 engines, I have never seen so many major problems in one instance. It is clear that the ninth injector is required mostly to fuel the front four cylinders, which perform the bulk of the work. Because of this the conversion is also extremely vulnerable to failure of the ninth injector system, which will guarantee the destruction of the engine in seconds.

Bearing in mind that these faults take several thousand miles to develop, you can have no knowledge of what state the engine is in when you apply a chip upgrade. So when it blows up your customer would blame you for it, and I expect you would get a call from his lawyer/attorney/solicitor.

So, I had to pick up the tab on my own because I made the change that destroyed the engine (by fuelling it correctly!), despite the fact that it would have blown up within 2000 more miles. Ironically I was only working on it because the original supplier could not cure the chronic pinking problems.

You may also be interested to know the power figures. A standard 4.6HSE makes 205 BHP on our Dyno. This one made 225BHP (with over 10% CO) when it came in. When I had set it up it made 255BHP just before it went bang. We can achieve this with cam, heads and chip.

Hope this is some help to you. My advice is, don't get involved - Keep Selling your successful 4.6 stage 3 or 4.8, 5.2s instead! After all, up to 334 bhp from your 5.2Efi stage 4 is a real engine so stay with it.> MARK

Why do I need to re-chip my ECU? ( 3.9. 4.2 and Some Early USA spec. 3.5s )

. If you are doing no internal upgrades, and your engine is in good mechanical condition, then using the 'Optimax' chip will not only optimize your fuel economy, but will provide far better low- and mid-range torque which is so frequently lost, causing the very poor acceleration 4wds suffer from, especially autos as they upshift through the gears. With the Optimax Chip fitted it is then possible to key in the appropriate fuel settings to the air mass meter and the throttle pot too.

. If you are undertaking any performance increases, especially capacity, e.g.. 3.9 to 4.6 you will need to re-chip your ECU to suit (see below). If you are upgrading a 'Carburetor engine', then you would be advised to use the Weber 500, or recondition your existing carburettors, as Second hand injection systems are not only expensive, but are never in optimum condition and the Weber 500 will give better part throttle economy, performance and more instant throttle response, as well as being very simple to install. If you do opt for adding injection to a non-injection engine, then you are embarking on a very problematic route to
experience gains worth up to 25bhp.
Where should I go next?
(more details and associated upgrades here)

TVR 4.0 4.3 and 5.0 upgrade issues chipping & more

Could you uprate my present cam on my 4L Chimaera to the HC version which involves piston skim, new ECU etc. If so, how much? Dave

It could for sure, but most of the impressive ability to achieve power upgrades would be achieved first by improving fuel mapping (chipping), ignition output & timing, and high induction flow ability by fitting the appropriate larger 4.6 air mass meter, and perhaps improving further the induction hardware (throttle body, intake trumpets & intake manifold).

All at once, or one at time, this is the way to improve the efficiency and overall power of any TVR or similar V8 hot wire EFi application, especially with the bigger-engined 4.3 and 5.0 Griff/other marques, as they are all strangled, trying to breath though a stock 3.9 air mass meter, and all have very poor igntion voltage output with higher than acceptable resistance through stock plug wires.

Some TVR upgrades can be found on our Web projects section
(Click Here)

How to change a 14CU (US spec.) to a 14CUX ? (US models only)

2. Upgrading from 14CU to 14CUX is required to accept Tornado or Optimax re-Chipping, if you have 14CU Model ECU (normally only US spec.) it is actually quite easy to convert from 14CU to 14CUX, but of course it does require your customer to purchase a 14CUX ECU as the 14 CU is not upgradeable to Optimax or Tornado. The 14CUX will plug straight in where the 14CU used to be, however, a simple wiring modification is required to make it work.

If you are replacing a 13/14CU with a 14CUX and keeping the oxygen sensors, then you do not need a tune resistor as the software types X33, X34, X38 do not look for one. But if you are not using Oxygen Sensors then you must have a tune resistor in place (if in doubt please contact us).

This is because the 14CU has no tune resistor. Instead, the pin used for the tune resistor is connected to the air-con system. All that is required is that the wire going to ECU pin 5 from the air-con is cut, and replaced with the correct tune resistor (probably 3900 Ohms) between this and pin 27. Now you are left with a cut wire which is an aircon enable signal. This only allows aircon to operate when the blower fan is running, to prevent damage to the system in cool weather (evaporator icing). The function can be replaced by use of a simple relay to remove the aircon demand signal on ECU pin 21 when the blower is not operating.

What problems will I have converting to Injection, and is it worth it?

The first problem is that it is normally very expensive. You could expect to pay £££'s for a full used injection system and computer, you could then expect to pay hundreds to recondition the injectors, then you need a new fuel pressure regulator, and these are only a few of the poor condition parts found on a used system. And of course you would need to re-chip it using the Optimax or Tornado Chip as detailed above if you want to get anything like a good system when finished.

The next problem is with the installation!

(May be time to reconsider that very fine Weber 500 Upgrade)

How do I get best fuel economy from my V8 EFi?

The way to best economy is re-chipping the ECU and using an Optimax cam, this can find 10-15% more economy on a good condition engine (more on a high mileage one). Also, the LPG System is very important if you want best economy, so beware the inferior systems (we know 'cos we have to replace them). The OMVL system with Lamda control is, in our opinion, by far the best (we can send you an info pack if you forward Lisa your address). I already run many LPG V8 Rovers (see demonstration vehicles) and you would expect to save an average 30% over Diesel running costs and 50% over Petrol, and with further planned government fuel price rises in the pipeline the savings are set to increase even wider, and the value of diesel powered vehicles will severely diminish.

How can I improve the fuel mixture of my EFi?

Advice applies to Hot Wire, Flapper and Gems Injection systems (regardless of how much you spent on other expensive bits) and is critical in order to gain even adequate engine performance and economy.

The CO & HC emission test/set up that you may have had carried out for your MOT or Service can be quite misleading. The reason for this is that they are generally only tested at idle or low rpm. When tested at idle this has very little reference to your actual fuel mixture. When driving on all Efi systems the engine is normally set up to run at what can only be called a 'compromise' and with all injection systems, many easy gains can be realized with taking control of the basic fuelling procedures,

On the Hot Wire System this is mostly taken care of by re-mapping the ECU and using either the Tornado or Optimax chip, this alone would ensure both idle, part throttle and power fuelling where all correct and large gains in engine economy, torque, and power would be instantly realized.

On the pre hot wire systems Flapper type, the same is true, but can be easily addressed/improved by using the Rising Rate (adjustable fuel pressure regulator), also, you will need to realize that these older injection systems may be suffering some age-related problems, especially when considering the spray pattern and efficiency of the injectors.

It is almost a certainty that with all Rover injection systems, your vehicle is running far less efficiently than it should be. The Efi Chip and Regulator changes are so sure to improve things that we offer a Plug & Play service, and if it does not achieve what you would expect, and it's not showing up another fault on your engine that was previously unknown, then you can have a full refund, including postage.

If you find you, or your engineer, are having some problem getting both low HCs and Low Cos, this is likely to be a good sign of worn Cam lobe or lobes (normally affecting only one or two cylinders so enriching or weakening 8 Cyls at once would cause the good cylinders to run weak/rich, depending on which way you adjusted to compensate). Or a problem with you ignition spark intensity of timing (including correct advance systems) (see relevant section).

The best engines are always those that are set up properly with components that are well matched and well suited to all other aspects of the engine in which they are required to work, and very importantly, your actual driving requirements. Even a Ferrari or Lamborghini engine would be slow with inappropriate or badly set up carb/injection system, or out of place in a quarry or on a mountainside.

What is the Tornado chip for?

When converting to a large capacity (4.6), it is very important to change the standard fuel map in the ECU. This is quite simple in most cases as the Rover's ECU chip is normally nothing more than an Eprom and is easily changed. The secret, however, is not to try to obtain max BHP and sacrifice economy and bottom end & mid-range torque. For this reason, our Tornado 4.6 conversion chip has been developed on a vehicle under exacting rolling road conditions to ensure perfect fuelling throughout the rev range of any engine, and should be considered an important part of your needs.

When do you need to re-chip?

All hot-wire type systems need re-chipping with any major engine changes. Carburettor engines are not re-chippable. The earlier Rover injection system Flapper type would not normally need re-chipping as the additional fueling required can be obtained by fitting an adjustable fuel pressure regulator.

What is Twin plenum?

To be more competitive on the track, Rover found the stock injection design to be somewhat lacking, and in order to pass homologation for racing they could only use parts actually fitted to the std. production vehicle so Rover ran a limited amount of Vitesses in production with this improved intake system for the EFI. The answer to your question is that although initially this system produces very little or no noticeable power gains, it does, however, lend itself to a higher state of tune than the stock single plenum system due to its ability to flow more air at higher RPM.

What Tune resistor should I be using?

Below is a description of the three possible scenarios of CAT and Lambda sensors and which Tune resistor to use in each case which is relevant to the Hotwire fuel injection system only.

Lambda sensors with CATs
A white tune resistor is required to run Lambda sensors with a CAT. This will enable the ECU to make adjustments to its fuel trim (be adaptive) and also to improve its diagnostic ability, as it is able to see what effect changes are having on the running of the engine.

Lambda sensors options
There are two options here, and generally option one is the best to go with.

> Option 1 - For the ECU to be able to make adjustments to its fuel trim (be adaptive) you still need to run Lambda sensors even if you do not have a CAT in your exhaust system, this means you require the White tune resistor. Without this Lambda feedback to the ECU the self diagnostic capability of the ECU is seriously compromised.

> Option 2 - If you have a vehicle that has an auto gearbox and a high lift cam, then it is sometimes best to run without the Lambda sensors, which means you need the Green tune resistor. The reason for this is that under these circumstances the engine will struggle to idle if it is trying to adjust itself from the Lambda sensors at idle. However, this is very rare, so it is always best to try running with the Lambda first.

Early EFi system with no CAT or Lambda sensors.
The Green tune resistor is needed here otherwise the ECU will show a fault code indicating faulty Lambda sensors, because it would be looking for them. Unfortunately, in this case the ECU loses its ability to be adaptive (to make adjustments to its fuel trim), and its diagnostic system will be compromised due to the inability to see what effect adjustments are having on the engine.

If your wiring loom is the early style that does not have Lambda sensors, then it is possible to add these, which is a relatively easy modification.

I have chipped my car but its still not right?

I've just installed your Tornado chip in my 1991 +8 (with cats) The car runs fairly well with the new chip having not adjusted the air mass meter or the timing, but yesterday it seems to be running a bit hotter than it did before the chip. I hope to find someone to adjust the timing next week and see if that helps bring the temp down.

Thanks for your help.
Gary K.
Grafton, OH

Every and any upgrade to a V8 Engine or its systems will lean heavily upon on all else on which it must rely upon, although a pain, that's not necessarily a bad thing, Why? because it highlight problems you did not know you had and moreover goes on to aid gain to so much more than you ever expected.

One predominant issue that's often resultant when having installed the Optimax or Tornado chip is that the extra pulse lengths created when more demand is fed-back will always cause the fuel rail pressure to drop a little and the mixture will burn leaner ( causing' run hot internally).So it would be a good idea to get the fuel rail pressure checked (most are too low) you will be looking for at least 36psi to be comfortable. and although stock regulator is not adjustable, adjustable ones are available.

Normally an increase in fuel delivery pressure is mostly all that's required to provide yet more gains to torque and efficiency

Add to his the fact that very low pressure will cause the opposite to happen as the fuel with not be injected cleanly (nice spray pattern) and 'dribbled' fuel into the engine will not burn & appear to be running very very rich, Thus chipping as part of any good upgrade is essential and it may render issues in other areas due its more corrective demand.

With regards to timing, it is so often the case that its current setting is one that matched the engines previous state, so this I suspect will also be an essential area for you to check.

There is a good check list for the distributors on our web pages and the following advice is useful

Its also worth noting that the best ignition timing in any given engine, is to achieve the most advance it can tolerate without pinking. (Audible pre-ignition).
This is achieved by setting your V8 timing to about 4 deg. BTDC (assuming you've been through the distributor check list completely). Then tighten the distributor so that you can (with effort) still turn it by hand. ideally put a tip-ex mark or small scratch on the distributor body and engine block to record this spot.

Next road test the car and simulate high load by quickly shifting into a high gear or if Auto allow to change quickly up to 3rd or 4th Ideally you need to find a small hill or incline, now if you apply full throttle the engine should respond without pinking, find a safe place to pull over, open the bonnet and turn the distributor through a couple of degrees only, anticlockwise, this will add slightly more advance timing and if you do the same test, and repeat it until pinking is noticed you will be very close to your absolute best timing criteria
So now all you need to do is turn the distributor clockwise by the same amount by an amount to counteract the last adjust, retest for the absence of pinking and that the job done, you will have just achieved the best maximum timing position for your car

Having done this an ideal engine would run perfect in all areas and pull as you would expect from all load and rpm areas. you would also expect the final timing position to be somewhere close to 6-8 deg. btdc, (exceptions assumed) However if this is not the case and or your engine developes other strange habits then it is almost certainly pointing to another issue with your engine of which there can be many.

Fuel pump low pressure
Leaky older or high miles injectors
Poor or pretending plug wires
Flashy plugs that ar'nt so flashy after all :-)
Throttle pot settings
Air flow meter settings
Coolant and fuel temp sensors
Lambda probe(s) if any
Distributor ability, both its output voltage and mechanical advance systems capability

to name but a few. !!!!!

Don't worry though, most have few issues that cause problems, albeit all have issues that hold back what's easily & potentially possible

For the records and the benefit of this advice I must assume the engine is in (known and not assumed) great mechanical shape,

Hope this does not cause overload
Kindest regards

Further Chipping Questions answered

Q. Does re-chipping affect things when using the Rover diagnostic equipment?
It's a fuel map we change and has no bearing on diagnostics at all.

What if it gets broken when we fit it?
A chip by nature is quite fragile but is in the capabilities of most to fit, ( 99% no problem) if a leg/pin broke then it could be repaired or replaced by us at a very small cost.

What about if I damaged my ECU fitting the chip?
Virtually impossible and thus far unknown. If the socket in the ECU broke or other minor damage occurred we offer a service to fix/replace the socket.

Q. How much would a new ECU and chip cost?
For all of our current ECU chip prices and more please either contact us or visit our online shop.

And in greater detail

I am interested in re-chipping my 1993 NAS 110. It has a stock 3.9 EFi. What are my options?
You can see details on our hot wire injection pages that will help you identify what Optimax/Tornado chip would be relevant (we also have unique USA/NAS versions).

What is the cost?
Please contact us for the latest price of the correct ECU chip.
I suggest you also consider plug, wire and ignition amp upgrades, then you could expect some healthy gains in torque bhp and efficiency, mostly (very) noticeable through the lower- to upper-mid range (see our customer comments section).
There is also an issue with lowering internal running temperature, as block cracking on un-chipped engines is not uncommon.
The main problem with the original fuel map is that it runs very lean through the mid rpm range, worsened in high load conditions ( hilly roads, hard driving & towing), we believe it's Rover's vain attempt atimproving economy, not realizing more throttle would be used to compensate for the otherwise dull performance.

What will the result be?
Very pleasing!

What will happen when a dealer plugs my truck into their diagnostic computer?
You mean you know a dealer that knows how too??? Seriously, though, nothing, as it's a software upgrade to the fuel/load/rpm map, and is invisible to any diagnostics.

What are the negatives?
Only the wait for the chip to be delivered & fitted.

My engine has 28,000 miles on the clock. 130,000 on the vehicle.
Ignition options are quite important for any fuel map upgrade to do what it always can, but at least with your engine mileage it should be the only other immediate option worth attention and consideration.
Another interesting point is, embarking on these issues will create a need to check and reset some basic engine settings with regard to ignition and EFi components.
This in itself, when done with the guidance available on our web pages, can almost always yield further potential that your engine already had as well as the expected increases.

Hotwire 14CUX ECU pin outs.

Pin Number
Pin Description
Idle air control valve with ignition on - output  
Engine control relay with ignition on - input  
Throttle position sensor with ignition on - output  
Module coding plug - input  
Vehicle speed sensor while vehicle moving - input  
Engine coolant temperature sensor with ignition on - input  
Heated windscreen - input  
Diagnostic line  
Malfunction indicating lamp - ground  
Injectors even numbers (2,4,6,8) - ground  
Engine control relay - ground  
Injectors odd numbers (1,3,5,7) - ground  
Battery voltage - input  
Fuel pump relay - ground  
Evaporative emission canister purge valve  
Ignition switch - input  
Throttle position sensor - input  
Airconditioning refrigerant pressure switch - input  
Mass air flow sensor - input  
Left heated oxygen sensor - input  
Right heated oxygen sensor - input  
Fuel temperature sensor - ground  
Idle air control valve while ignition switched on  
Module coding plug while ignition on - ground  
Idle air control valve - output  
Idle air control valve - output  
Not used  
Not used  
Fuel temperature sensor - input  
Air conditioning compressor clutch relay  
Supplement resistor - input  
Mass air flow sensor - input  
Air conditioning condenser blower motor timer relay - output  
Not used  
Not used  
Ignition coil - input  

And more.

There is much more information including setting up of air mass meters and throttle potentiometers, plus tune resistor and chipping details on the following EFi pages and relevant sections

Hot Wire injection.
(Most 3.9 EFis but some earlier US 3.5 models)
Also 3.9 to 4.6 airflow meter upgrade

Flapper Injection.
(As fitted to SD1 saloon cars and early Range Rovers, plus other early injection types)

Gems Injection.
(Mostly Range Rover 4.0 and 4.6 models '95 on, plus late USA sped Discoveries and 50th aniversary Defender D90)

links to other FAQ pages
[ V8 Engine Fitting Information ] [ Rover 3.5, 3.9, 4.2 to 4.6 Conversion ] [ LPG Conversion details ] [ Fuel Injection Section ]
[ Weber 500 & SU Carbs ] [ Mallory Ignition Systems ] [ General Engine Problems ] [ General Information ]

Prices do not include local EU.Tax.(VAT).
Prices & stock are subject to change without notice. Information and advice, as always, is free.

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