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MG MGB GT V8 Factory Originals Technical - EFI Options

I'm in the process of rebuilding a Rover V8 I pulled from a US-spec (1980) SD1. This is eventually to find it's way (with the LT77 gearbox) into my '73 B. I'm planning to use as much as possible from the Rover, including the EFI. I do not, however have an overwhelming feeling of security in regards to the "federal" AFM and the notoriously dodgy 4CU ECU. The fact that it's 25+ years old is enough to dissuade me from putting my trust in it. I've been doing a bit of research on couple of aftermarket systems such as Megasquirt. It seems I can dispose of the AFM and the ECU and use everything else. This appears to be a good alternative to me. Anybody on the board have any experience they could offer on the subject?

Thanks for your comments.
Steve Mc

Do a search on this site for megasquirt and you should pull up a few threads. I think Arnold over on the supercharger forum may be using it but I'm not aware of anyone else except me using in in MG's. Though several are thinking of ditching the factory controllers for it few have actually done it yet. From my personal experience I can say that it is the right move. I run it in my MG and also in my truck (a '71 I-H Travelall) and though tuning is more complex than setting base timing and selecting a tune resistor, it is infinitely more flexible. Anyway you are on the right track. Run that search and read what comes up, it should clear things up some for you. Let us know what you find.

Jim Blackwood

With some help from Glenn Towery, I installed a later version of the Rover FI, parts from various cars, but the basic system is from 1989 thru about 1992. This is a terrific system, easy to install, at least equal to a 4 bbl carb, but with better gas miliage, great starting first time, regardless. I will never go back to a carb.

Computer is a 14CUX, most parts cheap on E-bay, a little hard to find the wiring harness. Worst case, should be under $400.00, as cheap as $200.00.

Some machining is required for hood clearance.

The Federal system you have is garbage, and as you say, the computer is notorious for failures.

My system has no problem with a performance cam, headers, manual transmission, no speed sensor, etc.

If you are interested, I will be happy to help.
Jim Stuart


Thanks for the feedback. I've spent the last couple of days googling the Megasquirt websites. I've even down loaded a couple of range rover 3.5l map files that I can use as benchmarks.

I was originally interested in going to the later Rover hot wire system (14CU), but I found the necessary parts difficult to come by. Didn't have much luck on ebay, but then again I didn't spend alot of time trying.

The research will continue and I'll pursue both options for the time being.

Thanks again.
Steve Mc


Steer clear of the 14CU, (that's the one Rover sold to the US), go for the 14CUX, loads on UK E-bay, even with shipping costs to the US , they should not be 3.5 has this system, it's brilliant, loads of gen on V8 sites, have a look at RPI or V8 Developments web-sites, these chaps are the real Rover V8 experts.
M Barnfather

Hi Steve,

I had the identical FI from the same year SD1. TOSS IT AS FAR AS YOU CAN! I used the intake manifold and plenum from the SD1 because it gives adiquate hood clearance and converted to a late model (1990) EFI. These units are cheap to buy and have lots of resources for parts and troubleshooting. The 14CUX is nice because it displays the error codes that make it easy to repair. I would not use the stock SD1 injectors either as they are prone to clog. The later 1990 and up are a much better design in fact the entire fuel rail off the later EFI bolts directly onto the early manifold. You will need only to bore the injector ports on the manifold out to 11mm to fit the later injectors. I would be wary of not connecting the speed sensor, while it may run OK it has has a real affect on decleration and engine braking as well as stalling and fuel consumption. My system works very well (meets CA smog standards)and the car starts every time. Keep it Rover EFI it's a known good system where the megasquirt systems are as easy to get wrong as they are to get right just my opinion. Is aftermarket EFI legal for emissions in CT? It's not in CA.

M Mallaby

Can't beat MS for fittign about any system you could want to do. They even have them out there on Seadoo watercraft!!

I had it in my MG right before I sold it. and bought it back when the new owner returned to carb on the car...
Larry Embrey

Mike Mallaby,

What tune resistor do you use ?

Edd Weninger

In the UK, Range Rovers and TVR's use Green ( 470 ohms in old money)
M Barnfather

Hey Larry, what do you think you'll build for your next MG?

Jim Blackwood

Right now I don't have one heh

Current project is a 351W Turbo 88 mustang notch. very low budget (under $1300 so far including car)

Larry Embrey

I have run carb & 6 years ago I put F/I on my 4.2 & I got 5 mpg futher per gal!!!!! I will not do carbs!!!!! The f.i. is so sweet & you can make it fit under a steel hood with the right parts cut down. I have never seen a 3.5 14cux, in the ststes & if I put the 3.9 e.c.u. in I can smell a rich mix. at idel. Were can I get a 14cux for a 3.5? or can I get the 3.5 chip that plugs into the 91-95 14cux?
Glenn Towery

I've read that the hot wire 14cux should be able to cope with 3.5's no problem. Afterall it doesn't care how big the motor is , only how much petrol to add to the air coming in
You will be able to lean out (or enrich) the mixture by adjusting the resistor on the intake airflow meter (that blanked off screw).
The catch is that you will need to have a exhaust gas measuring widget, which most tune up places have. I don't :( , however I did cautiously play around with it at one time by first measuring the voltage across the various combinations of the three wires that go to the meter and writing these down. That way I could reset it back to orrigional.

Afterthought, could be the signal from the temperature sender is telling the computer that it is colder than it actualy is. Swap it for a different temp' sender.
At one stage I was playing around with controling the mix by using a variable resistor on the sender wire.

The 14CUX works fine on my Vitesse engine which has larger inlet tracts, and throttle, the ECU copes fine, and I can get 30 miles to the (Imperial) gallon on the motorway at a steady 70 (plus)mph.
M Barnfather

Too Edd,
I use the stock US 470 ohm tune resistor. I also used a 500 ohm resistor to ground on the transmission switch to tell the computer to ignore the trans switch. this allows good running without tripping the fault code in the computer. I got this little jewel of info from Evan Amaya. Thanks Evan.
the 14CUX will run rich if some of the sensors are not connected. The ECU senses an error and goes into limp mode that is richer that the constant monitoring of the mixture in normal mode. Do you get any error codes with the 14CUX on your 3.5? If it is rich enough to smell I would think you would get a code 44 or 55 (O2 sensors).
M Mallaby

Has anyone tired a throttle-body injection(TBI) on a 215" Buick or rover engine. i.e. the Holly Projection or a TBI off an early GM products (I think the GM trucks and Suburbans had then). In theory it should be more efficient than a carb but not quite as efficient as a port injection system. It should be easier to install and require less feed back sensors?
Boyce Reeves

Leon Zak did.
Carl Floyd

> Has anyone tired a throttle-body injection(TBI) on a 215" Buick or rover
> engine. i.e. the Holly Projection or a TBI off an early GM products (I
> think the GM trucks and Suburbans had then).

Either will work.

> In theory it should be more efficient than a carb but not quite as
> efficient as a port injection system.

TBI can have better cold start, won't have a problem with hard braking,
cornering or acceleration and tuning is via a lap top rather than wrenches
but it isn't necessarily more efficient. You can actually get better cruise
economy with a properly set up carb than you can with most production EFI
systems. A carb's venturi boosters do a very good job of atomization at
cruise speeds (better than low pressure TBI and sometimes better than high
pressure port) and it's easy to go lean of stoichiometric at cruise for
best fuel economy. Most production EFI systems are designed to use narrow
band O2 sensors that dither around stoich at cruise. This is done for
emissions (lean increases NOx) and catalytic converter life (OEM's have
to meet 100K mile emissions standards). With the right programming, EFI
can use wide band O2 sensors or even apply a bias to the narrow band signal
to do lean cruise but few OEM applications do that. Many of the aftermarket
systems have provisions and some of the hacked GM and Ford code will
permit it. If doing TBI, a single plane intake is preferred over a dual
plane, though both will work.

> It should be easier to install and require less feed back sensors?

TBI can use the same number of sensors as port but that depends upon the
control strategy. With speed density, it would be the same. If the port
is mass-air and the TBI speed density or alpha-N, then you'd have less.
Early Holley Pro-Jections were alpha-n but I think the GM stuff was
speed density. A big plus for the GM stuff is built-in diagnostics plus
there's a big aftermarket and user support community.

Dan Jones
Dan Jones

On the presumption that the Megasquirt can utilize a wide-band O2 sensor (I haven't learned enough about it yet) and allows full mapping for start-up, cruise, WOT, etc. I'm interested in whether anyone has controlled the Rover hot-wire system with one.

I'm not looking for much more power for my 3.5L with hot-wire run by 14cux, I just think having an optimized system would be cool and I've not heard of anyone hacking the 14cux. I know there are ROMs available, but they're not tunable.
Edd Weninger

Does anyone have a wiring diagram or instructions for wiring the rover hot wire (14cux) into the MGB?
Scott Shirk

Holley has an arrey fo FI systems that are simple.
Also they have universal kits.
Bill Guzman

Edd, I'm running the megasquirt (MS) on my Olds 215, using a modified rover fuel rail on an offy intake modified with injector bungs positioned as on the rover intakes. The MS controller will run the rover hot wire system, but because it is a fully mappable speed/density (s/d) or alpha/N system (your choice by setting in software) the MAF meter is not needed. It can be left in the system but will have no function. I understand it can also be run as a mass airflow system but have no idea of what is required to do that and do not know anyone who is doing it. The basic difference between the two is that with s/d you tell the controller how much fuel to use under all conditions whereas with MAF you supply target air/fuel ratios and the processor tries to match those based on airflow and O2 sensor feedback. In reality the line has blurred greatly between the two. MS now has A/F ratio settings and auto-tune feedback loops using wideband O2 sensor inputs, and hacking an OEM controller is not a simple matter due to the huge number of control parameters involved. There are plenty of proponents of each approach, but I ran a Ford EEC-IV system on my car for some time using the TwEECer control device, was never able to get satisfactory results and it was in all a frustrating experience, whereas the MS system has been straightforward and relatively easy to understand and tune. GM controllers may be a little easier than the Ford unit, especially if you hook up with the right group of tuners but there are still unknowns because all of the OEM controllers use proprietary software and they aren't telling anyone what the software does. I am not aware of *anybody* hacking the rover controller so that would be a nightmare.

Having said that, several people have had quite good results with the Rover controller, doing no more than changing the tune resistor. For simplicity of installation this is most likely the easiest way to go. I think it comes down to a question of how much tunability you need, and what you want your engine package to look like. In my case I wanted to use an Enderlie style blower inlet scoop and while it is technically possible to incorporate a MAF into this configuration nobody makes one and I did not feel comfortable trying to do it myself. A similar situation would exist if you wanted to use a 4bbl intake manifold and throttle body with a conventional round chrome air filter. Under these circumstances MAF is near impossible but s/d works very well. When using the later Rover EFI hardware either can be used of course. An exception in the case of the 4bbl configuration might be to use a fully enclosed filter housing with a snorkel and ducting cold inlet air in through a MAF meter to the snorkel and presumably if somebody wanted to try that it could be made to work with a Rover efi controller. But on a cautionary note, it is quite possible you could run into unexpected tuning issues such as the surging problem I was never able to cure with the Ford system. Nice thing about the MS, it can be made to work correctly under just about any concieveable conditions.

Jim Blackwood


I'ts an easy hook-up as the MG uses the same coloured wiring as Rover.

Let me have your e-mai l address, I've got a file I can send.

I've also got the official TVR 14CUX service booklet which was issued to the TVR service engineers (living round the corner from the factory helps ), if you need any tech details....the RPI website in the UK is a massive source of info....they really know their Rover V8 tuning or go on the official MG , where lots of knowlegeable owners hang out.
M Barnfather


The engine wiring harness for the 14 CUX is a stand alone harness. All the obvious connections are required to engine components- injectors, sensors, air flow meter,TPS, etc.

A list of connections that are less obvious follows:

3 ground wires to the body- black

1 brown or brown/green wire from the main relay(black base) to constant hot.

white purple wire from the fuel pump relay(blue base) to the fuel pump

white/black wire to - coil

white wire to ignition on

I bought a CD on E-bay that contained the complete Rover service manual for a 1992 Range Rover then printed out the section on FI. It is pretty comprehensive. Cost was $15.00

Jim Stuart

Thanks Jim. I have 2000 4.0 (with 5500 miles) with the last system that replaced the hot wire, no distibutor, crank fired, and totally different intake plenum system. Through many discusions I decided it would be to much trouble to install and no way to get it under the hood, so I have aquired a 93 3.9 to transfer all of the FI parts from. I did not get to take the engine out so not sure where some some of the wires ran. There are 2 multi pin connectors that I am not sure where they go or if they are even needed. Also have 1 connector that looks like it may accept a relay. I will watch for the cd, I have one for the 2000.
M Barnfather, I would appreciate your info to.
Thanks, Scott
Scott Shirk

PM sent, Scott
M Barnfather


I just bought a spare harness off E-Bay, which should arrive mid week. As it is un-modified, I will try to make a list of all the connectors if that will help.

If you don't find a CD, send me a fax number and I ca fax you all the relevant info.

This is such a simple system with no obvious drawbacks in a year of driving, it is too bad more people aren't using it.

Jim Stuart

I'm with Jim on this,

I converted from flap valve to hotwire a couple of years ago.....the advantages are better pickup, and much improved fuel economy....big consideration over here where a fill up of 97 or 98 octane costs $75 !!!!

I use the V8 for touring in the regularly does 5000-6000 miles per
year....longest trip so far Northern England to the Monaco, via Champagne region, Le Mans, and the foothills of the Alps.....only fuel injection problems so far have been throttle pot (they wear out in time)and extra air valve (needs cleaning out every few thousand miles).

I'm sure that you will be very pleased with this system.
M Barnfather

Great information on this thread. Thanks everyone. Alot of questions that I haven't even thought to ask have been answered. Keep the info coming.

Thank you all again.

Steve Mc
Steve Mc

You may not need to wire in the fuel pump via its relay near the computer. I did, now it occurs to me I could have just used the existing MG wiring. For those using the speed sensor (I'm not) this would also be a good way to ovoid the range rover speed limiter (120MPH) in the chip.

Fuel supply- After trying a variety of set ups of varying degrees of complexity, expense and difficulty, I found the following to be the most effective. Easy to set up, quiet, reliable and cheapest. The very late model fuel gage sender may be fitted to earlier tanks. It has a fuel uptake line in it. Run a fuel line from this to a very large, beer can size, fuel filter. Run a fuel line from the filter to a 'feeder pump'. Run a fuel line from the feeder pump to the main high pressure pump. Thence to the engine and from there back to the old fuel uptake on the tank.

These are all standard, 'off the shelf parts' so they may be replaced with ease if the need arises.

The big filter (less than, $20 Kmart) acts very effectively like an antisurge tank, as well as protecting your fuel pumps and injectors. I'm using a Bosh fuel pump as the main high pressure pump The feeder pump is made by Peirburge and it's part # is 12001. Available everywhere. This feeder is a high volume, good suction, pump and can pull through a filter up to half a meter above the top of the tank. This means you can stash the filter and two pumps in the boot if you like.

Why use two pumps? There are two main factors-
A-High pressure delivery fuel pumps deliver good pressure but they are very bad at sucking the petrol to them, especially though the very necessary filter. If stressed they will cavitate noisily and wear out fast, even if they are managing to get fuel to your engine under those conditions.
Conversly a strong suction pump won't deliver the high pressure.

B-Unlike water, petrol has a very high vapour pressure and so obviously does not siphon well. After it has been around the hot engine and been released though the pressure valve it will also have developed lots of tiny vapour bubbles. The initial boiling point of petrol may be as low as 18degC which gives you an idea of the problem. Any EFI fuel delivery system must have a way of venting off that vapour. Running the petrol back though the tank is the best way of doing this. Allot of these light fraction (butane etc) bubbles also redissolve back into the main bulk of the petrol.

Machining the air intake-

When you remove the small throttle water heater you will find that you can lower the air intake a maximum of 33mm before the rocker cover interferes with the throttle mechanism.
You can probably get all you need from the trumpet tray.
The two pairs of trumpets at the front and back are set lower in the trumpet tray than the four in the middle. Measure and record this height difference, then remove the 8 trumpets. You can get the trumpets out of the tray by heating the whole thing in your oven. They pull out quite readly when hot because Aluminium has a larger coefficient of expansion than steel. I used silicon to fix them back in place after all the machining and cutting down.

Have a shop weld up the three vacuum take offs on the side of the tray. They should tidy up the outside and grind off the remnants of the take offs otherwise they may interfere with the fuel rail.
Then get them to machine;
Up to 16mm from the bottom.
Up to 10mm from the top. You can get 12mm, it works, Iíve tried it, but it makes the tray lip a bit thin.
This cost me less than $100 (Australian) to have done at a local engine rebuilding shop. 14mm off the bottom and 10 mm off the top in my case.
You can machine 5 to 7mm off the top cover as well, if necessary, but will cost you more and may not be necessary. Also keep in mind the 33 or 34mm limit imposed by the rocker cover clearance.

You will also need to cut the trumpets down according to how much you take off the top of the tray (and possibly top cover). A minor complication is that when you machine 14 or 16mm off the bottom of the tray you remove the front and back pair of trumpet steps, which are set lower than the middle four. The trumpets are all the same size (to begin with) it's the tray steps that are different heights. To make up for this you must shorten the front and back trumpets more than the four centre ones in order to maintain the requisite (previously recorded) height difference.


Thanks for the response. I'm have a good-running Hot-Wire with 14CUX now, but can't "fiddle" with it in any meaningful way except for the tune resistor, hence the thought to use a megasquirt or ??. I think using a wide band oxy sensor with a modern CPU would be interesting.

I believe you're the local guru. Google brings up tons of stuff. Besides the official site, where is the best stuff worth reading?


Edd Weninger
Edd Weninger

I have just had a 14cux and 93 Discovery 3.9 EFi attached to my former carbed V8. When cold it runs to pefection but once it is warm it falters at WOT. cruise is fine. What would you suggest be the order of tests that we should take.



You can use part of the MG fuel pump wiring, but you need to use the Rover relay to control the fuel pump. Hooked up he way the factory intended, the fuel pump will shut off after about 6 seconds unless the engine starts running. This is a safety feature and also prevents unnecessary recycling of the gas from the tank to the fuel rail and back to the fuel pump.

I have not figured out how to use the speed sensor with a T-5 trans, so the 120 mph limit is not a problem.


It could be the temperature sender, too rich, or not connected so in default mode. You could try searching around the rover , triumph, Morgan sites.
What is WOT by the way?

Wide Open Throttle, I believe.
Steve Mc

Kevin ,

Throttle pot failure can give similar symptoms, you will need a volt meter to check it..... with the engine running...couple the meter to the centre and one of the outer wires, it should read 0.3v at idle, and go smoothly to about 5v at full throttle if the pot is in working order.
M Barnfather

This is a very good fund of information. It should enable you to work your way through the possibilities


This took me a moment or two to work out,
Click on the relevant page, window opens, and then expand by clicking in bottom Right Hand corner
Or copy to word and expand from there.

The link Peter has provided should be downloaded and printed by anyone considering a FI installation. It is a copy of all the relevant info from the Rover owners manual. No need to buy CD. On the same page is another article on clearing trouble codes. Copy that as well.
Jim Stuart

Likewise, here is the manual for the megasquirt controller.

It should come up at the wiring diagram, but if it doesn't, it is near the bottom.

Jim Blackwood

OK that was just for the external wiring diagram but it contained the instructions for assembling the board as well. This link:

is the entire Mega-Manual and both is very detailed and breaks the information down into usable pieces that are reasonably easy to find. Check it out, it's worth a look.

Jim Blackwood

This thread was discussed between 10/10/2006 and 26/10/2006

MG MGB GT V8 Factory Originals Technical index

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