MG-Cars.info

Welcome to our Site for MG, Triumph and Austin-Healey Car Information.

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGB GT V8 Factory Originals Technical - EFI Wiring question

I'm trying to source a 14CUX and harness from a local yard, and need to know what sensors I have to have for a 4.0 T-5 conversion? Additionally I understand the EFI harness is pretty much a "closed system" (only 4 wires to hook up) but what about the 40 pin plug to the ECU, is this the same harness or am I going to have to get a plug that's been deCAPitated from it's harness and splice this into the EFI harness.
One more "?" can I use 3.5 injectors on a 4.0?
Hal
Harold McMillan

Hal, Here are the sensors you MUST have to make this thing work:

Air flow meter
Throttle position sensor
Coolant temperature sensor
Fuel temperature sensor
Two (2) oxygen sensors - one for each manifold.

Get the harness from a 91-95 vehicle and the accompanying ecu. All years will plug right into each other and there will be no cutting, clipping, or changing of anything if you keep within 91-95 model years. for all intensive purposes, 3.9 is the same as 4.0, so no worries in that dept. You *could* use 3.5L injectors, but I don't know why you would? Just buck up and go get a new set of injectors for your system, it's a worth while investment. The Oxygen sensors should be purchased separately (ANY 3 wire heated oxy sensor will do, so DO NOT pay land rover prices for them, it's highway robbery!) If you need any help with the plumbing, or getting the system up and going, I have a hotwire fuel injected V8 and I am VERY familar with what has to be done to make it work.

Good luck!
Justin
Justin

Harold, The Rover hot wire can go on a 4.0 & with a bit of mods. I can get the hood to close with no bubble! The injectors are the same in the 3500, 3900, & 4200 & I think the 4.6. I have 4 B V-8s that I have on the road running with F/I & it is a cool set up + 4 more M.P.G. The newer gems F/I will take a lot more work to do for the motor has no dizzy & you have to use the crank timming stuff. I am not that far from you, come over & ck it out.
Glenn Towery

Thanks Justin,Glen,

About the harness (one more time) is this the complete rover harness I want (it's comming from a '94)? Isn't the "closed loop" harness for the EFI different/seperate from the 40 pin plug to the ECU?
Sorry to sound daft but I want to make sure I get everything I need (this time).

Hal
Harold McMillan

Hal, If the 94 motor has a dizzy this is what you need & what I have used.
Glenn Towery

Hopefully this will answer your question.

The harness for the engine and fuel injection is 'stand alone', and interfaces to the vehicle through one connector located under the dash.

Most junkyards will call this the 'engine harness' or 'fuel injection harness' and most know that it must be removed intact without cutting any wires.


The ECU of the doner Rover should be mounted under the passenger seat along with a couple of relays. You'll need the harness complete with the relays, the tune resistor and the connectors intact.

Once all the sensors and grounds are disconnected in the engine bay, the harness is pulled into the cab thru a hole in the firewall. As I recall there is about a 3" diameter hole with a grommet on the fuel injection harness.

Hope this helps. Can send you pictures of mine if you think it would help.

Phil
Phil

Fuel temp sensor?? I have never heard of that. I know my ford buddies are always fighting with EFI they use:

Air flow meter (mass air sensor)
Throttle position sensor
Coolant temperature sensor
Air Charge temp
Idle air bypass
sometime Manifold Vacuum
Two-four oxygen sensors - one for each manifold, pre and post Catalytic.

Larry Embrey

There is a fuel temp sensor on the Rover hotwire system located at the front of the fuel rail. It screws into a blind hole on a boss on the fuel rail. (Not in physical contact with the fuel)

There is no air temp, per se; I believe that is a part of the air meter.

There is no manifold pressure (MAP) sensor

My Rover factory manual pages only shows two O2 sensors - pre cat.

The only thing missing from Justin's list, but included on Larry's is the idle air control, a four pin connector on the firewasll side of the inlet plenum.

By the way, if you can get the fault code reader box at the junkyard, get that too. It is about the size of a deck of playing cards or a pack of cigarettes and should be mounted very close to the -14CUX ECU.

Make absolutly certain you get a -14CUX and not a -14CU ECU and harness!

Phil
Phil

My bad on the air idle control. I didn't even think about it because they're almost never removed from the plenum chamber. And if they are, they're about $29.99 at any auto store (1986 Buick Grand national V6). There's virtually no chance of ending up with a 14cu if you stick between 91-95. Certainly won't happen if you went 92 or newer.

Phil,
Did you ever pickup a 14cux for your system? I held off as my new 4.2L is arriving on Wednesday, and I need to source one specific to the 4.2L Yay! More power!

Justin
Justin

Hi All,
I didn't knoe the O2 sensors were a requirement. I thought I read somewhere that you replaced them with a resistor?
Regards
Tony
Tony Bates

The voltage coming from the O2 sensor varies with the heat produced by the engine, and the amount of oxygen in the exhaust. If you replaced them with a resistor, the cars computer could never adjust the mixture to account for varying conditions. 3 wire oxygen sensors can be gotten brand new for around 40 bucks. They're all the same. A 3 wire land rover O2 sensor is the exact same as a 3 wire Ford sensor, as a 3 wire Chrysler sensor. The only difference is the plug going to the harness. Just cut the wires, and use your own butt splices to connect them in. Nothing difficult.

Justin.

P.S. don't mix up the wires!
Justin

Justin-

Sourced a -14cux, the tune resistor and the fault code box at a junkyard here for $95. Ran with the new engine for the first time yesterday, so I've not set the idle air or the CO, but it won't be long. All the intermitant problems with the -14CU box seem to have gone away.

Regards,
Phil
Phil

Everyone,

With all your information I feel fiarly well "armed" with enough knowledge to at least get what I need from this salvage lot.

The fualt reader is another question:
My wife recently bought a '93 Rangie she lets me work on (and sometimes drive)! I was "window shopping" under the passenger seat the other day checking out the ECU and noticed another (empty) 40 pin plug laying on top of the ECU (didn't see the Fualt box though). Anybody have an Idea 'bout this other plug? My first guess is this car has been worked on before and instead of removing the old plug/harness they just ran another.
Any guesses?
Hal


Harold McMillan

ABS ECUs were under seat mounted, has your RR got this and if so is it functioning?

14CUX was not listed as being for cat or non cat vehicles, just VIN number dependant with the application of white, green, red and yellow tune resistors to apply to the specific vehicle spec.

No one has mentioned idle speed control has a controlling input of road speed via an appropriate sensor. Being as the RR has an electronic output and no mechanical cable you have the same situation as applied to the MGRV8 which used a simple pulse generator inserted into the cable. This provides 4 pulses per cable revolution and the simplest solution for those in the Uk is to find another early Rover car in a scrap yard and pich the sensor from that. Alternatively the part costs about 50ukp new.

Idle speed control is active only when the road speed is measured at below 5 or 6mph, the variation due to the rather simple input source, and when engine coolant temperature is above 35 degrees C. I have for some time not bothered to add the road speed sensor, although I have one. This can see some inconvenience where the idle speed can be jacked up when your travelling at light throttle and low speed in traffic as the system believes the car is at rest with no road speed inputs. Beyond this there isn't an issue.

Air temp is indeed calculated via the two wires in the bypass port of the AFM. One is heated and one is not the value of airflow and air temp is calculated through the changing values of these two wires.

The fuel temp switch is just that a swicth operating when the fuel rail temp reaches around 90 degrees C. It has been a feature of many other Hot Wire equipped engines and in a temperate climate such as the UK this is pretty much a waste of space, as was the cold start system on the earlier air flow meter system on earlier Rover V8's. If it is not present then usually the problem is starting a hot engine in hot weather. The switch simply bypasses the coolant temp signal and this triggers extended injector open time.

Once again if not present then you can sometimes see a bit of a spluttery attempt to start the engine. Although cranking provides double injector pulsing this may not be enough in really bad conditions so if you don't have the sensor leave the harness plug accessable and then use a paper clip or bit of wire to short the two pins in the plug together. This imitates the fuel temp switch operation and once the engine has run for around 20 seconds the fuel flow through the rail and purging of hot fuel in each injector should have returned the engine to 8 clean cylinders. You must remember to remove the clip/wire from the plug. (Yes this can be used as a fuel boost device, but it is ineffective when the engine is cold and operating on coolant based enrichment.)

The Hot Wire is a system I have been playing with since it arrived on 4 cylinder cars in 1984, the 6 and 8 cylinder applications are very similar indeed.

Rog
Roger Parker

Harold - I ran without a speed sensor for a while but found that the revs would dip after slowing down (at lights for example) and the engine would stall. I was told it would be most simply cured by increasing the idle speed but reasoned that higher engine speed would increase fuel consumption and run counter to the original reason for fitting FI.

The system is sensitive to voltage changes and there are a couple of places where you can hook up a link to warn the ECU that for example the fans or a/c are coming on.

The supplier of my harness (almost as helpful as RP above) told me that the system is set for auto gearboxes and that I should fit a resistor which he sent. #

Roger - you were right - the system settled down quickly and the car is a joy to drive.
Roger

This thread was discussed between 17/12/2002 and 28/12/2002

MG MGB GT V8 Factory Originals Technical index

This thread is from the archives. Join the live MG MGB GT V8 Factory Originals Technical BBS now