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MG MGB GT V8 Factory Originals Technical - Hotwire FI and Lucas 14CU/X ECU

I sourced my hotwire system from a ’89 Range Rover 3.9 and found that I did not have provisions for a tune resistor; that feature was not available until about 1990. Evidently I have a Lucas 14CU box, and the later box is a 14CUX. The 14CU box requires a piece of specialized test equipment to read the fault codes, whereas I’m told the 14CUX has a display.

RPI’s website says that the 14CU box can be replaced with a 14CUX with only minor modifications required to the harness to add provisions for a tune resistor.

I continue to have problems with my hotwire system where it seems to run lean occasionally in the upper RPM band and intermittently feels like one bank of cylinders isn’t being fueled for a few seconds.

Does anyone have experience with the Lucas 14CU electronic box and found a solution to these problems? What’s the experience with the later 14CUX electronic box, with and without the tune resistor? Does it make a big difference in performance? Any sources for a 14CUX electronic box?

Phil Dooley


Phil

I'm happy to find I'm not the only one with questions about the 14cu ecu. whenever I take the car out of gear while driving, and coast, the idle will sit at about 2100 rpm's for around 15-20 seconds before it drops back down to 900 rpm's. Additionally, if I'm in say 4th gear doing 35mph (about 1600 rpm's) when I hit the clutch, the rpm's will jump up to 2100 rpm's for that 15 seconds before falling back down to 900.

I think our problems have something to do with the lack of an idle speed sensor, but I'm not sure. I've also highly considered having a 14cux ecu rechipped and shipped from rpi directly, but I'd like to find stateside options first.

Justin
Justin

When I first installed my hotwire I had the same problem and it turned out to be a sticky throttle cable. I put another revolution on the return spring and put a pully to turn the cable with minimum friction, and this problem went away.

Having said that, my idle will be fine then droop so the engine will be on the verge of stalling, then climb back up to 800 rpm. Don't understand this but intent to put +12VDC to one of the load signals like AC and see if this helps.

PED
Phil

I was lucky enough to get a CUX sytem from the start but it may be of interest that the engine would not run properly without the correct tune resister. (I don't have a catalyser).

It was important also to have both a speed sensor and the correct resister to tell the computer that it was dealing with a manual gearbox.

I would have thought the best answer on tune resistors might be to run a catalyser. As for the speed variations, I can't comment except that the idle speed should be around 700 - 750 - worth a try ?
roger

Roger,
Do you know which resistor should I be useing for the manual gearbox and how do I recognize it?
I'm just about to start the motor swap and have a '94 hot wire. Any suggestions on what speed sensor to use and how to apply it?
Peter

Peter,

For a manual box you need a 510-ohm resistor connected between ground and the Orange/black wire to the ECU, the Rover part has male spade connections built into the resistor.

The tune resistor is (Green) 446 to 494 ohms for non-cat and 3700 to 4100 ohms for cat applications.

I haven’t bothered with a speed sensor and the system appears to work perfectly, starts and runs well with a steady idle and it doesn’t stall but I guess the fault light would be on if I had the Black/yellow connected. The Efi Rover 216 and Honda equivalent had a speed transducer built into the speedo cable, you would need a two part speedo cable but it would be very easy to fit to the B and I might get around to fitting one to see what difference it makes.

Geoff
Geoff King

This site has more than you probably want to know about tune resistor values...

http://www.rangie.com/rrkb/nf_articles/212.htm

When I started this string I asked if anyone had converted a Lucas -14CU to a -14CUX. Anyone?

Source for a -14CUX ECU?

Thanks and regards,

Phil Dooley
Phil

As always I'm impressed with the helpfulness of people on this site, thanks Phil & Geoff
Peter

Phil - e-mail me if you can't find a 14CUX locally
Peter/Geoff - I too thought I might dispense with the speed sensor - after all it is a fiddle to split the speedo cable and when fitted, the 14CUX limits your speed but the speed input also tells the ECU when you are slowing down, when you are rolling and generally maintains sufficient fuel to prevent stalling.

over-riding the ECU to set a high(er) idle speed might also prevent stalling but has the disadvantage of reducing fuel economy. In the end 650 - 750 rpm will save you money - particularly in traffic !

The RV8, Range Rover and Vitesse had the same speed sensor unit.
Roger

Phil,

I read your comment when it first came out, but it hit me as I read it again tonight that you also have a 1989 Range Rover EFi harness. Well so do I and Ive been told that mine should have a tune resistor... but Ive been looking and looking and I cant seem to locate one. And you said at the very beginning that they didnt come out until 1990 or so. I find that interesting and Im trying to figure out why so many people told me that my harness had one. I was wondering what one looks like (just to know)

The other thing about this whole 14CU/X ECU thing... How do I know what I have?? My ECU has a sticker on it that has some numbers and thats about it. To me its not clear. These numbers are in the top left corner of the sticker, PRC6999 and these numbers are in the top right corner of the sticker, 84913B. And it does say 'Date Code 1890' So Phil, since we have the same system, is mine also a 14CU?? (It's out of a Range Rover County if that makes any bit of difference)

And what's up with not being able to screw on an up-gradable fuel chip on the side of the ECU? Mine doesn't have that option. I ask because I was reading the book "Tuning Rover V8 Engines," By David Hardcastle and it clearly shows a picture of an ECU which is clearly marked 14CU and it has a fuel chip that can be up-graded

Thanks for "re-visiting" this thread.

I appreciate the help,
Wally
Wally Jonker

Wally - I can't tell you what one looks like because I've never seen one - mine definatly does not have one.

Here's a picture of the one that RPI sells-

http://www.rpiv8.com/carbs-2.htm

Keep scrolling till you see the tune resistor section -it's quite far down.

I went to the local Rover dealer and they were kind eneough to let me copy the wiring diagram for the Range Rover. It clearly states in the schematic that the tune resistor isn't installed till after a certain serial number.

From what I can tell, there is three hotwire model boxes - the 13CU (the number 13 and Lucas, wow), the 14CU, and the 14CUX. I don't know what the 13CU was installed on, or if it was even shipped to the states.

The 14CU is limited to 1989 Range Rovers 3.9 and have reported problems with idle speed and cylinder banks cutting out intermitantly. (My symtoms exactly)To the best of my knowledge, this ECU was not sold in UK but was for export. To read the fault codes requires a dedicated diagnostic tool available only at the dealer ($100 to read the codes only!) I've never taken mine apart, but the RPI website says if you want to run their PROM you have to upgrade to the 14CUX, implying that the box is not upgradable, at least not easily.

RPI says the 14CU ECU can be upgraded to the 14CUX. Here's a quote form thier website-

"Upgrading from 14CU, to 14CUX required to accept "Tornado or Optimax" re-Chipping, if you have 14CU Model ECU (Normally only USA 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 upgrade-able 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."

"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."


In 1990 they went to the 14CUX with a module for reading the fault codes. These codes are posted at various places on the web. My understanding is that some of the early boxes have the PROM soldered in, making them somewhat difficult to pull the chip out.

I think there is about three part numbers for the -14CUX box - I'm looking for a early 90s one to do the modification that RPI suggests. They are pretty pricy at the dealer, but you can find them on car-part.com by searching for 90-94 Range Rover and 'engine controller' (or something close to that)

Good Luck,

Phil Dooley
Phil Dooley

Wally,

According to CAR ELECTRONIC SERVICES, http://www.carelect.demon.co.uk/frame.html

NORTH AMERICAN RANGE ROVER (3.5 LITRE ENGINE - WITH CAT) During the period 1985 to 1989 (approx.) 3.5 litre Range Rovers were produced with the Lucas 13CU hot wire airmass fuel injection system for the North American market. This system can be identified by the ECU, which is a large pressed steel (painted black) rectangular box with top cover held in place by 4 'pop' rivets. We believe this system was only shipped to North American (LA?) and Swiss markets but please email if you know better! Part numbers PRC 6977/5053/others.
DISCOVERY WITH 3.5 OR 3.9 LITRE ENGINE (CAT & NON CAT) fitted with Lucas 14CU fuel injection ECU and hot wire airmass meter, 1990 on. ECU part numbers PRC 8138/9059/(3.5) and PRC 9010/others (3.9). ECU is black painted cast alloy box with 4 cover retaining screws.
RANGE ROVER WITH 3.9 LITRE ENGINE (CAT & NON CAT) fitted with Lucas 14CU fuel injection ECU and hot wire airmass meter, 1990 to 1995. ECU part numbers PRC 6999/7081 - superseded by 8702 and 9061/ 9611/9515/others. ECU is black painted cast alloy box with 4 cover retaining screws.

The above indicates that ECU PRC 6999 should have been fitted to a 1990 to 1995 RANGE ROVER WITH 3.9 LITRE ENGINE (CAT & NON CAT) with Lucas 14CU fuel injection ECU and hot wire airmass meter.

Geoff


Geoff King

Geoff-

I read the Car Electronic Services website too.

It contradicted everything else I could find on the internet relative to the 14CU and 14CUX ECUs. The years and engine descriptions don't match what I find in the wrecking yards here in the states.

Could CES just have left off the "X" in their description of the later box?

Here's what I think are the facts-

Pre '89 Rovers SUVs in the states were 3.5L and had the 4CU or 13CU with a flapper type AFM (Is this where the 13CU is used?)

'89 was the first year of the 3.9 with the hotwire air mass meter. This had the 14CU Lucas ECU with no tune resistor. This I know for sure because that's the description of the Land Rover I pulled my hotwire system from. I can't rationalize what I saw with what Car Electronics Service's website and can only conclude it is in error.

'90 to '95 (thought it was 94 before) is the hotwire system with the 14CUX with the tune resistor on the 3.9L engine. There seems to be several part numbers.

His text never mentions the 14CUX, but it is mentioned extensively on othe websites as being the 14CUX for the hotwire system.

I hope someone out there can give a definitive answer to this. I'd like to start shopping for a new ECU, but I'd sure like to know the facts first. (Hoping to avoid getting out the checkbook and getting a Haltech!)

Geoff, thanks for your help. Any further insights?

Phil

Phil

Every 14cux ecu I've seen has said "14cux" on the label on the front of it. They can be had for as cheap as $125.00 on car-part.com Just have to keep looking through years. I'm betting any year 1991-1995 will all be the same. Don't forget, that discos has 14cux ecus in 94 and 95 too. My unofficial goal is to pay $200.00 for an ecu this winter, then have it rechipped by either rpi, or east coast rover here in the states.

Maybe we're making this too hard?
Justin

p.s. Don't forget to check ebaymotors for an ecu too.
Justin

Thanks Phil for the web site. I dont have that much time right now to read and compromise, but I will tomorrow. So I will see what's up with all this new info tomorrow. Thanks for responding. And Phil, is your ECU marked '14CU' with a sticker? I get the feeling with what you've said that it isn't.
Thanks again
Wally
Wally Jonker

I think I have a 14CU and I want a 14cux so I can run a non-cat tune resistor. The car is stored about 25 miles from here and I wont have a chance to look at it till Sunday to see what it says.

Bottom line: get a 90-95 ECU if you want a tune resistor. Stay away from the 90 ECU because it may have the chip soldered in, which is only important if you think you might install an aftermarket chip.

Phil

Phil

Wally and Justin-

Bought a '91 Lucas 14CUX, tune resistor and connectors, and a diagnostic box today at the junkyard for $100. Will let you know how it works out.

There is a box on ebay for sale. Search "Rover ECU"

Phil Dooley
Phil

Phil,
There were two boxes up there, and I bid on one unsuccessfully -- the reserve was never met. I have this feeling they probably want $250.00 for one, and you're right, that is a bit ludicrous. I'm anxious to hear how well this box works for you, and if it solves problems, I'll be out ECU hunting this week.

Justin
Justin

I was the high bidder on the first box but he had a reserve.

I wrote him and asked him how much it would take to buy the ECU and he said $250

Car-part.com had lots of them starting at $75.

By the way, I took the cover off of the one I bought, a PRC9060, and the chips were soldered into the board. This appears to be a rebuilt as it says "Rebuilt by Lucas" on it.

I've found the copy I had of the factory wiring diagram for the ECU, the diagnostic box and the tune resistor.

If you'd like a copy, I'll scan it and send it to you.

Phil
Phil Dooley

After all these great posts I'm totally confused. I have a PRC9060 ecu that has a removable chip. Is this a 14cu or a 14cux box. The harness does not have a tune resistor but it has the terminals for one. Heres the question? do I rechip my prc9060 and what tune resistor should I use. Is there anyone in the states that offers a performance chip
Jim

The PRC 9060 should be a 1991 Lucas 14CUX ECU.

If you sourced it off of a Land Rover with a serial number subsequent to LA451517 and through the 1995 model year, it should be this ECU.

You can check if you have a tune resistor by measuring the resistance between pins 5 and 27. If you got your FI from a NA spec Rover the value should be nominally about 3900 ohms +/- 200 ohms. They are sometimes hidden in the wiring loom and not obvious.

To check for the tune resistor, pull the connector off of the ECU. Looking into the connector, pin 1 is the pin in the lower left hand corner. The next row up of pins begins with number 14, and so on. (make sure the ignition switch is off)

Phil
Phil

Justin/Jim/Wally-

Installed the 14cux ECU this morning - worked perfectly and was without the idle dropout and intermitant bank firing.

I'm using the 3900 ohm tune resistor- have yet to try the non-cat tune resistor.

If anyone can answer the following questions, I'd appreciate the help-

1) Can the non-cat tune resistor be used without taking off the cat? Will it overheat or do some other damage? Cats are run on carbureted cars, so they must tolerate a fairly wide range of fuel air mixtures.

2) What, exactly, is the difference in the cat and non cat tuning profile in the ECU?

2) I want to install the diagnostic box from the Rover too, but the pin sockets are missing off of the connector. Does anyone know where replacement pin sockets might be found?

Thanks in advance for any help you can offer.

Phil Dooley
Phil

Phil

With a cat tune resistor the tuning profile and behaviour of the ecu in response to temp, throttle sensor etc is much the same except on partial throttle (i.e. cruising rather than accelerating)-with a cat tune resistor the ecu uses the input from lambda sensors in the exhaust manifold to adjust the mixture to keep it at an ideal fuel/air mixture of "lambda" (14.7:1). This optimises fuel economy and should prevent damage to the catalytic converters which would be caused by over rich mixture.

Geoff
Geoff Richmond

This thread was discussed between 30/08/2002 and 15/09/2002

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