3.9 V8 auto 14CUX limp mode/no power

Hi all,

I’ve recently installed a 1994 3.9v8 auto from a disco 1 into a defender 110 puma, retaining all the running gear and engine wiring. I do have a conversion box to allow puma cluster to display engine info.

The engine ran lovely in the disco, but as soon as I’ve installed it in the defender it is overfilling and underpowered (max rpm in drive: 2000rpm / 4000rpm in neutral). I’m lead to believe it has entered limp mode (although I’m not entirely sure it has this feature?).

Engine management light is on and temperature gauge shoots right up at start up. I’m not sure if this is the conversions box getting confused, or it should be displaying this as a precaution.

I have installed a SS twin exhaust system with no cats, but I have installed the lambda sensors. Again, I’m not sure if removing the cats is having an influence on the 02 sensor readings. I had been doing some test driving without the lambda installed initially and convinced this may have caused the ecu to enter limp mode.

My questions is, do I need to get the ecu mapped to deal with the removing of cats? If not, how is best to re-set the ecu to exit limp mode? I have tried disconnecting the battery and ecu plug but no luck.

Any help would be appreciated.

Thanks,
Dion

That's a lot to take in in 1 post.

So which gearbox? (take it its auto)
is it really getting hot have you checked? (probably not as you say its when you switch it on) but what signal is the ecu getting? Cos it may over fuel and restrict performance to protect engine or gearbox.

I am not familiar with the 14CUX but thought it was pretty simple to run standalone as a donor. So don't think the exhaust de cat is your issue.

Just trying to chuck ideas to make you think.
Temp sensor ok? does it have 2?
Have you tried to disconnect this "conversion" box?
Do the signals to said box "piggy back" or are signals sent in then sent out?
What time frame are we talking for the conversion? I take it all the ignition system is good (not sure that would put the EM light on but I have no idea about this box thingy)

Oh and Welcome show us some pics

J

A symptom of over fuelling is a lot of black smoke from the exhaust tail pipe, once you get the engine started.
The engine management dash light illumination plus the reduction in power is a good indicator of a limp mode, but not the cause, it requires something what is missing, the ECU requires a engine temp taking via a coolant sensor, plus fuel temp taking from the fuel rail sensor, so may an iffy sensor or connection at the sensor or ECU.
So clear the engine management light first, as there‘s a list of other items in the engine bay that can cause poor running that may require looking at, unfortunately.

Some gauges have been known to go to the other end of their scale simply due to a missing ground connection (earth), other than the earth straps under the bonnet the disco has/had a few connections the driver/passenger foot well.

lastly the removal of the Cats requires a different fuel trim, the a simple change of a resistor from with catalyst 3k9 ohm (White) to non-catalyst 470ohm (Green) incorporated in the engine harness at the ECU.

I assume your not in the UK, if you were then the engine in a D1 would fail is annual MOT test, just by cats not being present on the vehicle.

And kindly let the forum know how you get on.

Get rovergauge. make or buy a cable. Download the ZIP from Github. It's free, except the cable, but I think they were 4o pounds on ebay, or about half that to make, but you have to get all the bits.

14CUX has no "limp mode" in the traditional sense. If it's not running right, it's reading something wrong. It will use the "default" map, under certain conditions, but it should run OK, just a *bit* rich.

The 14CUX has 5 maps on board all the time. The tune resistor switches between them. On a disco, it would usually have been found in the ECU loom, under the steering column area.

It doesn't care if there are cats or not, just Lambdas. If there are lambdas, they need to be the correct ones and running a Lamba/Cat tune resistor for the ECU. If there are no Lambdas, run a non-cat tune. I have no cats, but lambdas, so run a cat-tune. Cats are post lambda, so cats or not makes no odds to the ECU reading the lambdas.

Removing the ECU main fuse or battery removal will clear codes - it doesn't store them in non-volatile memory.

If the engine light is back on straight away, something is out of spec.

You either need to measure every sensor, or plug in Rovergauge and see what it readings are. It'll give you the fault code too.

It's a very simple system. Way easier than a carb even

The temp gauge uses a differerent sender to the ECU. On a serpentine V8, there is an ECU temp sensor, Gauge temp sensor and a thermo-switch for the fans. Some diagarams have them listed wrong.