ECU Resistor

[crazycraig]

Is there anyone out there that has an idea as to what this resistor does?



Whilst in the drivers footwell the other day to replace a fuse, I noticed a resistor with a blue plug unconnected coming from the loom.

I know for sure I haven't unconnected it and the car seems to run fine as it is, so I'm a little reluctant to plug it back together until someone can give me a pointer as to what it is!

Craig

[harrow_chim]

The value of the resistor sets the ECU for either catalytic converted or not. There should be one connected. It is covered in Mr Heath's fine book (aka Bible) and in various posts in the Chimaera forum.
Nick

[crazycraig]

So if it is the ECU cat/non cat resistor, by not having it connected, I guess that would mean it's running on the wrong map and would be running under powered, or am I wrong?

Can someone explain?


ps- the car has all it's cats in.

[Graham]

Thats a white resistor which puts the ecu into cat map. the green one changes it to non cat.

Im not sure quite what the ecu would do without one, but If you've got cats I'd plug it back in sharpish, or you could bugger the cats.

It can be quite handy to diagnose a lamba sensor fault by changing the resistor. we've just had a MG RV8 with an odd running problem. changed the tune resistor to a non cat and it runs fine !!!! pointing to the lambas giving off odd reading..

G

[Mark Adams]

The Lucas ECU contains six tunes. There are three non-cat ones, two cat ones, and a default ("limp-home" version. A cat tune requires the use of Oxygen sensors, whereas they are ignored on non-cat tunes.

If the tune resistor is absent or defective, the ECU has to use the default tune which is always a cat tune.

Note that in the TVR modified program, they never change the default tune from the standard Land Rover 3.9 version (I always change the default tune in my Tornado software to an appropriate default).

Since your car is a cat 5.0 Litre with no tune resistor, it is running on a default 4.0 Litre cat tune.

I would strongly advise that you plug the tune resistor back in, but be aware that doing so may reveal an underlying fault. After you have re-fitted the Tune resistor, you should reset the ECU as follows. Make sure the ignition has been switched off for at least ten seconds, and then simply release the plug from the ECU. Wait ten seconds, reconnect the ECU and you're done!

[crazycraig]

Thanks Mark.

So by plugging it back in, does that mean I'll bring back on the 'Warp Engines'.

Seriously though, the cars been running well, as far as I know it's not been connected in the year I've owned it, but from what you've said I guess it's not been performing as it should.

Excuse my ignorance, but does the 4 ltr map limit the amount of fuel/air into the engine or retard something that should be there on the 5 ltr, please expand.

Your humble servant.


Craig

[Graham]

Mark Adams said:

The Lucas ECU contains six tunes. There are three non-cat ones, two cat ones, and a default ("limp-home" version. A cat tune requires the use of Oxygen sensors, whereas they are ignored on non-cat tunes.

SO does that mean with a little help from someone like your self i could come up with 3 maps ( non cat) for the racer. DRY, Wet and transport (i.e. when its at the paint shop so they cant do donut!!!) and All i'd need to change is the resistor, or does the tune only tweek the main map


cheers

G

[geoffvalenti]

Graham said:

Thats a white resistor which puts the ecu into cat map. the green one changes it to non cat.

I'm not trying to be funny, but it looks blue to me

[Graham]

geoffvalenti said:

Graham said: Thats a white resistor which puts the ecu into cat map. the green one changes it to non cat. I'm not trying to be funny, but it looks blue to me

THATS the connector not the reistor. its the wires that are coloured

[geoffvalenti]

Graham said:

geoffvalenti said: Graham said: Thats a white resistor which puts the ecu into cat map. the green one changes it to non cat. I'm not trying to be funny, but it looks blue to me THATS the connector not the reistor. its the wires that are coloured

So to clarify things (for me) and so I haven't got to grovel in the foot well of my Griff in this weather

The plastic sleeved resister in the picture is connected to the blue plug (it's not clear in the pic) and the two blue bits shown should be connected together?

Sorry for the stupid questions, but if you don't ask etc.

As you can probably tell, I've only had my Griff a few months

[trackcar]

Graham said:

Mark Adams said: The Lucas ECU contains six tunes. There are three non-cat ones, two cat ones, and a default ("limp-home" version. A cat tune requires the use of Oxygen sensors, whereas they are ignored on non-cat tunes. SO does that mean with a little help from someone like your self i could come up with 3 maps ( non cat) for the racer. DRY, Wet and transport (i.e. when its at the paint shop so they cant do donut!!!) and All i'd need to change is the resistor, or does the tune only tweek the main map cheers G

you could do it yourself with a 200 pounds megasquirt .. or different sized blocks of wood under the loud pedal

[Graham]

geoffvalenti said:

The plastic sleeved resister in the picture is connected to the blue plug (it's not clear in the pic) and the two blue bits shown should be connected together?

yes and the different coloured wires going from the blue connector to the sleaved resistor tell you what resistor it is ( or you could read the clolured bands on the resistor is self ).

if you do go grovelling around down there dont be surprised if all the wiring and the ecu fall on your head. thats normal and nothing to worry about

[crazycraig]

geoffvalenti said:

So to clarify things (for me) and so I haven't got to grovel in the foot well of my Griff in this weather The plastic sleeved resister in the picture is connected to the blue plug (it's not clear in the pic) and the two blue bits shown should be connected together?

The plastic sleeved resistor is connected via 2 cables to 1 end of the blue connector and this should be plugged into the other blue connector which in turn is taped back into the loom and back to the ecu.

Also, if you are checking the resistor and have a multimeter, it may be worth checking the value of the resistor as if it's broke, then the ecu will not see it and you'll be in the same boat as I was, ie. a 5ltr running on a 4ltr map.


Craig

[Mark Adams]

geoffvalenti said:

The plastic sleeved resister in the picture is connected to the blue plug (it's not clear in the pic) and the two blue bits shown should be connected together?

One of the joys of Griff/Chim ownership is an unwelcome familiarity with the gubbins in the footwell! It's not a silly question at all IMHO, so ask away.

As Graham says, the blue bits are the connectors. The Tune Resistor itself is located in the clear plastic heat-shrink tube, connected to the blue plastic plug by two wires. Tune resistors are identified by the major colour of these connecting wires, and it is important to have the correct version for your vehicle. So yes - the two parts of the blue connector should be plugged together.

Graham said:

SO does that mean with a little help from someone like your self i could come up with 3 maps ( non cat) for the racer

Yes you can. Each tune contains quite a lot of information, including rev limits. The only slight pain is that you need to reset the ECU after changing a tune resistor, although just swapping such a simple component is a very convenient way to achieve the result. A 2500RPM rev limit would definitely take the fun out of a donut!

crazycraig said:

does the 4 ltr map limit the amount of fuel/air into the engine or retard something that should be there on the 5 ltr, please expand

There are several reasons why the different tunes are important. Firstly there is the overall fuel requirement, which is obviously higher for the larger engine. The second issue is related to the way in which fuel is metered, in this case using the airflow meter.

In order to calculate the fuelling required for the engine, the ECU looks at engine speed and load. Load is calculated by airflow into the engine, which is proportional to the torque output. Clearly then, airflow is closely related to engine capacity. The ECU program contains details of the highest airflow that will be seen for the engine, and hence determines the operating load range.

Where a 5.0 Litre engine is used under a 4.0 Litre map - although the engine will run reasonably well - the effect is as follows. At light throttle the larger motor will make much more torque, so the ECU will be working much higher up the operating range than is appropriate. In this case, the fuelling is likely to be over-rich.

As the load increases past half to two-thirds throttle, the ECU will now be working at the upper limits of torque for the smaller motor. This means that the fuel is already at a maximum, so as load increases there is no more available.

In practice this means that the engine runs over-rich at light throttle, and too lean at full throttle. For cars on a cat tune the Oxygen sensors can correct the light throttle low-speed area to some extent, however there may be some conflict (shunting) if the Oxygen corrections are very large. At high/full load, the engine will run too lean.

[crazycraig]

What can I say.



Thanks Mark


Craig

[JonRB]

Mark Adams said:

Where a 5.0 Litre engine is used under a 4.0 Litre map [...] In practice this means that the engine runs over-rich at light throttle, and too lean at full throttle. For cars on a cat tune the Oxygen sensors can correct the light throttle low-speed area to some extent, however there may be some conflict (shunting) if the Oxygen corrections are very large. At high/full load, the engine will run too lean.

Sounds like exactly the symptoms my Chimaera 500 is exhibiting.

(Having said that, Mark, you've seen the dynoplots for my car and concluded it wasn't looking too bad for a standard 500)

[chassis 33]

Mark Adams said:

Yes you can. Each tune contains quite a lot of information, including rev limits. The only slight pain is that you need to reset the ECU after changing a tune resistor, although just swapping such a simple component is a very convenient way to achieve the result. A 2500RPM rev limit would definitely take the fun out of a donut!

Mark, surely this isnt really a problem on a race car, becasue once the master kill switch is off the only thing thats allowed to have power to it is an electrically triggered fire extinguisher, the ECU will be reset by virtue of the fact it is without power for more than 10 seconds (from your earlier post).

Regards
Iain

[Graham]

chassis 33 said:

the only thing thats allowed to have power to it is an electrically triggered fire extinguisher

Which should be on its own independantly powered electrical circuit anyway ( i.e. a 9v battery)

[chassis 33]

Yes, but it is mentioned as the only thing allowed a permanent powersupply in the blue book.

Regards