Kangaroo Griff

[GreenV8S]

The ECU has different internal maps and modes of operation, and the tune resister is used to chose which ones to use. The tune resister needs to be within the correct range in order for the ECU to select the correct map.

[griffter]

GreenV8S said:

The ECU has different internal maps and modes of operation, and the tune resister is used to chose which ones to use. The tune resister needs to be within the correct range in order for the ECU to select the correct map.

Apparently the 14CUX ecu will default to the cat (500) map with no tune resistor fitted. Makes you wonder why one was fitted to the 500 at all.

[wixer]

GreenV8S said:

The ECU has different internal maps and modes of operation, and the tune resister is used to chose which ones to use. The tune resister needs to be within the correct range in order for the ECU to select the correct map.

Does this mean that re-chipping your ECU is a waste of time and money then ?? It sounds like all you need to do is piddle about with the resistor, until the car runs correctly. Be a lot cheaper aswell !!

[red griff 500]

I'm under the impression that there are only two states for the 14CUX - pre-cat or cat and each is selected by a different resistor value. If this is the case, then why does fitting a new Mod-wise resistor make an improvement, unless the original resistor is faulty?

Is this resistor a black plastic square thing with spade terminals at each ends, located in the harness next to the AFM? I have measured a volt drop across this, but never realised that it was the resistor that selected the cat/non-cat fuel map.

[raw-sewedge]

The resistor is attached to the loom in the passenger foot well. It hangs off a fly lead down there.

I can't find any evidence to suggest that there are more than 2 modes of operation associated with the resistor. As far as I can tell there are 2 resistors:

3.7K ohm - for cat cars, which enables the closed loop control with feedback from the lambda sensors
470ohm - for non-cat open loop control. No fine tune with feedback from lambda sensors.

I don't have enough info on the ECU to know exactly what this resistor does but my gut feeling is that it is simply an on/off input for the lambda feedback circuit.

No resistor should light the MIL light.

[griffter]

More info here:

www.rpiv8.com/faq-inj.htm#tuneresistor

and here:

www.rpiv8.com/carbs-2.htm#Tune-resistor

[red griff 500]

Thanks Griffter, I always wondered what THAT resistor was doing in the footwell. In that case, can anybody tell me what the black square thing with the spade terminals situated close to the AFM is then? It has "Lucas" moulded into the case.

[Mark Adams]

Everything you ever wanted to know about the Tune Resistor....

All 14CUX ECUs contain five sets of engine tune information. The tune to be used is selected by the choice if Tune Resistor. All 14CUX vehicles are fitted with a Tune Resistor, except certain North American Specification (NAS) vehicles. In some cases NAS vehicles may have provision for a Tune Resistor to be fitted (i.e. socket fitted to the loom in the normal place), whilst others have this resistor taped inside the wiring loom to prevent anyone interfering with it.

Always ensure that the correct Tune Resistor is fitted to the vehicle. If an interchangeable Tune Resistor is fitted, then it is located as follows. Follow the wiring loom back from the ECU plug. About twelve inches (30cm) away, a small group of connectors and relays emerge from the loom. Amongst them is a small blue plastic two-pin plug that connects to the Tune Resistor.

The Tune Resistor itself is located in a clear plastic heat-shrink tube, connected to a blue plastic plug by two wires. Tune resistors are identified by the colour of these connecting wires. There is considerable variation according to application so please check for the correct version for your vehicle. If the vehicle is modified then the supplier of the modified ECU software should have specified the correct tune resistor to use.

Colour Ohms Cat Common Application
Red 180 No Australian 3.9
Green 470 No Europe & UK 3.9 (or 3.5 Disco)
Yellow 910 No Gulf States 3.9, or Europe & UK 4.2
Blue 1800 Yes Gulf States 3.9, or Europe & UK 4.2
White 3900 Yes Europe & UK 3.9 (or 3.5 Disco)

If there is any doubt about the presence or value of a Tune Resistor then the simplest method of checking it is as follows. Disconnect the ECU plug, and measure resistance between pins 5 and 27. The table above gives a list of the possible values:

Note that certain NAS vehicles do not use Tune Resistors, even though there may be a facility to fit one. In these cases the ECU will always operate as if a White Tune Resistor were present, and Oxygen Sensors are mandatory. If a Tune Resistor is later fitted, then it will be ignored. This is a function of the software version used inside the ECU, so of course it may be modified by a software upgrade.

For those of you who wonder if there is some advantage to be gained by experimenting with the resistor value - the answer is no! It must assume one of five particular values – if it does not then the system will detect a fault condition.

It is of particular importance to ensure that the choice of a cat or non-cat tune is correct.

If a non-cat tune is selected where cats are fitted, then the cats may be destroyed. This happens because a non-cat tune will exercise no control over the cruise fuel setting. If the mixture is excessively lean or too rich, this can cause very high hydrocarbon levels (unburnt fuel) in the exhaust. This in turn can be burnt in the cats, leading to severe overheating. Certain fault conditions that cause over-fuelling will be undetected, which can also lead to severe catalyst overheating (and even a fire). Any input from Oxygen/Lambda sensors will be ignored.

Where a cat tune is selected, but no oxygen sensors are fitted, the car will run terribly rich. Eventually this will cause a fault flag to be set within the ECU, thus forcing it to drop into limp-home mode.

Note that the default (or limp home) tune is a cat tune, and will therefore always cause rich running on a car not equipped with Oxygen/Lambda sensors. If no Tune Resistor is fitted then the default tune will be selected (other than NAS vehicles described above).

Should the Tune Resistor be changed or disturbed for any reason, the ECU should be reset afterwards by disconnecting it for ten seconds. Failure to do this may cause the ECU to select the default tune.


>> Edited by Mark Adams on Tuesday 23 August 16:43

[raw-sewedge]

XLNT, thanks for clearing that up.

So I was correct in thinking that a 500 with a White resistor will possibly knacker it's cats if run with a Green resistor.

[Mark Adams]

Yes Dave - you are right. You should NEVER use a non-cat resistor on a cat car. You can actually set fire to the car if it is sufficiently overfuelled, since the cat can reach 1200-1500 Centigrade.


The TVR 500 cat chip only has a 3.9 tune on the Green map. This causes overfuelling at part throttle, and underfuelling at high throttle.

[red griff 500]

Thanks for the info Mark, very interesting and helpful. But back to my original thread question; why does my Griff kangaroo, or misbehave in other ways when it gets wet?

Also, just for interest, what is the black square thing which has a volt drop across it, with spade terminals at each end situated close to the AFM? It has "Lucas" moulded into the case.

Steve

[wixer]

red griff 500 said:

Thanks for the info Mark, very interesting and helpful. But back to my original thread question; why does my Griff kangaroo, or misbehave in other ways when it gets wet? Also, just for interest, what is the black square thing which has a volt drop across it, with spade terminals at each end situated close to the AFM? It has "Lucas" moulded into the case. Steve

And why is it when I tried another tune resistor, my car virtually ceased to kangaroo ??

The black squre thing is your ballast resistor. If you follow the wire through the loom, if you can, it will be connected to your coil.

[raw-sewedge]

wixer said:

And why is it when I tried another tune resistor, my car virtually ceased to kangaroo ??

I'd guess it's down to the feedback from the Lambda leaning your mixture out at Idle.

We could do with some way of monitoring the Lambda output, some form of oscilloscope to look at the output from the Lambda sensors to see what they think your exhaust gasses are like and how much it's compensating.

or

We need a Lambda Gauge

[wixer]

raw-sewedge said:

wixer said: And why is it when I tried another tune resistor, my car virtually ceased to kangaroo ?? I'd guess it's down to the feedback from the Lambda leaning your mixture out at Idle. We could do with some way of monitoring the Lambda output, some form of oscilloscope to look at the output from the Lambda sensors to see what they think your exhaust gasses are like and how much it's compensating. or We need a Lambda Gauge

Or a dyno session I s'pose ??

[MisterT]

wixer said:

And why is it when I tried another tune resistor, my car virtually ceased to kangaroo ??

Wixer
I have found the same, see my earlier contribution.

Am I being niaive to think or suggest that if a range of Griff 500's in standard trim are all suffering the same problem, then a dyno session to produce a modified ecu chip might work as well in the dyno'd car as all the others?

Clearly this approach may result in some sort of compromise along the way as it wont be as precise as an individual tailoring of the ecu map to an individual car. However, if the compromise was acceptable this could benefit us all as the cost of dyno session could be spread over a number of cars.

Also this doesnt take account of other possible maladies which might be causing similar symptoms.

raw-sewedge said:

it's down to the feedback from the Lambda leaning your mixture out at Idle.

I agree, based on my experience I am as certain as I can be (as a layman who is not technically qualified in matters ECU and fuel injection) that my symptoms are caused by some form of incorrect feedback from the lamdas to the ecu. I have two tune resistors, the original and one Rob at V8 Developments fitted, when I swap them the car changes like Jekyll & Hyde.

Mark
Would it be possible to produce such a chip 'to suit all'? I'm sure there are a number of owners out there who would dearly love to resolve this malady but cannot afford or justify the expense of an individual dyno session, but the cost of a chip change might be acceptable. What do you think?

Mike

[griffsmith]

I'm not disagreeing that the lambda feedback couldn't be one cause. But that wouldn't explain why my precat does it as well. Maybe the rich mixture caused by using a green tune resistor is only masking the effect for you..

Could this be down to timing? or sensitivity to combustion speed caused by lean mixture and the accuracy of the trigger point or inconsistency of spark size.. This may explain why so may people claim success from removing the vacuum tube as its removing some advance.

Mine seemed to get more noticeable when I changed to a new coil and amp (both 'correct' parts) they were doing a better job of sparking, thus changing the combustion 'burn' time?

[GreenV8S]

I believe that Mark Adams does have a range of 'off the shelf' chips for standard cars, and if your car is typical, and in good working order, this chip might give an improvement in tractibility and perhaps a slight gain in power. But it doesn't sound to me as if your car is in good working order at the moment (because they don't all do that, sir) so the right approach is to correct the problems at source rather than try to work round them with the fuel map. It may be that there are several cars with similar faults that need to be corrected, I don't think it follows that the standard maps are causing it.

I reckon your best approach would be to get a TVR specialist to check it over as a starting point, to see whether thee are any fault codes and whether the engine management system is basically working correctly. If that doesn't find a fault then get in touch with Mark Adams to give it a definitive once-over. This might show that the map is wrong, in which case I expect Mark would correct it for you, but I wouldn't expect him to do that until he had proved the rest of the system was A OK.

[mrsflipflopgriff]

Ours has been back 5 or 6 times to the builder of the engine so they should be able to sort it - no.
Tune resitor changed and it is about 85% cured. If it is this simple surely these guys should be able to resolve it. Not sure if the other 15% is cureable.
FFG (on Mrs FFG's machine)

[red griff 500]

I originally started this thread because my car was behaving diabolically in a kangaroo sort of way on one journey. It had recently rained, and my car often plays up after it's rained or been washed. Since then, it's been as right as rain (pun intended).

I conclude from this that damp has an effect on one or more sensor signals which causes the ECU to get its knickers twisted (I suspect the lambda sensors only because of their exposure and the exposure of their various connectors in the engine compartment).

If our systems are a bit sensitive to these signals, then the robustness of the signals needs to be sorted, changing fuel maps does not seem to be a good solution even though it may eliminate the symptoms.

It may be that the tolerance on the output of the sensors needs to be tighter than the manufacturers allowable tolerance to work satisfactorily with our systems.

[wixer]

red griff 500 said:

I originally started this thread because my car was behaving diabolically in a kangaroo sort of way on one journey. It had recently rained, and my car often plays up after it's rained or been washed. Since then, it's been as right as rain (pun intended). I conclude from this that damp has an effect on one or more sensor signals which causes the ECU to get its knickers twisted (I suspect the lambda sensors only because of their exposure and the exposure of their various connectors in the engine compartment). If our systems are a bit sensitive to these signals, then the robustness of the signals needs to be sorted, changing fuel maps does not seem to be a good solution even though it may eliminate the symptoms. It may be that the tolerance on the output of the sensors needs to be tighter than the manufacturers allowable tolerance to work satisfactorily with our systems.

I'm glad you did start this thread, as it seems there are alot of people out there with the same problem.

As your car only plays up when wet, have you checked all the lambda connectors ?? It wouldn't be the first time I've found a nice, green, furred up electrical connector on my car.