lucas power resistor

[tunepipe911]

Hey

Anybody knows where to find a LUCAS power resistor,the one fitted now is a 2PR 73184D,(Jaquar type??)
After driving the car today,it suddenly looses power and misfires sometimes,checked the resistor and could boil an
egg on it,so I quess this whas the problem,
Thanks for any help

Rudy

[KKson]

Was there one left over in the box of autojumble bits at the BBWF? There was certainly a resistor pack of some sorts?

Mark - is my memory failing me?

[mrzigazaga]

Hi Rudy..Yes Keith you are right i did bring one to the fest for the auto-jumble but Dominic took it home for me as i had no room in the car for all of it...I will see if he can post it on to you..I will call him later...Cheers..Ziga

[tunepipe911]

Thanks Mark,Keith,
I could transfer the money to him or have it send from a friend off mine in the UK,

Rudy

[hallsie]

Ive got one knocking about with my AFM and ECU, wherever that is at the moment!

You are welcome to it if the one Mark is talking about does not turn up.

Stu

[mrzigazaga]

Ok mate...I will call him a bit later and let you know..You are welcome to have it...Its not been tested as i bought it from fleabay..I can also send the bumper seal to you if you wish..Ziga

[honestjohntoo]

tunepipe911 said:

Hey

Anybody knows where to find a LUCAS power resistor,the one fitted now is a 2PR 73184D,(Jaquar type??)
After driving the car today,it suddenly looses power and misfires sometimes,checked the resistor and could boil an
egg on it,so I guess this was the problem,

Just looking for alternatives, perhaps not! If noticed immediately after the journey, maybe the fault is elsewhere and the heat observation is of the resulting symptoms.

If it's similar to the original resistor pack, inside the box are eight, six ohm resistors dropping nine volts each.

If they were on continuously then they will dissipate 8 X 6 X 9 = 432 watts. but they are not, I would reckon the maximum duty cycle is 10:1 so we are down to about 40 watts.

Imagine grasping a 40 watt incandescent bulb, still quite enough to be very hot with it all happening inside an aluminium box.

Even a 20:1 duty cycle would dissipate 20 watts. Still hot and therefore normal.

So given the sort of range the injectors would be firing at, and let's say driven enthusiastically, it's gonna be a pretty hot potato.

Is it possible this 'normal' heat has not been noticed before?

Moving on to the serious misfire! If, for example, your throttle pot was the cause, then the ECU would be energising the acceleration and full load fuel enrichment circuits quite a lot, sufficient to create more heat in the resistor pack than normal. Normal being with a good throttle pot!

And a bad throttle pot will really upset a perfectly tune system.

One can test both components quite readily with a multi-meter, deffo worthwhile if one is thinking of continued guesswork and pursuing the scatter-gun 'component replacement' route.

I'm sure someone will be able to do better arithmetic than mine to check for errors and omissions in the above suggestion.

Check out the test processes here: http://www.vintagemodelairplane.com/pages/Rover_Te...

[tunepipe911]

Hey

Could worth checking,
I was surprised by the heath it developped after driving,and to be honnest,never checked it before,

Rudy

Edited by tunepipe911 on Tuesday 10th June 18:52

[tunepipe911]

Checked voltage and instead off the 3.25 volts needed it had 2,2volts,
Will give it a spin next days and give results,

Rudy

[honestjohntoo]

tunepipe911 said:

Checked voltage and instead off the 3.25 volts needed it had 2,2volts,
Will give it a spin next days and give results,

Oops! None of the test requirements for the throttle pot speak about 3.25 volts but I assume you mean 0.325 volts. By itself that adjustment is not relevant to your problem.

The tests I have in mind are to check the smoothness of the throttle pot voltage as the throttle disc goes through the (approx) 90 degrees to wide open throttle.

I suggest you familiarise yourself with all the functions of the throttle pot to understand how and why a faulty carbon track can cause the effects I suggested.

At the risk of upsetting certain members of the forum I am pasting a section from my website to highlight the information you appear to need.

Testing

• Ignition on, engine not running.

• Check the integrity of the potentiometer, preferably using an analogue meter.

• SLOWLY operate the throttle mechanism by hand and watch the voltage reading
go smoothly to a maximum of 4.3 volts.

• If it proves impossible to get near the maximum voltage with the throttle fully
open then inspect the throttle quadrant and throttle assembly, the cruise control
quadrant (especially because it can foul it’s own mounting bracket), accelerator
pedal, driver’s side floor carpet and automatic transmission kick down cable.

• Correct any faults at these locations as they can prevent full throttle opening.

• Whilst not desirable, some set-ups may fall slightly short of the full voltage, say
3.7 to 4.1 volts, but it does not affect the system operation during normal driving.
However, full load driving (i.e. throttle wide open) may be adversely affected.

• If the reading is erratic or unstable causing the meter needle to flicker or vary
sharply then the potentiometer is probably faulty and will need to be replaced.

System response to normal and fault conditions

• Providing the voltage change is slow and smooth the injectors may be heard firing
or clicking just once as the assembly approaches full throttle. If the prior
maximum voltage measurement is undesirably low then, obviously, this function
cannot take place and the above mentioned full load fuel enrichment is denied.

• Open the throttle RAPIDLY and the injectors fire much sooner during rotation.

• This simulated fast acceleration, triggers supplementary injector firing to provide
extra fuel needed as soon as possible during the period of acceleration demand.

• However if the voltage rise is erratic it is very likely that the injectors will be
heard firing randomly or in sympathy with the sharply varying voltage reading
even when slowly operating the throttle.

• This is because the erratic voltage signal fools the ECU into thinking the throttle
is moving swiftly when it is not, triggering unwanted fuel enrichment under
casual driving conditions resulting in a randomly unstable fuel/air mixture leading
to very lumpy engine performance with gross adverse affect on fuel consumption.

• This random injection of extra fuel may not occur when the car is cruising at
constant speed with the throttle not moving. However even casual acceleration or
deceleration can cause havoc with mixture control.

• Alas, the potentiometer is prone to wear at the point where it is most used at
normal driving speed so the effects on normal driving are at their most noticeable.

• As already mentioned the erratic voltage readings are observed more readily with
an analogue voltmeter.

If necessary, I urge you to read all the EFi related information, there-in.