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MG MGB GT V8 Factory Originals Technical - Tune resistor Hot wire

Orrigionaly I set up my car without oxygen sensors and used a 470ohm tune resistor on advice from others.
I am trying to generate a little more power from the 3.9 I've got and was looking a putting in Oxygen sensors. However I came across a Rangerover site that leads me to believe that I don't actually need oxygen sensors if I am using a 470ohm tune resistor and would be wasting money and effort installing them. Infact the Rangerover site I accessed from the archives had a copied a large chunk from the rangerover shop manual and lambda sensors were under the heading of "Emmissions control, Lambda sensors-catalytic converter cars only".
Does anyone know this for sure?. Do lambda sensors increase power out put significantly or not?.It would mean someone deliberatly unplugging their sensors and plugging in a 470ohm tune resistor so that they can show that the trouble they took setting up oxygen sensors was time and money wasted. A fairly ballsie effort by someone genuinly interested in getting at the truth. Most people wouldn't want to know.

Anyway the 470 ohm resistor was under the heading "European non cat' cars" There was also mentioned a 910ohm tune resistor for Saudi non cat'. I know that higher CO levels generate more power & I'm wondering if the Saudi tune might generate a little more power since I have the impression (possibly mistaken)that Saudi care about CO levels a whole lot less than the Europeans. Any thoughts?
Peter

Pete,

I originally fitted the EFi without Lambda sensors.

The local Lucas Bosch guy told me the ECU runs the car in 'limp home' mode if it does not detect Lambda sensors.....no great problem with this, as the sensors evidently only come into play when the system is in 'closed loop' mode ( I think that means when cruising...when the ECU detects C0 levels and adjusts mixture accordingly) I found performance was unchanged, but fuel consumption improved slightly
when sensors were fitted.

Regarding tune resistor, I have the green one (470 ohm).

TVR experimented with a variable resistor fixed on the outside of their ECU at one time..( and my father had a Mercedes 280 coupe some years ago with a similar device under the dash)....you could try this , it should not be too difficult to wire a rheostat in the resistor plug, you would need to know the resistance range, I'ts got to be better than the scam 'tuning chips' offered on E Bay which just alter the water tepm sensor resistance and allegedly fool the ECU into running rich.


Mike
Michael barnfather

Micheal,
Thanks, it really sounds like lamda sensors are primarily aimed at not overloading the cat' converter with excess CO. ie not worth the trouble/expense unless you've already got them.
I might give it a shot, re: tune resistor. Wish I knew what the Saudi CO regulations were compared to European, that would tell us. I wonder if you can adjust/control the computer programed mixture with a variable resistor across a wide range. If TVR people (and Mercedes) was playing around with it it seems a possibility and if I were designing that computer I'd put something just like that into it for fine tuning the mixture.
Can't find that useful site I mentioned but this was the address, might work.

http://www.rangi.com/rrkb/nf_articles/212.htm
Peter

Peter,
According to the TVR service booklet on the 14CUX, they used the following resistors;

Australia (red) 180 ohm
European non cat (green) 470 ohm
European cat & USA (white) 910ohm
Saudi (yellow) 3k9

It's wired between pins 5 & 27 (earth) on the ECU.

Could Saudi petrol be different from European perhaps.....I'm considering the variable resistor option, the tune resistor wires are very accessable on my set up (in passenger footwell), and I'm sure it would not be difficult to substitute a rheostat....my wife works in an electronics service company AM, I will pick their collective brains.

Mike
M Barnfather

Not so much different petrol I suspect, but different emmissions regulations. As you know how rich or lean the mix is will determine how much CO is being generated. I seem to recollect that lean means the engine runs hot and produces more CO.
The optimum power and CO emmisions are unlikely to correspond. Infact we know this because older '60's style cars which were tuned for power without regard for emissions are known to make more CO.
Could you check that last figure for saudi non-cat, the rangerover site (which no longer seems availiable) had that as 910 ohm.
What I'm wondering is if increasing the resistance steadly changes the mix steadly, or conceiviably the program jumps to another set of parameters. I'm betting on steady given the rage of tune resistors.
Also possibly, along the lines of your remarks, the quality of fuels in saudi might be low and they are running the mixture rich to keep the engine cooler.
What will tell us are the CO emmission regulations in Europe vs Saudi, anyone know?

Well later in the week I'm off to the electronics shop for a 10 turn one kilo ohm resistor. Hope I don't blow up the computer!
Peter

Peter, bear in mind I'm using the TVR 14CUX service booklet, not the Range Rover one, and there may be some variations in spec between Saudi TVR's and Range Rovers.

I would not have thought that there is much of risk involved of damaging the ECU, but there are lots of S/H ones out there.... I have a couple I've been playing with (contemplation re-chipping).


Mike
M Barnfather

Came across the remark (archives ) that the Speed killjoy on the std chips works by switching off the petrol pump. If true this presents an easy way around it.
Peter

I've not got the speed sensor wired in, and I'm pretty sure TVR didn't use it either !!!

I've always assumed it was incorporated on the Range Rover because of the tyre ratings they used.


Mike
M Barnfather

Thats interesting, I've not either however I was going to wire one in on the assumption that the speed of the car would effect the program more than the oxygen sensors, apparently not. I'm told also that the absence of a speed sensor can cause idleing problems. I do know that after extended periods at high speed, when I stop, the engine does drop a little too far in revs hunt around a bit before stabilizing at 600.
If it's true about the way the speed limiter works it's sort of ironic really. People going to all the trouble of running wires back to the computer and its relay and then all the way back to the pump(s) and then haveing to rechip to override the kill joy, when they could have simply attached the injection pumps direct to the SU wires.
Peter

Yes Pete,

I understand that the idle is smoother with the sensor in place, but mine's not that bad in the first place.

I don't think many use the speed sensor on their conversions

Mike
Michael barnfather

Hi Pete & Mike,

I've got a speed sensor on my roadster, they are used not only to limit top speed on Land Rovers, but also to put the ecu into 'idle mode' when the vehicle has stopped moving. TVRs with rover v8s do use a speed sensor, but the speed limiter function is disabled, which is essential on a TVR!

Mike
m clemas

Mike Clemas,

What have you used to provide the speed information? something on the speedo cable or propshaft, or what?

Mike H
Mike Howlett

Peter,

There is a company here in the UK called Emerald which has a web site with some very useful information.
The link is http://www.emeraldm3d.com/em_ab_em.html

I found it an interesting read, hope its of help.

Kevin Jackson.
K.R Jackson

Mike H,
I used a Range Rover speed sensor, the speedo cable comes out of the gearbox (SD1 5speed) into the sensor, and another speedo cable comes out the other side of the sensor to the speedometer gauge. I had the cables made by 'Speedy Cables' as the R.Rover ones had different fittings. There are only two connections on the sensor, one goes to ignition, the other to pin 6 (yellow wire) on the ecu (14cux) If your intrested I'll send you a picture of the sensor fitted on the car.


Mike C
mike c

Mike C,

Too many Mikes! Yes please, I'd like a picture if it's no trouble. Sorry I haven't responded sooner, but have been out of contact for a couple of days.

My e-mail is shown above.

Mike H
Mike Howlett

Today, I wired up a switchable tune resistor system for my 3.5 hot-wire system. One position for the 470 ohm (European non-cat) and one for the 3900 ohm (UK and America with cat). I haven't much testing on it, but it seemed to me that the ECU only reads the resistor value upon initial power-up. Changing the resistance value when running did not seem to produce a change.

The 470 ohm seems richer, at least at idle. When the 3900 ohm was selected before starting, the idle mixture seemed leaner (non-scientific sniff test). However, when start-up was done with the 470 ohm then switched to 3900 ohm whilst running, there did not seem to be any change in the idle mixture.

Both settings seem similar driving around the block. In fact, the system works without any resistor in place but smells very rich. More testing to do.

I was trying to determine if I could fool the ECU into producing longer injector pulses if nitrous is injected.

Anyone have any insight regarding this?

Thx,
Edd Weninger

Edd,

Mine goes into the local Lucas/Bosch agent on Thursday for it's annual pre-continental trip check-up, I'll have a word with him and see if he knows the answer.


Mike
Michael barnfather

This thread was discussed between 26/05/2005 and 13/06/2005

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