Discussion
have been playing around trying to get the griff better at tick over and low revs,and on checking the voltage on the afm found this set at 1.8 volts which is the correct cat setting, but as I have a fully decatted car with green fuel resistor, decided that perhaps it would be better set on the pre cats setting of 1.2 to 1.5 volts, and have therefor set it to 1.3v.
then set up the throttle pot and tickover, with the tickover set when engine was up to temperature, but, then read on the rpi site that the afm settings should be done when the engine is warm as well, whereas I did it when cold, I know the obvious is to re check again when warmed up, but do you think it will make a difference?
then set up the throttle pot and tickover, with the tickover set when engine was up to temperature, but, then read on the rpi site that the afm settings should be done when the engine is warm as well, whereas I did it when cold, I know the obvious is to re check again when warmed up, but do you think it will make a difference?
Just a warning shot about changing the map. TVR alter the Range Rover fueling in the Eprom in the ECU, but a chip I examined from a 3.9 Chim' only had the catalyst map modified,(There are 5 separate maps, ) and on the non cat resistor it was running a very lean Range Rover map, thats potentually bad news. Your best bet is take the cats out, but let it run the cat map,(unless you are 100% sure your non cat map is modified) as it all goes open loop above 2500 rpm anyway, so you dont loose any power.
You,ve confused me now. The green map is non cat, ie it does not need the lambda probe inputs, and is open loop all the time. The base CO setting is more critical on this set up, as you have no ability to alter the mixture via the ECU. The white map is for catalyst, and it makes no difference if the physical catalysts are installed or otherwise, as the lamda probes are pre the catalyst, so the ECU can tweek the mixture to keep the emmisions low and optimise the effectiveness of the cat, up to 2500 rpm (ie the for MOT emmisions test only.) Taking the cats out will help exhaust flow, but theres nothing much to be gained by running the non cat map.
sorry , probably didn`t explain it very well, running on green resistor, no cats at all, llambdas are left in so at mot time I put the main cat back in and switch to the whiter tune resistor, and presume that the afm will also need to be set back at the cat volts setting as well.
Edited by clive f on Wednesday 15th August 12:36
Edited by clive f on Wednesday 15th August 12:36
I beg to differ on the placement of cats. The standard lambdas are after the pre-cats and before the main cats.
However, the cats shouldn't affect the reading from the narrowband sensors. (unless they are those funny cats with an additional air pipe)
Oh, and since the Lucas ECU is MAF based, then engine size should be compensated for automatically to a reasonable extent, as long as the sensor doesn't hit the limit of what it'll read.
However, the cats shouldn't affect the reading from the narrowband sensors. (unless they are those funny cats with an additional air pipe)
Oh, and since the Lucas ECU is MAF based, then engine size should be compensated for automatically to a reasonable extent, as long as the sensor doesn't hit the limit of what it'll read.
Edited by dnb on Wednesday 15th August 15:14
Interesting, as Ive only seen the ECU with cats on a Ginetta, and the probes are pre cat. As they are oxygen sensors , maybe the oxygen level does not change significantly through the pre cat ? I would have thought the precat would reduce the oxygen as it changes some carbon monoxide to carbon dioxide, but Im not a chemist. Im told the range of the probes used is so narrow, that they will only toggle between .3 and .7 volts below 2500 rpm. Above that they simply show rich. The important bit Im trying to say, is there is no active fuel adjustment above 2500 rpm with the lamda probes. Even with all the various sensor outputs (including the MAF) you are still relying on the fixed digital data held within the Eprom, and if this is wrong in the first place (as it is on the Range Rover map) it will still make the engine run lean. Ive measured the Range rover map,(3.9) and it runs around 14:1 a/f ratio above 4500 rpm where I think you really need about 12:1 for maximum power, and to preserve your engine from the perils of running lean at high RPM.
Mark
Mark
blitzracing said:
Interesting, as Ive only seen the ECU with cats on a Ginetta, and the probes are pre cat. As they are oxygen sensors , maybe the oxygen level does not change significantly through the pre cat ? I would have thought the precat would reduce the oxygen as it changes some carbon monoxide to carbon dioxide, but Im not a chemist. Im told the range of the probes used is so narrow, that they will only toggle between .3 and .7 volts below 2500 rpm. Above that they simply show rich. The important bit Im trying to say, is there is no active fuel adjustment above 2500 rpm with the lamda probes. Even with all the various sensor outputs (including the MAF) you are still relying on the fixed digital data held within the Eprom, and if this is wrong in the first place (as it is on the Range Rover map) it will still make the engine run lean. Ive measured the Range rover map,(3.9) and it runs around 14:1 a/f ratio above 4500 rpm where I think you really need about 12:1 for maximum power, and to preserve your engine from the perils of running lean at high RPM.
Mark
The Blade will be along shortly Mark Mark
spend said:
You do know what they mean by pre-cats? They are small free-flowing cats in the headers to assist in warm-up emissions before the main cat gets up to operating temperature. The TVR lambda sensors sit between the pre-cats and main cat.
Dave
Only h0m0s use <2500rpm anyway!
Dave
Only h0m0s use <2500rpm anyway!
How you doin Dave 
If you mean whats this imposter doing here ??, The Ginetta G33 was part designed by an Ex TVR engineer Noel Palmer, Same engine setup, desiged along simular lines (although much lighter and basic construction) at the same time to compete with the TVR S3 and Griff, but bad cash flow meant never more than 100 where made, so I feel a kind of kindred spirit. Apart from that the TVR forums have been most informative !!
Don't take a fence... Its just a very confusing term we have 'precat' cars (before legislation), we have 'pre-cats' (in the manifolds) and often it could be interpreted as 'before the main cat'. Its hard enough write clearly about the things even if all are careful, the possibilities of misinterpretations are great There is also a large variation in the maps used across the TVR chips, I don't think you can take anything for granted 
Dave
There is also a large variation in the maps used across the TVR chips, I don't think you can take anything for granted Dave
blitzracing said:
Stuff including "Im told the range of the probes used is so narrow, that they will only toggle between .3 and .7 volts..."
Mark
You summed that up pretty well there. Other than you should differentiate between high revs and high load. You only need a rich mixture when the engine is under load. When cruising, the mixture can be leaned out quite substantially - even past the stoichiometric point. (Mind you if you experiment with these things, make sure you have a decent EGT and wideband lambda meter to keep an eye on things!!)Mark
I'm not sure if the Lucas ECU switches the lambdas based on load, RPM or both. (I know of ECUs that do one, other or both) Whatever happens the car runs open loop under even mild acceleration. (Unlike mine which is just odd...
) Would have replied last night, but I was trying to fix my sticky Griff speedo while stopping the cat (the sort that goes meow) from getting tangled up in the wiring...
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