throttle pot anomoly
Discussion
You're never too old, or been working on these things too long to find something new.
Not all throttle pots are the same. eek.
Background : I've got a cerbera in for the new emerald k6plus dual lambda dual throttle and adaptive trim tables.
All went well, car made 411hp which is great.
The problem came with the midrange running .. the fuelling on the odd bank was trimming nicely and I was mapping/updating the fuel map based on the trim table on the odd bank .. however the even bank was trimming more and more negative .. into the teens of percent negative in the mid load areas.
It was ok at idle, and ok towards full throttle .. but in the middle of the loads sites there was a curious inbalance.
At first I thought it was the usual cerbera issue of the throttle arms being at the incorrect angles relative to each other .. it's sometimes the case that one bank is effectively higher geared on opening than the other. The factory knew about it and corrected it and indeed on most cars the inbalance doesn't really make a great deal of difference to the running, but on some other cerbs it does. I modify the arms on the worst cars to bring them both back in line.
Except on this car that wasn't the case.
On opening the throttle I could watch the even bank percentages rise much faster than the odd bank .. resulting it reading a higher load row on the map, adding too much fuel, and causing the adaptives to trim massively on that bank.
So during a process of elimination and getting towards the end of my ideas of what it could be, in depseration I swapped over the throttle pots bank to bank .. and now it was the odd bank rising too quickly, and having the negative trimmed table ..
The output of the two throttle pots was different for any given throttle angle by as much as 8 percent in the mid load area.
Both are blue pots and both are marked E2936 so have both come from a tvr parts supplier.
I found that the last of my black pots from the group buy last year was an exact match for one of the blue pots on the car, so the car now has two pots which are in-sync and the adaptive tables differ only a few percent as you'd expect.
So .. just because you have a blue throttle pot with the correct part number don't assume it's electrically identical to the ones already fitted.
I've never seen this mentioned before, but has anyone else ever come across a similar situation ?
Not all throttle pots are the same. eek.
Background : I've got a cerbera in for the new emerald k6plus dual lambda dual throttle and adaptive trim tables.
All went well, car made 411hp which is great.
The problem came with the midrange running .. the fuelling on the odd bank was trimming nicely and I was mapping/updating the fuel map based on the trim table on the odd bank .. however the even bank was trimming more and more negative .. into the teens of percent negative in the mid load areas.
It was ok at idle, and ok towards full throttle .. but in the middle of the loads sites there was a curious inbalance.
At first I thought it was the usual cerbera issue of the throttle arms being at the incorrect angles relative to each other .. it's sometimes the case that one bank is effectively higher geared on opening than the other. The factory knew about it and corrected it and indeed on most cars the inbalance doesn't really make a great deal of difference to the running, but on some other cerbs it does. I modify the arms on the worst cars to bring them both back in line.
Except on this car that wasn't the case.
On opening the throttle I could watch the even bank percentages rise much faster than the odd bank .. resulting it reading a higher load row on the map, adding too much fuel, and causing the adaptives to trim massively on that bank.
So during a process of elimination and getting towards the end of my ideas of what it could be, in depseration I swapped over the throttle pots bank to bank .. and now it was the odd bank rising too quickly, and having the negative trimmed table ..
The output of the two throttle pots was different for any given throttle angle by as much as 8 percent in the mid load area.
Both are blue pots and both are marked E2936 so have both come from a tvr parts supplier.
I found that the last of my black pots from the group buy last year was an exact match for one of the blue pots on the car, so the car now has two pots which are in-sync and the adaptive tables differ only a few percent as you'd expect.
So .. just because you have a blue throttle pot with the correct part number don't assume it's electrically identical to the ones already fitted.
I've never seen this mentioned before, but has anyone else ever come across a similar situation ?
Nope none of them have the same end to end resistance but two are close but not the two you'd expect.
the bad blue one is 4.25k
the good blue one is 3.63k
the black one is 4.58k
so the blue and black ones I'm using have significantly different end to end resistance, but behave perfectly in-sync on the car. The blue one I've discarded has similar end to end resistance to the black one, but behaves completely different to either of the others on the car.
Also - I've just measured a brand new grey pot used on the 4.2 and that has 3.7k end to end.
I've measured the grey pots on my own 4.2cerb and ones is 3.9k and the other is 4.3k ...
As it's a potentiometer it's the ratio across the wiper that's important, but why the discrepancy in end to end resistance ? and why does one pot seem to have a different middle sweep output?
the bad blue one is 4.25k
the good blue one is 3.63k
the black one is 4.58k
so the blue and black ones I'm using have significantly different end to end resistance, but behave perfectly in-sync on the car. The blue one I've discarded has similar end to end resistance to the black one, but behaves completely different to either of the others on the car.
Also - I've just measured a brand new grey pot used on the 4.2 and that has 3.7k end to end.
I've measured the grey pots on my own 4.2cerb and ones is 3.9k and the other is 4.3k ...
As it's a potentiometer it's the ratio across the wiper that's important, but why the discrepancy in end to end resistance ? and why does one pot seem to have a different middle sweep output?
End to end resistance won't be critical unless the ECU provides significant loading on the wiper pin,a technique sometimes used to produce a psuedo log function, in which case it will become significant.
Since you have a fairly wide variation of end-end resistances that work fine, I'd have to say it's a badly manufactured device where the carbon track width or thickness has not been well controlled. If you aren't intending to return it, it'd be interesting to crack it open and take a look.
Since you have a fairly wide variation of end-end resistances that work fine, I'd have to say it's a badly manufactured device where the carbon track width or thickness has not been well controlled. If you aren't intending to return it, it'd be interesting to crack it open and take a look.
Sorry I don't have too much offer on the pot to pot variation, but I am interested in the new dual lambda Emerald.
When I spoke to Dave back in August, this was not an option, glad to hear that it is now.
Presumably, having two lambda's allows for smoother running, but in general, very keen to hear the improvements you are finding over the single loop system.
Thanks!
When I spoke to Dave back in August, this was not an option, glad to hear that it is now.
Presumably, having two lambda's allows for smoother running, but in general, very keen to hear the improvements you are finding over the single loop system.
Thanks!
Hi yes Karl at Emerald very kindly succumbed to my frequent asking for a dual throttle / dual wideband / dual adaptive table version of the ecu and the first version was delivered late last year but didn't make it to my dyno until early this year. In fact at that point it was the first version anywhere - not even Emerald themselves had run one on a car at that point so I was very pleased to get my hands on that 
The emerald had until that point been a slight compromise in that it only read one throttle with only one adaption table.
The latest update gives you all the features of the std k6plus (drive by wire, triple maps etc etc) with the added benefit of exceeding the standard MBE unit's capability which although does have twin inputs and adaptive tables is limited to lambda=1 or off. The K6plus allows targeted afr tables to be populated from twin wideband sensors. As such it now exceeds the std MBE in every respect.
Whether it brings any smoothness benefits depends on how well it's installed and set up of course, but it gives you a damn good chance.
HTH
The emerald had until that point been a slight compromise in that it only read one throttle with only one adaption table.
The latest update gives you all the features of the std k6plus (drive by wire, triple maps etc etc) with the added benefit of exceeding the standard MBE unit's capability which although does have twin inputs and adaptive tables is limited to lambda=1 or off. The K6plus allows targeted afr tables to be populated from twin wideband sensors. As such it now exceeds the std MBE in every respect.
Whether it brings any smoothness benefits depends on how well it's installed and set up of course, but it gives you a damn good chance.
HTH
nawarne said:
I'm a bit confused by the 'numbers' in this thread!
Joolz? - Does this mean that you 'could' put on a white TP on each/either end of the throttle pot linkage for the Speed6??
TIA, Nick
Not sure why you would want to do that .. Joolz? - Does this mean that you 'could' put on a white TP on each/either end of the throttle pot linkage for the Speed6??
TIA, Nick
I did detail substituting a white pot for a blue one on the cerb4.5 when blues were unavailable , but it relied on the fact you can rotate the pot mounting collar on the 4.5 intake to accommodate the different mounting hole positions of the reversed white pot. On the sp6 the holes are driled into the throttle body and as such is a bit of a none-starter really.
My white-for-blue swap was a bodge to get us out of trouble in the short term.
spitfire4v8 said:
Hi yes Karl at Emerald very kindly succumbed to my frequent asking for a dual throttle / dual wideband / dual adaptive table version of the ecu and the first version was delivered late last year but didn't make it to my dyno until early this year. In fact at that point it was the first version anywhere - not even Emerald themselves had run one on a car at that point so I was very pleased to get my hands on that
The emerald had until that point been a slight compromise in that it only read one throttle with only one adaption table.
The latest update gives you all the features of the std k6plus (drive by wire, triple maps etc etc) with the added benefit of exceeding the standard MBE unit's capability which although does have twin inputs and adaptive tables is limited to lambda=1 or off. The K6plus allows targeted afr tables to be populated from twin wideband sensors. As such it now exceeds the std MBE in every respect.
Whether it brings any smoothness benefits depends on how well it's installed and set up of course, but it gives you a damn good chance.
HTH
Thank you Joolz, this is most helpful.The emerald had until that point been a slight compromise in that it only read one throttle with only one adaption table.
The latest update gives you all the features of the std k6plus (drive by wire, triple maps etc etc) with the added benefit of exceeding the standard MBE unit's capability which although does have twin inputs and adaptive tables is limited to lambda=1 or off. The K6plus allows targeted afr tables to be populated from twin wideband sensors. As such it now exceeds the std MBE in every respect.
Whether it brings any smoothness benefits depends on how well it's installed and set up of course, but it gives you a damn good chance.
HTH
I almost pulled the trigger on a K6 late last year, but had a nagging feeling about the single lambda/TPOT implementation. Although I do know there are many Cerbs out there, running very well with this setup (better than factory I presume).
The inherent mismatch bank to bank, whereby the injectors spray onto the back of the throttle butterfly’s on one bank (vs straight into the opening on the other bank), seemed at odds with the single bank setup of the original K6.
Wideband lambdas are of course way better than the original setup (not least for troubleshooting).
Exciting stuff!
Thank you!
Imran999 said:
The inherent mismatch bank to bank, whereby the injectors spray onto the back of the throttle butterfly’s on one bank (vs straight into the opening on the other bank), seemed at odds with the single bank setup of the original K6.
I'd never even thought about that before!!Ideally there would be a cam between the two throttle bodies so the butterfly action were mirrored
A couple of people have converted their cars to have the spindles rotating opposite to each other. I guess they must have experimented to decide which way was better ..
But .. if you get the airflows balanced properly you find the mixture is the same both banks, so where is the advantage ?
I know that as standard it *looks* wrong .. but is it actually? And with the std mbe being batch fired you have a lot of time (relatively speaking) where fuel is just in the port with not much to do ..
I remain unconvinced of the benefits of getting the spindle rotation the opposite way to each other. If anyone can prove to me otherwise that would be great, always learning
But .. if you get the airflows balanced properly you find the mixture is the same both banks, so where is the advantage ?
I know that as standard it *looks* wrong .. but is it actually? And with the std mbe being batch fired you have a lot of time (relatively speaking) where fuel is just in the port with not much to do ..
I remain unconvinced of the benefits of getting the spindle rotation the opposite way to each other. If anyone can prove to me otherwise that would be great, always learning
I have very minimal experience with engines, so forgive my novice observations - but during setup, I always find the odd bank performs worse than the even bank.
I know there’s an ECU anomaly whereby the odd TPOT has a noisy signal, but I doubt this noise actually makes it through to the injector signal.
So, I’ve always assumed that the cause of the poorer performing odd bank, was the injectors firing onto the back of the butterfly (vs straight into the air-path on the even bank).
In general, the AJP setup seems to be quite forgiving, and various ‘fine tuning’ methods prove to be unnecessary (or yield little benefit), but when you consider all the efforts that performance engine designers go to, to improve airflow and injector location/spray, one would think it would make a big difference.
I have further convinced myself of this logic, when driving and experiencing the part-throttle lumpiness - but I’m sure Joules will confirm that that is down to the god-awful factory mapping...
Yes, the absolute volume of air on each bank may be identical, but is the time taken to achieve that airflow identical? Such that when you open the throttle, does one bank reach that given air volume faster than the other?
I know there’s an ECU anomaly whereby the odd TPOT has a noisy signal, but I doubt this noise actually makes it through to the injector signal.
So, I’ve always assumed that the cause of the poorer performing odd bank, was the injectors firing onto the back of the butterfly (vs straight into the air-path on the even bank).
In general, the AJP setup seems to be quite forgiving, and various ‘fine tuning’ methods prove to be unnecessary (or yield little benefit), but when you consider all the efforts that performance engine designers go to, to improve airflow and injector location/spray, one would think it would make a big difference.
I have further convinced myself of this logic, when driving and experiencing the part-throttle lumpiness - but I’m sure Joules will confirm that that is down to the god-awful factory mapping...
Yes, the absolute volume of air on each bank may be identical, but is the time taken to achieve that airflow identical? Such that when you open the throttle, does one bank reach that given air volume faster than the other?
Edited by Imran999 on Saturday 15th February 00:24
Edited by Imran999 on Saturday 15th February 05:33
spitfire4v8 said:
Not sure why you would want to do that ..
I did detail substituting a white pot for a blue one on the cerb4.5 when blues were unavailable , but it relied on the fact you can rotate the pot mounting collar on the 4.5 intake to accommodate the different mounting hole positions of the reversed white pot. On the sp6 the holes are driled into the throttle body and as such is a bit of a none-starter really.
My white-for-blue swap was a bodge to get us out of trouble in the short term.
Thanks Joolz…..I wondered if it would get address the issue of NIL stock of the blue pot.I did detail substituting a white pot for a blue one on the cerb4.5 when blues were unavailable , but it relied on the fact you can rotate the pot mounting collar on the 4.5 intake to accommodate the different mounting hole positions of the reversed white pot. On the sp6 the holes are driled into the throttle body and as such is a bit of a none-starter really.
My white-for-blue swap was a bodge to get us out of trouble in the short term.
Now I've got my brain in gear....I see that the action would be reversed...Doh!
Nick
Imran999 said:
So, I’ve always assumed that the cause of the poorer performing odd bank, was the injectors firing onto the back of the butterfly (vs straight into the air-path on the even bank).
When the engines run lumpy they are on a tiny throttle opening .. typically throttle sites 2 and 3 .. at that point the injectors are spraying onto the butterflies on both banks .. only when the butterflies are well open does the mis-matched spraying into air/onto butterfly occur, and that's not when the engines are lumpy.If you look at what happens when the throttle is cracked only partially open (as with 99 percent of driving) you will see the injector squirts onto the back of the butterfly and this bleeds to the edge of the butterfly/throttle body where it gets pulled through a very small gap where air speed is high. This is the effective atomisation point I guess .. and by the time that emulsion reaches the chamber, via the sharp bend, does the chamber really care where the injector initially squirted?
My gut tells me it doesn't care one bit .. but as I say if anyone can show me proof that it does I would love to see it
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