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Change from TPS to MAP for the Alps etc


Ian Kinder (Bagpuss) - Joint Peak District AO

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Ian Kinder (Bagpuss) - Joint Peak District AO

I've enjoyed reading Peter Russon's excelent write up about his trip to Spain, in which he mentions changing from TPS based load map to a  MAP sensor based map to cope with the higher attitudes seen on such trips. I'm curious how my fellow S2000 powered owners such as @Terryathome and @Tom (T3OMF) - Cotswolds AO have faired on similar trips to altitudes not usually seen in the UK?

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Thrustyjust

You've been reading the Spain trip in the new mag. Just off my throne having done the same thing :o . I wonder whether having a lambda would lessen fuel being injected , if it detects it running rich ? MAF would prove awkward with bonnet clearance . 

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Dave Eastwood (Gadgetman) - Club Secretary

You can tap the MAF off a fresh spot on the intake manifold, so clearance isn’t an issue. You’d most likely want to use a new aftermarket MAF sensor if retro fitting anyway, as they’re notoriously difficult to adopt OEM sensors.

its not necessarily a case of either or, it’s usually more common to have both, with either tps based plus MAF compensation table, of MAF based with tps compensation table.

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Thrustyjust
30 minutes ago, Dave Eastwood (Gadgetman) - Club Secretary said:

You can tap the MAF off a fresh spot on the intake manifold, so clearance isn’t an issue. You’d most likely want to use a new aftermarket MAF sensor if retro fitting anyway, as they’re notoriously difficult to adopt OEM sensors.

its not necessarily a case of either or, it’s usually more common to have both, with either tps based plus MAF compensation table, of MAF based with tps compensation table.

Does that mean a new table for MAF has to be made with the correct environment on the rollers ? or do they just make a compensation table for air pressure relative to the fuel map ?

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Dave Eastwood (Gadgetman) - Club Secretary

If you stay TPS based, then it’s just a compensation table, so not a full map IYSWIM.

So the ecu would normally use the TPS map, it’s just able to add an increase/decrease of fuel to the tps map setting, based on the compensation table. The table is just flat 2d though, so a column for air pressure and a column of corresponding fuel correction.

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Thrustyjust
7 minutes ago, Dave Eastwood (Gadgetman) - Club Secretary said:

If you stay TPS based, then it’s just a compensation table, so not a full map IYSWIM.

So the ecu would normally use the TPS map, it’s just able to add an increase/decrease of fuel to the tps map setting, based on the compensation table. The table is just flat 2d though, so a column for air pressure and a column of corresponding fuel correction.

So, the lambda wouldnt lean off the fueling instead ?

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Dave Eastwood (Gadgetman) - Club Secretary

Not really, no.

as far as the sort of aftermarket ecu’s that we use go...

To stand a chance, would need to be a wide band for a start, to operate over a meaningful range of engine loads, it would then need to be fast and responsive enough. The problem is, it would always be trying to hit a predetermined afr which would only work well at a steady engine load. It’s a closed loop system, so typically when it detects rich for example, it will keep turning the fuel “down” until it goes lean, then it will add a little more fuel till it just goes rich, then trim a tiny bit of fuel until it just goes lean, steadily zeroing in on a preset target.

In practice, of running a steady speed and steady revs, that works alright, but if you have lots of throttle changes it can often struggle to keep up. It’s also a bit of an imprecise/imperfect system, that can be affected by transient driving situations, that could cause the ecu to try and swing the fuel changes to greatly, so it’s common to restrict how much the ecu can increase or decrease the fueling in any one action. So if using this system to base map a car, for example, everyload site has lots of passes over it, effectively averaging out the final value over time. Even though, (when mapping), it’s common to have to go in and manually smooth out and fine tune the map a wee bit, for best results.

With a system where you have a primary load measure, TPS and a correction from MAF OR MAP (or the alternative, MAF/MAP as the primary, with a TPS for correction), the feedback to the ecu is near instantaneous and it’s a known constant amount of correction that needs  to be applied, so no risk of corrupting your base fuel map.

(Nort forgetting that with this sort of correction, you can also include ignition timing, which is impossible just from a lambda sensor).

(Note, modern production car ecu’s don’t always work quite the same now. While they may still use compensation tables, they are hugely more sophisticated these days, and tend to use mathematical engine models, rather than something as crude as a basic ignition or fuel map. But even here, they still tend to use an air quantity measure as well as a throttle angle measure, despite having way more advanced lambda and knock control strategies available).

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Ian Kinder (Bagpuss) - Joint Peak District AO

@Dave Eastwood (Gadgetman) - Club Secretary, I suspect your crapple device has auto corrected again and I assume by MAF you mean MAP. i.e. Manifold absolute pressure rather than mass air flow. I'm still curious to see how others have coped with altitude to see if it's vital or if it's something nice to have @Davemk1 how high up are you?

 

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Ian Kinder (Bagpuss) - Joint Peak District AO
8 hours ago, Thrustyjust said:

So, the lambda wouldnt lean off the fueling instead ?

My understanding of most ECU's is lambda is only used for steady state closed loop control when you're cruising at a constant speed etc (see https://secure.lambdapower.co.uk/TechNotes/Tech-3.asp). Therefore under dynamic driving conditions it's not really used and hence can't be relied upon to protect your engine when blatting hard Just like 'dieselgate' the Lambda control is used for emission testing at idle but isn't really a real world test.

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Ben(EBD-ENG)

On my turbo mx5 engine with the omex ecu. It uses both tps and map. Omex does support a maf aswell though doesn't it but the narrow band lambda won't alter the fueling to the conditions and I'm not convinced that omex supports wideband. 

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Kit Car Electronics

A simple rule to remember is 10% air density reduction per 1000m altitude. So if you don't correct for barometric pressure, that's how much richer you'll tend to run at large throttle opening. Ignition will be retarded slightly from ideal, so safe.

At low throttle opening, the airflow is sonic, which means that it doesn't depend on the upstream pressure, so largely unaffected by altitude.

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Terryathome

@IanK (Bagpuss) Mega S2000. Going through the alps (twice) I didn't notice any difference at any altitudes  what's so ever in the performance or mpg. Just enjoyed the car/scenery and company in what turned out to be one of the best drive/holiday you could ask for with @marcusb

 

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Dave Eastwood (Gadgetman) - Club Secretary
1 hour ago, IanK (Bagpuss) said:

My understanding of most ECU's is lambda is only used for steady state closed loop control when you're cruising at a constant speed etc (see https://secure.lambdapower.co.uk/TechNotes/Tech-3.asp). Therefore under dynamic driving conditions it's not really used and hence can't be relied upon to protect your engine when blatting hard Just like 'dieselgate' the Lambda control is used for emission testing at idle but isn't really a real world test.

That’s typical narrow band lambda, hence me mentioning wide band previously, but yes as I went on to say, it does really need to be at either steady state, or to have had multiple passes through the target cell on the fuel map.

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5 hours ago, IanK (Bagpuss) said:

@Dave Eastwood (Gadgetman) - Club Secretary, I suspect your crapple device has auto corrected again and I assume by MAF you mean MAP. i.e. Manifold absolute pressure rather than mass air flow. I'm still curious to see how others have coped with altitude to see if it's vital or if it's something nice to have @Davemk1 how high up are you?

 

I live at just shy of 5000 feet and often drive to over 7200 feet. Am I correct in thinking that typically the ECU senses altitude/air pressure?

dave

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Ian Kinder (Bagpuss) - Joint Peak District AO
26 minutes ago, Davemk1 said:

I live at just shy of 5000 feet and often drive to over 7200 feet. Am I correct in thinking that typically the ECU senses altitude/air pressure?

dave

Hi Dave, Looks like our ECU has the capability, however it's not enabled and you'd need a pressure sensor.

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