That's good to know. I wonder where the "doesn't fit" comments came from. These things usually have some fig of truth to them even if they aren't totally accurate.

Maybe it's just the mounts are missing on an earlier car or something.

mad-as wrote:

silly question
even if it only read close to the parameters, (thats a differant MAF) wouldn't the computer trim it in or just not read it .

The long term trim is a single multiplier applied to the whole curve. If the whole curve was somehow scaled, then the trim would work.

The curve however is not linear. Voltage changes much faster at low airflows, and much slower at high airflows. Which means if the curve ends up the wrong shape the ECU simply cannot trim it out.

Once I get some more data points I'll throw up a graph showing how different the curves can be.

I've decided to create this thread to document my efforts at creating a replacement for the GEMS MAF. As some of you will know, the GEMS MAF is unavailable anywhere other than landrover (if its even still available) and costs a fortune. Aftermarket units are junk. After buying probably 4 or 5 used MAFs at this point, i wanted to find a solution.

My thinking is simple. If we can figure out the curve, we can build a "module" which can translate the values from some other cars MAF, over to signals the GEMS ECU expects.

Having had some background in tinkering with 2000's VAG cars, i know that their Motronic 7.5 ECU's contain a 512x1 table which contains the MAF calibration in a very simple format: kg/sec against voltage. As such i have curves available for many common VAG MAFs. Those VAG MAF's are ubiquitous, readily available, and cheap new. I also already have a few units knocking around i can use for testing. Half the problem is thus "sorted"

If we can acquire the same curve for the Lucas 20AM, we can then create a translation table between the two.

Trying to find this information online seems pretty much impossible. Tuning info on the GEMS is rare, and i havent been able to find the factory calibration anywhere. However when replacing my broken MAF with yet another used one recently i noticed something potentially useful. RAVE provides airflow figures that should be seen at various engine speeds. One reason i know my newest-old MAF is junk is that it massively overreads against these figures. However while staring at the Nanocom, i realised it was showing both airflow in kg/sec and MAF voltage...

My first attempt then was to drive around, and use the nanocom logging function to log these two values. Unfortunately nanocom updates extremely slowly and seems to only pull one value at a time, which means the displayed airflow and voltage dont line up in time, and thus its all a bit random. Perhaps with many miles of logged data, we could get something resembling a curve, but i wasnt happy with this approach at all.

Spent some time thinking about it, and threw together a MAF "stimulator". Essentially its an Arduino Nano, and a MCP4725 DAC. The arduino is programmed step from 0v to 5v in 0.3125v intervals. Fishing about in my box of parts i found a matching connector for the harness MAF plug, so i can plug this contraption in, inplace of the MAF. The idea being that instead of driving around, i can just sit on the drive, ignition on, engine off, and feed in the sequence of voltages and log the output.

So, tonight, i went to give it a try. And, provisional results are that it worked, kinda! Nanocom kept disconnecting, and i realised the battery was flat, which potentially was causing the nanocom weirdness, however i managed to capture a bit of data before i gave up with the battery down to 7 volts and went and fished out the battery charger instead.

Interestingly you can see the lag i was talking about in the log due to how the nanocom polls each value. In order to try and minimise this, i'd set the Arduino to step the voltage once every 10 seconds. It appears to update the voltage first, then airflow shortly after.

As you can see it was a struggle to keep the thing connected for more than about 30seconds, but you can also see some nice clear data points. Will revisit later in the week when it has a charged battery and see if we can capture the full sweep.

Early cars have two brake pipes in the middle of the axle that loop up to a bracket in the middle of the floor.

Later cars moved the pipes out onto the body and dropped into the axle from the wheel arch instead.

I think the "T" section of the later exhaust would conflict with the brake pipes on an early car.

romanrob wrote:

I've had a lone Hurricane alloy on eBay for 1yr+, dont hold ur breath, not sure what the demand is these days

ebays hit and miss, but i do sell a fair bit on there from cars i've dismantled. It boils down to price and postage.

If your only offering collection, you instantly shrink your audience to a tiny fraction of what it was. As a result you then need to either wait for a long time for someone willing and local. Or you make it cheap enough that someones willing to travel for it.

Taking a quick look, several single Hurricane wheels have sold in the last month or two alone, so there is clearly some demand, suggesting that there was something "wrong" with your listing.

An auction with a high starting price isnt a great move, IMO. I tend to go one of two ways. If something is in fairly high demand, and i know it'll get bid up, i will list it as an auction for a 99p starting price. Gets folks in the door and interested, and so long as you've got a couple of interested parties bidding its going to sell for what its worth.

If somethings likely to be in low demand, ie where a 99p auctions going to end up with 1 bid, i will instead use a buy it now listing with offers enabled.

Also, do your research thru completed listings and figure out what your item is actually selling for. Theres no point listing it for £300 collection only if everyone else is selling them for £200 with free shipping.

In this case, theres also the unfortunate combination of good tyres, which should add value, but they are winters, and its May!

On the petrol models there are actually two brake switches. The brake bulb output from the normal brake switch is connected to the cruise ECU, then the brake vent valve also has an additional switch which is also connected to the cruise ECU. Then the vent valve itself acts as a redundancy mechanism to dump the vacuum.

For petrols theres a very good diagnostic guide in rave, which steps you thru checking all the sensors and things. Might be worth looking to see if the same exists for the diesel version.

on the factory P38 setup, the midbox does most of the work, so i could quite believe it will be fine with just straight piped backboxes.

On an aftermarket system, they may or may not have quite matched the complexity of the factory midbox. Mine for instance uses a "straight thru" style middle box, which certainly doesn't take as much of the noise out as the factory box did.

usually with aftermarket/"tuner" systems they inject a water methanol mixture, not just plain water, so the methanol has combustive properties. Its mostly about charge cooling and reducing detonation though, which means as above, you can run more boost or more aggressive timing. Doubt it would do much on NA motor.

Even the spitfire application was using it on a supercharged engine. In aircraft, turbo/supercharging is normally used to offset lower atmospheric pressures at higher altitudes. In the spitfire, they rejigged this a little to allow the charger to provide additional boost at lower altitudes when it had "spare" capacity. The water/methanol was thus used to reduce detonation risk in those conditions.

can you get a quote from a local exhaust fabricator?

On mine, it came with typical rotted out aftermarket boxes. First thing to go was the rear box. I happened to find a stainless rear pipe on ebay, but it didnt have a silencer, was just pipe. I sectioned the end of it and let in an OEM (stainless) box which came from my brothers E90 BMW he'd broken for spares. Luckily mine is the single pipe system, so half the effort to replace!

Some months later the middle box disintegrated. I took it to a local exhaust fabricator, who cut back and replaced the end of the Y pipe (it had rotted thru at the flange), added a V band, and then a big stainless silencer, and mated it all up to my existing rear pipe and i think it cost around £300.

overheating will thin the oil out, which may in turn cause a loss of oil pressure if the pump cannot pump enough displacement to keep up with the thin oil. Thats ofcourse very engine specific, some engines have loads of oil pump headroom, and others have none.

I had a high mileage 1.8T in my first A4 where the oil pump was pretty worn out, and had an oil pressure guage fitted. Under normal driving it was fine, but if stuck in traffic with the coolant temp up nearer 100c than 90c, instead of the normal 15psi or so at idle it would drop down into the 7-8psi range, and the lifters would start depressurising and ticking. Lifting the engine RPM would get the pressure back up, but would also mean the engine ran hotter, creating a bit of a feedback loop. Was always a bit nervewracking stuck in traffic with that engine.

I've also heard of engines seizing due to overheating, presumably due to thermal expansion closing up running clearances.

dave3d wrote:

Hi Kev / Aragorn,
yep, must get pretty thirsty in Mordor or is it Gondor.

I don't use Solidworks. I don't like paying for software. I used Openscad for the cup holder.
It is based on writing lines of code that build up mathematical shapes. I can find my way around it and I can cut and paste sections of code from other designs. It is also what is known as parametric. Each dimension is a variable or parameter and it is easy to change the value and scale up or down.
Let me know if you want it. Have you got a 3d printer?
I designed it to take a couple of small cans, I think 48mm diam. which is ok. As Marshall8hp pointed out it is still a bit of weight hanging off the dash. A fat water bottle might be too much. For open top cups it is also not so good as they are at an angle.

Thanks, yeah send over what you have and i'll have a look. not played with OpenSCAD before but can have a play around and see what its like. We have 3 or 4 3D printers at work, and I can usually get some personal time on them if its a quiet day. Same story with the CAD packages. Can flash up at lunch and sketch up a bracket or something. Not ideal for big projects ofcourse, but for tweaking or adjusting a design it can be handy.

When i spun a bearing in my track car the conrods were totalled. They'd got so hot they had turned blue. Crankshaft was destroyed too. It wasnt even making a knocking noise. Feels like you'd have to be super lucky to get away with just installing new shells :(

Thanks, i guess i'll be masking it up then! I think i have a huge roll of brown paper somewhere, need to find it!

Couple of cheaper ones on ebay with the deep cup holders, will buy one when i get paid i think.

Dave, do you have a Solidworks model for the clip on cup holder? Intrigued to try modifying that to fit my fat insulated bottle.

Cheers
Kev

yeah the fixed rear windows that look into the boot space. I found two screws on the leading edge, but removing them didnt seem to do much and i didnt want to break anything.didnt really want to have to mask up half the car to paint them in situ but looks like i'm gonna have to 🤣

My car has a sad cup holder like this:

https://i.ebayimg.com/images/g/arUAAOSwzixc77dp/s-l1600.jpg

Its rubbish as its too shallow and cups fall out.

I came across this however (ignoring the ludicrous price):

https://www.ebay.co.uk/itm/294301903188?hash=item4485c2a954:g:P6kAAOSwwchhAlIq

Much deeper cup holes... Was this a later revision? Or is it some sort of aftermarket addition?

Doing a bit of exterior TLC, i painted up the trims along the top of the door as they were badly faded, and now the rear window trim looks awful.

Anyone know how it comes off?

yea i've also gone with N+1. Still managed to bite me a few times though.

A couple years ago the A4 steering rack failed in early December, removed it (in the awful weather) and sent for a rebuild, but took quite a few weeks due to the time of year. Around the same time, noticed a small leak from the radiator on the P38 but was managable with just top ups for local running. Until one morning it was no longer a small leak... I had the EV at work, and the wife managed to arrive at work (5 miles up the road) with the temperature needle jammed in the red. Took two kettle fulls of water to fill it back up again and she made it home again after. Literal stream of water pouring out of it when it was running! Except now we were down to N-1 cars! I was straight online to get a new rad, which arrived a few days later, went out in the evening and fitted it to discover water pissing out the end tank. It had got cracked in shipping. Refund applied for and another new rad sent out.

That lot had the wife somewhat pissed 😂

Even this year, the A4 failed its MOT in January and the weather was awful so i had been putting off fixing it. In the 2.5 months we were stuck with only the P38, it managed to kill its MAF and kill an ABS sensor. MAF was especially bad as while i could get it started with it unplugged, wifey couldnt resulting in her ending up stuck in the nursery car park. 💖

That was also my approach for a long time tbh, you'll note from my signature i've got a 22 year old Audi and a 28 year old Range Rover :P

However old vehicles are unreliable, and i got fed up with being stuck outside on the driveway in the rain, trying to fix some critical issue ready for work in the morning. With the young family arriving, time to work on things reduced, but things still broke and needing sorting, and wifey becomes less tolerant of breakdowns when theres kids in the car!

I ended up buying the 330d with a 6 grand loan, hoping to get something newer and less breaky. Unfortunately 9 year old cars also need fixing, albeit less often and generally less critical failures. The 6 grand loan also meant i was paying out a couple hundred pounds every month. It also needed various bits of the front suspension replacing, a new set of wheels (that era of BMW are prone to cracked alloys), brakes, and various other fixes including a new throttle body.

Leasing the B250 was a bit of an impulse. For the money i'm spending on fuel, i instead get a new car. Total monthly spend actually went down significantly as i sold the beemer and paid off the loan, so instead of paying loan + fuel + tax + repairs, i was paying the lease fee and a small amount of electricity. It didnt need fixing and just got driven for 25k.

The Skoda is rather expensive, i agree. That ones not a lease however, it was bought with an interest free government loan scheme, so it'll be mine once its paid off. and yea, 380quid a month is a lot of dough. However if i still had the beemer i'd be over 320quid a month in diesel alone, plus tax, MOT's, repairs etc, and i know from the person i sold it to that it cost him a bunch more money with various other bits needing sorted in the time hes had it.

End of the day you need to look at the total cost you put into the car over a period of time. Financing buying it, depreciation, repairs, fuel, insurance, tax etc etc. Add it all up, and produce a cost per mile. Bangernomics is mostly about luck, but it also relies on you having time to fix the car and do the repairs yourself. You might get lucky and you buy something nice for 2 grand and it just works for years with minimal issues. You also might buy something nice for 2 grand and literally everything explodes inside a year costing you thousands in repairs (or you skip the whole car and buy again) Your trading money for time at that point.

In this instance, your comparing buying an expensive car with next to no running costs, with a cheap car with high running costs and a large input of time required. It all comes down to how many miles you do. If you dont do many miles, the fixed costs of buying the expensive car become a burden. But if you do lots of miles, the fuel is the primary cost, and being able to reduce that cost by 10x makes a huge difference to how the whole thing stacks up.

Even taking your example of your Jag, 180miles is costing you 40quid. As you say your mileage is reduced, but even 6 times a month its £240 a month in diesel. If you were doing double the trips your forking over £480 a month in diesel. Car costs are low, but fuel is huge. If you could instead reduce that fuel bill from £480 to £54, you've now got a bunch of cash you could use towards a car payment instead. Infact you could pay the £380 i'm paying for the Skoda and still have cash left over ;)

Its also largely why i went electric with the daily. My commute is 80miles a day.

I had a 9 year old 330d, which was costing about 17p a mile. Round trip commute was about £13 a day. For a months commuting say 20 trips a month it was around £260 in diesel a month. It was also at the age where every month it was needing something fixing, often minor ofcourse, but still requiring time and effort.

Same commute in the EV costs about £2 a day in electricity, or 40quid a month. The first EV i leased was £260 a month, basically paid for itself by the time you'd taken fuel and tax into account, not to mention it was new, reliable and had a warranty.

The Skoda is a bit more expensive at £380 a month, but fuels also gone up (if i still had the 330d i'd be paying £15-16 a day now), and its a bigger, nicer car with more range, so i'm happy with the extra cost.

Clearly its not for everyone, but when the fuel savings mean its almost free it can really work in your favour. Theres no way i'd have paid those monthly payments for a new ICE car.