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Some of this week's Letters to AutoSpeed!

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Airflow Meter Swap

I have a Peugeot 405 Mi16, the 108kW 1.9L model  (XU9J4Z motor) and I'm interested in using the Digital Fuel Adjuster featured in numerous AutoSpeed articles to help with a conversion from the vane type AFM to a less restrictive hot-wire MAF. I'm looking for improved throttle response and more precise metering. Not to mention the ease and low cost of replacing a MAF over the Bosch/Motronic vane type AFM.

Here's a hypothetical, please bear in mind that I've got very little practical experience with electronics and tuning. Say I've built the DFA and hand-controller, I have a hot-wire MAF from an RB20, 25 or 30 (suggestions welcome). Hot-wire does not measure intake temperature so I have to take the sensor from the original AFM and mount it in the intake. I've worked out which pins are power, earth, output. On the original AFM I've also worked out which wires are power 5V, earth, output 1-5v and intake temp (3.4v @ 20 degrees C approx).

I install the DFA on the original set-up first, disconnect the O2 sensor and with a pen and paper record voltage values at set load points. Every 250-500 rpm should be fine. I then disconnect the AFM and plug in the MAF (will use connectors so it's plug and play) and simply input the same voltage values at each load point. At this point I can let interpolation do it's thing, plug the O2 sensor back in and drive down to have everything checked with a wideband O2 sensor and dyno.

I'm yet to work out is the self-cleaning process on the MAF though. Most use a blast of heat to burn off any contaminants upon shutdown. I have a feeling that the one/two extra pins found on the MAFs are for this function. Is it simply a short providing the blast of heat or something more complex? Am I on the right track? I hope to combine this with an inlet cam swap and equal or surpass the 160hp UK spec Mi16's.

Jacob Cope

The process that you have suggested looks largely fine. However, to avoid problems with moving the intake air temperature sensor, devising a timing circuit to trigger the self-cleaning process, and the need to extensively recalibrate the shape of the new airflow meter output curve, we suggest that instead of replacing the vane airflow meter with a hot wire, you simply fit a larger vane airflow meter. As described at Real World Air/Fuel Ratio Tuning, it is a fallacy to suggest that at full throttle, vane airflow meters are restrictive. An appropriately sized one will in fact be less restrictive than a hotwire of the same nominal cross-sectional area. A larger vane airflow meter will need much less extensive mapping by the DFA.

More on Fuel Consumption

Bravo with the Driving Emotion editorial on fuel consumption.  The ideas on the issues, particularly risk, are well considered.  The capital cost of the car is an issue; if the car is cheap enough to be discarded if fuel prices rise substantially, it matters less.  It is also worth pointing out another recent editorial, that by Paul van Valkenberg in Racecar Engineering, where he points out that the (coming?) energy crisis is a social problem rather than a technical one.  It seems to me that the world is still looking for technical solutions.

Andrew McKellar

DIY Cars

Thanks for keeping me sane with a daily dose of real car information. Working and living in the UK, your new car tests and stories help to keep in the know, when family and friends ask for input in to their car buying decisions. Loved the articles about the kit cars (Lotus, Westfield and Skelta) and cannot wait to return to warmer climates and my tools so I can built something for myself. Next time you are out in Perth you may want to check this one out -

Ken Richard

Bedding-in Brakes

I was reading your new brake articles New Brakes for the Falcon, Part 1 and New Brakes for the Falcon, Part 2. You didn't mention that you did any after install bedding of the brakes.  I am curious, did you bed in your brakes?  If so, what process did you use?  If not, why not?

Tim Fulton
United States

Fair comment. Here’s what brakes supplier RDA has to say:

When a vehicle has had both new rotors and/or just new pads fitted, there are two processes or objectives to getting the brake system to operate at optimal performance.

The first step is to make sure the disc face is clean of all oils/anti rust or any foreign matter like previous brake pad material. If the rotors are not being replaced then it is imperative that the disc is machined prior to the fitment of new pads - without exception. The second step is heating (not cooking) the brake rotor and pads, to transfer the pad material evenly onto the rotor face. This step involves performing a series of stops, so that the brake rotor and pad are heated steadily, to allow the transfer of pad material onto the brake rotor friction surface.

While performing a series of brake applications to transfer the pad material, care should be taken to not come to a complete stop, as this can lead to the transfer of pad material unevenly on the disc at the point where the pad comes to rest on the friction surface. A typical program of 8-9 brake applications, from 60 km/h down to 10 km/h, without any cool-down in between, is sufficient. For performance pad materials, a further two sequences of ten stops will be required after a cooling down period between each cycle to ensure that the pads have reached the required higher operating temperature to allow for the pad material to transfer effectively. At all times during the bedding in process, care should be taken to not apply the brakes in a harsh manner or decelerate from high speeds, as this will corrupt the transfer of materials and lead to uneven material build up on the rotor surface, which in most instances will require machining to regain a flat rotor surface for optimal operation.

How will I know if they are bedded in? The two major visual indicators are disc rotor discoloration and machining marks on the friction surface of the disc rotor. (1) Disc rotor should have a slight bluish tint with a grey tint that indicates where the brake pads have come into contact with the rotor. Too much heat will cause the rotor face to be extremely blue. (2) If there is still a shine on the rotor surface, then not enough pad material has been transferred.

Once brakes have been bedded in, it is also important to keep them that way. If any brake pad is used below its adherent operating temperature over a period of time it will slowly remove the transfer layer on the rotor surface. Standard - and especially performance pads - like to be driven a little more aggressively every now and then to maintain this pad material on the rotor friction surface. Passive use of brakes over an extended period of time will in effect lead to unbedded brakes.

Falcon Pedal Travel

Regarding New Brakes for the Falcon, Part 2 you mentioned the long pedal travel. There’s an explanation for that. Grab a helper, get them to sit in the car and push the pedal to the floor while you watch the booster/master cylinder assembly. You'll be amazed at the amount of movement from the Falcon’s firewall flexing. This was demonstrated to me by a friend, and he also showed me how a simple stopper arrangement bolted to the shock tower, held against the master cylinder, goes a long way to helping the pedal feel! On another note, great article, I'm looking forward to more!

Jared Wuthrich


It was very interesting reading the article about upgrading the Falcon’s brakes, I know mine are soon due for replacement rotors. I find it interesting that the Falcon’s rear brakes did not work and who knows for how long that was the case. Every year in the Northern Territory my vehicles have to be inspected to be registered. I take my vehicles over the Motor Vehicle Registry pits where they test all axle brakes on a rolling test machine.

Brian Mullin

The Falcon underwent a roadworthy check prior to our purchase...

Format Feedback

The new format - Seems OK to me, but too soon to judge. I see you are going to pay close attention to how the articles are scored. Again, OK by me, but as soon as I scored an article I realised I wanted to add a comment, perhaps to say why I thought it was good, or not good, or good, but... I appreciate that pushing readers to vote is bad enough (ie, how many readers do vote, less than 20%?), and that pushing them to add a comment on every vote would reduce the involvement even further, BUT, I think it might be worthwhile (ie, I would use it) if the reader was offered the opportunity to augment or refine their vote by a text comment. "Do you want to comment on this article? Yes or No". For example, some articles may come across as good articles, but as I'm not really interested in the topic I'm not in a good position to judge. So here's another opportunity for refinement, two scores per article: How good was it?, and How relevant to you?

Scan tools - Tying in with this is your article on Scan Tools (see Scan Tools) which I see Doug Webb has already commented on. The article was good as an overview / introduction, and I scored it on that basis. If I had scored it against a measure of how much it enabled me to find the right Scan Tool, I'd have given it a low score. My text comment against that article would have been along the lines of 'Fine for an introduction, but you could (and should) run specific articles on specific tools, or at least find some commonality, say all the Scan Tools the trade say are good on Fords go in one article. One Scan Tool article a month (say) would build up to a really good reference. There are now a lot of detail functions built into cars, not just OBD2 or EOBD2 functions, and the private owner wants to know which Scan Tools can access these choices'. There are a lot of Scan Tools out there to review, possibly 12 articles a year isn't enough, but I realise you do need some variety. I was surprised to see you hadn't pointed out to Doug that the ST article wasn't one of 'yours', but if you adopt my suggestion it enables you to look in more detail at this particular unit, and a lot of others.

While I'm writing, I'm somewhat amused by the typical American assumption of one reader, that you should consider North American cars when you do articles. The writer doesn't seem to have caught on that you can only comment, in the technical detail required, on cars that have a physical presence near you, and that means Australia. Personally I accept the limitation exists, and still find the subscription worthwhile. Your change in emphasis will of course suit me and your other non-Australian readers, as technical principles can be applied across many cars, whereas mods that work on a specific Australian car cannot be said, with certainty, to be equally as useful on some non-Australian model. As an example of "technical principles can be applied across many cars" I used the 2 valve boost control developed on your Audi with great success on a turbo-charged diesel. As a global comment on all the I-Car articles you have run so far; they are good as an introductory overview, but I think you need to select them with care, and use them when you can see the opportunity to develop the theme, otherwise they are just teasers, gaining you a reputation for superficiality which no-one could accuse you of at the moment.

David Sparkes
United Kingdom

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