I’m looking for technical help or recommendations on: Remapping/Tuning/New ECU for Fuel economy.
Prior warning: this is a philosophical question and just thinking out loud and trying to avoid the easy answer of “you shouldn’t have bought an old sports car if you wanted fuel economy”.
The problem: So it’s getting drier and sunnier and I’m itching to use the Mx5 as my “weekly”. I work in Norfolk and commute there on the weekdays and drive back to Warwickshire on the weekends. Wanting to “weekly” it means driving it for 270miles on straight A-roads at 70mph so there’s not much action but a lot of wasted fuel.
It got me wondering, most people appear to get custom ECUs on their 5’s when they add a turbo/supercharger.
Has anyone added one to tune the engine for motorway cruising to eek out fuel economy? I’m not looking to immediately recover the cost of an ECU from it (would be more of a tinkering exercise and may be supercharging later so may need a custom ECU anyway).
If so, how effective has it been? Do any ECUs allow you to have multiple maps which allow you to flick between a power and fuel efficiency map via a button?
How many miles will you have to do to re coup £800 for an ECU £250 for a remap plus installation if you can not do it yourself ??? You might gain 5mpg if you are lucky.
My experience with installing an ECU for a while before supercharging is that you’d be lucky to gain more than a couple of mpg. The stock ECU does a fairly good job with fuelling. There’s a bit you can gain with care in the ignition timing. But fundamentally the compression, cams and induction won’t change so you’re not going to get modern high-compression 50mpg performance from your low-30s mpg Mazda BP engine with just an ECU.
I don’t want to put you off trying. Just to manage expectations so you’re pleased with what you get rather than disappointed.
I have no experience with changing ECU’s for fuel economy, but if fuel consumption is a concern I have noticed over the years on runs up to Scotland from Bristol I can expect a range of around 350 miles per tank with the roof down whiile on occasions when it has been raining and I have left the roof up a range of 400 miles per tank is achievable in Madge a 1.8 S-VT.
I agree with Maverick cruise control might deliver some benefit to fuel consumption on longer runs.
The NA used to run fairly rich at WOT - not sure about the NB. Of course, you rarely drive at WOT, so leaning it out there - if it didn’t cause pinking - would have very little impact on economy.
They aren’t dreadful for mpg if in good condition and not used for short trips. I could get almost 40mpg on a run. It didn’t seem to.matter how hard it was driven compared to the length of trip. They drink fuel when warming up compared to a modern car.
Well, mainly because I was afraid of the backlash, due to animal cruelly, of my original thoughts of putting a hamster in each wheel. But even in overcoming that, the technical challenge of getting them all to run in the same direction at the same time seemed unsurmountable. Then I looked at the down sides. It would take their attention away from their primary task, that being typing the tyre pressure information to the telex screen on the dashboard. But even if they were female Hamsters and could multitask, the risk of cross corner communication and unionisation would be real and could result in failure to work overtime or worse, might actually run backward resulting in the OP being even further from his destination.
This is precisely what I was now going to try… To do the same trip at the lower speed, gauge the difference in fuel consumption and weigh it up to how much I would weigh the cost of my time (and getting that bit closer to death)
Or get a grappling hook and aim for a truck in front and engage neutral
If 270 miles is 5 return journeys, then for each 27 mile leg 10mph slower would cost you less than 5 minutes. So economy driving is probably the best you can do. Run the tyres 2 or 3 psi higher than the recommended pressure, Avoid braking. If you can, time your journeys to avoid the worst congestion.
Speed is the big one. Most of your fuel is burnt to overcome aerodynamic drag, which is 36% higher at 70 than at 60. And is worse with the hood down.
