So my automatic fd3s is like a hole in the ground through which petrol is poured.

I'm not certain what is going on there, right now it is backfiring and gets about 143 kms on a FULL TANK! :o

It's been in to be sorted out, first mech failed, now it's been to a second, he's given up, says there was oil on the sparks, I'm not sure what that is meant to mean but he says he can't figure out the wiring etc... So basically he's swapped out the sparks and is leaving it at that.

I'm getting rather tired of the headache, I suspect it is a cpu issue as the hold light tends to flash on and off for no apparent reason but can't be too sure. I've been presented with an option to lose the twins and swap out to a single bigger turbo and run the engine completely off a microtech management and therefore bypass the stock cpu completely. The other was to do a swap on the engine for v8 not too interested in that option. (no flaming please, personal preference)

Interested to hear any opinions. Car is modded as follows.
200% larger radiator
HKS frontmount intercooler
thicker apex seals
pre cat has been removed but back cat is still in currently
Dumpvalve
steel AST
Fans have been wired to run when ignition is on to help with overheating issues.

 

The car is getting absolutely horrible mileage (kilometerage?) and backfiring.

Sounds to me like you may have an injector stuck open or something really screwed up causing it to dump a ton of fuel. You've got a rebuilt/new engine in there, so someone has been digging deep inside with all the wiring and so forth - causing who knows what damage.

I would start with the basics. What is the fuel pressure? Very high fuel pressure would use more gas and may make it run rich. What injectors are in there? Any mods to the ECU? Does the car stink like raw fuel under the hood or near the diff? (fuel leak).

Sounds like you are gonna have to go through the car step by step

 

Short a bad or aftermarket ECU, and/or wiring discrepancies between it & the transmission, the Hold/Overdrive light flashes as an alert of something physically wrong with the transmission. In the diagnostics box you can jump the GND & TAT pins to get the Hold light to flash a sequence, the same way you'd get the check engine light to flash a sequence/code on same era OBDI cars. I'm new to FD's but not 90's Mazda automatics.. and doubtful the flashing Hold light & horrible fuel economy are directly related, so long as the transmission's shifting/not simply staying in a low gear - good luck!

 

Agreed... Looks like this is going to become a quest. Will get her back tomorrow, seems that the wiring harness and the ecu are buggered. Thinking the best solution is to replace the harness and run off the New management system.

Will also look at the injectors while we're at it, both of your opinions sound right to me. The transmission I've checked and everything in there is fine, which means that the ecu is sending false signals or the harness is damaged and is not reading it correctly.

I know that the guy who has it now found a number of shorts in the wiring. Always dangerous having different people work on your car, it's hard to create a trail without an accurate work-mans history.

It looks like process of elimination is the only way forward. An expensive only way forward, swapping out for the microtech means ditching the twins in favor of a single bigger turbo, all in all it's a 20k job. Such is life.

Thanks for your advice guys, will see what can be done and update when I have some results in case others have similar problems with the automatic fds in the future.

 

their are other aftermarket ecu options that will allow you to keep the stock sequential twin turbos, ie, apex'i power fc. as for you problem, could be many things. good luck.

 

There's also a piggyback setup that'll allow your automatic to still work as originally designed, if swapping to an aftermarket ECU, sold by Banzai Racing. Without it, the tranny runs in limp mode, causing it to shift @ different points as well as no manual control of Hold/Overdrive etc.

http://www.banzai-racing.com/store/F...u_adapter.html

As far as your checking out the tranny & everything being fine, I imagine you'd have to almost be a transmission specialist to be sure about that, as it could be something as small as a sensor inside going bad somewhere, crud stuck in the valvebody etc. I've had trannies flash the Hold light @ me while seeming to still work fine. Eventually they failed though. I'm disabled, which unfortunately means stuck with automatics, and have always owned Mazda's.

 

Finally done, Thanks guys, well she's back and is lighter 1 twin setup, she's now running a single turbo, boosting a modest .5 microtech running the engine, spitronics running the gearbox, only issue at the moment is that I flooded her to death due to the microtech being incorrectly setup, far too rich on startup but not rich enough when in gear so she's dying when put into drive but holds her idle in neutral.

She'll go in on friday morning to be dyno'd and have the issue hopefully sorted once and for all. The flooding was a headache of note, 4 hours, 2 battery charges, a jumpstart, a couple of spark plugs and some 2 stroke later, she finally fired up and smoked out my entire block. Good times.

 

Good to hear man. I've found mine's a bottomless gasoline bucket as well. I'm hoping she just needs a typical Power FC re-tune/plugs/wires etc, as the previous owner says, heh. Unfortunately it's 4h to the closest shop & at 5mpg, it'll have to be hauled there. In the meantime, Bambi decided I needed a new hood ornament.

 

I Feel your pain, getting Miya back tomorrow from remapping, hoping that will sort out my fueling issues, I know she's overfueling horribly but keeping the faith that my guy will sort it. He's done everything else, but then again there's almost nothing original left under the bonnet anymore. Got more computers running this car than Nasa.

 

Good luck man! I'm a little interested in the Spitronics system you mentioned controlling the transmission, as well as wondering why you didn't go with the Banzai's solution.. is it not compatible with the Microtec setup?