How does a piggy Back ECU work? - Adding Bigger Injectors...

poison · Post by **poison** » Fri Oct 13, 2006 9:54 pm

This question is probably aimed at Glenn, or others please if you know.

I have a HKS Fcon mini which is a piggy back ECU. I have been told the advantage of piggy backs is the better round town and cold running as the normal ECU does this. So how does a piggy back work? Does it take over the timing and fuel at a certain rev range? Or over the full range? If so why keep the stock ECU?

I'm asking as I would like to up the boost on my turbo as it's currently only about 6PSI. To do this I imagine I would have to get bigger injectors (I just happen to have some GTX 330cc ones). So would my normal ECU still be able to make my car run smoothly at low revs and idle?

Or am I better to up the fuel rail pressure as is suggested with the Gready turbo kits. I have an 1800cc NB so anyone know at what kind of boost I can get up to with the stock injectors?

Or to put the whole thing simply, what do I need to do to get more grunt!

Cheers

Gazza

SLYDIT · Post by **SLYDIT** » Sun Oct 15, 2006 9:28 pm

Ok Gazza this is going to be long....

Piggy backs like the f con mini alter the fuelling by altering the airflow meter signal to the ecu, giving the correct fuelling for any situation within the realms of the factory programming. so if you fit 330cc injectors from a GTX you need to alter the aiflow signal by -30% to get correct fuelling at start up and cruise.

Now then you need to add fuel in the boosted zones...My e manage does this by directly driving the injectors longer than the factory duty cycle. i dont know how the F- con works in this respect.

Now for the fun stuff...........
when you alter the airflow signal you also alter the timing to an unknown amount.... i have no idea where my timing is at, but it doesnt knock on the dyno so thats good..

Also as you have an NB you face the single biggest hurdle to overcome and that is the factory ECU. The NA cars have a very simple ecu which runs its mixtures in closed loop(air fuel ratios of around 14:1) off the oxygen sensor at all light loads including idle. when you floor it it STAYS in closed loop until 4000rpm when it goes open loop on preset fuel maps in the ecu.THIS IS VERY IMPORTANT TO GET YOUR HEAD AROUND.it is a fact that a turbo can generate significant amount of boost below 4000rpm and the factory ecu tries to take out all that fuel that you are putting in via the piggy back ecu in an NA car you can simply add an "oxygen clamp" which tricks the factory ecu into thinking that the mixtures are ok and so it doesnt add or remove fuel and keeps your boosted mixtures at a turbo friendly 12:1.
It is very important to know that the NB cars stay in closed loop trying to keep the mixtures at 14.7:1 more so than the NA cars and that oxygen sensor clamps dont work as well because of the much more complex ecu that monitors emmissions and catalytic convertor status via the TWO oxygen sensors in the exhaust.if you add an O2 clamp, chances are that youll throw a check engine light for a faulty O2 sensor

SLYDIT · Post by **SLYDIT** » Sun Oct 15, 2006 9:40 pm

so the big question is what to do???

well id throw in the 330's and see how it idles. the one good thing about the NB ecu is that it does a good job of adjusting the mixtures. youll be rich at startup when cold though until the o2 sensor heats up.and also when you blip the throttle when cruising as the "accellerator pump" function operates.

did you ever get any tune up manuals for the f-con??if you give me some ideas on how it works i could come up with a tuning guide for you.the f-con is really going to be a headache to tune any way you look at it..have you considered other options???

getting some dyno time will sort out your full load mixtures but its at part throttle boost that is the big concern with running lean. you could try an o2 clamp and see how it goes.

Oh by the way you cant alter the fuel pressure on Nb cars as it has a returnless fuel system that cant be altered in the same way as the early cars can.

Post by **jif** » Sun Oct 15, 2006 11:45 pm

a few things:
- I think the NB fuel rail, although returnless, can be made into a return system (like the NA) by adding the fuel pressure regulator and return line. At least that's what they say on teh big list. (and I have a spare '99 head if you want to try it out first..)
- emanage ultimate (EMU) can adjust fuel *and* timing, if you choose to go down that path.
- I'd still wanna keep the NB ECU, just 'cos it does the gauges, alternator, and who knows what else! </broken record>

http://forum.miata.net/vb/showthread.ph ... light=xede - good thread, pretty informative.

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SLYDIT · Post by **SLYDIT** » Mon Oct 16, 2006 3:56 pm

The emanage ultimate is a waste of money on an mx5,,,most of the features of the ultimate are only used on cars such as GTR's and supras....why pay for a emanage ultimate when you can get a link for the same money...

My emanage blue is perfectly capable of controlling fuel and timing in the car. the only thing it cant do is the o2 clamp thing, but then ALL piggybacks have that issue.even the ultimate.

the best solution would be to get an emanage blue to run things seamlessly, but i guess you didnt want to hear that huh.

poison · Post by **poison** » Mon Oct 16, 2006 11:35 pm

Hi Guys,

Brilliant guys, thanks for that, top marks for the extra effort Glenn. I didn't realise that piggy back's don't do the timing, so do people just mechanically retard the timing or not??

Great idea re trialling the 330cc's worth a crack, I have not found any info on the tubing of the Fcon mini, I rang the guy I go the car off and he said he thinks it had 3 dials or pots to adjust. I believe that Redline performance are the HKS agent up here, so I will give them a call and see if they can help (I'm sure they will say yes - $$$$$) but a few questions will soon tell if they are up to it.

I must catch up with you soon Jeff anyway and you can explain this return fuel thing to me. Sorry you've lost me on the 99 head?

Gazza

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poison · Post by **poison** » Mon Oct 16, 2006 11:49 pm

SLYDIT wrote:....... when you floor it it STAYS in closed loop until 4000rpm when it goes open loop on preset fuel maps in the ecu......

I just realised, I have this 'issue' with my car, if I am driving around some tight chicanes in the road at say 3000 -3500 rpm in second (50k area) when I am on the point between boost and engine braking the car will surge a couple of times like it has got confused. This open/closed loop may go some way towards explaining this. It does not happen under normal acceleration or deceleration only when keeping the car speed about even at those revs.

I was going to come and hassle you to come for a test drive and your opinion Jeff.

Does anyone know what the maximum achievable boost is on standard injectors and fuel pressure? I would think about 6PSI, am I correct?

Gazza

SLYDIT · Post by **SLYDIT** » Wed Oct 18, 2006 9:54 am

id put money on the fact that the surging is because the car is lean at part throttle/low boost. my car had similar hiccups before i got my o2 clamp adjusted properly.also is your BOV recurculated or vented to atmosphere? a bov vented to atmosphere can cause surging when transfering between vac/low boost.

Post by **jif** » Wed Oct 18, 2006 10:22 am

if you go to the RC Engineering website they have some formulas for working our injector flow vs max-hp ... you can extrapolate back to boost psi from there

PS - the NB injectors are rated at something like 260cc @ 52 (?) psi ... ie not the standard 43 psi.

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zippy2 · Post by **zippy2** » Wed Oct 18, 2006 3:49 pm

[quote="poison

Does anyone know what the maximum achievable boost is on standard injectors and fuel pressure? I would think about 6PSI, am I correct?

Gazza[/quote]

I do not know - but I would think the injectors can take at least 8-9lb boost as the JR supercharger big boost kit uses the standard injectors for about 9lb, but comes with a replacment high flow fuel pump.

SLYDIT · Post by **SLYDIT** » Thu Oct 19, 2006 9:06 pm

yeah the rc formulas seem to work better at the lower standard fuel pressure of 43 psi and are very conservative. the NB runs 50-60psi pressure.