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Old 03-15-2013, 05:15 AM   #1
ochowdero
12psi boost
 
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uhm sooo, is there a more "basic" one?
i love the idea of data recording. its easier to detect problems but seeing how im new to fuel controller, i dont want to confuse my self specially when trying to go to work.
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Old 03-15-2013, 03:57 PM   #2
MA70-3.0GT
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cre, all this talk of f-cons etc, is that really necessary for 400bhp? I was under the impression that using the lexus kvafm/custom air screw, uprated fuel pump, adjustable fpr and 550+ injectors would be a good starting point on a stock GTE motor with the turbo wound up, while keeping the fuel cut feature, and then when funds allowed, add a decent turbo elbow, larger I/C and hard pipes etc just leaving the boost as 11-odd psi before finally uprating the turbo...

Would that not be sufficient to make 400bhp once the turbo was replaced & boost increased? IMO I'd feel happier using a similar setup & keeping the fuel cut for any unforeseen fuel system malfunctions.

I was reading this yesterday... http://www.suprasonic.org/lexusriemer/lexusnotes.html

Seemed to suggest that with that done around 330-340 would be realised with relatively low boost and with potential for more in future (I was getting near on bone stock hardware at the limit of the turbo's capacity, and running into fuel cut at higher revs on occasion, hence I'm on the lookout for the aforementioned injectors & afm as a precaution with the new turbo)

The only potential issue I can see with this, is that it could cause a rich condition on cold starts before the O2 sensor is in the game. However I don't see this as a major problem as cold engines like a richer mixture anyhow, and the O2 would warm up & the system go open loop in about 5 minutes anyway?
(and if it proved TOO rich in certain circumstances I'd think you could devise a switch/resistor setup to disable the CS Injector from the driver's seat & not throw a code?)
Obviously as injector sizes and boost levels increase the f-con etc would eventually become necessary as the closed-loop richness would become too much even with the CSI disabled & you'd get bad starting & flooding, but my point is that for the lexus & 550's etc mod and an upper goal of 400bhp, wouldn't the stock ECU be able to handle it?
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Old 03-16-2013, 12:30 AM   #3
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MA70-3.0GT, fuel controllers aren't essential but they're a very good idea and I wouldn't try for that level of power increase without a basic SAFC II at the minimum. Just because a 550cc/m injector flows 125% of what a 440cc/m injector flows it doesn't mean they flow the same amount at idle, low load, mid loads, or even high loads. You may waste fuel, lose power or in some odd cases find that the 550s flow LESS at low or mid loads. Depending on if your ECU is setup to still run closed loop you could spend a lot of time running quite poorly (whenever the system is operating in open loop). A fuel controller isn't going to change the fuel cut level, that's determined by factors such as the duty cycle of the injectors (which IS affected by the size of the injectors).

Ochowdero, sure there are simpler piggybacks than the MAFT Pro or MAP ECU, etc. There are a lot of simpler devices with fewer functions and a ton of support... I'm sure you've hear of the SAFC, SAFC II, NEO all by Apex'i. These are just fuel controllers, the list is quite long. The functionality varies per device, some support data logging and some will integrate with an on-board wideband which I also strongly recommend (and it's essential if you're looking to tune on your own). There are independent units for timing control and boost control. The 'super piggybacks' roll all of these into one package which uses one app for data logging but often at the expense of a steep learning curve.
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Old 03-16-2013, 01:48 AM   #4
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No worries, I was under the impression from that write-up that fuel cut primarily based on the frequency of the signal from the kvafm (partly why the lexus body was used, with the adjustable "bypass" to allow more air to be flowed than the ECU believed), and the ECU then used the O2sensor to correct the resulting lean mixture using the fuel trim.
Then the 550cc injectors were required to "correct" the fuel trim back to the basic level by flowing more fuel for a given pulse width hence leaving more room to correct when boost increases.

All that worried me about the f-con was that modifying further the kvafm signal might affect fuel cut, but you're right it'd still cut at around 80-85% injector duty cycle so no probs.

I was thinking of building a fuel trim monitor using the Vf terminal in the diag. socket, that'd be nice to know what it's doing through the rev range (guess it'd help you pick up a slow switching O2 sensor too)

Anyway, not wishing to hijack the thread sorry ochowdero. so I'll do a bit more research & any questions I'll be sure to bore you with them cre
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Old 03-16-2013, 08:05 AM   #5
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Haha your not hijacking. I like this info. I'm working on building an engine to perform reliable power and durability but for a low.cost. This thread is about that (well the title doesn't say so but I intended it to progress this way)so thank you for you input!

I'm looking for a fuel pump, a good one. Strong!. Any recommendations?
My fuel filter is clogged or something else going on in my fuel system but I can't get my hands on a fuel compression tester. I'm going to do further testing to see why my car stalls when slowing down but I plan on replacing my fuel pump with a stronger one anyway.

Cre- yes. I'm looking at Acouple but I am not fully understanding what I'm looking at. I feel slight shocked cause I worked with them quite often. But I am just lost. Haha, I.think it's Because I thinking about everything and not focusing on a Part at a time.
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Old 03-16-2013, 05:32 PM   #6
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MA70-3.0GT, fuel cut is based on a couple factors.... I think I remember injector duty cycle, RPM and airflow being the primary factors although I could be wrong. It doesn't matter much for this situation as duty cycle is largely determined by the airflow signal.

The adjustable bypass screw on the KVAFM isn't a fuel cut device (that would be a side effect though). IMO, It's a crude hack to fix poor idle and low load issues when running in open loop. This is precisely where a fuel controller is the better system as otherwise you're still not managing any imbalances in the mid loads and you've only got one single adjustment to try to balance out a pretty big range. The O2 sensor has a very tight range of operation, isn't referenced under a number of circumstances. It's unreliable as a diagnostic device and I'd prefer not to bet the performance and safety of my engine on it. I don't believe in cheaping out on this stuff especially when doing a better and more trustworthy job/setup doesn't cost that much more.

The Vf circuit is a crap circuit for monitoring fuel trends real time, on a regular basis, especially on any non-stock setup. When I setup a data logging system on a TCCS type Toyota I usually add that to one of the monitored auxiliary inputs but it's yet to provide anything useful which wasn't made more obvious by better devices and much more quickly. A slower responding O2 isn't going to help, you'd be better off dampening the comparator circuit for your Vf meter. Dampening the actual O2 signal is going to affect your entire system. I know a couple of people love Vf but half of those who do still agree that unless the car is bone stock it's worthless and it's definitely no substitute for proper diagnostic devices (namely a wideband).


Ochowdero - If you have tuning experience then you should be fine with any of the 'super p/bs'. Just wire them up and if possible skip wiring in optional functions until you're ready to work with those. With some decent experience under your belt the things that are likely to make things difficult diminish in number quickly. Certain finer things such as tip in enrichments, decay rates and the like and then the functions related to converting to a different type of air flow measurement system should be the only things you'll have to do significant homework on... Even the timing control isn't too bad (but you probably aren't even going to want to use that).
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Old 03-16-2013, 07:04 PM   #7
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Cool, not suggesting anyone "cheap out" on mods that handle the safety of your engine, just feeling out the limitations of the stock system. I was thinking the lex AFM body was mainly for increased flow capability with bigger turbos anyhow,
but the reading I did seemed to suggest that fuel cut would come in at a set KVAFM signal frequency regardless of duty cycle/rpm etc hence the larger unit would be required once fuel flow capability & boost were increased in order to make use of anything above stock max airflow rate.

Just one thing on the O2, I wasn't saying to USE a slower switching O2, was saying that if a Vf monitoring device was used it may help detect if the O2 was slowing down with age/damage. (though thinking on it I guess a wideband O2 sensor & a monitoring system directly signalled by it's output would be much more informative on the things that matter anyway)

It'd still be nice to have a Vf monitor as well though, with a min/max data hold to keep an eye on how much "reserve capacity" is in the ECU's map at a given boost & fuel system spec...



I suppose most of the information written in the link was written back when f-con's were in their infancy & he felt the lex/550 was a better solution than the then-basic programming of said f-con's, so maybe not so relevant now that the companies have had 10-15 more years of development time. I guess it's glaringly obvious I haven't really looked into any of them & really I should as they likely have all the monitoring capability & more that I'd ever need or want.

EDIT-: just thinking about it, using a MAP based fuel controller would eliminate the problem of AFM restriction completely, and in theory the fuel cut feature should still operate based on the injector's duty cycle right?
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'89 MA70 Supra GT aero 3.0turbo JDM, Rebuilt motor, K&N intake, 3" stainless turbo-back. New turbo and braided line kit...

'89 Honda NC27 400, NC23 cams, open pipe, PC36a shock & possibly Showa USD forks...

'83 Yamaha 29R XJ750E-II, number 69 off the line, only runner in the country? Original except Koni shocks

'95 Honda PC26 CB500R, Winter hack, hateful, trying to sell it
I'm not paranoid, they really ARE after me!!!

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