How to tune your engine (EFI) - Page 3 - Alfa Romeo Bulletin Board & Forums
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post #31 of 45 (permalink) Old 03-25-2009, 12:00 AM
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SPICA = sequential injection?

Brett,

The difference between your setup and mine is the location of the injectors; I'm using a SPICA manifold, which places the injectors in a fairly modern position much closer to the valves, while you've got throttle bodies with built-in injectors mounted much further out. Still, I've got what sounds like the same driveability glitch, with a slight lag when tipping the throttle in after running with the throttle closed.

Now somehow, the SPICA injection system didn't have this same lag, and the injectors are obviously mounted the same distance from the valves as mine are. I'm frustrated that I can't get my EFI system running at least as well as the old mechanical system. Maybe there's something particular about the injector spray pattern?

So, the SPICA system sequential, yes? Megasquirt can only support batch-fire injection. I'm wondering how much driveability is down to this difference.

Can't blame it on lack of spark control, since the SPICA cars obviously didn't have spark control, either.

Most of the advertised advantage of EFI (more effiecient, cleaner, can run leaner, etc.) seems lost on the Nord engine and individual throttle bodies. It simply wants a ton of fuel dumping in at all times to maintain driveability and responsiveness.

As for your erratic MAP signal... how bad is it? My MAP signal is nice and stable, and response is pretty much instant. I've run a 1/8" ID line from each intake to a fabricated plenum box on the inner fender (aprox .75x1.5x6" rectangle), and about 4 ft of 1/8" line running from there to my Megasquirt box. No restrictors or Mig tips. Do you have a common plenum, too? Maybe it needs to be bigger?

That said, the MAP signal strength is weak: about 75 to 80 kpa at idle, and jumps right up to 98 or so with the slightest whiff of throttle. So most of the "working area" in my fuel table is from 98 to 101 kpa. Hmmm... I'm surprised it runs as well as it does.

At any rate, this is an interesting thread, but I wonder if some of this is a lost cause on the Nord engine.

George
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post #32 of 45 (permalink) Old 03-25-2009, 01:26 AM
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Quote:
Originally Posted by gattia86 View Post
The difference between your setup and mine is the location of the injectors; I'm using a SPICA manifold, which places the injectors in a fairly modern position much closer to the valves, while you've got throttle bodies with built-in injectors mounted much further out.
This only makes a difference when my engine is cold as the fuel tends to puddle a bit on the cold manifold. This makes driving a little sluggish for the first 10mins ( still nowhere as bad as carbs), but once things warm up there's no problem.


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Originally Posted by gattia86 View Post
Still, I've got what sounds like the same driveability glitch, with a slight lag when tipping the throttle in after running with the throttle closed.
Have you tried xtau? I found that it ran a lot better under slight accel and deccel with it on. I also have the AFRs in the run down area (below 70kpa) fairly fat, 14.7, and this helps a lot too. I only get a slight hesitation under particular situations, eg certain RPMs and MAP, the rest of the time you wouldn't pick it from any other modern EFI engine.
I'm sure with a bit more fine tuning I'd eliminate it but can't be bothered as the engine with be coming out in a month or so.


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So, the SPICA system sequential, yes? Megasquirt can only support batch-fire injection. I'm wondering how much driveability is down to this difference.
I very much doubt it. Many other twin cams with ITBs run fine with MS.

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Most of the advertised advantage of EFI (more effiecient, cleaner, can run leaner, etc.) seems lost on the Nord engine and individual throttle bodies. It simply wants a ton of fuel dumping in at all times to maintain driveability and responsiveness.
That's the nature of the little beast. Still, I get some very good MPGs out of mine. Much better than when I had carbs and never plug fouled either.


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As for your erratic MAP signal... how bad is it? Do you have a common plenum, too?
No plenum, just restrictors. At idle it jumps around a couple of kPa but is pretty smooth when driving. Only problem I have is that small variations in throttle make big changes to MAP. I think this is down to the TBs being oversized.


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That said, the MAP signal strength is weak: about 75 to 80 kpa at idle, and jumps right up to 98 or so with the slightest whiff of throttle. So most of the "working area" in my fuel table is from 98 to 101 kpa. Hmmm... I'm surprised it runs as well as it does.
I'm about 70 at idle and 75 to 85 normal cruise between 1500 and 2500 rpm. Goes up about another 5 at 3000 rpm. Open the throttle a bit and it quickly goes to 95-100.
In the end your 3D VE table should resemble a skate board ramp with the VE quickly rising above 85kPa.
I've even seen some ITB VE tables with a little ramp at the lower end of the MAP range (below 30). This may give some insight into other people's problems with rundown fuel loading.

And yep, given the limited range of the MAP signal its very surprising how well you can get these things to run on speed density.

Bye for now.....
Brett.
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post #33 of 45 (permalink) Old 03-25-2009, 04:42 AM
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To echo what Brett said, I would very much look at transient fuel compensation, especially if you have one that is throttle rate based.

As for the betterment of EFI, even not so modern... it's all in the tuning. That, and SPICA can't really do emissions control- optimizing catalysts, being able to run for purge fuel flow, etc. But SPICA is a killer system, when it comes down to it.

If you went TP based instead of MAP based- you could replicate exactly what the SPICA did, since that's essentialy what it is.

Eric
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post #34 of 45 (permalink) Old 03-25-2009, 01:58 PM
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did you add a pot to the butterfly's? it is very hard to do acc-enrichment with out it.
MAP based enrichment is not very good.
TPS based enrichment is the way to go.
you can also do a mix of TPS/MAP if you have it.
one common way is use TPS for low bins and mix in the middle and go to MAP at faster RPMS. This also works out if turboed as you need to be MAP based under boost.

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post #35 of 45 (permalink) Old 03-26-2009, 06:30 AM
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did you add a pot to the butterfly's? it is very hard to do acc-enrichment with out it.
MAP based enrichment is not very good.
TPS based enrichment is the way to go.
you can also do a mix of TPS/MAP if you have it.
one common way is use TPS for low bins and mix in the middle and go to MAP at faster RPMS. This also works out if turboed as you need to be MAP based under boost.
Greetings: Take it for what it is worth from a newbie on EFI, but I have found the mix TPS & MAP to be working well on my Alfetta. The GoTech offers a pre-programmed mix, and little information about what that formula is. Nevertheless, it seems to simplify the tuning across a broad range, as confirmed by my wide-band O2 sensor.

This thread has been very helpful this past week, with many great links to resources.

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post #36 of 45 (permalink) Old 03-26-2009, 12:50 PM
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I'm just not seeing the requirements for a MAP/TPS set up for a multi throttle body set up for NA. The whole thing should be tunable via TPS only load sensing so long as you have an atmospheric pressure compensation map within the computer. That's how my uncle's Motto Guzzi is set up (factory Weber Marelli).
The only time I've seen the need for MAP and TPS combined is when there is boost pressure to measure at some point.

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post #37 of 45 (permalink) Old 03-26-2009, 09:50 PM
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Well, very interesting point about the SPICA system being purely TPS based. And it works very well. Megasquirt is really MAP based, but can do a mix or TPS only if you really want to. The idea is generally shunned by Megasquirt experts, but I'll have to give it serious consideration.

And most of the people I learned tuning from are turbo fans, so that could explain the reliance on MAP.

Yes, I've got a TPS sensor on the butterflys (from a Buick V6; easy to adapt to the SPICA throttle shaft, and one of the few that rotates in the right direction for this application).

OK, so I know the theory behind X-Tau, but I'm not sure I understand how to use it, with Megasquirt specifically.
What, exactly, should I do with it?

My engine tune deffinately changes with temperature. I fiddled with a non-linear manifold air temp (MAT) compensation table, and it does seem to run better... but I suspect the tune is affected as much by air temp as by heat soak in the head and manifold. It would exhibit poor running after extended high-speed runs and then idling in traffic, and ran worse on warm days (even when the plugs say it's running lean, not overly rich). At first I suspected fuel vaporization or maybe poor gas-tank venting, but those systems check out OK.

I'm pretty sure X-Tau is meant to deal with heat-soak issues, but I'm not sure how to approach the problem.

Thanks for any tips,
George
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post #38 of 45 (permalink) Old 03-26-2009, 11:23 PM
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xtau
MegaSquirt-II X-Tau
Just enable it and see what happens. Most seem to work well with the default settings. Some need to play around with xtau and accel enrichment.
I just switched it on and the flat spot I was experiencing when taking off from idle disappeared. Only problem I had was that when looking at my data logs I could see that it was triggering every now and then, especially at idle.
I turned it off and played around with the accel enrichment settings until the flat spot was gone.
I guess I could have played around more with xtau but you reach a point when you've just had enough.

MSExtra use EAE in lieu of xtau, might be worth a look.
MS2/Extra EAE tuning guide

For TPS control MS uses AlphaN mode (often misspelled alfaN). I've tried it with little success. Seems more suited to cars with big cams and like to run on race tracks. As others have said, you can also run a blend of the two. I looked into this in MSE where it seems a little easier to implement than standard MS.

One thing that I have been thinking about for ITBs is a MAF sensor on a common plenum. MS will do this but I've never heard of it being used in an ITB application.
Given the inherent difficulties in calculating mass air from weak and pulsating MAP signals, measuring mass air flow at a common inlet makes sense to me. But I guess there must a good reason why people don't do it.

Sly, never thought of the dash pot. I'm sure there was one fitted to the GSXR TBs. What's the theory behind using one?
Does it slow the opening and closing time enough to allow the system to keep up?

Bye for now.....
Brett.
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post #39 of 45 (permalink) Old 03-27-2009, 12:56 AM
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Quote:
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One thing that I have been thinking about for ITBs is a MAF sensor on a common plenum. MS will do this but I've never heard of it being used in an ITB application.
I don't know about the BMW M3s, but the turbo charged Skyline GTRs an RN14 Pulsar GTiRs used individual TB, turbo(s) and AFM(s). The 1st 20valve Toyota 4AGE used a vane/flap AFM but the later 1s usd a MAP sensor.

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Given the inherent difficulties in calculating mass air from weak and pulsating MAP signals, measuring mass air flow at a common inlet makes sense to me. But I guess there must a good reason why people don't do it.
Cost and perception I'd guess. 1 more thing to buy and the belief (often touted by after maket computer marketing) that an AFM is a restriction.
If you did decide to use an AFM, I'd sujest using the hot film type from either Bosch or Ford. They apparently don't require the burn off that hot wire types do after running.

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post #40 of 45 (permalink) Old 03-27-2009, 03:50 AM
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I bought a Siemens MAF sensor for my wife's Hyundai last year. It cost me about $150US for a genuine on ebay. About $90 for a non genuine.

There were 2 sensors fitted into a side stream port. One appeared to be the reference sensor to measure ambient air and the other I presume is heated and measures flow as a coefficient of temperature loss.

Apart from a square grid mesh on the inlet and some lamina flow correction it was virtually a straight through tube.

You would need the flow curves and to know the up and downstream pipe lengths for accurate measurement but apart from that it would be relatively easy to adapt.

Even if the flow measurement wasn't all that accurate. as long as the signal verses flow curve was repeatable and reliable you could still tune from it using a wb02 sensor for final results.

I very much doubt whether the mass air flow calculation for a speed density algorithm on an ITB setup would be all that accurate. Probably why the VE curves look so unusual.
So in theory a MAF flow meter would have to be better.

Bye for now.....
Brett.
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post #41 of 45 (permalink) Old 03-27-2009, 11:05 AM
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I did not think I said dash pot. but they can help with let off the throttle and the motor rpm drops so fast that the ECU can not open the IAC in time and the motor stalls or goes way under idle RPM. This should be not needed if the ECU software is doing its job. But if you have a problem of RPM undershot it will help.

but if you have a TPS use it for accel-enrichment (TPS based. Not MAP based)
you should be able to use MAP for everything else. I was running that way on my VEMS controlled spica pump. and it seemed to work OK. It had better response then the old spica brain(no accel-enrichment in the spica)
and use the biggest table size if MS let you pick. there is a lot of up and downs in the table.

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post #42 of 45 (permalink) Old 03-28-2009, 04:59 PM
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gattia...on my stock bosch system,( 84 spider) the tb is quite a distance to the valves, much less the injectors.. so the distance between the tb and the injectors... i dn't think that is the problem...

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post #43 of 45 (permalink) Old 03-28-2009, 05:04 PM
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Question

a tought.. on the org. 4 cly m3's they had itb's and ran bosch lh jet i belive.. they ran fine...hummmmm

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post #44 of 45 (permalink) Old 11-25-2012, 08:04 PM
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megasqurt map file

Folks
i know this thread is more then 3 years old, but I'm struggling to get my megasquirt tuned. I have the same set up as Bret had, but I just cant get it running properly. Is there any chance I can get a MAP file from anyone who hase there car running properly? It would really help me a lot
Thanks in advance
Sam

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post #45 of 45 (permalink) Old 11-26-2012, 06:33 PM
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Start with a simple 2D advance curve and get it running cleanly on that. Look at your data logs and make sure you're not losing your crank signal, your sensor inputs are clean, etc.

Are you running MS2 or 3? The ITB support improved with the latest release. People have also had to restrict the MAP feed to help dampen the pulses, though I'm not sure if this is still required on MS3.

The MS forums are fairly active. You may have better luck there.

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