550cc injectors on a V6... 5.1 required fuel glitchy

rebel2k4 · Post by **rebel2k4** » Fri Nov 18, 2005 6:13 pm

I have an MS1 with megasquirt'n'spark. I've had the car running on it for about the past 4k miles or so. So far, so good as far as reliability.

However, I have noticed some issues. I am using a req fuel of 5.1. 2 injections per cycle, alternating. its a 2.5L V6 with 550cc injectors.

I think I remember reading somewhere that anything lower than something like 8 RF is not recommended. Well, to start, it seems like all my settings are very close to each other. For example, my idle VE is 50 but my 7k rpm 15 psi of boost (~ 200kpa) VE is 85. There seems to be a very fine line in tuning it. I had to rework all the parameters to get it to run right, and they are nothing like default settings.

The issues I'm having are somewhat minor, but aggravating. The main issue is cold starts. It is fine above 60 deg F, although the settings are very odd (such as a 50% ASE and 160% warmup enrichement, for example) ANything lower, its almost like I can tune it one day, come out the next and I have to tweak the settings again. it seems like Im chasing around the perfect number, and once I find it, it changes? FWIW I use an LM1 wideband 02 to tune with.

I can start it at 30 deg F, within 2 seconds it stalls too fast for the wideband 02 to report anything. Afterstart enrichment right? well the catch is that i immediately restart it and it starts and idles perfect at a solid 11.5:1 afr. I have tweaked it over and over again, and it seems like it always does this.

I guess my question here is what can I do to have a higher RF and have more normal settings? Since mine are so close together, it seems to be the cause of it being glitchy. There is another guy with my similar setup with megasquirt and he reports having the same sort of issues.

Bernard Fife · Post by **Bernard Fife** » Fri Nov 18, 2005 6:28 pm

rebel2k4,

This is very much a result of a small reqFuel and the limited pulse width resolution (0.1 millisecond) in MegaSquirt-I. There's more here: http://www.megasquirt.info/v22manual/mtune.htm#idlepw

Your options are:

- live with it, (d'oh!)

- lower the fuel pressure to increase the reqFuel (or lower it selctively at idle/cruise with a rising rate fuel pressure regulator) - but this might not be enough,

- get smaller injectors (but only if they support your power level),

- acquire and install a second set of injectors (& fuel rail, etc., etc.) and do 'staged' injection,

- use a hi-res version of the code (most of these are quite old now, and lacking many of the new developemnts), or

- use MS-II, with its 0.001 pulse width resolution (100 times better).

Lance.

rebel2k4 · Post by **rebel2k4** » Fri Nov 18, 2005 6:34 pm

Lance-

Thanks very much for the suggestions.

I think my best option at this point is to go with some 370cc injectors. I can find a set for around $100, so no issue there. Last dyno was 395 whp, my goal is around 500 so I should be okay with the 370's.

I run stock fuel pressure (36 psi at idle/cruise) so dropping that down much with a walbro 190 would be difficult. It would also probably be worse for fuel atomization at idle/low rpms, seeing as these injectors are so large.

I will keep trying to tune and see if I can get it better, but if not 370's it is.

Thanks again. BTW- you woulnt happen to know where i can find the info about running too low a RF, would you? I remember seeing it a long time ago.

rebel2k4 · Post by **rebel2k4** » Fri Nov 18, 2005 6:52 pm

Reading further... that would also completely explain why I can try to hold a steady rpm in nuetral (say 3k) and it surges up and down by about 200 rpms because the closed loop seems to over correct and make it too lean. Also why my cruising seems to be unsteady as I get lean spikes into the high 15:1 AFR's along with its corresponding change in power. Without the ego correction on, no problems. Also with a relatively high IGN events per step (72)

I guess Ill live with it until perhaps MS'n'S gets high RES programming (i can only hope)

Bernard Fife · Post by **Bernard Fife** » Fri Nov 18, 2005 6:55 pm

the closed loop seems to over correct and make it too lean

rebel2k4,

Yep, that's it exactly. I wish there were a simpler solution for you...

Lance.

baldur · Post by **baldur** » Sat Nov 19, 2005 3:42 am

I personally prefer the method of staging injectors. It is better to inject some fuel further up the inlet runner when running at full throttle. Formula 1 cars have 2 or 3 injectors per inlet runner, not because they don't have the control precision needed and not because their injectors are very big (they only make around 80hp per cylinder)

SRoss · Post by **SRoss** » Sat Nov 19, 2005 6:39 am

I am experienceing problems with basically the exact same setup. 550cc injectors on a 2.5L engine. However I am experiencing problems that cause my MSII V3 to hang the injectors open. I don't understand what it is but it doesn't seem that my V2.2 board is doing this. I am not sure if it is a cold weather glitch somewhere or ...etc. However if I can not get the problem straightened out today I will probably have to run the V2.2 for the winter and aquire some 370's.

rebel2k4 · Post by **rebel2k4** » Sat Nov 19, 2005 2:30 pm

SRoss wrote:I am experienceing problems with basically the exact same setup. 550cc injectors on a 2.5L engine. However I am experiencing problems that cause my MSII V3 to hang the injectors open. I don't understand what it is but it doesn't seem that my V2.2 board is doing this. I am not sure if it is a cold weather glitch somewhere or ...etc. However if I can not get the problem straightened out today I will probably have to run the V2.2 for the winter and aquire some 370's.

Did you ever try those settings i sent you?

Im surprised I got it to run as well as it does really. Its just those little glitches that drive me crazy

SRoss · Post by **SRoss** » Sat Nov 19, 2005 9:00 pm

I just got to try them today and even though they were barely different from mine it did help out. Especially the prime duration! I just need to work out a bad hiccup I'm having when I'm in boost. I didn't try your VE table, I'm wondering if it is strictly because it is pig rich running with the 370cc tune on 550's.
~Shawn

ion332 · Post by **ion332** » Tue Nov 22, 2005 3:57 pm

Well, lets not forget that MY v2.2 board did this exact same thing, so I think its got to be mainly just our settings and/or battery voltage/compensation settings...

Actually mine did it twice... Boy my wife is still mad about the gas spilled in the garage to this day.