Fueling problems.....
 

Hey guys, I'm posting this for a friend (I've been helping work on his car) and we are running into some problems with Megasquirt on his turbo miata. To give you some background his car is:

90 Miata with a 97 1.8 Engine
Cheap T3/T4 50 trim turbo
Toyota 430cc Low Impedence Supra Injectors (but with JGS Tools resistors in line)
External Wastegate
Knockoff HKS SSQV BOV
Saab intercooler

Anyways, he had the car running decently on Megasquirt when it was NA (it ran both fuel and spark). Now that we have assembled his turbo setup, we are having some issues getting it running properly. We originally tried using Nate Sullys map as his setup is similar to ours and surprisingly on the first crank, its started right up. Unfortunately the A/F was out of whack so we began messing with it. Unfortunately, we were unable to get it correct and we kept having problems with it running very, very rich and idling too high.

Eventually, we tried Al Hounos' .msq file with minor modifications, and then it started with that and actually ran a little smoother than Nathans. We actually ended up driving it around the parking lot in the apartment complex, and it seemed not too bad, the A/F seemed to be fine under partial throttle. Unfortunately, the idle was off (we think its the trim pot on the 1.6 throttle body not functioning correctly). So after attempting to fix that, we tried starting it to no avail. After a while the engine stopped cranking completely, and after a while we removed the spark plugs to find the cylinders were full of gas and it hydrolocked the engine. We were like WTF, and then blew what fuel we could out and let the rest evaporate. After getting the engine to start after that, it ran rough again, so we killed it, and of course, after cranking for a while, it hydrolocked once again.

We started pulling our hair out trying to figure out why this was happening, and with some further testing, we found the injectors are NOT leaking, but more like megasquirt is holding them open too long or something. Overall, we aren't sure what setting we need to mess with to prevent this. Also, since we are using resistors on our injectors, what settings from Nathans map should we change to represent this (he is using low impedence DSM 440cc injectors).

Sorry for the long post, but I appreciate all the input!

Also, it seems that megasquirt isnt turning on instantly when the car is turning on, it takes about 5-10sec for it to show up on my laptop, what could be cause of that? (it didnt do this initially before all our problems started)

Im no pro when it comes to tuning. But from what you've posted to me it sounds like the injector characteristics in your constants page might be off. That would cause your injectors to be open for too long. I'm not sure what you should have them set at though, I have no experience with DSM injectors. I'm pretty sure though that since they are low impedence they should have pretty low PWM times.

Well as per the MegaManual, we set the PWM current limit to 100% and PWM time threshold to 24.5ms. This is for high impedence injectors which we are essentially running with the resistors inline with our supra injectors.

Its on, it just takes 5-10 secs for Megatune to see it.

http://msextra.com/viewtopic.php?p=132508

I had the same problem, I turned the priming pulse to once instead of twice and now I disconnect the injector plugs anytime I have to leave the MS on and the engine not running. I haven't had it happen since, but as you can see, I got no real answer as to why it happened.

Thanks Al, but you set your priming pulse to once instead of twice? I may be a little slow, but for the choices of priming pulses I see Power Up, Twice, and After 2 seconds, I'm guessing you set it to Power Up? Also, after further reading about injectors, I was setting the PWM current and timing threshold incorrectly. Because the injectors are low impedence(peak and hold) and I put resistors inline, I thought I should treat them as high impedence(saturated) injectors. This seems to be a mistake on my part as I should still treat them as low impedence. My question is, if I treat them as low impedence injectors as far as setting the PWM, what is the point of having resistors inline with them? Thanks

yep, power up. no, you should treat them as high impedance if you are using resistors. just go to the megamanual and double check that you have your settings correct for high impedance injectors.

what i think happened when i had the problem was i turned the ignition on twice, leading to a total of four squirts, which with 450cc injectors, might be big enough to flood the engine. Subsequent cranks squirted enough fuel to lock the engine. I've just been careful about not leaving the ignition on without starting it and i haven't had the problem since.

Al, after looking at the most recent .msq file you posted in the Settings thread, it looks as though you are using high impedence injectors as well. After further comparison between yours and Nathans .msq, I see numerous differences. The VE from you fuel table is quite different, as with the Req Fuel. Using the calculator for an AFR of 14.7, I got 7.2, Nathan is using 440cc injectors, so he got 6.8, but with your injectors (I believe you stated they were 450cc) yours is 5.9. What AFR did you enter in the calculator, and why? Thanks!

Nathan and I are using the same injectors - 450cc low-impedance DSM injectors, WITH resistors. So the only differences between our three setups is that I am a 1.6, and you are using 430cc injectors instead of 450 like us. He thought DSMs were 440s, but they are actually 450.
AFR is just a way to tell MT what fuel you are using. if you are using gas, enter 14.7, since this is stoic for gas.

Your req fuel should come out to 7.0.

Ok, I have been tweaking my MSQ file before actually trying it yet, and after more comparison between yours (Al's) and Nathans, I noticed some significant differences. The dwell time for yours is 4.5, but Nathans is 2.0 and 2.4 with a .1 minimum discharge time. Is this dependent on the type of coils you are using, 1.6 vs 1.8? Also, I noticed your AFR targets are slightly different (nothing all too major) but I wanted to know what AFR you idle at and RPM. Currently we are not using Idle Control on my friends car and I'm wondering how necessary it is, can I get away without it? (MSnS has completely replaced stock ECU, not running in parallel)

Here is my current untested MSQ file I plan on using(based more on Nathans file, but may switch to yours as it idled better last time we had the car running), would you mind taking a peek at it and giving me some feedback on it? Thanks!

I can answer this, 1.6 coils can handle higher dwell time, while the 1.8 coils cannot. Basically 1.6 coils > 1.8.

hmm, i think im gonna go browse msefi.com about injector characteristics :cool: