First off, it's an MS-I v3.0 and I've been running 029q2 firmware because it's been stable for me so far. (029V was terrible, and I haven't yet tried 029W). I am running all low impedence injectors and I have my staging set correctly and I have it stage at 4500 rpms with staging off delta set at 300 rpms. Also my constants are set at 90 and 15 for PWM current limit % and PWM time threshold. Also, anytime I set thePWM current limit % near 5, the fuse burns outduring cranking, but if it starts to run and then stalls out, it'll burn out then too. Anyway, my main problem is that I have a ridiculous stumble right at 4500 rpms, and most of the time, I cant's seem to rev past it. It just breaks up like crazy right there. But sometimes when I can get past it, then the car pulls nicely. What should I change in my settings to help fix this? Also, what do you think my max timing should be set at for wide open throttle for my engine setup? Lately, it feels like it's starting to detonate on the higher rpms when I have it set at 25 degrees. It's a 4-port 13B with 9.7:1 rotors, heavy streetport and exhaust port, full racing beat exhaust (no cat), no emissions parts of any kind, etc. etc., 460 low imp. primary injects and roughly 760cc or so low imp. secondaries (the 460 secondaries were no where near enough).Well, any input is highly appreciated and I look forward to any help because the megasquirt setup is running awesome and tuning is in progress (self-tune feature is the best!!)
Thanks, Brian

 

I'd strongly suggest flashing 029W. I'd run 100% and 25.5 ms to cut out pwm. You might want to watch your dutycycle1 right before 4500, I think that may be a bit high for the 460's(considering porting). I'd try something around 3600-4000. I had some great results by playing with the staging factor and staging delay.(for example, my "mathematical" factors out to 172, however I found that by increasing my factor by 15-20 and increasing the staging delay a tad made my stage transparent. I believe this is due to either pulsations in the fuel rails and/or the secondary runners being completely dry and/or my secondaries aren't flowing as much as they should be, but I do have a rather large pri to sec gap 800ccs ) 25 doesnt sound unreasonable if its really 25, but knock a degree or 2 to be safe. You may just be lean, but you are using a wideband right .

 

Injector PWM: Must be used with low-impedance injectors without resistors. If you also have resistors in your circuit, set to 100%, 25.5ms. Otherwise, tune the injector pwm per the manual.

Staging: I prefer TPS-based staging, and set the staging point where the secondaries have opened noticably. To do this, use the 'calibrate TPS' function in MegaTune to view the actual rawADC value of the TPS. Using this technique ensures you are firing into active runners, and helps the transition. That said, there are a variety of methods to configure this, so feel free to experiment.

Stumble at 4500rpm: Change your staging rpm to 2500rpm, and re-test. If the stumble is still at 4500rpm, then you are chasing the wrong cat. If you are using MS-controlled ignition as well, with missing tooth CAS mod, you likely have the CAS wires reversed. Swap them and re-test.

Timing: Full advance of 24 degrees BTDC for an n/a is quite common.

 

as far as timing, I run 25 degrees max at full throttle, and have done so without any problems.

 

how do you calculate the scaling factor? primary flow/ total flow (550/1550) gives me a fraction, which MS just rounds down to 0

 

megamanual should definitely have it, but off the top of my head its:

scaling factor = pri flow / (pri + sec flow) * 512

edit: just checked, the above is it.

 

Well, I definitely tried scaling the injector pwm to what the manual told me to, but like I originally posted, anytime I start bringing the number down to the single digits, my 2 amp fuse burns out and the car pretty much floods itself. And yeah, the fuse burns out really quickly too. I have it at 15 now without a problem, but I bet if I start to go lower, it will burn out again as usual.

 

Again, are you running with or without resistor packs?

 

sorry, no, I'm not running with resistor packs. How would you go about getting those anyway, and/or running them for that matter??

 

They come with 86 and 87 cars I believe... I think 87.5 got rid of the resistor pack.

If you have an 86 or 87 car it's likely you have the resistor pack already.

If you're having trouble with staging, it could be due to the 720cc injectors having different characteristics from the primaries...

 

Mine is a 91 with 86-88 460cc primaries and aftermarket secondaries. I just changed the staging point to 3500 with staging off at 300 rpms and it's slowly getting better the more I drive it and it self tunes. (innovate WB). Also, here's a quick question: Is it ok that the numbers in the higher rpms in my fuel graph near wide open throttle are reaching 240? Also, according to megalog, The max injector duty cycle that was seen was 115% for duty cycle 1 and 2.

 

I also flashed 029w today and it seems to work just fine, as opposed to the 029v that I tried before.

 

So, what should I do now about the PWM current limit % and PWM time threshold numbers? Like I originally stated, When I put in the numbers that the manual tells me to put in for low imp. injectors, the car floods immediately and the 2amp fuse blows everytime. If I go higher to 5, it still happens, but not as quickly. So, the manual said to set it at 1 and 75%. Mine is set at 15 and 90%. I'm afraid if I go any lower than 15, I'll flood and burn the fuse again for like the 20th time. What should I do?

 

well, a 2A fuse for injectors seems too small for starters... I'd use a 5A fuse and see if that helps.

If your injectors are going to 115% duty, there's a problem... Are you certain that you're actually staging? Is autotune leaning out or richening your fuel mixture?

If you really need to be at that high of a duty, you need to get a new fuel pump, or bigger secondaries... Or your PWM settings are wrong and your injectors aren't staying open. You should never go much over 80-85% duty.

Ken

 

Don't drive around with autotune on until you have the whole system debugged. Underlying hardware or software setup issues together with autotune could cost you an engine.

I'd suggest you go back to the basics, and sort out your injector pwm issues first. Injectors draw 1-2 amps each in saturated mode, and even more in peak&hold mode (which you are using). That little 2A fuse is not up to the task. For reference the MS documentation shows a 5A fuse for EACH injector output, so 10A total. The larger fuse will still protect against a short, but will also allow the high-current spike needed to pop those injectors open quickly in P&H mode. Now try following the manual's instructions again.

Next look at your req_fuel number, as it's likely way off for you to be seeing 240's in your VE table.

Once that's sorted out, then look at the injector staging, excessive duty cycle, some of which may disappear by fixing other problems.

With wideband, datalogging, MegaLogViewer and Megatune you've got a great set of tuning tools. Use them to tune manually until you think you can do no better. Then turn on autotune and see if it makes any significant corrections.

 

Ahh, yes, req_fuel... I just assumed that was set right...

That's the easy thing to check.... but if duty cycle is up at 115%, there is something else other than req_fuel going wrong.

 

Well, my required fuel has always been set at 9.4 in both spots, and I was referring to the 2 AMP fuse that supplies power TO the megasquirt, not for the injectors.(Check the diagram and you will see the 2 AMP fuse that I am talking about). My injectors already have 5 amp fuses. Should I change my required fuel number? I'm also running a TII fuel pump that has been rewired and gets 12-14 volts CONSTANTLY. The fuel filter is clean, as well as the fuel pump sock as well. Also, yes, the injector staging is definitely working. It's set to rpm based, and turns on at 3500 rpms. What can I set my PWM setting to without it instantaneously flooding and blowing the ECU fuse? (not the injector fuses). Do you think my street-ported 4-port N/A really needs bigger secondaries than my current 760cc's?

 

Something is wrong if the MS is drawing more than 2A... it shouldn't ever draw more than about 500mA... and even that is pushing it.

I'd say if you figure out what's causing your fuse blowing problems, you'll fix the other problems.

I wouldn't mess with reqfuel... I think your PWM settings are not holding the injectors open all the way, causing the MS to hold them open a lot longer to get the same amount of fuel in.

How did you run your ground wires? Did you make sure that the TIP125 transistors have the mica insulators between them an the heatsink? Did you verify that it's 60kohms of resistance between the heatsink tab on the TIP125's and the heatsink?

Once you fix your short problems, you should be able to fix the PWM settings, and should also be able to get that engine running better. Keep in mind that your PWM settings are might be different between primaries and secondaries since you're using different types of injectors, which may also cause problems.

Ken