Megasquirt voltage drop issue

[Shadow24]

Well, ive had my MS-II intalled and running my mitsubishi 6G72 3.0L v6 for over a year and over 10,000 miles. had a few hickups but for the most part its been quite reliable, even to the point of 30mpg highway driving.

however, ive recently run into a baffling issue that i can't seem to figure out and as the car is my DD it has caused me to be unable to go to work today. :x the initial issue started over the weekend where for some reason the car would run really rich and the only way i could keep it running was to either keep the throttle cracked or pop a vacuum line off and even then, instead of idling high at near 2000 like it should with the vacuum line off, it barely idled at 1000. it did this for a while and then stopped and ran fine. it did that twice over the weekend (900+ mile round trip) and yesterday did it again and hasn't "fixed" itself. What i did notice is that i believe it is tied to a voltage drop. Megatune was only seeing 10-11ish volts when the car was running (batt was at 14.xx volts measured at the terminals) also, i parked the car at the store for a minute and when i came out, the car started then died, the reason was that the relays were not tripping to provide power to the MS, fuel pump etc. I was able to get home buy hot-wiring the MS, FP and injectors and she ran like before, with the low voltage rich condition.

i haven't been able to figure out the issue, i tried to eliminate the relay board from the equation but the voltage drop is still there even though my source 12v wire i used to hotwire the car reads 12v, MT still only sees 11v at most. for wiring, i had the relay board on the inside passenger fender and the batt is on the drivers side. i had run switched 12 and constant 12v across the engine bay to the relay board with the occasional butt splice and some crimp wire taps for other 12v needs and the ground is only a short run to the aluminium motor mount (which is bolted to the iron block) and the batt ground to the motor connects to one of the aluminium heads.

im totally lost on this one and could really use some help. anyone have any ideas or advice? my plan at the moment is to re-wire the 12v, switched 12v and run teh ground to the same ground point as the battery to see if that helps.

[Kevin]

What else is pulling power from the constant 12v? That's should be a big no no for starters. How it's worked this long is impressive.

Low voltage rich = the injector open time offset will increase as voltage decreases. The ecu will then compensate by adding xxx to the injected pulsewidth to account for the injector that is slow to react. I'm assuming the injectors receive 12v from a different source and are probably actually at 14v?

[R/Tony]

Had a similar issue before on my MS... and it was a bad ground conection, you should probably start to look for all the grounds in your system, its really a pita trying to find those kind of problems but my suggestion its re-check all your grounds, actually I have ordered a set of grounding kit for me... the MS systems seems to be very picky with the grounds.

[turboshad]

+1, MS is picky with grounds. The easiest way to trouble shoot is to first run a wire directly from the batt + to the the relay board. Check the voltage on megatune and see if it changed. If not then go back to your original power wire and do the same test for the ground (to the - post of course) and check MT again. If still no change the jump both directly from the battery and check. Also ASFIK the relay board isn't meant to be mounted outside. It is not a sealed unit and as such could have developed water damage or some corrosion that is deteriorating the power and ground going to the MS.

DJ

[t3rse]

so why not pot the boards?

[Shadow24]

yeah i didn't seal it which was dumb. this time im getting a waterproof box from mouser to mount the relay board in so it doesn't corrode on me again.

i re-did the grounds from the relay to the block. i put it at the same spot as the main ground to the block and it still didn't help. right now i have the injectors, MS, fuel pump and fan all hot-wired to the switched 12v and i think that might be the voltage drop issue...too much load.

looking at some of the symptoms i think i was wrong in my initial diagnosis, i think my FPR might be f*cking up again so im going to try the one on the 3000GT VR4 fuel rail i got and see if it doesn't cure the issue

[karlak]

so why not pot the boards?

Spray sealer works great and no potting to remove when repairs are required.
Makes the board real shinny to. :thumb::thumb:

[risen]

Also, if you haven't checked and cleaned the battery terminals lately, try that it's pretty painless. I had a voltage drop that would come and go on my CSX and that's what it turned out to be. If I checked the battery terminals themselves, i'd get 12v, if I checked the terminals at their clamps with the wires I'd get 9 or 10v.

I believe that there's a 2d table in MS to correct the open time on the injectors based upon voltage. The table in yours may be *way* off if it's getting that rich; assuming that the voltage drop is the cause of the problem. I believe there's the same sort of table in the factory cal that you could probably copy in verbatim and see if it helps out any with the richness.