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Smooth idle then abrupt dip, then smooth idle returns
Posted: Sat Aug 31, 2013 8:58 pm
by gt eunuch
MSII v3.0 board, with MSII Rev 2.92000
Not running any idle control (aside from the idle screw on the TB), and have been working on tuning idle. I have it sitting well, from what I can gather, but I have this strange dip every 45 seconds or so. RPMs drop, and then come right back.
Attached is the MSQ and the Log file showing the dip. Any idea what is going on here?
Re: Smooth idle then abrupt dip, then smooth idle returns
Posted: Sun Sep 01, 2013 12:14 am
by trakkies
The battery voltage seems to dip just before the problem. That in itself shouldn't be a problem, but it makes me wonder about the supply to the MS and the grounding. The TPS output also appears to have a lot of jitter on it which would also suggest incorrect grounding.
Re: Smooth idle then abrupt dip, then smooth idle returns
Posted: Sun Sep 01, 2013 5:52 pm
by gt eunuch
Thanks for the quick feedback.
Everything is grounded to one spot on the engine block, but I may move it to see if I get any better results. I have noticed that the temperature seems quite jittery as well, maybe this could be the issue as well.
Re: Smooth idle then abrupt dip, then smooth idle returns
Posted: Mon Sep 02, 2013 12:17 am
by trakkies
gt eunuch wrote:Thanks for the quick feedback.
Everything is grounded to one spot on the engine block, but I may move it to see if I get any better results. I have noticed that the temperature seems quite jittery as well, maybe this could be the issue as well.
Sounds like you've identified your problem. The rule of thumb is:-
If you unplug the MS, would any sensor still have a ground?
If the answer is yes, it means the high current MS ground (for injectors etc) is being shared with that sensor. And the sensor input on the MS is attempting to measure tiny currents.
To explain further, any cable has some resistance. So there will be some voltage drop along it when drawing current. Now 0.1v won't matter at all to a 12v injector - but will to a sensor which may need to resolve amounts that small or even smaller.
So the correct way is to bring each and every sensor ground back to the DB37 connector, where they then ground to the MS ground plane. Which is in turn grounded to the engine block using separate wires.
Re: Smooth idle then abrupt dip, then smooth idle returns
Posted: Mon Sep 02, 2013 7:23 pm
by gt eunuch
So today I checked over my wiring, verifying grounds, etc.
I am running the Relay board, and that had been grounded well, however I was 'piggy backing' off that ground for my wideband o2 sensor. I had soldered the relay board, and the LC-1 grounds onto one wire, and then grounded that to the engine block. I have now fixed this, giving the LC-1 it's own dedicated grounding wire all the way to the block, where it is bolted to the same grounding bolt as the relay board.
Car idles quite well at this time, and maintains the idle nicely. Attached is a revised log, and MSQ. Does it seem better? Anything else I need to be concerned with? Next steps are going to be tuning via passenger seat while a friend is driving.