Datsun Deron Posted June 30, 2011 Share Posted June 30, 2011 (edited) Hi Guys, I posted at MSEFI about a week ago regarding this problem and haven't gotten anything back yet. Hopefully someone here might have a hunch as to whats going on. Heres the original post with the additional troubleshooting we tried. I'm having some major voltage spike and sag issues with MSII V3.0. I originally thought the issue was my tune until I started data logging. Upon closer inspection when the voltage spikes the car leans out immediately after, when the voltage sags the car goes rich. You feel the car shutter for a brief moment as well when this happens. This happens during all driving conditions as well as when im crusing at a steady rpm with constant light throttle. I was wondering if anyone has had any similar issues or if theres something else I can try for a fix then what I've tried below. For info on my car its a 1982 280zx Datsun and for Megasquirt im running MSII V3.0 with a relay board that a friend and I put together. also I'm running EDIS with a dodge caravan coil pack. The alternator is a 105 amp alt that was purchased online as well. (I think zman of washington?) I am also running version 2.889 of the firmware on Megasquirt. (we just upgraded from 2.6 last week to see if that helped) The battery has been mounted in the trunk of my car and I've got a thick (2-4 gauge) power wire running from the battery to the starter. The ground wire (2-4 gauge) for the battery is grounded to the trunk of the car. To try and remedy the problem of the voltage sags and spikes we re wired the relay board's power and ground wires with 12 gauge wire. The relay board now pulls power directly from the starter where the battery and alternator connect. The relay board also has one 12 gauge ground now that grounds on the starter where there is a thick (4-6 gauge) factory wire that grounds to the frame. The switched power (16-18 gauge) wire from the factory ecu is still in place. After re wiring the issue doesn't seem to have improved at all unfortunately. We then connected a wire directly from the alternator to the starter with an 80 amp fuse and bypassed the fusible link. This also unfortunately didn't seem to make a difference. After we did that we ran a power wire and ground all the way back to the battery in the trunk and still got the same voltage sags and spikes. Then the last thing we tried was pulling the fuse from the alternator to the starter all together and we still got voltage spikes and sags. So we're really not too sure what to try next. Here's whats floating around in my head for possible scenarios... Could something be acting up on my megasquirt or relay board that would be causing this? We double checked and made sure the power,ground and switched 12 connections are nice and tight on the relay board and that nothing is loose. If something on the board could be causing the issue where might I start looking? I have a large capacitor for a car stereo and was thinking of running that inline with the 12 volt wire to see if it'll smooth anything out. Could the EDIS coilpack be injecting some voltage into MS? I've included some screen shots of the voltage sags and spikes. You'll notice my AFR's follow the trend of the voltage spikes and sags when throttle is constant as is RPM. (im running an AEM wideband sensor as well). The pulse width not shown here echo's the AFR's and I can get screen shots of that if it helps at all. Thanks! Edited June 30, 2011 by Datsun Deron Quote Link to comment Share on other sites More sharing options...
Tennesseejed Posted June 30, 2011 Share Posted June 30, 2011 I don't think your electrical problem lies with MS. MS is a load in your electrical circuit. In other words, MS only uses, but does not produce, voltage. And while MS does provide some regulated voltage (5VDC), there is nothing about the operation of MS [that I know of] that can cause your system voltage to spike to 19 volts. My guess is you have an intermittent diode (very rare) or a an intermittent short in your voltage regulator. Quote Link to comment Share on other sites More sharing options...
Datsun Deron Posted June 30, 2011 Author Share Posted June 30, 2011 (edited) Thanks tennesseejed, (I'm assuming the voltage regulator your talking about is in the alternator?) We were suspecting a bad diode in the alternator too however we still saw the same voltage spikes with the alternator completely disconnected from the battery. In the datalog the voltage ran consistently lower since it wasn't being charged off the alternator but we still saw some major sags and spikes and felt the car surge. Edited June 30, 2011 by Datsun Deron Quote Link to comment Share on other sites More sharing options...
Tennesseejed Posted June 30, 2011 Share Posted June 30, 2011 Thanks tennesseejed, (I'm assuming the voltage regulator your talking about is in the alternator?) We were suspecting a bad diode in the alternator too however we still saw the same voltage spikes with the alternator completely disconnected from the battery. In the datalog the voltage ran consistently lower since it wasn't being charged off the alternator but we still saw some major sags and spikes and felt the car surge. Well that is curious indeed. Quote Link to comment Share on other sites More sharing options...
johnc Posted July 1, 2011 Share Posted July 1, 2011 Check all your grounds, clean and sand away any paint between the ground wire and the bady. Make sure there's a good ground from the engine to the chassis. Maybe even run a ground from the alternator mounting to the chassis. Quote Link to comment Share on other sites More sharing options...
wayner Posted April 29, 2012 Share Posted April 29, 2012 Did you solve your spike problem ? I'm thinking I need to add a 8910EIS and MSD noise filter 8830 .. Quote Link to comment Share on other sites More sharing options...
FricFrac Posted April 29, 2012 Share Posted April 29, 2012 Number one is to make sure you have a good ground. Back EMF from coils (ignition and even the solenoid in the injectors) and noise from your brushes arcing, etc can produce voltages much higher than the supply voltage of the battery. All of these can be induced back into the rest of your harness and into your ECU. A good ground starts with a decent gauge wire from the battery to the ECU - crimped and soldered. All other sensor and power grounds should all run to the same lug that the battery ground comes to near the ECU. Again this lug is crimped and soldered. In your case you have power hooked to the alternator which is a great source of noise. I would route power and definately the ECU ground back to the battery. The battery will act as a sort of buffer for noise from the alternator. A poly (etc) cap around 0.1 to 1uf, etc will filter out the higher frequency noise. A high capacitance electrolytic cap like a stereo stiffening cap isn't designed to filter noise but remove ripple. You should have a noise supression cap on the alternator itself as well (and the ignition coil). Running shielded wiring is also very important to keep noise out of your sensor wires. At the very least you should use a twisted pair with the signal and ground wires twisted together to reduce noise. Quote Link to comment Share on other sites More sharing options...
Datsun Deron Posted May 7, 2012 Author Share Posted May 7, 2012 My apologies, I never got an email saying I got a reply. Looks like my notification settings were outa wack... Anyways yes the problem was solved!, I found this thread http://msextra.com/forums/viewtopic.php?f=101&t=28178&start=20 Long story short I did what the first post says (220nf cap on the H1 position) and problem solved. Car runs solid as a rock ever since last year. Quote Link to comment Share on other sites More sharing options...
jacob80 Posted May 17, 2012 Share Posted May 17, 2012 Are all Megasquirt boxes sent without this capacitor installed? Should a user only install said capacitor if they're experiencing the symptoms described by Datsun Deron? Quote Link to comment Share on other sites More sharing options...
sqweekykneecap Posted March 28, 2014 Share Posted March 28, 2014 Hey, Sorry to resurrect an old thread. Recently, I had the same issue with my 260z /L28et/MS2 v3 board setup with low z injectors. My voltage was spiking and dropping for .2-.3 seconds at random intervals. The fix was just what OP did, I installed a similar .22uf Capacitor at the H1 port (boot header) next to the daughter board on the ecu. Now my voltage is flawless, and I cannot be happier. 1 Quote Link to comment Share on other sites More sharing options...
Mike280zx Posted August 9, 2023 Share Posted August 9, 2023 Hi all, I'm resurrecting this old thread in the hopes to obtaining more info on this mod/repair. I seem to have the exact problem that is described with the exact same hardware and setup (MSII v3.0) and I would like some additional detail if possible from anyone that has done it or even understands clearly how to do it. I'm somewhat handy with a soldering gun and know some electronic basics however have some questions: -are there any other relevant specs I need to know when I go to my electronics store looking for a .22uf capacity? (wattage? voltage?) -does the capacitor have polarity and if so which way does it go? -is there a clear description on where to install it? (i'm still trying to find the "H1 port next to the daughter board") Thanks in advance to anyone that can help me out. Mike Quote Link to comment Share on other sites More sharing options...
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