zack_280 Posted November 29, 2011 Share Posted November 29, 2011 99% of the time my car seems to run fine. But every once in a while it stumbles as if the fuel has been cut for a split second. I checked my log file and found voltage spikes high to ~21V and low to ~6V. Here is a screen print from my log file. Then I connected an oscilloscope to the relay board 12V and ground and got the following graph. Note that the spikes were somewhat erratic and it took a few tries to capture the spikes on the screen. I spoke to Matt Cramer via e-mail and he suggested grounding the relay board to the engine block. I plan to do that tomorrow, but I have pretty low expectations for that solving anything. I was hoping to maybe get a bit of wisdom here between now and then. System Info: My ground circuit is as follows: Battery->Engine->Ground Plate->Everything else. All components are grounded directly to a steel ground plate bolted to the firewall with the exception of the spark plugs (grounded through the head). The cable that connects the battery to the engine and engine to ground is a 1/0 cable. I am running Low Z injectors using PWM and a coil per plug setup using the IGN-1A 'smart' coils from DIY Autotune. I disconnected the charging circuit and there was no noticeable affect on the voltage signal. Quote Link to comment Share on other sites More sharing options...
Metro Posted November 29, 2011 Share Posted November 29, 2011 I was getting wild swings just like you described (7 to 22v). First off, you'll definitely want to check your grounds like Matt said. If improving your ground doesn't help, you might want to look into the PWM mod and putting a cap (I used c30) in the boot header. What ultimately helped me was moving the BIP323 out of MS. Basically, giving the ignitor it's own ground to the motor (not going through the MS PCB). I'm not sure how your coils and their ignitors get grounded, but that might be something to look into. While my voltage still moves a bit, it only varies from .3 to .5 after doing those changes. msextra.com PWM mod thread Quote Link to comment Share on other sites More sharing options...
zack_280 Posted November 29, 2011 Author Share Posted November 29, 2011 Thanks, Metro. I actually found that thread a while back, but it referenced a deleted thread on how to fix the problem. Looking through it now it looks like the fix is described on the second page. I'll try to get the capacitor installed this evening. My 5V signal to the ignitors is grounded to the same place as MS. The 12V and coils are grounded directly to the head. I'll let you know how it turns out. I will start with the capacitor and see what happens. Quote Link to comment Share on other sites More sharing options...
mobythevan Posted November 29, 2011 Share Posted November 29, 2011 From my experience, installing filter capacitors usually works best to get rid of spikes like you show in the scope plot. If you look at the frequency that spikes occur you can then use online calculators to size the capacitors correctly. Quote Link to comment Share on other sites More sharing options...
zack_280 Posted November 30, 2011 Author Share Posted November 30, 2011 I installed a 220nF capacitor on H1 and there were no visible voltage spikes on the scope. The weather hasn't been great here, so I didn't drive it tonight, but I'm planning on taking it for a drive tomorrow. Based on the scope it looks like the problem could be solved. Either way it was a definite improvement. Quote Link to comment Share on other sites More sharing options...
S130Z Posted November 30, 2011 Share Posted November 30, 2011 I also had similar problems. Where is your ignition coil located compared to your TPS? Also Matt had me run a 12v wire straight from my battery to a specific spot on the board(i will have to check some emails to figure out which one it is to). That solved my problem. Quote Link to comment Share on other sites More sharing options...
lowrider Posted November 30, 2011 Share Posted November 30, 2011 I've been having similar problems, I guess I'll have to bust out the soldering iron and install a cap! Quote Link to comment Share on other sites More sharing options...
zack_280 Posted December 1, 2011 Author Share Posted December 1, 2011 (edited) I drove the car for about 30 minutes today and logged the whole thing with no noticeable voltage spikes. But I was running the heater and the lights and my battery voltage was dropping to about 11V when the RPMs got below 1500. But that's something I think I can fix. I'll post up a more detailed writeup in a new post later this week or this weekend to help anyone else having this problem. Hopefully S130 will be able to add his solution if he ended up doing something different too. Edited December 1, 2011 by zack_280 Quote Link to comment Share on other sites More sharing options...
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