Like the title says, Im getting crazy interference (i think) when I'm plugged into a laptop (got same results on two different laptops). I have a DIYPNP and the car runs perfectly without a laptop connected to the ecu. As soon as I plug it in, start up tuner studio, and do a pull all hell breaks loose. Symptoms include TPS reading to read 85% max even with pedal to the floor, AFR's to go lean and stay lean; on power it stays off the chart and at idle it tries to be like 17, muy no bueno. As soon as I power cycle everything goes back to normal until I try to do another pull. If I unplug my pc its happy as a clam.

Now I have seen posts about interference issues with USB extensions and for that reason I specifically switched to a serial extension and the serial to USB adapter sold by diyautotune. Being that this only happens with the pc hooked up Im thinking that its not wiring or ground related.

Details on car:
DIYPNP running 3.3.3
Stock wiring harness
FAB9 cops (potential noise contributor?)

 

I would still guess it's a wiring/ground issue, or possibly a broken Megasquirt. Something is "barely working" as it is normally, and hooking the laptop up sends it over the edge (from whatever small current draw or new ground loop that may cause)..

Can you do a log while it "freaks out"? Are there any other sensor readings that go haywire? Also, is the actual AFR:s that go bonkers, or just the wideband O2 reading? If you set it to open-loop (0% EGO authority) it shouldn't affect actual fuelling unless you have something rather serious going on.

 

Do you have the jumper for BL/TH installed?

 

The AFRs are real. My EUGO agrees with tunerstudio and the car barely runs. Right now I have closed loop fuel off all together (don't include afr...) Ill upload a log when I get home from work tonight, I should have done that in the first place.

No I dont.

 

Ok, so here is a datalog of the problem. There is a spot in the log where overrun fuel cut muddies the water a bit (between 256sec and 268). At 244sec I do a light pull in 2nd, 3rd, and 4th and things go haywire.At 358sec I power cycle the car and you can see the AFR's go right back to normal. While things are going nuts, my tps seems to also loose its zero.

 

So I "think" I found a ground issue. The picture should explain it better but basically the microsquirt is grounded to the diypnp "GND" pins and that in turn is grounded to the 4a pin on the harness as it should be (94/95). The problem is that non of those 3 grounds are bonded to the case/db connector sheilds. Also nothing is bonded to the "GND" pin on the edge connector. Im going to add a ground strap from the microsquirt ground pad to the case/mounting bracket (should I not?) and see if things improve.



Edit: This is what I added.



Edit 2: That seems to have fixed it!