Fuel Pump EMI Noise Suppression

[Spittybug]

If your running the VR coil for RPM than that should be better than using the ignition coil. Is that VR coil wire shielded?

See one post up.

[lazabby]

I added one choke to each wife coming off of the fuel pump. Made no difference. I tried putting the chokes going into the Megasquirt unit. That meant trying to get five or six wires into each of the two chokes. I'm sure not sure how effective that was but it made no difference on the sync loss issue.

Dave, coming to Houston anytime soon?

[Bitsyncmaster]

I added one choke to each wife coming off of the fuel pump. Made no difference. I tried putting the chokes going into the Megasquirt unit. That meant trying to get five or six wires into each of the two chokes. I'm sure not sure how effective that was but it made no difference on the sync loss issue.

Dave, coming to Houston anytime soon?

I would think MS already did this but it's worth a try. Feed power to the MS through a diode and put a large cap after the diode to ground. All car power is very noisy. The cap filters the noise and the diode prevents other things from drawing power from the cap.

Do you have a schematic of the MS unit I could look at?

[Spittybug]

http://www.megamanual.com/index.html

A frustrating site. I'm not a web guy, but their URLs don't change when you navigate and that confuses me! The left navigation panel will lead you to the 3.57 board and full schematics.

[Bitsyncmaster]

http://www.megamanual.com/index.html

A frustrating site. I'm not a web guy, but their URLs don't change when you navigate and that confuses me! The left navigation panel will lead you to the 3.57 board and full schematics.

Nice schematics.

Looks like they do use the diode and capacitor but the capacitor is only 33 uf. and it shares that voltage with the stepper.
I would have driven the 5 volt regulator with it's own diode and cap (100 uf. min). ref. page 6, C16 and D10.

Also if your using the "Ignition Driver" to drive your coil, That ground on Q16 should have been a separate return line not common the the MS ground. Q16 page 5

I see they have a filter for the VR input. Have you tried adjusting the hysteresis (R52) and set point (R56)? I would need to get a scope on the VR circuit to check if it's optimal with our VR signal.

[Spittybug]

Nice schematics.

Looks like they do use the diode and capacitor but the capacitor is only 33 uf. and it shares that voltage with the stepper.
I would have driven the 5 volt regulator with it's own diode and cap (100 uf. min). ref. page 6, C16 and D10.

Also if your using the "Ignition Driver" to drive your coil, That ground on Q16 should have been a separate return line not common the the MS ground. Q16 page 5

I see they have a filter for the VR input. Have you tried adjusting the hysteresis (R52) and set point (R56)? I would need to get a scope on the VR circuit to check if it's optimal with our VR signal.

Dave, I'll have to look at the schematic to digest your first couple of points, but regarding the VR signal, we've scoped it. I chucked the dizzy in my drill press and took it up to very high speeds. The signal never appeared to breakdown. We keep the same nice shape the whole time. I looked to see if I still have the photos, but I do not. I may be able to retrieve them from when I posted them over at the Megasquirt site. Now, under very low speeds it does, but that is to be expected based on the physics of the matter. The guys at DIY had us trimming both R52 and R56 and while we can minimally change some of the behavior of just when the sync loss occurs, we are not able to eliminate it. This problem has been going on so long now that I forget all of the things we've tried and failed with. I want to say that despite the nice appearance of the incoming analog signal, the resulting square tooth wave that the MS unit converts it to for the coil driver IC ended up breaking down at higher drill press RPM. The power supply for the MS in this case was a bench top 12vdc, not a car. I'd forgotten that. That would imply that the problem isn't in the car....

To me (an observer and non-trained in such electronics), it looks like although the VR signal isn't breaking down, the 3.57 MS unit is losing its ability to process it into the clean squared wave form at the higher frequency. My 3.0 box doesn't appear to have this limitation at all.

http://www.msextra.com/forums/viewto...art=40#p319355 This link will take you to a post in the MS forums that has the o-scope pictures and writup of what we saw. A couple of posts further down is interesting too. I hope the pictures are available to you as a guest to view. If not, I'll try to download them and post here, or you could join (its free).

[Bitsyncmaster]

If both MS circuit are the same with the same values than most likely the new PCB layout is causing the difference. I really think the common ground used for the ignition coil driver would cause a lot of noise on inputs to the MS. You could lift that pin on the driver and wire it to an extra connector pin. Then you use a ground external to the MS to that pin.

[Bitsyncmaster]

I looked at your MS forum. I see if you adjust the POTs to work at high RPMs then a problem shows up at low RPM. So the circuit cannot handle the full dynamic range. I seem to remember our VR signal runs from 1 volt/PP to 100 volts/PP depending on RPM. I looked at both the 3.00 and 3.57 schematics and it uses the same circuit with the exception of the two signal transistors. XTX554 for 3.00 and PZT2907 for the 3.57. The specs look a little better on the XTX554. So maybe that is making your 3.00 handle the full dynamic range. It could just be the new PCB layout causing problems. SMT parts work better than leaded components since the inductive leads are eliminated. So the new board should theoretically have less noise.