Troubleshooting my ignition (MS2 extra) with VR sensor

[trond]

VR signal direct to MS2 which then fires two M&W S10 CDI ignition modules and two coils and a JB 12 point distributor

Now engine runs and idles well

However I still have two issues;
1) the CPU resets at random, every few minutes. Never did that before with EDIS

2) I used a strobe and set tooth angle until timing in tuner studio matched timing marks at 1200 rpm. However at different RPMs the offset set at 1200 RPM don't work. Timing mark on pulley matches as seen with strobe at 1200 RPM with a 77 degrees offset, but at 2500 RPM I need to change trigger offset to 60 to make mark on pulley match. With 77 degrees offset at 1200 I get the 10 degrees I have in the spark table, but at 2500+ I don't get the 25 degrees, but 35.

Grateful for any advice !

[75 911s]

Does number of coils have to be changed to 2?

[jpnovak]

Trond,

A few things.

To verify the trigger offset you need to make sure you set the upper right to "fixed timing". It can be difficult to find an advance value where the engine will run from idle up through 3K. Usually 15 deg BTDC will work.

If the timing still drifts with the fixed timing you need to adjust the "spark hardware latency". In this case, you will lock timing at low rpm. Then raise engine speed and check spark. increase the latency value until the timing matches at both places.

Usually a VR sensor has very low latency. You did not mention what sensor you are using. Is it the same sensor as you had with EDIS?

Regarding the ECU resets this is usually indicative of input power issues or ground connection issues. Did you use a fully shielded wire from the VR sensor all the way back to the ECU. The VR sensor puts out a lot of voltage at higher rpms. It can produce noise spikes that will interrupt power to the ECU. make sure you have quality shielding for a VR sensor. Also make sure the shield ground is only connected on one end. I usually ground at the ECU end, not the sensor end.

[trond]

signal from ECU is split so number of coils =1 is correct

Re VR sensor; I got a new sensor, a Honeywell 3015A17, with 0.1 mm clearance to 36-1 wheel. Reason for the new sensor it how it is fitted to the engine; the old VR bracket could no longer be used with the new distributor

I already tried locking ignition at fixed value but was thrown off completely by how it still drifted significantly with RPMs and so created a 15 deg flat area in spark tables instead, and then observed drifting at the pulley. Never thought about adjusting spark latency as that was never an issue with Ford sensor and EDIS. Will try playing with latency settings in a few days when i get back home

On resets; yes I used shielded all the way and grounded shield at ECU end.

[smurfbus]

Maybe try to route the vr wire separately and I woud try bigger gap too.

Resets might be groundin issues. Also check that your vref has 5volts and not somethink less.

Here is a nice video from Andy for ecu and sensor grounds. https://www.youtube.com/watch?v=EJ2TeodWDUE&t=319s

[trond]

drifting timing was cured today by changing Spark Output to 'Going Low' . Minor drifting was then tweaked away with setting hardware latency to 10 ms.
I found I get no VR signal at all from the Honeywell sensor unless it is perfectly aligned and very close. That is 0.08-0.1 mm . Now VR signal is good and stable and timing is solid

Still have to find reason for resets. Seem to get worse with more RPMs... But good to have the VR signal and timing sorted

[trond]

[ian c2]

Is the ecu power seperate from cdi power ?

http://www.mwignitions.com/pdf/Pro-10E%20S3%20instructions.pdf

[trond]

ecu power and cdi power are separate, with ECU powered from battery and CDIs powered from starter motor terminal. Before, with EDIS I had no issues with resets. I have Magnecore plug cables which I have been told should be good wrt EMI and used shielded cabling from CDIs to coils, for VR sensor and also for spark input between ECU and CDIs.

Also not a ripple on sensors when logging or when resets occur. That is no visible interference on voltage, IAT, coolant temp and TPS traces. Had some small disturbance to 12V supply to ECU from AFR, but after adding capacitor to 12V supply to ECU mostly gone. No resets at idle but around 2500rpm not a second without a reset. What to do ?