• Hello Guest, welcome to the initial stages of our new platform!
    You can find some additional information about where we are in the process of migrating the board and setting up our new software here

    Thank you for being a part of our community!

Sync Error Troubleshooting

CAPT_BLOTTO

#Crush It
Joined
Jul 19, 2005
Location
Kansas City
I'm having rpm sync issues. They seem to be intermittent. I've seen it a lot during cranking, but today it started up fine. Then it started when I would roll into the throttle. I drove it a couple miles no issues and stopped. Then when I was heading back home it just lost all crank sync and was stuck in traffic. Sorry to all the angry people behind me. Anyway I saved some logs from that drive.

The car has the lh 2.4 sensor. It has a 10k resistor in the EZK then goes to the microsquirt.

I have the speed data logger file but not sure how to interpret this chart. Or where to start. Do I need to look at the sensor or signal issues? Or could there be voltage problems to microsquirt?

51943565650_0ffa630703_c.jpg



51943274934_08a021cdbd_c.jpg
 
look at grounds, wiring to the sensor (harness type stuff.. shake it when the car is idling and see if it drops sync, etc). the 10k... is that across vr+ and vr- or just in-line with one of them?
 
I haven't had any issues at high RPM and it seems to just come intermittently. It's most common when trying to start the car but even then it's not all time.
 
my car did the same thing, it was discussed in that thread.

I've wired two systems exactly like you have (VR+ to Pin1, VR- to Pin2, Shield to Pin3 and tied into sensor ground), and have had to use a 5k-10k Shunt on both of them to get to 7500 RPM or higher. I think the ignition setups are identical as well.

I still randomly get sync errors when cranking/low RPM, but it's not perceivable in how the cars start or run. So I just let it be and don't worry about the sync errors too much.
 
I've wired two systems exactly like you have (VR+ to Pin1, VR- to Pin2, Shield to Pin3 and tied into sensor ground), and have had to use a 5k-10k Shunt on both of them to get to 7500 RPM or higher. I think the ignition setups are identical as well.

I still randomly get sync errors when cranking/low RPM, but it's not perceivable in how the cars start or run. So I just let it be and don't worry about the sync errors too much.

Honestly I haven't thought about this in so long I'd have to go back and make sure I didn't make any subsequent changes. I know at one point the car was randomly dropping sync and I found that a stray shield wire was occasionally grounding to the resistor I had in the connector and BOY that was fun to find.

My logs these days will show like one or two instances of sync loss, but like you said it's imperceptible so I just ignore it.
 
Drove it around today ≈ 50 miles no issues while driving. I had gone through and checked all the connections were good. Added the diode to the IAC. And fixed the alternator tensioner that broke. Not sure if any of those were my issues. It still cliks and loses sync when cranking. But I can usually get it started.
 
I'm running out of patience with this thing. It left me stranded the other day. I've redone the wiring, replaced the cps. I can't seem to get any useful information from the data logs.

At this point should I just ditch the stock sensor and go with something else? What can I use that's actually reliable?
 
The car has the lh 2.4 sensor. It has a 10k resistor in the EZK then goes to the microsquirt.
You could try wiring direct from the CPS connector to the MicroSquirt using 2-wire shielded cable (link). Connect the shield wire to sensor ground at the MS end and to the shield pin at the CPS connector, and add the 10K near the MS, or within the MS box if you're good at soldering small parts.

You could also try using a Hall Sensor (link) with an custom Mueller adapter (link)
 
At this point I'll try anything. Yesterday I spent a few hours trying to diagnose it. I took a connector and wiring from a spare harness I had and ran the lead from the CPS through the firewall and hooked everything up directly to the wires from the MS harness. Trying to eliminate all possible connections and unknowns. Sometimes I would get no signal. Sometimes I would get a poor signal with missing a lot of the teeth. I was checking every on on the MS for continuity. Can I rule out the flywheel if the car has run fine for at least periods of time?
 
From the Composite Logger graph in your 1st post, it looks like it skipped a bunch of teeth and lost sync when accelerating from ~2400rpm. This is weird - I'd expect a bunch of lost teeth possibly during cranking, but not at cruise.

A few things to check/try:
- do you have noise filtering completely disabled on the MicroSquirt? It can cause issues and may mask something that would help with the diag.
- can you check the 10K resistor color code: brown-black-orange, or measure across it with power off and the CPS disconnected.
- you could try removing the 10K and see if the behavior changes - normally, it's needed to prevent sync problems at high RPM, but can cause problems during cranking.
- Someone on here in the last year had a LH2.4 no-start that eventually was traced down to a brand new CPS that had a weak output. Try searching for paperclips and see if you can find the post.

If you had a bunch of runout in the flywheel, it might cause the MS to skip a bunch of teeth, but I'd expect the flywheel to vibrate horrendously. Is it a standard flywheel and did it run fine in a stock LH2.4 setup?
 
From the Composite Logger graph in your 1st post, it looks like it skipped a bunch of teeth and lost sync when accelerating from ~2400rpm. This is weird - I'd expect a bunch of lost teeth possibly during cranking, but not at cruise.

A few things to check/try:
- do you have noise filtering completely disabled on the MicroSquirt? It can cause issues and may mask something that would help with the diag.
yes its disabled. Tried with and without.
- can you check the 10K resistor color code: brown-black-orange, or measure across it with power off and the CPS disconnected.
Yes. Verified with my multimeter. Also tried a 4.7K resistor.
- you could try removing the 10K and see if the behavior changes - normally, it's needed to prevent sync problems at high RPM, but can cause problems during cranking.
tried that too
- Someone on here in the last year had a LH2.4 no-start that eventually was traced down to a brand new CPS that had a weak output. Try searching for paperclips and see if you can find the post.
tried 2 different sensors. same issues

If you had a bunch of runout in the flywheel, it might cause the MS to skip a bunch of teeth, but I'd expect the flywheel to vibrate horrendously. Is it a standard flywheel and did it run fine in a stock LH2.4 setup?
I changed the flywheel to an STS flywheel when I changed to the getrag at the same time I did the MS. No vibrations and there's been times when it will work just fine.

Hall sensor is on order btw.
 
Hmm...., it's certainly a strange one.

One more thought, how's the alternator? Bad diodes in the alternator can cause a lot of extra electrical noise, which might confuse the VR signal/circuit. Do you have access to a lab scope? Pics of +12volts and the VR signal would help.
 
I looked at your MicroSquirt Tooth Logger logs and think I understand most of what I'm seeing, but I'm still puzzled by your original picture where it was running OK and then lost sync at ~2400rpm.

Below are some example CPS VR oscilloscope voltage measurements from my wagon (LH2.4). Notice that there's a fair amount of peak-peak voltage variation within a single rev, and that the peak-peak voltage goes up as the rpm's increase. The once around 60-2 "sixty minus two" missing tooth region is clearly visible (click pics for bigger versions):

1) cranking ~200rpm, ~0.9V peak-peak

2) idle, ~850rpm, ~3.3V peak-peak

3) rev'd up in park, ~3100rpm, ~10V peak-peak (I'd expect ~20V peak-to-peak at ~6200rpm)



The problem MicroSquirt has with the 60-2 VR sensors is the overall range of peak-to-peak voltages from cranking to max RPM (~0.9V to ~20V with LH2.4, maybe more with MS). Without the 10K resistor to reduce the peak-to-peak voltage, the MS becomes very sensitive to flywheel finish and height variation in the missing tooth region - at max RPM, a little variation can generate enough voltage to look like an extra tooth. The flip side is that the 10K resistor also reduces the already small voltage seen during cranking, and may cause starting difficulties.

Below are MegaLogViewer screenshots from your 2022-05-22_11.08.12.csv Tooth Logger file. The graphs are the time per tooth in milliseconds. To convert to RPM, simply calculate 1/tooth_time, for example, a tooth time of 0.5ms is 0.0005 seconds, which gives an rpm of 1/0.0005 = 2000 rpm [the full equation is RPM = 60seconds/minute * rev/60teeth * 1/0.0005seconds_per_tooth, but the 60's drop out]

1) running properly at ~1850rpm (0.54ms) - notice that there are 57 normal pulses then a 3x longer pulse (due to the missing 2 teeth getting lumped into the next tooth's time), and that there are no unexpected skipped or extra teeth.

2) idling at ~900rpm (1.1ms) - notice that there is a little twice-per-rev speed variation due to slight slowing and accelerating before/after TDC and BDC. No skipped or extra teeth.

3) cranking at ~200rpm (5ms) and startup to ~720rpm (1.4ms). Notice the pronounced speed variation during cranking, and the somewhat inconsistent tooth times during the slowest regions, but no skipped teeth. After startup, notice that teeth are being skipped, resulting the long tooth times at non 60-2 spacings - this is bad.

4) cranking but no start - notice that there are lots of skipped teeth, resulting in long spikes at non 60-2 spacings. My guess would be that the VR signal voltage is too small during cranking for the MicroSquirt to reliably detect. Changing to a Hall sensor should fix this.



Let me know if there are questions or confusion (I didn't proofread this).

One more question - what version MicroSquirt do you have? The newest AMP EFI version has internal dip-switch selectable pullups for Hall sensors, which would cause problems if enabled with a VR sensor.

-Bob

edit: here's a link to the MicroSquirt V3 VR Sensor documentation link
 
Last edited:
Back
Top