Hi all,

As mentioned in my introduction thread, I've recently swapped a 1.8 VVT, which has been rebuild by a friend and I, into my mx5. This is the third swap that my friend has completed, but this one is giving us headaches..
Specifically with Losing sync on the crank sensor and cramp running/ bad ignition. I've been diagnosing differnet issues for some time now and have been able to pinpoint it to a timing issue.
Today I decided to do a check with the oscilloscope to verify it the cam and crank sensors where actually working as they should, this way I would be able to exclude any ECU "issues".
Both the cam sensor and crank sensor are new genuine Mazda units, the trigger wheel is also new.

discoveries:
- Cam sensor - > no issue
- Crank sensor -> functions correctly when testing on a "seperate" setup, on the engine it does not always give the correct response or atleast an interruption is noticeable -> see screemshot from scope.
- Need feedback on the composite logger data log (added a couple of logs). Currently suspecting that the timing belt might be off, If I look at the cam and crank signals.. However two people checked the "timing" on the engine stand while building the engine.

Mostly looking for some confirmation if I'm correct in stating the actual timing belt might be an issue.. before I start the tedious job of checking the timing belt. ​​​​​​​

 

Did you install the trigger wheel the correct orientation? I did a timing belt for a friend a week or two ago and accidentally put it on backwards which caused a no start.

Also I recommend load testing the wires between the ECU and the crank/cam sensors. Use a power probe or some 12V source to apply power through each wire with a headlamp bulb connected to ground. This should show you if the wire is good enough to carry current. You could do a resistance test but if there is the chance that with low resistance the wire is bad since it can't send a proper signal through.

I know that sounds like a tedious test or may seem unnecessary but if you're stuck then it may be a good test to rule out a wire issue.

 

I did verify the position before installing, but granted that was done in March of this year... So that's indeed something I can check.
As for the wiring, good idea. I would think that it's fine, since it's what was being used by the 1.6 for the most part. But then again it's 30 years old.

If anyone can post some known good composite logger logs or screenshots that I can use to compare the pattenr/behaviour against, that would also be a big help.

 

When you did the swap did you solder all the wires needed to run the different sensors? Or did you use crimp/butt connectors?

 

Most have been crimped/connectors installed.. but for some reason I decided to solder the crank and cam sensor wiring. I am however going to change that this weekend.. Invested in a crimper and Deutsch DT connector set, changing over to those for all connections.

 

I always solder all wiring. I never use crimp connectors for anything. If I'm installing a new connector with new terminals I even add a small dab of solder to the crimp where the wire and terminal meet.

Working for General Motors has shown me all sorts of things on how terminal tension, wiring connections can cause funky issues.

 

hmm agree, both have pro's and con's I guess. But solder can also cause it's own issues in a vibration sensitive environment. Main reason for connectors on the coil harness for example is ease of removal/maintentance/.. if I decide to go full COP down the road.

I do find it annoying that mazda decided against using shielded wiring on the cam and crank signal wires.. Would also be an improvement.. Haven't decided on that route yet, want to get to the bottom of these issues first.

 

Wiring seems to be fine, position of the trigger wheel as well. Bit at a loss, to be honest. I figure that I really should verify the mechanical timing.. If this turns out to be correct.. well then I do not know anymore.

Screenshot shows a log comparission from a friends car which has been running for more than a year.. and a couple of logs from my setup.

 

In the mean time i've been able to resolve the issue(s). Few bad contacts and msot importantly a combination of settings in the Megasquirt and crank angle sensor positioning.
Still not in the running phase, but this time due to a mechanical issue related to the cylinder head revision that a guy did...

 

HI Guys,

Sorry for the thread revival. But I'm facing a similar issue with a MS3 and VVT engine installed in my NA. Revs up perfectly fine up to 4300-4400 rpm and at that point it looses sync and acts as if it hits a limiter due to the sync loss. It recovers again after some time. the Sync loss reason is given as 31 or 32 depends. Which indicates an issue with the cam
- 31 = Miata 99-00 - 2 cams not seen
- 32 = Miata 99-00 - 0 cams seen
Although the composite log seems to show a missing crank puls. I copied the data into excel and could indeed notice a change in the trigger sequence (cam signal).

Things I have checked:
- Checked ground connections, add verified that they were good.
- Both cam and crank sensor are good.
- Crank sensor gap is set to spec (credit card thickness)
- I have no noise filtering on.

I have added three logs and composite logss which show the behaviour I mention at 4300 rpm give or take. Also added the excel where I looked at the data from the composite log around the sync loss point.

as for the sync loss locations:

- 2023-01-07_14.55.04.csv Page 11, time: 25321.71
- 2023-01-08_11.27.29.csv Page 42, time: 118196.51
- 2023-01-08_13.20.27.csv Page 90, time: 269201.38

This was all test on jackstands/stationairy so no load on the engine. Bit at a loss as to what it could be exaclty, tried jiggling the connector of the Cam sensor when stationairy but that caused no problems at all.
I have a trackday planned at Spa Franchorchamps the end of March and still need to get this thing run in and mapped, so on a bit of a schedule. :/

Turning on noise filtering makes the symptom worse or lowers the rpm at which it cuts/loses sync. Also decreased the crank sensor air gap but that did not really change anything.
Currently thinking of installing shielded wire on both cam and crank sensors to see if this fixes something..

Any help would be appreciated.

 

issue resolved, ECU was the culrpit. bought a new official MSlabs MS3 and it was gone.

 

Were you running MS3 basic before or did you switch to it? I have an MS3 Basic now and am having sync issues only when cranking and can't get to the bottom of it.

 

I had a MS3 "basic" which I bought from a guy that I assume made them himself. I suspect him of using subpar components which caused the issues.. should have bought an official one from the start instead of trying to safe 200 bucks..

 

My problem was the human interacting with my tune (me), but Rev fixed it.