Cutout at 5600 rpm MS2

[digger]

Yeah the clearance between hole and bolt gives some adjustment. Note this means you could end up at the far end of the spectrum if it wasn't checked during install

[JIMBOkye]

Got a PM asking how I adjusted the CPS gap, so I figured I'd share my response in-case anyone had any input or was also wondering the same thing...

What I did was turn the crank until a tooth lined up with the metal tip of the CPS sensor. Then I measured that gap (was about 0.040"). I then loosened the two bolts on the CPS mounting bracket (had to remove the CPS to get to lower one), then reinstalled the CPS on the bracket and put a 0.030" feeler gauge between the sensor and tooth and pushed the sensor tight on it while tightening the top bolt on the bracket. Once that was tight I removed the CPS sensor, tightened the lower bolt, reinstalled the CPS sensor on the bracket and rechecked the gap.

There is quite a bit of play in the CPS mounting bracket. My plan was (if I could not adjust the gap down far enough) to file or drill out the holes on the bracket a bit to give more adjust-ability. But that was definitely not necessary.

[JIMBOkye]

let sleeping dogs lie

haha yes, I will not be changing it unless the problem comes back.



Another thing I noticed now is the idle seems to be smoother. I guess, with a better signal from the CPS, this makes sense.

[Digitalwave]

As I said before, the metal ones are more than double the price. I think I paid $145 for mine.

[digger]

UPDATE: Changed the gap to 0.030" and that fixed it.

I am running one of the cheap plastic ones, as I have not been able to find any of the metal oem style ones. Anyone got a hook up for that style? Looks like Pelican is out of them, don't see any on Blunttech or Amazon either... Looks like ECS has one, but $150...

let sleeping dogs lie

[JIMBOkye]

UPDATE: Changed the gap to 0.030" and that fixed it.

I am running one of the cheap plastic ones, as I have not been able to find any of the metal oem style ones. Anyone got a hook up for that style? Looks like Pelican is out of them, don't see any on Blunttech or Amazon either... Looks like ECS has one, but $150...

[ForcedFirebird]

Also make sure the plastic cover is on the sensor wires as they pass behind the water pump pulley, or they can rub on the pulley and short out.

I can't tell you how many times I have seen this. On the race cars, we run them over the timing cover, and on the endurance cars, we even have a spare CPS zip tied next to functioning one to make an easy swap if it goes bad.


Also if the sensor is old, they tend to crack right were it meets the wire and can cause an issue.

[nando]

yeah, I was just confirming, because I'd bet the cheap plastic ones are even more problematic, and we don't know what the OP has.

Anyway, since the OP had issues with the stock DME cutting off at the same RPM I doubt the Megasquirt is the primary issue - he should follow what you posted above.

[Digitalwave]

I was talking to the OP, Chris. ;) I've heard bad things about the plastic body CPS's, which are way less expensive. I went right for a metal body one when I replaced mine.

[nando]

Mine has a metal body, same as the original stock one.

Also make sure the plastic cover is on the sensor wires as they pass behind the water pump pulley, or they can rub on the pulley and short out.

[Digitalwave]

Are your new CPS's the OEM style metal body ones or the plastic ones? I had issues with my CPS that were fine with Motronic, but gave me hell with Megasquirt. The Dederic board has a 10k resistor on the VR signal. DIYAutotune recommends an 18k resistor. I had tried that and it did not make a difference. Replacing the CPS with a new metal body one fixed my issue. I have mine set at the stock distance spec which I believe is 0.040"/1mm.

If it is not the sensor, I would check that 1) your crank wheel is okay 2) start checking and testing the wiring between the CPS and the ECU.

Your unit is Microsquirt based, so it does not have a potentiometer for adjusting the VR signal resistor like MS2 boards have. Like others have chimed in, once I fixed my issue, I have not had any trouble constantly running this M20 w/ CPS to 7,200 RPM all day long without any sync loss on the track.

Here is a copypasta of a reply from Derek when I was diagnosing my CPS lost sync issue:

You are correct in that microsquirt inverts the VR signal. There are a few things in this email I can have you check/change but I cannot guarantee a solution—these are only what I can think of off the top of my head, from my experience. You may try all or none of them, but usually the ECU’s are as sound as could be. I have tested them on a variety of m20’s for long lengths time, with many different engine harnesses, all with varying degrees of wear. The product is as stable as I can make it, but may take a bit of ironing-out to suit your specific vehicle.

On to the stuff you could check:

• Try the 18k 1/4w resistor in place of the 10k, it may help buffer the signal. I would try this first, as it’s the cheapest and easiest.
• Replace the CPS. Sometimes these fail for MS, and not Motronic. Motronic may have a better designed buffer for the VR circuit, since the circuit in the factory ECU was designed for this system specifically.
• Check your engine harness terminals for wear
  • check resistance while moving around the connectors and terminals. The m20 harness in my experience tends to die at about 25 years from failing terminals, corrosion, etc…. Some last only 20, some haven’t died yet. This could be a culprit, I’ve had a customer chase a ghost just to find out it was the harness that failed. I have yet to take on the task of cutting and replacing all of the terminals on a harness, but it is something to consider if it is too expensive to replace in whole.
• When was the last time you changed your crankshaft harmonic balancer?
  • I’ve only had one vehicle lose sync, right in the same RPMs too. I changed everything I could think of from the CPS to the mount, the settings in MS, to the ECU from MS back to Motronic, and in the end it was from a faulty crankshaft dampener/toothed-wheel/harmonic balancer.
    • The crank dampener is constructed of two main pieces, the inner ring (6 hole mount to crank), and the outer ring (timing wheel, 60-2); This outer wheel is mounted the inner wheel with a ring of molded rubber. When the rubber fails, which is hard to diagnose from just looking at it, you may lose sync. I theorize because the tooth wheel is either shifting or harmonically untrue; 60-2 teeth vibrating out of balance causing sync-loss.
    • M20b25 Standard “i” Dampener – 11231726961
    • M20b27 “Super eta” Dampener (also requires water pump pulley) - 11231714855

I hope this helps. LMK what happens.

-Derek

[nando]

I've set up many and I've never found it fiddly. I've never even messed with the sensor gap.

[pazi88]

yeah, that's just not true. I've run with a VR sensor for 11 years now (MS2 and MS3). It's actually often a misconfiguration (wrong jumpers or settings) or a hardware issue (sensor gap, etc).

I didn't say it's impossible to run vr sensor with megasquirt. It just can be really fiddly to get it working reliably by getting rid of the noise and get the pots adjusted properly especially without scope. I don't say it can't be done. But easier way is to swap to hall sensor.

[ForcedFirebird]

I put my money on CPS gap, had it happen to me on multiple cars. I just put it as close as you can without rubbing, as mentioned. Rotate the crank so a tooth is at the sensor, push it in until it touches, then back it off ever so slight. The stock ECU doesn't seem to care much.

[nando]

VR sensors have quite often issues with megasquirt. Grab cherry hall sensor, configure ms2 to use hall sensor and your problems are gone.

yeah, that's just not true. I've run with a VR sensor for 11 years now (MS2 and MS3). It's actually often a misconfiguration (wrong jumpers or settings) or a hardware issue (sensor gap, etc).