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[Aero]

So I was having trouble today with getting megasquirt to sync and pick up an RPM signal.  Took apart the CAS to test it, found it had gotten wet and not getting a CAM signal out of it.

In the process of trying to figure out the issue, I think I observed at least part of the issue that causes the random misfire codes that are common for 6bolt swapped 2gs to pop up.  At first I thought maybe something was wrong with the CAS or cam slot, but I tested two separate heads, with different cams and cam sensors like this I got the exact same amount of play while eyeballing it.

I'm not sure if the play is in the pin in the shaft or in the slot, but I would guess a bit of both.

Here is a video I took with my phone of the play.

http://www.youtube.com/v/ONvdmFLPg9A

I'm not sure what would be different with the black top cas that would help prevent it, but I know the 97+ CAS threads into the end of the cam and would help eliminate the play.


Just something I didn't expect to see and had never had the cover off while it was mounted before. Even if its only a degree or two on the head, double that at the crank and I can see it causing issues with the random misfire detection.



For me the random miss stuff doesn't make any difference since I'm not on a stock ECU, but it just doesn't seem good from a performance or engine safety standpoint either.

 Seems like there would be some way to help tighten things up a bit for someone willing to do a bit of work or is it not as significant as I'm thinking?

[Robb]

Pull the cas and look at the end of the shaft. Not supposed to have that much slop. I don't think this has anything to do with getting it wet, but I still wonder what the hell makes em fuck up when they do get wet. I'm gonna kill one to find out.

[Joseph Davis]

Motors aren't a smooth, fluid thing.  They are stop-start pulsing type affairs, and the top end of the engine more so due to how it bounces around at the other end of the rubber band aka timing belt.  If you have a little play it'll get amplified all right, and not just by the difference between cam and crank gearing.

Robb, I'd be more than happy to help you out on your wet CAS quest.  Say the word and I'll pee on any of the DSM products in the driveway.

[Aero]

Motors aren't a smooth, fluid thing.  They are stop-start pulsing type affairs, and the top end of the engine more so due to how it bounces around at the other end of the rubber band aka timing belt.  If you have a little play it'll get amplified all right, and not just by the difference between cam and crank gearing.

Robb, I'd be more than happy to help you out on your wet CAS quest.  Say the word and I'll pee on any of the DSM products in the driveway.

So my main question was, should I not worry about that amount of play in one part, or try and do something about it? 

[TTC]

I thought the missfires were usually from the lack of resolution on the wheel. Isn't there a company out there that makes a new one?

[Joseph Davis]

Motors aren't a smooth, fluid thing.  They are stop-start pulsing type affairs, and the top end of the engine more so due to how it bounces around at the other end of the rubber band aka timing belt.  If you have a little play it'll get amplified all right, and not just by the difference between cam and crank gearing.

Robb, I'd be more than happy to help you out on your wet CAS quest.  Say the word and I'll pee on any of the DSM products in the driveway.

So my main question was, should I not worry about that amount of play in one part, or try and do something about it? 

Robert knows your exact application, not I.  He says that amount of play is NOT what should be there.  If your car were my first DSM, all my other experience aside, if he said that to me I'd nod and act upon it. 

[92CXyD]

Motors aren't a smooth, fluid thing.  They are stop-start pulsing type affairs, and the top end of the engine more so due to how it bounces around at the other end of the rubber band aka timing belt.  If you have a little play it'll get amplified all right, and not just by the difference between cam and crank gearing.

Robb, I'd be more than happy to help you out on your wet CAS quest.  Say the word and I'll pee on any of the DSM products in the driveway.

So my main question was, should I not worry about that amount of play in one part, or try and do something about it? 

Robert knows your exact application, not I.  He says that amount of play is NOT what should be there.  If your car were my first DSM, all my other experience aside, if he said that to me I'd nod and act upon it. 

Reading some of his posts on forums.ds-map.net I would defiantly agree. :yes: ;D

[Aero]

Robert knows your exact application, not I.  He says that amount of play is NOT what should be there.  If your car were my first DSM, all my other experience aside, if he said that to me I'd nod and act upon it. 

That is what I automatically assumed too.  I did check 2 different 1g CAS's in two different heads/intake cams and they had basically the same amount of play in them while just eyeballing them and doing what was in that video.  Maybe they are both worn, god knows how much wear there could be after who knows what mileage there is on them.


Makes me wonder if I should eventually go to a toothed/missing tooth wheel mounted on the crank for some extra resolution and to avoid this BS.

[Robb]

Can you verify what "side" the free play is on? My gut says its wear on the cam end, which would be an easy fix...

[asx]

Are you running a lowpass filter on your cam input?
Miata runs the same wheel and we stole that trick from your people. IIRC DIYAutoTune's install article covers it

Without tye filter you get a fairly random miss. Noise causes a false trigger since the second input has no other filters

[Aero]

Can you verify what "side" the free play is on? My gut says its wear on the cam end, which would be an easy fix...

I think most of the play is in the pin that goes through the T that goes into the end of the cam.  Some of it may be in the slot too.

Are you running a lowpass filter on your cam input?
Miata runs the same wheel and we stole that trick from your people. IIRC DIYAutoTune's install article covers it

Without tye filter you get a fairly random miss. Noise causes a false trigger since the second input has no other filters

I don't actually recall, those mods were done like 4-5years ago. I don't think it was though, I'll have to check. Thanks for the heads up.