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Old 05-30-2010, 10:20 PM   #1
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I swear I fix one ******* thing and something else is waiting right behind it to fail. The car has always had a little issue from time to time with rough running after starting the car, both hot and cold. It would spit and sputter a little under load but within seconds it would go away. Yesterday it got much worse, and for the entire drive anything over about 10% throttle under load would cause it to bog and completely cut out. I can drive with a very very gentle foot though, and make it to where I need to go. Idle is fine but touch the throttle very much and the power vanishes. I did unplug the O2 sensor a few days ago, and it will be replaced as soon as the rain goes away, so I thought at first maybe it was related, but it didn't do it like this for the first day or two without it. The code it is throwing other than the 2 oxygen sensor codes (15 and 17) is the 4 code, which is SGC, from the CAS. I would think if it wasn't getting a signal, it wouldn't run at all, so why only under load would it cut out? I better not have to be finding a replacement CAS, since those cost too much. Any idea? Don't know if it could be ground related, but they are all tight and clean as far as I know. WHA ZE SHEET!

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Old 05-30-2010, 10:32 PM   #2
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I have a CAS if you need it although I think your issues might be fueling.
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Old 05-30-2010, 10:46 PM   #3
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I thought fuel at first too, but I don't know why it would be throwing the code for the CAS. Everything I have read has said that with that code being thrown, the car should either not run at all, or run very poorly, which it is doing. I think the SGC is also responsible for telling the computer where TDC is, and uneven pulse, and in return controls the fuel injectors as well, from what I am reading anyway. Electronic end of these problems has always been my failure point. If it was mechanical I would be all over it. Can't really SEE electrical issues, so for me it's like voodoo magic is messing up my ****!

Not sure exactly what could fail in the sensor though. The 1.8 sensors are magnetic, a wheel/rotor and a magnetic pickup. Wouldn't think either of those could really fail. I may risk taking the cover off the sensor and have a peak at it. If it is really bad, I can't make it any more "bad".

How much would you want for the sensor? Even the cheapest non OE reman ones are like $250 or a little more. That breaks my heart.

Also, wouldn't it make sense that the SGC wire would go straight to the computer from there? Surely it wouldn't be wiring related. I have seen somewhere that the CAS plug on one end or the other is prone to getting loose pins, and making a poor or no connection. I will also check this tomorrow to see if maybe that pin is just loose and needs to be fixed.
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Old 05-31-2010, 03:30 AM   #4
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I don't know why I would be getting a 4 code because of my oxygen sensor, but after doing a lot of reading at the evil m dot net (actually useful for something for the first time in years) my symptoms sound identical to people who have changed O2 sensors and fixed the problem. Bog and sputter until or if you reach ~4000rpm and then it takes off like a rocket. I actually had it kick at 4000 and spun tires, which is an amazing feat for a stock n/a Miata. I have also been iffy about my coolant temp sensor for months, which can also cause hesitation and poor running issues, so I will change it too and see what that does before considering the price tag and hassle of the CAS. I would hope my luck isn't that bad, with the CAS shitting itself at the same time I unplug the O2 to cure another issue. Maybe the dumb ECU works and thinks in mysterious ways and I am not reading what it is trying to tell me.
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Old 06-05-2010, 09:16 PM   #5
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Not a CAS question. Can anyone conform that this is the PRC solenoid valve? It's been broken since my rebuild, and I would assume is the cause of my occasional hot start problems. My Haynes vanished, so I have no diagrams and can't find them on google.
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Old 06-06-2010, 12:04 AM   #6
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That looks like the charcoal canister purge valve to me.
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Old 06-06-2010, 12:13 AM   #7
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That is the charcoal canister purge valve, and I have the same issue with my car. Start it, and randomly it will bog and run like crap. About 10 seconds later it runs fine. No idea what is causing it but I know it's not the ECU.
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Old 06-06-2010, 01:17 AM   #8
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What does it do? And is it "critical" to have. I would assume not if it's related to the charcoal canister, which is long gone. Would I be better off just bypassing it and leaving it unplugged, since one of the nipples are broken off and has been unhooked for well over a year. While the car is down, I'm trying to tie up any loose ends I can find. While waiting on the new CAS, I will be replacing the coolant temp sensor, already have the new O2 sensor in, which was the cause of my electrical issues due to a melted jacket on the wiring harness, might as well replace the plugs as the current ones probably have 15k miles on them. By the time the new CAS is in, I expect this ************ to run like a sewing machine. I'm tired of these little intermittent problems, as that was what my rebuild was for. Might even pop the fuel rail off and replace the seals, since I have suspected a small leak, as I smell fuel all the time in the area.
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Old 06-07-2010, 08:02 PM   #9
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What does it do?
In the stock configuration, it goes between the canister and the intake manifold, post-TB. The ECU opens it when you are in stable cruise, to vent the collected nastiness out of the canister, and closes it when you're in idle so that the leak it creates does not interfere with the function of the IAC valve.

Since you have no canister, you should plug the nipple on the manifold that it goes to.
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Old 06-07-2010, 08:38 PM   #10
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Which may be related to the problem. Vac leak can mess things up.
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Old 06-07-2010, 10:25 PM   #11
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Which may be related to the problem. Vac leak can mess things up.
I'm pretty sure he's running MAP just like me, so it really wouldn't be that big of an issue at all.
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Old 06-07-2010, 11:22 PM   #12
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I had a CAS code way before I ever went megasquirt and the problem turned out to be a leaking fuel line was causing a lean condition. Thats the problem with OBD1 vehicles is that it doesn't recognize where the problem is but only whats affected by the problem. So in example, a lean condition like mine caused a CAS, MAF, O2 sensor and Ignition Coil code. All of which were caused by the one lean condition of a leaking fuel line. So I wouldn't jump to just trying to diagnose a CAS problem, cause chances are its not related in the sense your thinking.
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Old 06-08-2010, 07:21 AM   #13
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I had a CAS code way before I ever went megasquirt and the problem turned out to be a leaking fuel line was causing a lean condition. Thats the problem with OBD1 vehicles is that it doesn't recognize where the problem is but only whats affected by the problem. So in example, a lean condition like mine caused a CAS, MAF, O2 sensor and Ignition Coil code. All of which were caused by the one lean condition of a leaking fuel line. So I wouldn't jump to just trying to diagnose a CAS problem, cause chances are its not related in the sense your thinking.
I can't imagine much else that would cause this kind of problem, to the point I can't drive the car. I can see some other issues that may have similar, but far less severe consequences. Everything I have read with people with CAS codes, and them swapping the CAS has been the problem most of the time, and their issue goes away. If it's not, oh well, that is another $250 I can't afford to spend on this car? It's already eaten thousands of dollars on non go fast parts/maintenance. Would have no idea how to track it down anyway, if it's not the CAS. No other codes, nothing else leading up to the issue that I can tell. Could be diagnosed as so many other things of less severity, so I'm actually hoping it's the CAS, since at least that is straight forward enough.

Thanks for the heads up on the valve doodad. I think I had enough sens to plug the manifold end, I hope. Pretty sure I did, as I recall I have a nipple on the manifold I had to plug, and I assume that was the one. I guess I will just check the area one more time to be sure, and then leave it off.
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Old 06-19-2010, 10:46 AM   #14
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Thank god that seemed to be it. I'm going to be watching my *** all day though, because that bitch slid right into place, offset gear lined up with the cam, and it popped into place on the very first try, took all of 20 seconds, and most of that was trying to wedge it past the coils. I had to step back and look at it, and started to take it back off because I couldn't believe it went on that easy. Swapped out the O2 sensor, and started it up and set the timing, and was annoyed to see the same damn codes being thrown for both sensors, and remembered I had to clear the stored codes from the ECU. I was about to have a break down. Changed the oil and took it for a test drive and all seems well. Still have that damn vibration/pulsation in 5th under load though. It's troubling because I don't mind spending money to fix it, but I wish I knew for sure what it is, and I have no idea how to narrow it down.
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Old 06-19-2010, 11:33 AM   #15
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Thank god that seemed to be it. I'm going to be watching my *** all day though, because that bitch slid right into place, offset gear lined up with the cam, and it popped into place on the very first try, took all of 20 seconds, and most of that was trying to wedge it past the coils. I had to step back and look at it, and started to take it back off because I couldn't believe it went on that easy. Swapped out the O2 sensor, and started it up and set the timing, and was annoyed to see the same damn codes being thrown for both sensors, and remembered I had to clear the stored codes from the ECU. I was about to have a break down. Changed the oil and took it for a test drive and all seems well. Still have that damn vibration/pulsation in 5th under load though. It's troubling because I don't mind spending money to fix it, but I wish I knew for sure what it is, and I have no idea how to narrow it down.
Well glad to hear the car is driving again. Looks like I'll be ordering a CAS for mine.
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Old 06-19-2010, 12:33 PM   #16
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Still have that damn vibration/pulsation in 5th under load though. It's troubling because I don't mind spending money to fix it, but I wish I knew for sure what it is, and I have no idea how to narrow it down.
At what speed? If you're below 40, it's simply the engine lugging. Stay outta 5th until you are above 40 and just cruising. Anything less than 45 or so and mine will protest.
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Old 06-19-2010, 05:14 PM   #17
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At what speed? If you're below 40, it's simply the engine lugging. Stay outta 5th until you are above 40 and just cruising. Anything less than 45 or so and mine will protest.
No, it's at higher speeds, like on the interstate. And it's more at a frequency that something in the drive train would be at, not rmp related that I can tell, just load related. Cruising it does nothing, give it positive throttle and the more you give it, the more it pulses/vibrates. Similar feel to an out of balance tire, but that makes no sense as I have never heard of one only shaking under load, it would do it all the time, so it's gotta be an axle, drive shaft related, or my trans about to take a dump on me.
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Old 06-19-2010, 05:19 PM   #18
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Well glad to hear the car is driving again. Looks like I'll be ordering a CAS for mine.
I got mine from ebay for $220 shipped.

http://cgi.ebay.com/ebaymotors/ws/eB...d=300437618290

Beat any other price I could find, and side by side looks identical and maybe even slightly better casting and build from what I can tell, compared to the OEM part. Used would be the route I would probably go though, I just couldn't find one I trusted soon enough.
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Old 06-20-2010, 10:11 PM   #19
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Non CAS related, but certainly not worthy of a thread.

How much fluid do you have to get around the spark plug in the well before it starts causing issues? I just noticed today while changing plug that my valve cover seals around the wells are leaking a little. Number 1 plug scared me because when I pulled it the threads and end were covered with oil, and my heart stopped, having just rebuilt the engine 15-20k miles ago with stuck oil control rings. Upon further examination, it was just a little puddled oil around the plug that dripped down when I threaded it out. Piston tops were dry and looked good for a 20k mile engine, a light and black dusting of carbon. It's not a bad enough leak to warrant me messing with it, since it's been so many miles and over a year and only a little had found its way down there. I was also pleased to see the plugs were all perfectly worn, slight grayish tan color, do major deposits or white spots, on all 4 cylinders. I'm feeling more confident in putting a little boost on this engine. Not much boost though.
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Old 06-20-2010, 10:17 PM   #20
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No, it's at higher speeds, like on the interstate. And it's more at a frequency that something in the drive train would be at, not rmp related that I can tell, just load related. Cruising it does nothing, give it positive throttle and the more you give it, the more it pulses/vibrates. Similar feel to an out of balance tire, but that makes no sense as I have never heard of one only shaking under load, it would do it all the time, so it's gotta be an axle, drive shaft related, or my trans about to take a dump on me.

I'd say that it's a U-joint in the driveshaft. Had the same problem on a Dodge Dakota, and it shook the whole truck.
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