Typical Cranking RPM
 

Hello All,

Working on getting my 91 NA working on my MSPNP2 that I got used here a couple of months ago. So far I have not been able to get it running, cranks but doesn't start. Looking at the laptop dashboard i'm not seeing any RPM, it actually reads 1, and just stays there, weather cranking or not. So far I have been troubleshooting the CAS, based on not seeing any RPM as I crank the motor. I'm not getting spark or fuel which also points to not getting any RPM signal, this is on either ECU, stock or MS. I did find the CAS plug was cracked and broken, so i sourced a local one and wired it in. Still no start, luckily I was smart and didn't set the shrink wrap on the solder joints so i was able to get my multimeter on there. I have power on the red and black, and when I started checking the signal wires (white and blue/yel) I wasn't getting any signals on the white, and only one per rotation on the blue when I rotated the crank with a ratchet while the key was on in the ignition. I sourced a known to be working CAS convinced this was the problem, swapped it in, checked the signal wires and was getting my 4 pulses per rev and still only 1 on the blu/yel wire, tried to fire it up, still not RPM signal still no start.

I went back to check the signal wires and was getting some very inconsistent readings, instead of getting 12vdc on the white 4 times I would get a consistint .023 vdc and then it would drop to -.001vdc 4 times. I thought this was very strange, I disconnected the plug that the White and Blu/yel wires tie into on the ECU and it was doing the same thing. I disconnected the other plug from the ECU and I got my 4 12 vdc signals again. I was in the middle of trying to take a comp log yesterday and the battery started to die, so I disconnected it and put it on the charger over night to tackle it again tonight, mainly to get over my disappointment.

My next course of action i'm going to run new signal wires from the CAS plug to the ECU just to make sure I don't have a short anywhere. Maybe I damaged them when I removed the AC evaporator and fan box. But if this doesn't work i'm out of ideas.

Background:
I parked it running and driving on the stock ecu, in the mean time I removed the entire AC system from condenser to evaporator, including the Air box. Installed the intercooler, mainly so I can do the IAT sensor once and not twice, in the process of wiring up the IAT I destroyed the AFM by removing the screws that connect the plug to the AFM, i ended up just soldering to the leads on the back end and taping it all up instead of trying to get tabs to go into the ECU side, (this reads just fine on MS). I installed an LC-1, wiring to the switched radio supply (as i removed all the stereo components). and installed a mechanical boost gauge in the cluster. I have all the turbo stuff ready to go, but i'm not doing jack till I get it running on the ECU first.

Any words of wisdom to check on, or things that i'm not doing right, or inadvertently forgot to reconnect when removing the extra parts and what not would be greatly appreciated. I'm quickly running out of ideas.

Thank you in advance

Doesn't the 91 also have a crank angle sensor? I believe it does. I think it needs both to register rpm properly.

I thought the CKP was only 94 and up, I dont have any sensor on my crank stock

Maybe I'm wrong, or that's only the smog versions.

take a composite log during a 20sec crank.

is that any activity on the green or blue traces?

My 94 got crank and cam signal from the CAS. No VVT so there's no need for both sensors. Of the 4 wires going into the CAS, you have power and ground, and then one is the "crank" signal, and the other is the "cam" signal. I don't believe the 1.6 system is any different.
Will it run if you plug a stock ECU back into it? It should at least start without the AFM, I think?

Something funky going on if you're getting 12V on the white/red and connector 1 is unplugged.
https://www.miata.net/garage/ECU_Pin-Out.png

I'm not getting any spark or fuel from either ECU, that's what drove me to the CAS, wont run without the AFM, I forgot to put it back in once and it ran for 5 seconds till the fuel ran out then wouldn't fire back up. I will take a comp log tonight once the batt is charged up, was in the middle of one yesterday before she started to die.

Great news, after disconnecting the batter and charging it for a day, hooked it back up to do the comp log, and she sputtered to life. Not exactly sure how charging the battery affects the CAS but shes running now. She was cranking just fine for a long time, odd how either a full discharge of any stray voltage or a fully charged battery would bring it back.

So this morning it was doing the whole not starting thing, I grabbed a comp log and took the truck to work. I got home did absolutely nothing but get in the car and turn the key and she started right up. Any insight would be greatly appreciated.

https://drive.google.com/open?id=0B4...1BjSFVUUno5TUU - folder for the comp log and the current tune file

I am having nearly the same issue. But I have seemed to narrow it down to how hot the coolant or the air temp is. I tried jumping my car this morning after being able to start all weekend over 7 or 8 times no issue. No nothing but let it sit over night and now it will not start. I get the cam signal sometimes for like a second but not enough to start. But every time it does not start the coolant temperature is below 80 and when it does get a signal and start the temp is above 80. Any help would be great.

link to my thread
https://www.miataturbo.net/megasquir...mittent-93695/

the CAS is a pretty simple device, but needs 12v to run. either the CAS is bad, or battery is bad.

I agree, I swapped mine out because I wasn't getting any signal from one of the wires as I rotated the crank. I think we are looking at the CAS because it appears we are not receiving any trigger signal in the comp logs. I did notice that at one point I got some weird readings when testing the new cas until I unplugged both of the harnesses from the MS (not just the one that houses the signal wires from the CAS). I'm on board with the temperature theory, is there a chance that the cold engine enrichment programming could be affecting the trigger signal. The battery is cranking over the engine just fine, and I have had it go from not running to running without touching a batt charger to it, it was just later in the day.

I too had the same issue with it running and starting even after a day of sitting no problem. But it seems like if the car sits over night and the coolant and air temp is below 80 it does not seem to work.

Davidh,
Try disconnecting your IAC,

I was working on my car today, and it didn't start, coolant temp was above 80 (91). I cranked it for a bit, checked the comp log and not get any rpm, I check the CAS plug to make sure i wasn't get any short, check the engine compartment for lose wires or grounds and what not, didn't find much. But when I went to start it she turned over. Idled for a bit then died, hmm that was odd, then would restart same thing no RPM. Then all of a sudden the MS went offline and would communicate to TS. Ok, now I know its a short or ground. I unplugged one of the harnesses and she started talking again. So after looking over what wires were on that harness I had an idea where to start. Last summer I blocked off the coolant and IAC due to it malfunctioning, constant idle around 2k, so i knew that there was an issue with that valve and it correlated with your connection to the temperature, and the no start. If there is a short in that valve motor it could be causing a problem with the reading of the CAS. I disconnected that plug and she fired right up. I am going to keep an eye on this, but give it a shot, see if it works for you.

So I got home coolant temp was above 80 and it started up no problem. Dident do or change anything. Could it still be the valve?

So they way I understand the valve, don't quote me but it is a drive open, drive closed type. So if it doesn't need to change then no voltage is going to it, and as its trying to control your idle which it sounds like when it tries to open (allow more air past the throttle body) the motor shorts out, but when it closes (like when its warm) its fine. This is just a theory, I have no idea if it is causing it or not, but it got me running, I even cut the plug off, taped the wires as one of them was frayed, and disabled it in megasquirt to be sure. But it is a common part on both of our engines, has something to do with coolant temp and could affect the readings on other sensors if its going to ground on the board in the MS. So far i've shut it down and started it back up prob 10 times playing with some other settings and drove it up the road and she felt great. I had to park in the street since they are paving my drive way next week and won't be able to touch it till Monday so I'll try it again then.

This morning again no start. No cam signal. Changed the settings on the IAT and the coolant temp to make it read 90 and still no start. So it has to be the physical temperature of something. I tried unplugging the valve and still no luck. I am going to try installing a much larger battery into the car and see if that has anything to do with it. My voltage reading is 12.2 before I start. And while it is cranking it drops down to 9.5 or 10 maybe not enough to feed power to the cam sensor while cranking?

no, that's quite normal for a miata.

david, you probably have a bad '99 cam sensor.

ndlswntr has a bad CAS.

So even if my cam sensor can start the car with factory ecu it can still be bad?

you've said your issue is intermittent. where it worked all weekend and then it didnt. how do you know the stock ECU is always working?