I'm at the point where i'm trying to break in my brand new engine after it had a forged bottom end installed. The car is a 91 with a MSPNP2, and 1.8 swap from a 97. I extended the CAS wiring, new TPS connector and new IAC connector are the only wiring mods I have done to the car. I was trying to set my base timing with the fuel injector fuse pulled so the car wouldn't start. My timing light refused to work on the Miata, but worked on my Jeep. Next, I tested for spark on all 4 cylinders, no spark. I have another 1.6 Miata I robbed the igniter and CAS from and had no luck. Then, I got a brand new coil-pack after multi-meter bench testing my old one as it was reading really low, still no spark with new coil-pack. I also swapped to different plug wires and have triple checked all wiring. I took 2 datalogs of cranking the car testing for spark, and 1 datalog trying to start car with injectors connected. On the datalog with fuel, the car backfired through the intake, which has me stumped. For it to backfire through the intake it would have to have some spark, right? Another part where i'm stumped is the datalogs show RPM, but my tach doesn't move while cranking, so CAS problem?

 

I haven't been able to figure out my problem over the past few days. Here is a list of everything I have tried so far:

• No spark when grounding plug to valve cover or when using an inline tester.
• Replaced coil pack with brand new unit
• Swapped igniter with unit from parts car
• Multimeter on CAS extension, igniter and coilpack connectors, have +12v on all of them with ignition on
• Have used both the 1.8 CAS and the 1.6 CAS
• Checked all fuses in the engine bay, and under the dash.
• Swapped main relay + 80 amp fuse with ones from parts car.
• Checked my CAS extension wiring, all wires are crimped and to the right wire.
• The cam timing is spot on, engine is at TDC on #1

I will also attach some more datalogs, a composite log, and my tune.

 

I'd appreciate some help, I now get no RPM signal in the datalogs and get a no sync in tunerstudio along with no tach movement. With the ignition on and the CAS disconnected I get some strange readings on the connector with a multimeter. 0v for ground, 12v for the White/Red, 12v for the all white wire, and 5v for the Blue/Yellow wire. I should be getting 5v for the all white wire, not 12v correct? Any suggestions for what to try next?

 

Another update, after plugging in the stock ecu, I get 5v at the sgt signal (white wire). The Megasquirt still shows 12v at the same wire and 5v at the yellow/blue wire. I thought I had a short, so I de-pinned the wire from the ecu side of the harness, but the wire reads 0v. I also don't believe it is a short because I get the correct voltage from the stock ecu. Does anyone know why my megasquirt is sending the wrong voltage? I opened the case and inspected the boards and they visibly look fine, no burn marks or other obvious issues.

 

Hello,
While I can't suggest anything of use, I have a very similar problem at the moment. My car starts, but I have no spark on one whole coil. I too am getting the odd reading of ~12v on the white wire, but can't seem to find much if anything on the internet regarding this. My ecu is a DIYPNP megasquirt on a NA 1.6 (also a 91). I'm led to believe it must be an ecu problem at this point after trying to get it running for a while. No response from diyautotune about this.

Something I noticed when testing the CAS signal output was that the CAS clicked audibly when plugged into the stock ecu as it spun, but it never did when plugged into the megasquirt? I tested with the CAS plugged in and rotating it, the SGT output went from 11.5v down to 0.5v during the rotation when using the megasquirt. The SGC output went from 5v to about 0.3v (Did not actually hit 0v like it did when plugged into the stock ecu). I assume that even though the signal does seem to change from full voltage to ~0v, that the CAS cannot work with that input voltage (and that this was not always the case and an intentional design in the megasquirt?).

Check my thread if you want to see what I have gone through so far in an attempt to fix the issue.

 

I heard back from Matt at DIYautotune, he said "MSPNPs run the CKP signal at 12 volts and the CMP at 5 volts – this was the way the first MegaSquirt installs on these cars were set up, and while it's not what the stock ECU does, we've done the installs the same way ever since." So, I am now stumped as to what is wrong.

 

Damn, that changes things then. I did start to think that it may have been a design thing for the megasquirt. No idea either now!

Thanks for letting me know about the 12v signal. Will let you know if I come up with anything to fix this.

 

This may not be much help to you, but I reloaded my base map and while generating a new composite log for Matt, I gave it some throttle. The car was able to start and after adjusting my VE Table, it idles. I guess something was wrong in my tune this whole time.

 

Ah good to hear you sorted it though!