NA8 with MS3 intermittently dies
 

Hi, folks. I've been wrestling with an intermittent stall issue for about 6 months and would appreciate input on whether you see anything. I've uploaded my tune and a couple of log files. Please check out events after records 5500 and 5594 in the 07.25.11 log. The 07.37.33 log is short and has a couple of events in there.

I experienced this trouble as I had been driving on the highway for about an hour this morning. Everything had been working fine up until then. So I was going along happily when the engine lost power and I saw 22.4 on the O2 meter. This happened for a few seconds and the engine started running again. I had this stalling problem for about 10 minutes this morning and pulled over in a rest stop to safely figure out what was going on. The engine restarted so I turned around and headed back home. I took another log, plus a composite log, but the car ran fine for the 90 minutes it took to get back home.

As I've been troubleshooting this the last couple of months I thought for a while that the problem was the main relay blowing due to electrical overload. I rewired a bunch of stuff and things seemed to improve but still had trouble. Next I took some logs and saw RPM signal dropped out right before a stall. My CAS wire was dodgy so I fixed that and replaced the CAS sensor while I was at it. I checked the 07.25.11 log wondering if I'd see the same trouble on the RPM signal but it looks OK to me.

I'm wondering if there's a loose connection on a sensor wire but I can't see it in the logs. Can you see anything in there?

Electric overload of the main relay? What did you rewire?

After you fixed the CAS wiring, had it done the same thing?

I rewired the fuel pump and cooling fan by adding relays to take some load off the main relay. This was based on suggestions from the forum and from FM. The main relay is running *much* cooler now so I'm figuring that helped something at least.

I fixed the CAS wiring a few days ago and this was the first time I'd taken a long drive since then. I'd previously cut the CAS wire to support the old JR bandaid timing controller and hadn't patched it properly. I drove the car yesterday and everything was fine so I was hoping I'd fixed the problem.

In looking a little closer at the logs, I see Fuel Pressure 2 suddenly goes low (to about 70 kPa) when the engine goes lean and then goes high (to as much as 156 kPa). Is this an accurate number? I didn't think the Miata had a fuel pressure sensor built in. But if it does and this is an accurate number then could inconsistent fuel pressure be causing this? I also see in the first log that fuel pressure is consistently around 100kPa before I have trouble, which is what I'd expect. In the second log I see fuel pressures around 140 kPa while the engine is running.

My fuel pressure regulator is a pretty new OEM unit so it seems likely that would be OK. Maybe the pump is running inconsistently?

Miata doesn't have fuel pressure sensor in oem.

OK, that's what I thought. I can't find much about Fuel Pressure2 using a Google search so I'm unsure where it's coming from. Perhaps it's a calculated value?

In any case, would these fuel pressure readings point us toward the problem? Something else?

Edit: Now that I think about it, it seems unlikely to be the problem because the engine simply dies. It's more like the fuel stops than a lean condition caused by low fuel pressure.

OK, I found the source of the problem. The car died yesterday when I had composite logging running and I saw the CAS signal drop out. The car wouldn't start - which was kinda new - so I went through all the connections and everything looked decent. Then I noticed I could make the engine run for a while if I pulled on a pretty deep part of the wiring harness. I'm figuring there's a dodgy wire in there, and it's not too surprising considering how hacked up my wires are. I'm thinking my best option is to replace the entire harness with a clean one from another car. Now I just need to find a harness for a 94 or 95 with ABS...