Are your battery terminals tight? And is the battery tie down tight? We thought for sure my friend's car with a hydra just had the fuel pump die after I tuned it. Turns out the tie down was loose and the battery was shifting and grounding out the the frame which was causing the hydra to shut off.

I just saw your replay to this. I'm going to hook up the lappy and see what I can do. Thank you.

Coming back to this.

I tried to adjust the Hydra settings. I was seeing elevated (14.7-15v) when revving the car up to my cruise rpms and adjusted the PWM settings to where voltage was stable. But I'm still getting the power cut.

I've also recently noticed that when it cuts off my CEL light is not illuminating. If I turn the key off and on, sometimes it still won't display. It takes a few tries for the CEL light to com on in the "acc. key position. Only when the CEL is illuminated will the car start up...if no CEL is on, it just turns over. I've also noticed that the green main relay under the hood is getting pretty hot :(

Next up is the alt. swap. I'm not looking forward to fucking with the wiring though :( Do the FM instructions on the other page apply to the Hydra or is it a matter of following the first half of the instructions (rewire at the alt) and turning off the voltage control on the ECU?

No CEL = no power. Try jumping the relay next time it happens.

Yeah the ECU isnt getting juice. And its intermittent so I would go with a loose terminal. Do you have other lights when this happens? Are they dim?

Nope. All other functions work normally. Headlights, radio, gauge cluster lights.

I suspect it's the green main relay that is tripping up, but I don't know why. I have swapped it out and nothing changed. So it has something to do with the control of the main relay...which I'm going to guess is a 12v signal. But what I don't know is what happens if the 12v signal changes voltage...

The relay requires a minimum of 9V to operate, so voltage to it isn't the issue. Just jump it next time and see if that works.

Well what controls the main relay? I'd imagine whatever controls the actuation of the relay is the root of my problem (duh). Wouldn't jumping the relay just test the operation of the relay itself? Would too much voltage change the operation of the switching of the relay?

Would it be a bad idea to bypass the relay completely if the switching circuit is causing the issue? (is this what you mean by "jump"?) Does the switching voltage have it's own circuit that controls other relays or is there a dedicated 12v source specifically and only for the main relay? My other concern is that if I bypass the relay, I need to drive the car a good bit to confirm no power loss issues and I don't want to fuck something else up by bypassing the switching circuit. (see attached document of system)

I saw a thread on Mnet of someone having a similar issue on a stock NB2 and it was recommended that the connectors holding the relay in might be fault. I'll tinker with that when I get home to eliminate that possibility.





I guess this outs the crank and cam sensors as suspects lol

I'm also curious about this, as the NA8 alt swap is probably in my near future.

I have found a few thread on Mnet about bad relays. On stock computer cars. Which makes me wonder if the voltage spike issue I was having is just a seperate issue and isn't related to this main relay issue.

This makes me really curious as to why these relays seem to have such problems. I wonder if there is a more robust relay out there that has the same connector (maybe on a Ford product?)

Ben- At this point, I don't think the NA alt. will help my situation, so that's going on the back burner.

The main relay is controlled by the ignition switch.

When I say jump the relay, I mean remove the relay and jump the COM/NO contact sockets in the fusebox - ie substitute the relay with a nice heavy gauge wire.

Alrighty. So I made a nifty little jumper and jumped the com/no sockets. Drove the car a bit an no problems. I put the relay back in and within 1 minute of driving it cut out and back on. FML. The jumper works well, but I don't want to have to open the hood every time I start/stop the car lol

So clearly the issue is the 12v stiching of the relay. My next step is to check the ground for the relay and see if that might be the problem. If not, I don't know what to do. Ignition cylinder?

Bench test the relay, it could just be the relay on its deathbed.

I'll go pick a new one up from the dealership/parts store/MazMart today. But I doubt two in a row are bad. Besides, others on Mnet have had issues with multiple relays :(

I finally gave up on my car and put a different relay in there.

What relay did you you? Plug and play or rewure the fuse box and place the relay elsewhere?


Similar issue from mnet..

post #8
Engine cuts out - it's not the crank sensor - MX-5 Miata Forum

Wow...so many threads on Mnet about dying relays. Amazing. But what is the cause? I know when mine died earlier this year, I popped one in from Jenn's MSM (that has NEVER had a problem) and it still happened. That's what is telling me it is not the relay itself, but the 12v signal that operates the relay? Staring at the wiring diagram, I jsut can't make sense of the situation. If it's the source of the 12v signal to the relay, then it would kill power to the coils as well (and a/c)....meaning that the "jumper" fix wouldn't actually work and the car would still stall. But it didn't (not yeat at least). So that *should* eliminate the 12v source to the relay....meaning , to me, that the ground is suspect. After that, I'm stumped.


I could go all mad and find a different switched 12v source for the relay and rewire the fuse box lol....I just need to find 12v that stays on while cranking.


BTW here is the correct wiring diagram for the 01-05 cars. Note the ground after the relay (signal side)

http://www.miataforumz.com/1990-200-...agram_2002.png

Our relays click so they're not solid state, so they can just wear out with use and our cars are getting old.

Reverend should be able to correct me if I'm wrong on that one. I'm not an electrical guy.

The relay part that fails is the "switch" contacts, not the coil contacts. If you take a look at the COM/NO contacts in the relay, you'll see that they are probably burnt a little and the plastic around has melted from high temperature. The relay may click but still no power as the contacts have melted internally.

Btw, that my wiring diagram that I sent to Rick to upload to miataforumz, lolz.

Yeah, I noticed on the first bad relay that the contacts were heat cycled/a bit blue and the plastic case indeed came apart when I removed the relay. This leads me to believe it's either a bad design or something causing a heat issue of some sort (the thing gets really hot!). Maybe the 12v signal is too much for it? Might be a way to reduve the voltage to keep it from getting too hot? How would I reduce the 12v to 9v? This is why I am wondering if a more robust relay will hold up...like you have done.


I have a FSM at home..