Help! Car died. Fuel pump not priming. SOLVED: Main Relay
 

Ok so I'm stuck in the city. I pulled into a gas station to get something and when I got back in the car it won't fire. I can hear that the fuel system is not priming when I turn the key. Turns over fine but will not start. I checked the fuse and it's fine. What else can I look into that signals the fuel system to turn on? I'm running hydra 2.17 FWIW. There have been a few time in the past where when I am driving the Ecu seems to lose power for moment and the car fires right back up. Jeremy at FM said that some of the older hydras have a twitchy 5v power supply that can go bad. Id rather it not be that so I'm looking for some other things to check before takin the down time to send the ecu back to hydra for diagnostics.

Ok so I plugged the wirin harness back into the stock ecu and I'm still not getting fuel, don't know if that rules out the ecu or not :(

I think it does

Something is blocking power to the ecu, the CEL doesn't light up when turning the ignition on

Bang on the top of the tank a few times. It's worth a shot. :squint:

eh...nevermind.

Main relay is shot. Has happened to me 2 times so far. The CEL and battery light should light up when you switch the ignition on.

Rev- if you're right, I'll PP you $20 lol (seriously). I'm up for just a moment and will go down to the car in a bit. I had a hell of a night and took 2 Tylenol pm at like 3am....I'm going to sleep the rest of this off.

Where is the main relay again? Oh ---- why am I asking, I have sprinted FSM in the garage.

Big green relay in the engine fuse box.

Car is alive. Thanks Rev. I honestly wouldn't expect that to shit the bed considering my luck with breaking things.

I find it quite amusing that I went to my car today, only to have this problem...again. I'm going to swap that thing out for a solid state relay.

What would cause this? Why are you blowing so many?

I'm going to end up buying a spare one to keep in the car....Rev is going to make me paranoide with his third relay failure lol

The failure on mine was the pin that runs to the side that gets switched...it got so hot it turned the pin blue. Maybe the diode sh!t out? I understand how a relay works, but don't know how one side (don't know if it's main power coming in or going out) could get that hot without flipping a fuse.

Apparently all NB2s do for some weird reason. Most likely the relay is underrated.

The B6S8 relay from the NA is a interchangable part. I wonder if its construction is any better since it is a different mfg.

I'm thinking more like that the NB2 has more current passing through the relay. Not that the relay itself is bad. Just not capable for the amps that flow through it on the NB2.

Or it could be the specific make/model of the relay as you've said.

I'd be curious to hear other chime in of having relay issues as well...and if they are on the stock ecu or aftermarket.

The first time around I was still on the stock ECU. I know at least 2-3 other cars that were on the stock ECU (but had band-AIDS on them, ie Powercards).

Interesting. This is my first dealings with having a main relay having issues.

Keith Tanner had the main relay fail on his V8 Targa car during the event last year. In this post he seems to suggest that it's a not-infrequent failure on Miatas of all vintages:

http://www.flyinmiata.com/projects/t...ld.php?UID=212

--Ian

I'm going to look into solid state relays (noob w/ electronics). I've spares in the trunk now at all times though.

I actually haven't had one die on me (stock ECU everything), I thought it did though one time. Wasn't getting power to fuel pump, picked up a relay from Alex/2ndchanceroadster but while there, tested mine on his race car and it started up fine. Went back home and his relay worked on my car.

Days later, fuel pump dies, but wasn't the pump. The fuel pump assy wiring burnt a hole the ground wire to the FP, the plastic clip crumbled (literally) trying to pull it out. The positive wire was perfectly fine. As I said, I'm a noob w/ electronics but i'm guessing it has to do w/ the relay... maybe sennding too much power, overheating the ground wire? There's a burn mark on the plastic that the interior fuel tank wiring plugs into..

I've had issues with this relay too.

Same symptom, no ECU power (no CEL when keying on).

Replaced the relay with a new one, old one tested fine. Assumed the relay intermittently failed.

Had the same issue pop up with the new relay.

Ended up that the contacts for the relay in the box were a bit wonky. Move the relay around a bit, and it would work. Tightened them all up, all has been well since then (9ish months ago).

Would you ever have an issue with the car is driving? i.e. Cruising along and the tach dithering or the car just stalling out while sitting still?

If you were referencing me, yes, I did.

Sometimes just the right bump in the road would give a quick stumble and the tach dropping to (or attempting to drop to) 0 RPM. It would always just be a quick on/off, never stalling out fully (would restart by itself).

I have had that too. But I've also had it happen when stopped. That .25 seconds is enough to make you look a fool at a stop light :facepalm:

Here is the weird thing for me. When mine crapped out, I took one out of a friends MSM and my car fired right up. SO I left the house and not but 10 minutes later, it did a quick cut off/on while crusing. This relay never did it in the MSM, but did in my car. I wonder what is up with that. I wonder if I should look into the wiring/power supply on the signal side of the relay...maybe something in the ignition cylinder?

I've experienced the SAME exact symptoms as everyone else in this thread! I have a 2000 NB and I pulled the B5B4 relay today and took the top cover off to manully engage the relay and it shows continuity. I also plugged the relay back and watched/heard it click over. So everything points to a good relay. However upon closer inspection it looks like the plastic around "ON" pin has slightly melted.

[IMG]https://www.miataturbo.net/attachmen...ine=1403564080[/IMG]


I'm going to try another relay and see if my car starts up and double check to make sure that the terminals are clean and making good contact.

Has anyone found an upgraded relay?


-B

*knock on wood*

I have not had a problem with mine since I started this thread, nor I have not heard of any better quality relays though. That one in the pic is definitely bad.

UGH!!!! My car died on the freeway again even with the new relay! I wonder if it's possible to bypass/jump the main relay with a paper clip or to get me going?

-B

I played it safe and had the car towed home. When I yanked the mainly relay it was REALLY hot! I'm assuming it's handling too much current and something inside fried on the new relay.

The only thing that I can think of is the Toyota COPs and maybe the Deatsch Werks DW300 320lph fuel pump pulling too much power?

I also took apart the new relay and discovered that it's a solid state relay! So in theory it should be able to handle a higher load.

https://www.miataturbo.net/attachmen...ine=1404423360

-B

I know this thread is old, apologies for the massive thread revival.

I've been having this issue lately as well, stock ECU (car is a '95 1.8 Eunos). I've gone through probably 5 relays in around 8mths (both the black Denso and green Imasen kind). I have a temporary fix/bodge wired in from the fuel-loom to a permanent live in the fuse box so when the relay dies, I can just plug it in and get the car home again. Symptoms usually involve a sudden misfire, tacho needle dropping and usually the aftermarket temp gauge shooting up to 90deg (OEM gauge doesn't move though so assume the temp isn't actually changing) followed by a complete loss of power. When I pull the relay out it's hotter than the Sun (no scorching/melting marks though).

I'd like to get to the root of the issue instead of just buying new relays all the time. Any ideas? An auto-electrician at work guessed something is drawing more power than it should be but said it could be expensive/time-consuming trying to problem solve. Anyone have a good idea of where to start?

I had a similar problem a few years back. I don't have the diagnostic equipment to determine the loading but my empirical information was exactly that - that I was drawing too much load through the relay, causing it to overheat and not function correctly.

What seemed to be the problem was that the (mechanical) relays would get hot enough so that the support for the contacts would move far enough away (due to heat-loading?) to make intermittent, or no, contact. I only "know" that because when my relay "failed" I took it apart and used pieces of paper as shims to move the support arm enough to get the relay to work again.

Since then I created a heat-sink from an old computer CPU and cut an opening in the fuse box cover for the heat-sink to poke through. That made it better - as in fewer no-start conditions. As a fail safe, I ran some heavy-gauge wire from the fuse block to a heavy-duty switch in the car interior. When (if) the relay flakes out, I simply remove the relay, plug in the spade lugs on the wire ends into the appropriate places, flip the switch and away I go (I just have to remember to turn the switch off later).

Of course, since I've done all of that, the latest relay hasn't "failed" in over a year!

....and a month later, the relay shit out on me. Awesome.


blown33- where'd you get that replacement/ss relay?

Add me to the list. I just had my second failure in 4 months. Went to go start the car and nothing. Same as last time and same pin as others here.

Must be overloading with either:

- AEM 320lph fuel pump
- Zeitroinix ZT-2 with EGT, AFR, MAP, and Coolant temp

....and mine is dead again.


Curious to order a new one from Mazda to see if it's the solid-state like the one pictured above. Fucking thing is $83.

I'd just like to say: Whichever mod changed the thread title, I like it. That should be a thing.

DG - I hard-wired my AEM 320 pump with it's own 40a relay and I haven't had any issues since with main relays. I think the issue may be due to fuel pumps that draw more voltage that the system is designed for. Are you running an aftermarket fuel pump?

You can also try the 80a drop-in replacement I am currently running. Part number JE16.

I got fed up with this too.

Took a fried one, gutted it except for the diode, did a major clean up on the terminals. Soldered wires to the cleaned terminals, passed them through a hole in the case. On the other end of the wires I mounted a standard relay base with a $4 relay. The wires I made long enough to exit the fuse block and mount the base to a nearby 6mm bolt.

No relay failure since and I keep a couple of $4 spares in the glove box.

AFAIK- the pump was stock up until this past Sunday when I replaced the dead stock unit with a DW. I think this failure was just bad timing and not related. If I could up the amp rating on the relay, would it be safe to do so?
The one that died didn't look bad/melted...it was even clicking with the key on/off, likely the diode is dead.

Looking around on the web, it seems some people have the problem regularly and others never have it. Who knows what idiosyncrasies are involved here...

No problem upping the amp on the relay, that just refers to its ability to pass and switch current.

I had one that clicked just fine. When I pulled it out and disassembled it I found that the contacts were so badly burned that there was no connection. When I cleaned those contacts it worked fine for a few months.

Your observations around the web are astute. I've known guys with stock cars have repeated failures and guys with heavily modified cars have no problems (and of course, vice versa).

I like Barbycar's solution. Use a bad one as a plug, make good soldered or crimped connections to a base plug, and buy a bunch of cheap relays in case it burns out. Seems like the problem would be solved then, or at least the cost of the repair greatly reduced.

Well, the Mazda dealer by me wanted $73 for one, Arlington Mazda online wanted $19. So I ordered 2. I might temporarily wire in a generic 30A/12V relay in until they get here....or modify the 2(if they aren't SS) and see how the wired-solution works.

The caveat to my solution is that the root cause of the failure is not addressed. If, as I suspect might be the case, the cause of the heat buildup is a lack of close engagement between the pins of the factory relay and the sockets in the fuse block, using a bad one as a plug, without improving the contact, may eventually lead to a failure elsewhere. When I did mine, I closed up the sockets in the fuse block with a small screwdriver to give a tighter grip on the mating pins.

It's just an under-rated relay. I installed a 40A generic one 4 years ago and no problems ever since.

In a fun twist of things...

So today I broke out some wire and connectors to make a temporary pigtail for a generic relay setup. I got the "harness" all nice and perfect. I then picked up my generic relay to check the pins against the OE green one and about punched myself making a facepalm....the generic relay has the same plug and fit right into the fuse box. I did take the cover off to compare it to the green one, and I found the construction to be a little less than optimal- like the wire for the coil being notably thinner.

Update- received the 2 new relays and neither are of solid construction...both are coils.

Took barely 2 weeks for one of the "new" ones to fail. When checking it out, I see the prong on the power circuit has melted the plastic where it meets the plastic housing. I know others have seen this too, but I'm surprised at this after such a short amount of time.

In another fun twist, I took the "old" one and plugged it in and it worked. WTF?

Pic of the "new" one with the melted plastic.

Looks like all the failures I had. I know how frustrating this is.

Try a JE16 relay. Supposed to be rated at 80a, and it's a direct drop-in part built for the Miata. Here's one for $9: Relay Denso 056700 8780 JE16 Used Warranty | eBay

Thanks Ian. I'll order that,but in the meantime I'll be swinging by the parts store to see if I can find a generic 40A+ relay to pop in there.

Found a generic 40A relay at AutoZone. Will hook it up to the harness I made and see if/how long it lasts. While trying to leave the parts store, the relay was acting up...letting the car starts, but dying 3-4 seconds after startup.

Dude you got something seriously wrong with your car. Every 1-2 months is frequent for these failures. Every few days? Serious short. Get your alternator checked at autozone or something.

Well, there was one relay that was old...like I don't know how old. That failed. I put a cheap Chinese foglight kit relay in there and it died quick...but to ve fair, before I put it in I checked its construction against the Imasan one and it was very noticeable that it was of lesser quality. Then when that died, I put the old one in and it worked again...but died later. Then put a new one in and that's the one that surprised me when it gave me an issue.

The odd thing is that ALL of them when "dead" still click/close the loop when the coil is powered up. Ive also noticed how hot they get when pulled after driving around...I wonder if its a heat issue causing them to distort in some way.

We'll see how the cheap 40A holds up while I wait on the above-linked Toyota 40A to get here. The only thing I've changed recently is the fuel pump, but that shouldn't be a problem.

But as I type that, I wonder- if my fuel filter was causing a resistance in flow and making the pump work harder (if it even does that), could the extra draw cause the circuit to run "hotter"? I know I've changed the filter not too long ago, but can't remember exactly when that was.

-double post

Bad connections can sometimes heat up causing issues. Corrosion is usually the culprit around here. Check the terminals of the fuel pump and the connector it plugs into.

Maybe you got some bad gas and it plugged the fuel filter?

I highly doubt that. I'd look at the relay terminals themselves, I be those are nasty after all these failed relays.

Bad connections should cause intermittent loss of power (maybe some arcing), not pull high current. But I'm not much for diagnosing electrical issues; just throwing out ideas.

Something is overloading those relays to cause them to heat up and fail. Would a bad motor in the pump cause it to draw more power?

Late to the party, but...

That is definitely not a solid-state relay, merely an enclosed mechanical relay.

Solid state relays, particularly those capable of dealing with significant DC currents, are both very large and very expensive. This is what a solid state relay rated for 20A DC looks like:

https://www.miataturbo.net/attachmen...1&d=1432212611

It measures 1.9" tall x 1.75" wide, and costs $65.73 from Digikey.



What you have in the picture there is a regular mechanical relay that happens to be enclosed in a plastic case, like this one:

https://www.miataturbo.net/attachmen...1&d=1432213737

That particular relay is rated for 30A, and costs $1.47 in quantity.


This is not a bad thing. Mechanical relays, all else being equal, are astoundingly reliable devices which are used in all manner of safety-rated applications ranging from spacecraft to nuclear reactors to passenger elevators every day.




There is absolutely no direct correlation between current-carrying capacity and whether a certain relay happens to be solid-state or mechanical.

At high loads, in fact, solid-state relays tend to produce considerably more heat than their mechanical counterparts. This is because, like all semiconductors, they have a relatively high on resistance. The unit I pictured above has an on resistance of 0.039Ω, meaning that at 20A, it will cause a voltage drop of 0.8v, and generate a massive 15 watts of heat. (for such applications, the relay is required to have a heat-sink attached.)

A typical mechanical relay, by comparison, will have a contact resistance which is about an order of magnitude lower (just a few milliohms) and will therefore generate far less heat in operation.



Again, we're speaking only to the physical relay itself, and not to the plug-in terminals on the bottom of the relay / the socket into which it plugs. From the pictures I've seen in this thread, it certainly appears that this is where the problem is occurring.




Unrelated, but cute; Here is a picture of a cat named Zener standing atop a giant wooden replica of an NE555 integrated circuit:

https://www.miataturbo.net/attachmen...1&d=1432213937

this this this this this

I dunno, maybe it's cause you guys have uber high mileage cars, but I've never ever had to replace any relay on any nb ever

Thanks for all the info/clarification Joe.

Curly- the terminals on the box look OK, there are some markings on the connector that has been overheating.


Here is the temporary 40A test rig...(I will be insulating/covering the exposed areas on the relay before installing)

<p><br /><br />I'm going to re-state and reinforce what Curly said, as I'm not certain it's been understood fully.<br /><br />1: It appears that the damage is concentrated mostly around the area of the contact point between the relay terminal and the socket into which it plugs.<br /><br />2: There doesn't appear to be any damage inside the relay itself, nor is it common for relays to generate a lot of heat internally.<br /><br />3: It is, however, fairly typical for heat to be generated at the interconnection point between two devices (such as between the terminals of a relay and a socket) when a large amount of current is required to flow across a marginal connection (one which is loose, corroded, undersized for the application, or at which insufficient contact area exists.)<br /><br />4: The male pins on the bottom of the relay are not readily deformed, and certainly not in a dimension that would be critical here.<br /><br />5: By contrast, it's entirely possible for the female socket terminals in the fusebox to spread out, which would contribute to the failure mode noted in point 3.<br /><br /><br /><br />So, with reference to the temporary test rig&nbsp;you've pictured:<br /><br />1: If the thickness of those crimp-on male terminals is greater than that of the terminals on the bottom of the melted relay, then this will improve the contact at the socket in the fusebox. If those female terminals are in any way degraded, however (spread out, corroded, etc), then this is at best a temporary fix.<br /><br />2: If the thickness of the aforementioned terminals is not significantly greater than those on the relay, I would expect heat to continue to be generated at the contact point.<br /><br /><br /><br /><br /><br /><strong>TL,DR: The relay itself isn't likely the root cause of the problem. </strong><br /><br /><br /><br /><br /><br /><img alt="" src="https://www.miataturbo.net/attachment.php?attachmentid=140207&amp;dateline=14 32235318" /></p>

I

To quote an earlier post of mine:

One other concern: With bad connections at the the main relay the ecu will see a lower voltage and ramps up the alternator voltage to compensate. It is already high.......

Apologies for resurrecting an old thread, but that seems helpful in this case. One suggestion in this thread was to use the NA's JE16 relay instead of the NB's B5B4. I've had quite a bit of trouble with both the JE16 and the B6S8 before them in my NA, which makes me think they're not better than the B5B4.

My car blew a relay yesterday and I'm looking for a replacement. I'm hoping to find something that won't keep failing. Any ideas?

For example, has anybody tried the NF02 relay from an FD RX-7? 93-95 Rx7 Main Relay (NF02-18-821A). The relay physically looks similar to the JE16 but I'm suspecting Mazda could have specified a higher rated relay in those more powerful cars. That would address Reverant's comment that the NA and NB relays are underrated and can't handle the loads we need.