17 replies to this topic

[DrDomm]

I'd really appreciate some help here, as I'm banging my head against a wall and have wasted a ton of time trying to figure this out.

 

Yesterday I warmed up my car in the garage.  It started right up, idled for about 30 minutes until the fan kicked on, and then I shut it off.  I tried to restart it a few hours later, and it wouldn't start.  

 

It cranks great.  Voltage is good.  Fuel pressure (at test port in engine bay) is great.  Spark plugs are firing, but plugs are dry.  (It will run briefly when gas is put in plug hole)

 

So I figure the injectors aren't working.  Why won't the injectors work?

 

The injector fuse is fine.  The "main relay" seems to make contact when turning over, but I'm going to replace it tomorrow anyway.  I have cleaned all 3 grounds that I can find in the engine bay.  I've reconnected every sensor.  The crankshaft sensor seems ok, as I can get the EGR valve to click when I hand crank the motor.  I swapped cam position sensor.

 

I switched ECUs...and that didn't help.

 

I'd love to hear some new ideas?

[Ron Alan]

Fuel injector relay?

[Johnny D]

Got gas ?

J~

[Bench Racer]

http://www.yorbalind...iring/99sys.pdf

[DrDomm]

Fuel injector relay?

 

Also called "main relay"...yes clicks open when ignition on, but I ordered a new one and will change it this morning anyway.  Not optimistic.

 

Got gas ?

J~

 

Yeah, great fuel pressure and flow at test port.

[Brandon]

On my '96 at least, there are two relays in the under-hood box: main & FP

The main one is bolted in and the FP one you can remove by hand.

 

I also had a similar problem (nearly identical in fact; drove it off the trailer at the track, next AM, no start) and it turned out to be a simple fuse in the box UNDER THE DASH!

Which I was not aware of at that time....so....anything blown in the box under your dash?

 

HTH!

Brandon

[Bench Racer]

You said you have fuel pressure.  (If either the fuse, or the main relay, or the fuel pump relay, or the fuel pump were not functing you would not have fuel pressure.)

You said you have spark at the plugs.

You said when you pour fuel in plug hole the engine runs.

Seems the next step would be to check for electrical power from the ECU at the injectors. Two things happen at the injectors, amount/volume of fuel and timing of fuel. I have never done that power check at the injectors from the ECU..

Reasons for my posts are because I am well intended and when I had an engine oscillating issue between 2,200 rpm and 1,700 rpm no one posted a thing. Maybe my info will fuel a thought.

 

Another thought:

Look in your FSM under Fuel and Emissions Contyrol Syetems under Dechoke Control System. With my 1.6 NA, the ECU receives info from the throttle sensor, the water thermosensor, atmospheric sensor, the CAS and the ignition switch.

[Jeff Wasilko]

Is it a 1.6? Can't the AFM fail in a way that kills the engine?

[Mike Collins]

15A "engine" fuse" under the dash??????

[DrDomm]

Thanks everyone for all the thoughts...I did check all those things (fuses/relay in engine bay, fuses under dash, grounds, ecu, etc.).

 

I found an old thread with a post by Dave Wheeler mentioning a way to test fuel injector connectors to see if they are signaling injector to fire...NOID tester.  To get to the connectors I took off the top part of the intake manifold.  I unhooked the 1st and 4th connectors and tested them by cranking the engine...they worked.  So I knew all the sensors and ECU were working.

 

I changed all the injectors, and voila it starts.  A wise man tells me it's prolly just that something is up with the injector harness, and that my messing around with it "fixed" the problem.  Hopefully it's permanent.  Car has started multiple times.  If there's a problem, I'll change the injector harness.

 

(At least I understand how the fuel system on a Miata works.)

[Parity]

Similar problem just happened with Wechsler's car. He had Planet Miata replace the harness and they did find a short.

[DrDomm]

Paul, it's just so annoying because you go chasing every sensor, fuse, relay, etc. before you actually take apart the manifold to get to the harness.  In hindsight, taking apart the manifold and disconnecting all the injectors was a lot quicker than some of the other things I did.  I can tell you it was a lot less painful that swapping the ECU.

[Parity]

Domm, sounds like a pain and thanks for posting. Main reason I read these forums is so I'll have some idea where to start when it happens to me. Good luck at WGI. Wish I was going.

[HoneyBadger - BrianW]

I can't remember if your car is a 99 or not... If it is you can still buy the injector harness from Mazda. Memory tells me it's like $120 or so. I have a new one for both of my engines.

[DrDomm]

I can't remember if your car is a 99 or not... If it is you can still buy the injector harness from Mazda. Memory tells me it's like $120 or so. I have a new one for both of my engines.

 

It is a '99.  I have a spare one now if this one fails.

[Zack Benham]

DrD,

 

I know this was all a big PITA for you, but it was a very entertaining and educational thread, thanks for posting...

[DrDomm]

DrD,

 

I know this was all a big PITA for you, but it was a very entertaining and educational thread, thanks for posting...

 

LOL!  I admit it was educational, but I think I've got more entertaining stuff than this.  Glad I could help though.

[PRFGDWRNCH]

Hi Domm,

Just for peace of mind you may want to have the old injectors checked. If there was some debris in the fuel system it could be blocking the filter screen at the injector inlet. If that were the case, you may want to drain the tank. If Gene does not have some one he uses, you could try Tim at Marren Injection in Oxford, CT. He is in the same development as Chassis Dynamics.

It probably is the harness but if it isn't it could save you a DNF.

Have a good season.

Dave P