17 replies to this topic

[dstevens]

I'm troubleshooting a no start issue.  I've swapped the ignitier as the shade tree resistance test from miata.net show it out of spec.   One side of the coil primary is out of spec by about an ohm but the other side specs.  No spark on either.  Rather than throwing more parts at I've started step by step.  It's looking like the ECU.  I'd removed the instrument cluster so I had to go get it from the boneyard and hook it up to see the MIL.  No MIL but power to the ECU.  I'm checking for grounds or shorts, hoping I left one off.  I'd rather not put any more money into it as I just want it to start and drive.  And it doesn't even have to run that well.  

 

Rather than counting blinking lights I have an opportunity for a pro grade scanner/recorder at a screaming pawn shop deal.  It's the current version of software for that tool family so I'd use it on the street cars but if I could use it with the speced adapter for a Mazda ODB1 port.  The software manual says it will work on an ODB1 Miata for basic codes.

 

Is anyone using any of the Snap On diagnostic scanners/recorders for Miata ODB1?

[Ron Alan]

Do you have fuel pressure and injector pulse? Just no spark? 

[dstevens]

The fuel system doesn't respond even with the f/p diagnostic jumped though power is where it needs to be.  That's leading me to believe ECU or a ground or short.  There was a case at Miata.net where the AFM shorting loaded down the +5 rail on the ECU causing it not to throw codes or even light the MIL.  Once I make sure all the grounds are good I'm going to unplug the AFM, TPS, CAS and anything else so I can at least get to the point where I can get some codes from the ECU.  It should throw codes for some of the stuff that is disconnected.  If it doesn't Willy and Blake have some used 1.6 ECUs.  If I can't get the MIL in the cluster to work due to wiring or lamp there is a trick to put an LED into the test port and get the codes that way.

 

Of course I'd rather be able use this as a justification to buy something that I probably really don't need anyway but would like to have....     

 

Regardless if I get the tool I'll get this up and going.  It's a case of "well hell it worked before I took it apart...) 

[Steve Scheifler]

I can send you a loaner set of all the likely parts that I just stripped off a running car.

[davew]

Check all the fuses first. There is one under the dash that will cause a no start. I think it is labeled "ROOM"

 

Dave

[Steve Scheifler]

Check all the fuses first. There is one under the dash that will cause a no start. I think it is labeled "ROOM"

Dave

Or maybe ZOOM.

[Bench Racer]

http://www.yorbalind...iring/90how.pdf

 

http://www.yorbalind...iring/90sys.pdf

 

http://www.yorbalind...ring/90diag.pdf

[dstevens]

Check all the fuses first. There is one under the dash that will cause a no start. I think it is labeled "ROOM"

 

Dave

Thanks.   I've checked all the fuses.   The ECU is getting power from that circuit.  IIRC it's 10 amps, and called "Room".  There doesn't appear to be any signaling coming from the box.  

[dstevens]

http://www.yorbalind...iring/90how.pdf

 

http://www.yorbalind...iring/90sys.pdf

 

http://www.yorbalind...ring/90diag.pdf

Thanks Bench.  I've got the factory book and the Enthusiast Guide.   Both are great references.

[FTodaro]

edit

[LarryKing]

Have you checked the connector at the ignition switch?

[Bench Racer]

Posted info showed no fuel pressure and no spark.

 

My reasoning for posting the schematics is they show the main relay (under hood), circuit opening relay (under dash), main fuse block (under hood), diagonal box (under hood), crank angle sensor, AFM, fuel injectors and fuel tank/pump all play together with each other and with the ECU which plays with the ignitor and ignition coils. Along with all negative grounds.  

[Dave D.]

Scanners don't interface with the Mazda OBD1 in a 1.6 Miata, no live data feed. If you don't have a check engine light even with key on engine off, you are missing power somewhere. I don't have access to schematics right this moment, but you need to get a pinout of the ECM and check for power and grounds as there are more than one power line in. As Dave said, check your fuses, under the hood and under the IP. Diagnose before throwing parts at it, it is easier and cheaper in the long run.

[B(Kuch)Kucera45]

You have to watch when buying a scan tool especially a snap on one. The updates for them are expensive we just paid $1,500 to update the one at our shop.

[dstevens]

No ODB1 return live data, only codes.  The tool decodes the pulses to return the code.   That's how the SST Mazda uses does it as well as the higher end tools that do read ODB1.  For this it's basically a really expensive code reader.

 

I'm pretty familiar with the Snap On diagnostic tools and they are expensive to update.  I'd never get on off the truck new, can't justify it.   For $1500 the update sounds like it's for a Solus or one of the other two way scan tools.  The Ethos and Ethos + updates I can get from the guy on the truck for about $800/year or 3 years for $1500.   Someone else also thought an Ethos Tech with 15.4 software, the current version, was a good deal as it was gone when I went back to get it.    At $500, it was a steal.  The pawn shop probably thought it was an Ethos or Ethos + and not an Ethos Tech when they priced it.

 

 

I'll put my parka on and head back out into the garage to check ground point continuity.  It's downright frigid tonight, just above 50.      I might have to put on long pants...

[Bench Racer]

When you've completed your ground and fuse checks, check and see with the ignition key on if the relay under the dash is clicking when the flapper in the AFM flapper is opened and closed by hand. IIRC without the air filter stuff attached to the AFM I used a long stick to open and close the flapper while I touched/felt the relay under the dash. I pulled the relay out of it's attaching bracket so it's wires let the relay hang lower towards the bottom of the dash.

[Bench Racer]

Dave, skip removing the valves (other thread). Did you get whichever Miata running???

[dstevens]

Best Answer

The valve tool thread was from almost 4 1/2 years ago.        Got the OTC, works great.

 

Today I prepped it for some welding, drain fuel, vent tank, removed ECU, removed some of the paint.

 

The issue right now for starting seems to be, wait for it....   the wiring harness.  I didn't get a couple of grounds the first time.  The issue is still no 12 volts to terminal 1B of the ECU.  Unless 1B gets 12 vdc, the ECU doesn't start the power up and self test cycle.  I've hot wired around the ignition switch to put it in run.  The switch, while tested working per the FSM terminal B2 has some serious current damage in the plastic or whatever composite the switch assembly is cast from.  B2 on the plug shows some melting as well.  The relays used in that circuit test per spec when out of the car.   The ground point there shows quite a bit of voltage drop with the lug connected, about 4 volts, but when the lug is removed the ground point tests good, 12 volts.  It's pointing toward something in the harness that loads down the circuit when grounded.  I don't want to throw relays into it particularly when they tested well on the bench.  There may be some short or something introducing a butt load of resistance.  I'm only able to get 1.5 volts (connected or not connected to the ECU) to 1B and not counting the relays that's a straight shot through the ignition switch down some wire to the ECU.  Worst comes to worst I'll wire it like a proper race car with a start button and switch and tag a new cable to the loom.  It's not like I'm going to go through tech with the thing.  At this point were it going to the track I'd have bought a new loom already and some relays.

 

To put a period on the OP, yes, the Snap On diagnostic software will decode ODB1 from a 1.6.  It will read and clear all the basic codes listed in the FSM or that the SST does.  If you have one of the upper end models the troubleshooter feature even works. Truck dude will loan me one of the cool units but not being able to get the ECU to boot doesn't really do me any good.