A note on mk1 diagnostics

[ryan]

I'm posting my recent experience with the mk1 diagnostics port, just in case anyone has had similar issues.

Having done an aggressive strip-down of the mk1 wiring loom to suit the Exocet, I decided to see whether the diagnostic port (pre-OBDII) is still working.

There are plenty of instructions online about jumping TEN to ground, and connecting an LED across FEN and B+ in order to read ECU fault codes. (i.e. www.miata.net/garage/Engine_Diagnostics.html). All of the instructions say to read long flashes as tens, and short flashes as ones, and then compare the codes with a sparse list of codes from 1 to 34.

I made the necessary connections, switched on the ignition and got very excited when long and short flashes started to show. (Having binned the charcoal canister and EGR setup, I expected some minor complaints.) The sequence of codes was:

10 14 14 13 11 14 10 12

Firstly, I was confused to see 10 12 and 14 (intake temp, TPS and atmospheric pressure respectively), as the car is running perfectly. Also, no EGR faults, and codes 11 and 13 don't exist on any of the online lists...

Eventually, I stumbled across a workshop manual supplement which describes a completely different system of fault codes: by ignoring the long flashes, and reading the digits in groups of four. So, the above sequence becomes:

0443 1402

And according to the new lookup table, these correspond to "0443: Purge solenoid valve" and "1402: EGR valve position sensor". Success! 

I apologise if this is common knowledge, but I couldn't find any information about this system online, and I think it could be useful for others with mark 1s.

Here is a summary of the fault codes using the "new" system:

Old   New   Meaning
---------------------------------------------
03   1345   Camshaft position sensor
08   0100   Mass air flow sensor
09   0115   Coolant temp sensor
10   0110   ntake air temp sensor
12   0120   Throttle position sensor
14   1195   Barometric pressure sensor
15   0134   Heated O2 sensor (inactive)
16   1402   EGR valve position sensor
17   1170   Heated O2 sensor (inversion)
25   1250   PCR solenoid valve
26   0443   Purge solenoid valve
28   1485   EGR solenoid valve (vacuum)
29   1486   EGR solenoid valve (vent)
34   0505   Idle air control valve
-      0500   VSS
-      1602   Immob. ECM comms error
-      1603   Immob. ID num unregistered
-      1604   Immob. Code word unreg.
-      1608   ECM internal malfunc.
-      1621   Immob. Code word mismatch
-      1622   Immob. ID num mismatch
-      1623   Immob. read/write error

Source: rikitaun.foroctr.com/MX5/NA/MX-5%20Workshop%20Manual%20Supplement%201509-10-95I.pdf

[jgilbert]

Very useful reference. Thanks for sharing.

[PardonWhat]

Brilliant, this is really useful thanks.

[gwnwar]

Good info.. but the 2 number system works for the NON OBD connector.. and 4 number system is for OBD systems with plug for scanner.

[snowbird1]

This may be of interest - I've been playing around with the spare engine I have here in Wales.

This is a little video of some engine tests.

[gwnwar]

John.. great video.. You must be driving wife crazy so she sent you to the shop to play.. Have you picked up any bits for your build while home..

[ryan]

That's some seriously analogue gear! I'm curious: how have you mounted the engine out of the car? Is it just timber?

gwnwar: are you saying that systems with the 4-digit codes should have a different connector? Ours is exactly like the one here here? Anyway, it's good to know that the OBD codes can be read using the cheap-as-chips LED method...

[mrjingles705]

My understanding (correct me if I'm wrong here) is that the later Mk1's (with the OBD connector) have both the OBD and the original Mazda diagnostic one in the engine bay.

[snowbird1]

Jul 18, 2014 18:39:24 GMT gwnwar said:

John.. great video.. You must be driving wife crazy so she sent you to the shop to play.. Have you picked up any bits for your build while home..

Gunwar - you sussed it, enjoying the Welsh weather though a bit frustrated with the car 8000 miles away, collecting a few bits and looking forward to getting back when things cool down a bit in October.
Doing a bit of self training on the engine, I may pull the head as I'm still a bit puzzled about the coolant flow.
And - yes the engine is just sitting on wood blocks.

Just curious - has anyone used this power train in a car without the PPF?