ECU Compatibility for 1992 NA 1.6 Engine

Sugoi · Post by **Sugoi** » Sat Sep 22, 2012 10:03 pm

Hi There,

I am having a few issues with my Automatic MX-5 NA.

I drove to work on Friday morning, at night it would not start.

Cranking well.
Fuel getting to Fuel Rail.
Good Spark.
Fuel Injector resistance is within limits (14 ohm.)
It seems that injectors are not firing.

As far as I can track down it looks like the ECU has died. Can I just drop in another one from any 1.6 litre NA, or is there anything specific that I need to check.

Or is there anything that I have missed checking?

na6*dori · Post by **na6*dori** » Sat Sep 22, 2012 11:45 pm

can you get access to a noid light or are you sure there is no pulse at the injector?

Sugoi · Post by **Sugoi** » Sun Sep 23, 2012 10:23 am

Hi There,

I fogot to add that I have put a noid light on, that was how I was able to find out that the injectors were not firing.

I will also add that I changed the fuel filter yesterday, as I thought that might be restricting the fuel flow. I can hear and feel the fuel pump running and when I use a jumper on the diagnostic connector to jumper the fuel pump to ground so that it runs with the Key in the ON position,I can hear fuel being pumped in the hoses in the engine bay.

Also when I pulled the spark plugs to check spark, it was dry rather than wet with fuel.

I also did a compression test on cylinder 1 while I was there 160, not too bad for 185,000 km I guess.

So that's a bit more information on the testing that I have done.

Any more ideas?

Can I just swap in another computer, and if so what do I need to check on it with regard to comatibility, will any B6 computer work?

sprsta · Post by **sprsta** » Sun Sep 23, 2012 11:05 am

any MX5 Auto B6ZE ecu will work, but it has to be auto as the TPS is different for controlling the trans

WideOpenThrottle · Post by **WideOpenThrottle** » Sun Sep 23, 2012 11:53 am

Have you got power to the injectors & to the ECU?

WideOpenThrottle · Post by **WideOpenThrottle** » Sun Sep 23, 2012 12:40 pm

These pics might help.

WideOpenThrottle · Post by **WideOpenThrottle** » Sun Sep 23, 2012 12:53 pm

and more

Sugoi · Post by **Sugoi** » Sun Sep 23, 2012 1:42 pm

sprsta

Thanks for the info about making sure that I get a computer from an auto.

The code label on the computer from my MX-5 is:

B66B
EGI
B66B 18 881B
079700-3051

WideOpenThrottle
Thanks for the wiring and control diagrams.
We were getting power to the Injectors, but they were not switching. From what I can figure the ECU was not grounding them. We had 12 Volts on both pins of the injector with the key ON.

We checked all the ground connections, and the looked good, we took them off and cleaned them and put back on again and all OK. The two we checked were in the engine bay on in front of the passenger side.

I figure we had power to the ECU as the engine was cranking and we had good spark - is that a fair assumption?

I saw some instructions on Miata.net about getting the check engine light to flash a fault code, and tried that, but it did not work. (It is meant to flash one set of flashes, then a gap, then a second set, to give a 2 digit number.)

SLYDIT · Post by **SLYDIT** » Sun Sep 23, 2012 6:27 pm

A multi meter will not really register the voltage correctly especially with the negative switching of an injector. You SHOULD have 12 volts on both injector pins when the ignition is on but not cranking.
Also you need to use a good quality LED light to check the injector channel as a normal test lamp cannot respond fast enough.(we are talking about 4 milli seconds here)
try wiggling the wiring loom to the engine while cranking to see if its a bad plug or broken loom wire especiallty where the loom cable ties to the engine.

I am pretty sure the ecu has seperate earths for the injectors.(it has multiple ecu earths).
The ecu earth plug is under the windscreen wiper motor and washer bottle on the chassis rail.. it is a large flat white plug with about 6-8 wires in it, and i have heard of them failing requiring the wires to be cut off the plug and re-crimped into a lug....

so before replacing the ecu i would unplug the main ecu plug and check that ALL the earths have continuity between the chassis and the plug pin. and also that the two injector switching wires have continuity from the injector to the ecu plug.

if thats all good and you still have no fault codes then replace the ecu.

I cant help but get a nagging feeling its a CAS fault though..

Sugoi · Post by **Sugoi** » Mon Sep 24, 2012 1:28 pm

Hi Slydit,

Thanks for you suggestions.

With regard to the injectors the power stayed +12V on both pins even when cranking. We put a "noid" light in place of the injector, and it did not flash when cranking.

I will check the earths that you suggested, and verify that they are all OK. I will need to get some longer wire to check injector to ECU continuity, but will do that and see how that goes.

We were still getting spark when cranking, would this be the case if we had a faulty CAS (presuming you mean Crank Angle Sensor?) Is there any way to test this sensor?

Bye for now

SLYDIT · Post by **SLYDIT** » Mon Sep 24, 2012 6:36 pm

how did you get on checking ALL the earths? remember theres more than 1 ecu earth.
For starters, theres 2A,2B,2C,2D to check on the ecu plug to ground
i bet you a chocolate fish that it isnt the ecu, but some external factor like a bad sensor/oil pressure switch or even a signal from the auto trans ecu...
do you have an alarm/immobiliser fitted?

may be a long shot but there is an airflow cutoff switch in the airflow meter so if the engine stalls it cuts the fuel to the engine... you may have a faulty air flow meter...
if some nice person has the wiring diag for the AFM, you could jumper across the switch and see if it fires... (I THINK the pins are Fc and E1 on the connector that need shorting but not 100% on that.)

WideOpenThrottle · Post by **WideOpenThrottle** » Mon Sep 24, 2012 7:27 pm

Here's what i got

WideOpenThrottle · Post by **WideOpenThrottle** » Mon Sep 24, 2012 7:41 pm

My old airflow meter had corroded pins.

I assume you have checked all fuses [engine bay & under the right dash].

Has your cas moved by any chance?

Has the crankshaft pulley key sheared? [timing could be out].

Has your timing belt broke?

I have even seen a stuck flapper vane in an AFM.

thinking,thinking!

SLYDIT · Post by **SLYDIT** » Mon Sep 24, 2012 8:46 pm

theres a heap of similar posts on the various forums which turned out to be a faulty injector loom. as mentioned above the loom can break where it is cable tied to the inlet manifold

Sugoi · Post by **Sugoi** » Fri Sep 28, 2012 1:09 pm

Hi Guys,

Thanks for the ideas of what to check. I now have a heap of extra things to check and more of an idea of where to look.

The car is stashed at a friends place out of town, so I will head out this weekend with the diagrams a photos of what to check and see if I can find the problem and drive it home.

Will keep you posted with results.

Sugoi · Post by **Sugoi** » Mon Oct 01, 2012 11:26 am

Hi There,

After spending a couple of ours unplugging most of the electrcial connectors I could find, I still have no luck.

I did manage to get the diagnostic port to flick me up a code on a small 12v light that I had. It was blinking 2. From what I can see that means it could be the Crank Angle Sensor, so I am going to look at replacing this with a new one and see if that helps.

I am getting good spark still. If it was the CAS, is it likley that I would get spark, but not fire the fuel injectors?

WideOpenThrottle · Post by **WideOpenThrottle** » Mon Oct 01, 2012 2:30 pm

I have a spare CAS if you need one.

Sugoi · Post by **Sugoi** » Sun Oct 14, 2012 8:44 pm

Hi Guys,

Thanks for your help, I have replaced the CAS and now my MX5 is running again. Now my next job is to set the timing.

Bye for now,

Aaron

ECU Compatibility for 1992 NA 1.6 Engine

ECU Compatibility for 1992 NA 1.6 Engine

CAS Maybe?

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