- My model of MX-5 is: __ 1990 mk1 Eunos
- I’m based near: __ Warrington
- I’m looking for technical help or recommendations on: __
While trying to track down my misfire, I took out the injectors to inspect them. All seemed fine, and then I put them back in wrong and pinched two of the top gaskets and they started leaking. Ordered a replacement injector rubber set and fitted them today and that fixed the leak. I’ve primed the fuel pump by shoring F/P to GND in the diagnostic box and the pump is humming like it’s on. All this, now it won’t start.
I also noticed spark plugs 3 and 4 had petrol on them after I pulled them out, so thinking there’s petrol on the tops of those cylinders, I took out all the plugs and left if for a few hours to evaporate off. Reassembled, tried again and still no start.
Other than that, I recently took out, inspected, cleaned and refitted my CAS and rocker cover (both with new gaskets) which meant I had to unbolt the coil pack and shuffle it around.
Timing - is it possible to put the CAS in upside down/180 out of phase, or ruin the sensor entirely?
Spark - Is there possibly something I messed up with the coilpack, HT leads or spark plugs?
Fuel - have I somehow created and airlock in the system, or blocked/broken the injectors?
Compression - thats probably fine.
Did you disconnect the fuel pipes from the rail? If so, have you put the back the right way round?
The CAS will only seat in place one way. If it was 180 degrees out, it will not push into place. It’s possible you have put the leads on the wrong coil packs. It’s cylinders 2&3 on the left. 1&4 on the right. Have you got a timing light? Can you check the spark timing is at 10 degrees?
Didn’t touch the fuel pipes to the rails, so they’re definitely still on the correct way around.
Leads are in the correct places. I always take a picture on my phone and refer back to it when reinstalling. Hooked up to the coil pack 3, 2, 1, 4 from left to right.
I don’t have a timing light. Will a generic £20 one from amazon do the trick, if I were to get one?
Is checking spark by pulling the plugs, connecting them to a HT lead and touching the threads and/or tip to a ground, and cranking a reliable way to check? I tried it and didn’t get a spark with any plug, so I figured I was just doing something wrong.
Read up some more, and thought I had figured it out - that it was an issue where I never marked my CAS position before taking it out. While still an issue, I went and fiddled with the CAS in multiple positions and I still couldn’t get it to start. I tried 10-12 different positions across the CAS span of movement. Even though guessing the position would make it run badly, I figured I could have at least started it like this.
I tried testing for spark again, testing a dozen or so different ways, swapping plugs, leads, coilpack position, grounding locations, etc. and never got a spark.
Took out the coilpack and tested the 2/3 and 1/4 resistance and got about 11.5k Ohms on each, so all good there.
I also bench tested the CAS based on info from this link:
https://www.rivercityroad.com/garage/cas.htm
I took a normal mains 12V DC power supply with a barrel connector for 12V power to the CAS, using crocodile clips to hook up to the pins. Then with a digital multimeter I moved the rotors into place and probed for a 5V output when it was within range of the hall effect sensor, and 0V when it wasn’t.
At first I got 0.5-0.8V output from both sensors, then for a very short time I got the correct 5V output (for about 10 seconds only), and then since then the output remained below 0.1V. Haven’t been able to get it back since.
I don’t have access to an oscilloscope, but even without it I believe I should get a steady 5V output if the hall effect sensor is triggered. Sounds like the CAS is broken to me, but would be great to have someone sanity check me before I start throwing parts at it. Does this sound like a dodgy CAS?
You should be able to read a reliable 5 volt on and off output from the CAS as you rotate it by hand.
It was the airflow meter all along, CAS is fine lol. I broke the AFM when I tried to dismantle the electronics enclosure it to clean it better. Unplugging it made the car start up (albeit very roughly).
As a side note my bench test was actually bogus. Rob from mx5bitz on ebay told me his bench test was to check continuity under those circumstances, not voltage. Testing it like that indicated my CAS was actually fine.
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