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NA Miata intermittant spark problem on startup. HELP!

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markdp1 mark depersio
riverwoods, Illinois, USA   USA
New member here with a problem. Former shop owner who is stumped. My 1990 miata out of the blue refused to restart one day. Diagnosed as no spark. Had to tow to dealer. Dealer can't fix it! Symtoms: Turns over just fine. And starts perfectly, SOMETIMES. When running, it's perfect. No stalling, hesitation, etc. You can start it over and over just fine until it won't. Then maybe it will start tomorrow or an hour later. Hot or cold doesn't matter. This is ONLY on start up. Checked connections at ECU, igniter, coils, cam position sensor, TPS. No luck. If someone can point me in the right direction I would appreciate it. I have an enthusiasts manual and followed the ignition trail of sensors but I don't have the special service tools the manual references. Please help.

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Mazdasportster James H
Chesterland, OH, USA   USA
I had an Austen Healey that did this. It had a hairline crack in the coil. Whenever it was humid it woyld short. I'd look for an intermittent short in the wiringcoil, etc.

Skye Avatar
Skye Webmaster Skye Nott
Vancouver, BC, Canada   CAN
1964 Vespa VNB 125
1966 MG MGB "The Bomber RIP"
1983 Suzuki MC GS750E "Kate"
1986 Merkur XR4Ti "The Rally Car"    & more
The ignition system has a high-voltage (coil to plugs) and low-voltage (distributor/ecu to coil) side. When it's not starting, pull a plug and lay it next to the block, turn over the car and see if there's any spark. If not, check the coil is getting voltage. Try applying voltage to the coil low tension side, then when you remove the power it should generate a spark at the plug (collapsing coil field). If it all works but the car won't start, then the low voltage side isn't getting the correct signal to "open" the connection from the ECU or sensors. Also check the resistance across the coil LT (low tension aka voltage) terminals, it should not be open (infinite resistance)

There are a couple of articles in the Library that might help:

http://www.mx5world.com/article/spark-tester.html

http://www.mx5world.com/article/understand-ignition.html

HTH



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99TexasMiata Paul C
Georgetown, Texas, USA   USA
I have a 1999 NB, white, tan top, it is the best car in the world, and I'm lucky to own it.

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Rewind Les W
Leeds, Yorkshire, UK   GBR
I had exactly the same problem, it took me three weeks of checking by changing out parts with second hand ones from a scrap 1990 MX5. It turned out to be an intermittent fault with the cam angle sensor mounted on the back of the inlet camshaft. Changed it for a known good one and it has never missed a beat since. Easy to find secondhand ones on Ebay.

Skye Avatar
Skye Webmaster Skye Nott
Vancouver, BC, Canada   CAN
1964 Vespa VNB 125
1966 MG MGB "The Bomber RIP"
1983 Suzuki MC GS750E "Kate"
1986 Merkur XR4Ti "The Rally Car"    & more
Great tip, thanks for posting that Les!



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Rewind Les W
Leeds, Yorkshire, UK   GBR
No problem Skye, it was a bit late considering the original query was from 2014 but I only just joined! Hope the tip helps someone else, the problem was driving me mad, I had only just bought the car, a low mileage early Eunos and changed everything I could think of including the ignitor unit, the plugs, plug leads, coil pack and ECU before trying the Cam Angle Sensor.

Skye Avatar
Skye Webmaster Skye Nott
Vancouver, BC, Canada   CAN
1964 Vespa VNB 125
1966 MG MGB "The Bomber RIP"
1983 Suzuki MC GS750E "Kate"
1986 Merkur XR4Ti "The Rally Car"    & more
No problem, lots of people come to this website through Google and other search engines, so the answer could be very helpful to other Miata/MX5/Eunos owners. Feel free to answer any other old unanswered questions you happen to see winking smiley

Skye



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Rewind Les W
Leeds, Yorkshire, UK   GBR
Just one more comment, the person who posted the original query on this said he did not have the proper diagnostic tools. Since I traced my problem to the Cam Angle Sensor I have bought a diagnostic tool which consists of a 12V LED on two bits of wire and also a short piece of wire for bridging out terminals To use it is simplicity itself. Bridge out terminals GND & TEN in the diagnostics socket using the short piece of wire. This sets the diagnostics to test mode. Then connect the negative terminal of the LED to the terminal marked FEN and the positive lead on the LED to the +B terminal (note that the +B terminal is connected directly to Battery Positive and care must be taken not to short this to Ground which will cause a short circuit). Switch the ignition on but do not start the engine. Observe the LED which should illuminate for three seconds then go out, this confirms that the self diagnostic system is working. If no more flashes occur then there are no faults to be found. If it produces a further series of flashes the ECU computer has detected one or more malfunctions in the input or output engine control sensors. The fault code for the Cam angle Sensor is 02 which would be shown as two short flashes on the LED. Long (1.2 second) flashes represent 10's digits and short flashes (0.4 seconds) represent 1's digits. In the case of the Idle Speed Control valve which was faulty on mine it showed fault code 34 which is 3 long flashes followed by 4 short flashes. Simplicity itself and the kit cost me just £9.98. If I had had this when the Cam Angle Sensor failed it would have saved me much time and trouble.

I bought mine from Autolink UK who trade on Ebay. Look up Ebay item number 400429915759 if anyone wants to buy one.

Being of a certain age (69) I was brought up on Carburettors, Contact Breakers and simple stuff like that and I had always been wary of getting involved in the "new fangled" electronics stuff. However, it was a pleasant surprise to find that the diagnostics on the early Mazda MX5 cars are simple and easy to diagnose with some quite basic kit. Apparently the Mk 2 cars from 1998 to 2000 model years are equally simple using the same kit but the codes are four digit instead of two digit. On the Mk 1 there are 17 different fault codes for the various faults whihc can be diagnosed.

I hope members find this useful.

GT6M Avatar
GT6M Markus Bewley
Scaryport, Cumbria, North West Englandshire, UK   GBR
As above, I had the same, tried every thing,
intermittant, fault most of the time, butt some times just would,nt start at all.



It was the key, apparently, they got a code in em,
check by dooing a spare key test.

a Marra of mine in the trade, said, bung the old key in the freezer for a day,

it worked when tried it, butt, with that key, its still intermittant

M

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