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I have not alot of knowledge about wiring or eunos roadsters so ill try to explain the issue as well as i know it. I have a 1992 Eunos Roadster 1.6L, it has an aftermarket immobiliser fitted the ignition barrel has been changed before by previous owner. The issue with the car is it only starts and runs very rarely. Most of the time it fires up for a second and then completely cuts out. It has fired up, idled for a long time and even dríven up and down the driveway with no issues. The previous owner said it could be an immobiliser issue but that wouldnt explain why its starting up. Another thing i have noticed is the buzzing noise when u have the car key in the third position comes on sometimes but normally doesnt make a sound and it sometimes makes a small sound going on and off when the car is on and is running fine. I know its not much to go on but hope it helps, cheers

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Probably best to find a way of getting it to an auto electrician with experience of Jap cars of the 80s/90s. There's nothing very special about NA MX5s. They're pretty generic Jap electrics of the time.

If you want to play about there are a few pathways you might check. Others here might suggest other ways to diagnose.

First is the AFM. It may be faulty. Detach the plug from the AFM and see if it runs.


Next is the fuel circuit. The buzzing noise you heard is probably the fuel pump, it's in the fuel tank behind the driver's seat. There is a diagnostic port behind the left headlight. Open that up and span the F/P and GND ports with a paper clip. Then switch on the ignition (don't start it) and listen for the sound of the fuel pump running. If not then there's something going on with the fuel electrical circuit or the pump itself.


Next is the immobiliser. Old immobilisers are an absolute pain. They intercept wires all through the system and many are now suffering from dry/cracked solder joints. Find where the immobiliser intercepts the main ignition wire from the key barrel. Make up a temporary by-pass with a wire with a simple switch in it. Then try starting with the switch off then on. If that fixes it then, at a convenient time, I'd get an auto leccy to remove the immobiliser and restore all the intercepted wires. TBH I've had a by-pass wire and switch in mine for 12 years waiting for me to get round to fixing it properly.

Good luck

Omg thank you so much, this is perfect. Ill get onto testing these right away. Does a faulty immobiliser really let the car still run even tho i dont have the immobiliser key/chip? Also the buzzing was more of an alarm in the dash and not the pump behind me.

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manga_blue wrote:Probably best to find a way of getting it to an auto electrician with experience of Jap cars of the 80s/90s. There's nothing very special about NA MX5s. They're pretty generic Jap electrics of the time.

If you want to play about there are a few pathways you might check. Others here might suggest other ways to diagnose.

First is the AFM. It may be faulty. Detach the plug from the AFM and see if it runs.

afm3.jpg

Next is the fuel circuit. The buzzing noise you heard is probably the fuel pump, it's in the fuel tank behind the driver's seat. There is a diagnostic port behind the left headlight. Open that up and span the F/P and GND ports with a paper clip. Then switch on the ignition (don't start it) and listen for the sound of the fuel pump running. If not then there's something going on with the fuel electrical circuit or the pump itself.


Next is the immobiliser. Old immobilisers are an absolute pain. They intercept wires all through the system and many are now suffering from dry/cracked solder joints. Find where the immobiliser intercepts the main ignition wire from the key barrel. Make up a temporary by-pass with a wire with a simple switch in it. Then try starting with the switch off then on. If that fixes it then, at a convenient time, I'd get an auto leccy to remove the immobiliser and restore all the intercepted wires. TBH I've had a by-pass wire and switch in mine for 12 years waiting for me to get round to fixing it properly.

Good luck

Omg thank you so much, this is perfect. Ill get onto testing these right away. Does a faulty immobiliser really let the car still run even tho i dont have the immobiliser key/chip? Also the buzzing was more of an alarm in the dash and not the pump behind me.

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Basically there's no telling what an old aftermarket immobiliser will do. Combination of faulty joints, dying circuitry and the likelihood that someone has buggarised around with it as well

Non electrical people working to fix electrical problems rarely concludes well.

Red_Bullet wrote:Non electrical people working to fix electrical problems rarely concludes well.

Wise words, im looking into getting an auto electrician to have a look

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[i][i]Another thing i have noticed is the buzzing noise when u have the car key in the third position comes on sometimes but normally doesnt make a sound and it sometimes makes a small sound going on and off when the car is on and is running fine.[/i][/i]

Could be the fuel pump working