MX 5 Mrk 1 1.6 1990 jap import cranks, starts, dies then just cranks.

[Robbie260]

I’m so I have had an ongoing project for a customer which has been driving me round the bend a bit. It was a car that was sent for restoration not finished and I took on putting it back together and getting it working again. All back together again but I’m a bit stumped as to were to go next with it. I have run through all the following and checked the MAF sensor and it kicks in the fuel pump when opened. Scratching my head a bit now in all honesty.

https://www.miata.net/garage/ECU_Pin-Out.png

Link to the ecu pin out diagram I was using for reference. Didn’t have a high resolution multimeter with me so unfortunately all readings are in just whole numbers.

Have any ideas as where to go from here? The full set of ECU and relays has been changed for ones out of a known good car of the same age with no joy either. There was an aftermarket immobiliser which I believe I have successfully bypassed but I could be missing something any help appreciated.

It was found the fuel lines were on the wrong way round this has now been sorted and fuel flows as it should.

 

[iNf]

Crank position sensor?

 

[Misterg]

It was found the fuel lines were on the wrong way round this has now been sorted and fuel flows as it should

Is the original ECU back in the car since you found this?

Are you getting 12V at the connectors to each injector?

(If you're getting a spark, I *think* the cam angle sensor is OK - don't think there's a crank angle sensor on one this old)

 

[Blobber]

10 volts on cranking sound low?

 

[redlig]

What does the battery voltage drop to when you crank the engine ? If it is an excessive drop check starter motor bearings.

 

[Robbie260]

Is the original ECU back in the car since you found this?

Are you getting 12V at the connectors to each injector?

(If you're getting a spark, I *think* the cam angle sensor is OK - don't think there's a crank angle sensor on one this old)

Aye original ecu is now back in same result.

I’ll have a check of that tonight at the injectors but was showing 12v at ECU pins unplugged.

 

[Robbie260]

10 volts on cranking sound low?

Battery was a tad flat at that point had been trying a while.

 

[Robbie260]

What does the battery voltage drop to when you crank the engine ? If it is excessive check starter motor bearings.

Was dropping from 12v to 10v when battery was well charged.

 

[redlig]

Was dropping from 12v to 10v when battery was well charged.

Hmm .Can you piggy back another good battery . I had an electronic ign on my trials car that was a ba*****d to start on the starter but would run on a push start . Changed S/M and all good. The bat voltage was just below the requirement for the ign to fire. Slim chance but .......

 

[Blobber]

I think a lot of ECUs like 12v on crank, much lower and they won't go

 

[Robbie260]

Hmm .Can you piggy back another good battery . I had an electronic ign on my trials car that was a ba*****d to start on the starter but would run on a push start . Changed S/M and all good. The bat voltage was just below the requirement for the ign to fire. Slim chance but .......

Aye still won’t do it with a running van attached via jump leads so not the issue I’d say. @Blobber

 

[tom2207]

immobiliser.

 

[atomant48]

Is it a B6 or a BP engine ? If the former it is the same as my 323. They have an issue where the crank keyway wears and knocks out the timing. There is a way of telling (big nose vs small nose) cranks whether it is an earlier or later one and therefore whether it’s likely to be the issue.

 

[Hotstuff]

Was the engine known to be running before it was passed to you for restoration?

Is the ignition key coded?

I realise she’s too old for OBDI/II but does it have a blink code for reporting faults?

 

[dave h 2]

As this motor is new to you - what's the compression like? All you need is a bit of valve recession or busted rings and it won't work.
If this motor still starts then stops can you dribble fuel into it and keep it going?
Is there a water temp sensor, have you tried disconnecting or grounding it's lead?

 

[Cobbler]

Is it a B6 or a BP engine ? If the former it is the same as my 323. They have an issue where the crank keyway wears and knocks out the timing. There is a way of telling (big nose vs small nose) cranks whether it is an earlier or later one and therefore whether it’s likely to be the issue.

The number of holes/slots in the front pulley, I think it’s 6 & it’s the long nose. I’ll have a look in the book later. We had a problem with my son’s MX5 trying to start it after a rebuild. Turned out it was the crank sensor, all looked ok, but with a scope on it suddenly it would give allsorts of funny waveforms & timing when you tried to start it. Changed for another & started straight away.

 

[Robbie260]

Is it a B6 or a BP engine ? If the former it is the same as my 323. They have an issue where the crank keyway wears and knocks out the timing. There is a way of telling (big nose vs small nose) cranks whether it is an earlier or later one and therefore whether it’s likely to be the issue.

The key way was apparently refurbished during the restoration due to slop.

 

[Misterg]

If it runs on Easy-Start (etc.) then ignition is OK. Fuel pump is now running the right way, so that leaves injectors - If you have 12V on them, then check ECU grounds. Might be worth using a test light, rather than a meter to check the 12V to make use it's a 'real' connection.

Have you got access to a 'scope or anything to see if the injectors are pulsing?

 

[qwakers]

worth testing the injector feeds with noid lights

 

[Robbie260]

If it runs on Easy-Start (etc.) then ignition is OK. Fuel pump is now running the right way, so that leaves injectors - If you have 12V on them, then check ECU grounds. Might be worth using a test light, rather than a meter to check the 12V to make use it's a 'real' connection.

Have you got access to a 'scope or anything to see if the injectors are pulsing?

Unfortunately not really I do have a power probe with a wave form function that may be able to get a reading