MX5 mk1 dying immediately after start
Discussion
Hi guys
'94 NA 1.8 UK spec
Drove 300 miles without a problem up the country. Decided to stop in a pub 2 miles from home for a bit of grub, then hop in my car to go home.
The car starts, then dies immediately. At first I thought it was the aftermarket immobiliser, which I bypassed. No avail. (Worth noting it's a BPF8 ECU). Reinstalled the immobiliser as I ruled that out.
I tried swapping my CAS with my spare "get me home" CAS, no avail. Checked spark, had spark. Checked vacuum, no leaks or intake ducting hanging off. Lamda & MAF all plugged in and secure. Confirmed it wasn't just typical vacuum/idle issues as it died even when holding in the throttle. It behaves like something is cutting the ignition. Ruled out fuel by forcing the pump on with the diag connector.
Now - here's the kicker (and wondering if I broke something by being lazy...). Before I went to the pub, I decided to fit a wheel from an NB with an airbag, converted the connectors over etc. Connected the new bag up and drove it to the pub without issues, no warning lights, etc. In my infinite wisdom to save time reprogramming my radio, I decided to simply unplug the Airbag fuse under the bonnet, along with the ABS and BTN (though that took out the radio anyway...). Just wondering if my symptoms would at all be caused by a failing airbag computer or if I could've done something to the ECU doing that? What's the first port of call to check when diagnosing this bizarre electrical issue? Worth noting the airbag light illuminates then goes out as normal
Naturally, car doesn't start without the airbag plugged in either.
'94 NA 1.8 UK spec
Drove 300 miles without a problem up the country. Decided to stop in a pub 2 miles from home for a bit of grub, then hop in my car to go home.
The car starts, then dies immediately. At first I thought it was the aftermarket immobiliser, which I bypassed. No avail. (Worth noting it's a BPF8 ECU). Reinstalled the immobiliser as I ruled that out.
I tried swapping my CAS with my spare "get me home" CAS, no avail. Checked spark, had spark. Checked vacuum, no leaks or intake ducting hanging off. Lamda & MAF all plugged in and secure. Confirmed it wasn't just typical vacuum/idle issues as it died even when holding in the throttle. It behaves like something is cutting the ignition. Ruled out fuel by forcing the pump on with the diag connector.
Now - here's the kicker (and wondering if I broke something by being lazy...). Before I went to the pub, I decided to fit a wheel from an NB with an airbag, converted the connectors over etc. Connected the new bag up and drove it to the pub without issues, no warning lights, etc. In my infinite wisdom to save time reprogramming my radio, I decided to simply unplug the Airbag fuse under the bonnet, along with the ABS and BTN (though that took out the radio anyway...). Just wondering if my symptoms would at all be caused by a failing airbag computer or if I could've done something to the ECU doing that? What's the first port of call to check when diagnosing this bizarre electrical issue? Worth noting the airbag light illuminates then goes out as normal
Naturally, car doesn't start without the airbag plugged in either.
If it starts at all it isn't an immobiliser issue. I think the airbag thing is a red herring, I can't believe a car that age would have any link between the airbag and engine ECU. It sounds like a fuel issue, easy enough to test if you have a can of 'easy start'. Open the airbox and take the filter out, squirt a bit in. Get someone to crank the engine over and when it fires up, pulse some more squirts in there. If it keeps running then you know everything else is fine, it's just not getting the fuel it needs.
There's a fuel filter at the back under the car, near the tank, it might be blocked.
There's a fuel filter at the back under the car, near the tank, it might be blocked.
I had something broadly similar recently on my newly acquired NB. Used it for a week no problem, then one day within 5 mins of starting it died and wouldn't restart.
Long story short it turns out the drain hole by the filler cap is clogged and water has been getting into the fuel lines. When I removed the spark plugs they were completely soaked (with water). I ended up needing to drain the entire fuel tank, and replace the fuel filter. Put 5l of clean fuel in and tried to crank the engine. It wouldn't start but it sounded like it really wanted to, just wasn't getting the necessary compression. Ended up towing it behind my derv up to just over 30mph, put it in second gear and dumped the clutch. Car started, rough idle for a few minutes but is now completely back to normal. Starts and runs fine.
So maybe check the spark plugs and see if there's fuel there or perhaps water ingress? It has been raining a lot recently...
Long story short it turns out the drain hole by the filler cap is clogged and water has been getting into the fuel lines. When I removed the spark plugs they were completely soaked (with water). I ended up needing to drain the entire fuel tank, and replace the fuel filter. Put 5l of clean fuel in and tried to crank the engine. It wouldn't start but it sounded like it really wanted to, just wasn't getting the necessary compression. Ended up towing it behind my derv up to just over 30mph, put it in second gear and dumped the clutch. Car started, rough idle for a few minutes but is now completely back to normal. Starts and runs fine.
So maybe check the spark plugs and see if there's fuel there or perhaps water ingress? It has been raining a lot recently...
Open the diag box and insert a bridge (paperclip) between 'FP' and 'GND'.
This permanently energises the fuel pump. See if it runs.
If it does, the problem is your fuel pump not getting the 'run' signal.
The fuel pump gets powered initially (to prime the system) via a different circuit, so the engine will start and run for a few seconds till the pressure in the lines to the inejctors is exhausted.
The second, fuel pump 'run' circuit is fed through a seperate feed from the ignition, and also relies on the signals from the AFM/MAF depending on whether its a 1.6 or 1.8.
On a 1.6 the circuit is made by the flapper in the air flow meter being opened by the passing airflow. Even sometimes mounting the airflow meter upside down can stop this working.
This permanently energises the fuel pump. See if it runs.
If it does, the problem is your fuel pump not getting the 'run' signal.
The fuel pump gets powered initially (to prime the system) via a different circuit, so the engine will start and run for a few seconds till the pressure in the lines to the inejctors is exhausted.
The second, fuel pump 'run' circuit is fed through a seperate feed from the ignition, and also relies on the signals from the AFM/MAF depending on whether its a 1.6 or 1.8.
On a 1.6 the circuit is made by the flapper in the air flow meter being opened by the passing airflow. Even sometimes mounting the airflow meter upside down can stop this working.
Didn’t think of water in the fuel but definitely got fuel pump working. Hard to think it could possibly be that though, just filled up a full tank at Morrison’s prior to this episode! Have bled some fuel off from the send line into w Jerry can - anything I should look for to confirm dirty fuel?
New ECU is giving the same behaviour unfortunately. Took some video footage to demonstrate what’s going on - you can hear it’s not intake related with the throttle not keeping it alive.
MAF is all plugged in and working, also tested a known good CAS
https://youtu.be/OwoDJ8isMs4
https://youtu.be/VhnhC0VeG7U
Interestingly my tachometer just stopped working which is very strange....
New ECU is giving the same behaviour unfortunately. Took some video footage to demonstrate what’s going on - you can hear it’s not intake related with the throttle not keeping it alive.
MAF is all plugged in and working, also tested a known good CAS
https://youtu.be/OwoDJ8isMs4
https://youtu.be/VhnhC0VeG7U
Interestingly my tachometer just stopped working which is very strange....
I had just filled up my tank as well- but enough water got in to cause issues. I suppose the problem is water and petrol separate so a small quantity doesn't just dilute the fuel.
From the video it's hard to say but regarding water in the fuel I discovered water on the spark plugs and worked backwards from there until opening up the filler cap and realising how much water was in it. I also discovered under the boot on the L/H side there was a lot of water presumably also from the filler cap area but I can't figure out how it was getting in.
From the video it's hard to say but regarding water in the fuel I discovered water on the spark plugs and worked backwards from there until opening up the filler cap and realising how much water was in it. I also discovered under the boot on the L/H side there was a lot of water presumably also from the filler cap area but I can't figure out how it was getting in.
Did a flow and called auto link under suspicion of coil pack death, and the symptoms of weak spark in an mx5 are there. Car wants to start, cuts out when it gains RPM. If you do it with throttle, it dies quicker. Doesn’t want to restart immediately but if you let it charge/settle with ignition on it will go again.
Then of course I completely forgot what kills coil packs on 1.8s - ignition on but engine off for extended periods of time. Got stuck on a slip road on the M25 for nearly an hour so of course kept ign on so i still had fans and didn’t burn through petrol! Must’ve done the same when testing my airbag installation - it’s possible that was the final straw that broke the camel’s back.
Coils should arrive on Thursday with fresh plugs and leads - will let you know the result.
Annoying that in an attempt to save fuel and eek the car a few more miles out to get to my parents I’ve cost myself more than just filling up at motorway services and preventing fuel anxiety. Bugger!!!!!
Forgot to mention, had the plugs out when I checked for spark and looked all fine and dandy
Then of course I completely forgot what kills coil packs on 1.8s - ignition on but engine off for extended periods of time. Got stuck on a slip road on the M25 for nearly an hour so of course kept ign on so i still had fans and didn’t burn through petrol! Must’ve done the same when testing my airbag installation - it’s possible that was the final straw that broke the camel’s back.
Coils should arrive on Thursday with fresh plugs and leads - will let you know the result.
Annoying that in an attempt to save fuel and eek the car a few more miles out to get to my parents I’ve cost myself more than just filling up at motorway services and preventing fuel anxiety. Bugger!!!!!
Forgot to mention, had the plugs out when I checked for spark and looked all fine and dandy
Edited by mrciarano on Tuesday 25th June 19:15
Could be the ignitor too - I can't 100% remember if the 1.8 coil is the same as the 1.6 coil, but if it is, the ingitor is a seperate unit to the coilpack, on the RHS front inner wing. This signal from the ignitor also drives the tacho (yellow wire?).
If the ignitor is burnt out, you will get no/weak spark and no tacho signal either. They don't like getting hot, I fried one on my turbo car.
If the ignitor is burnt out, you will get no/weak spark and no tacho signal either. They don't like getting hot, I fried one on my turbo car.
Happy days - found the tach fault - looks like I killed a dying tach signal wire from the coil pack loom connector just under the brake servo. It's not that easy to get to so I wrapped a wire along the lambda sensor wire from the coil pack/temp sensor loom connector and spliced into the ign - wire underneath the diagnostics connector.
"Get me home" kind of fix as the loom really isn't easy to get to without taking the braking system apart - and I figure if I have plans to turbo it eventually I may as well make/refurb my own loom to put in the car with a megasquirt ECU. As far as get me home fixes go, if you had never seen an MX5 1.8 engine bay before, you'd think it's factory.
"Get me home" kind of fix as the loom really isn't easy to get to without taking the braking system apart - and I figure if I have plans to turbo it eventually I may as well make/refurb my own loom to put in the car with a megasquirt ECU. As far as get me home fixes go, if you had never seen an MX5 1.8 engine bay before, you'd think it's factory.
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