Eunos Roadster MK1 - heat sensor broke, loss of power since
Discussion
Hi all,
I am new to PistonHeads and need some help diagnosing an issue with my 'baby' please.
Eunos Roadster, Mk1, 1.6
A few weeks ago I was driving on a motorway and all of a sudden heard a loud banging under the car. I managed to pull over and could see a cable hanging down which was hitting the road and the underneath of the car.
Unfortunately due to the length of my drive the cable eventually came off as I couldn't reach it to tie it to hold, and it turns out it was the heat sensor, leaving a considerable hole in the CAT. Naturally my car drove like she was misfiring but I managed to get home.
I have spent the past two months driving on rubbish roads with major pot holes and think the sensor just rattled itself free.
Initially my garage welded the hole in the CAT and said the sensor wasn't needed as there is no warning light on the dash. But the car kept losing power, hot / cold running, low or fast speeds. This happens a few mins after starting the car or constantly while driving.
So the garage cut a new hole in the CAT and attached a lambda sensor. Same problem. A diagnostic tool was used and a 'short' fault was found with the air filter housing, so this was all replaced. Same problem. Another fault found and the water temperature sensor was replaced. Same problem. This is now a few weeks on, can't be good for the car, she is drinking petrol and costing me a small fortune trying to resolve.
My garage are great and trying to help with this but are somewhat stumped, they now think it's due to the ECU.
The problem is exactly the same from when the heat sensor first came off, so I'm convinced it's to do this with and not the ECU.
She massively over idles and then drops almost to the point of stalling, so long as I keep pumping the accelerator she'll keep going. But I really need this fixing as there have been a few hair raising moments where she just stops at any speed, and ie: on dual carriage ways etc.
The spark plugs have been changed and I'm going to put on new HT Leads.
I've been doing some research and have found drivers with similar problems but not identical. Changing camshaft and crank sensors have been mentioned but I don't want to just keep changing parts for the sake of it.
Can anyone please please help??
Thank you!
I am new to PistonHeads and need some help diagnosing an issue with my 'baby' please.
Eunos Roadster, Mk1, 1.6
A few weeks ago I was driving on a motorway and all of a sudden heard a loud banging under the car. I managed to pull over and could see a cable hanging down which was hitting the road and the underneath of the car.
Unfortunately due to the length of my drive the cable eventually came off as I couldn't reach it to tie it to hold, and it turns out it was the heat sensor, leaving a considerable hole in the CAT. Naturally my car drove like she was misfiring but I managed to get home.
I have spent the past two months driving on rubbish roads with major pot holes and think the sensor just rattled itself free.
Initially my garage welded the hole in the CAT and said the sensor wasn't needed as there is no warning light on the dash. But the car kept losing power, hot / cold running, low or fast speeds. This happens a few mins after starting the car or constantly while driving.
So the garage cut a new hole in the CAT and attached a lambda sensor. Same problem. A diagnostic tool was used and a 'short' fault was found with the air filter housing, so this was all replaced. Same problem. Another fault found and the water temperature sensor was replaced. Same problem. This is now a few weeks on, can't be good for the car, she is drinking petrol and costing me a small fortune trying to resolve.
My garage are great and trying to help with this but are somewhat stumped, they now think it's due to the ECU.
The problem is exactly the same from when the heat sensor first came off, so I'm convinced it's to do this with and not the ECU.
She massively over idles and then drops almost to the point of stalling, so long as I keep pumping the accelerator she'll keep going. But I really need this fixing as there have been a few hair raising moments where she just stops at any speed, and ie: on dual carriage ways etc.
The spark plugs have been changed and I'm going to put on new HT Leads.
I've been doing some research and have found drivers with similar problems but not identical. Changing camshaft and crank sensors have been mentioned but I don't want to just keep changing parts for the sake of it.
Can anyone please please help??
Thank you!
I had a 92 mk1 1.6 for ages with a decat pipe, the sensor was unplugged and cable tied to the PPF and it always worked fine. Given the amount of different sensor issues you're having it does seem more likely the main cause could be something like the ECU.
Have you considered either fitting a 2nd hand ECU from somewhere like Autolink UK, or sending yours off to somewhere like EcuTesting (I think - gets mentioned in Car Mechanics magazine a lot)?
Eg - £50 for a used one:
http://www.autolinkmx5.com/ecu-b64f-mazda-mx-5-16-...
Have you considered either fitting a 2nd hand ECU from somewhere like Autolink UK, or sending yours off to somewhere like EcuTesting (I think - gets mentioned in Car Mechanics magazine a lot)?
Eg - £50 for a used one:
http://www.autolinkmx5.com/ecu-b64f-mazda-mx-5-16-...
Edited by anonymous-user on Sunday 13th May 14:35
Hi JimSuperSix,
Thanx for the quick and helpful reply.
I've got her booked in to two different garages to see if they can work together to diagnose and resolve the issue.
The noise and how she is driving is exactly the same as when the heat sensor first came off, hence am not sure it's the ECU, but am more than happy for this to be eliminated. It's as if there is still a hole in the exhaust somewhere.
Am by no means an expert but have owned my baby for nearly 16 years so I know enough to get by and maintain and change the basics.
In my ignorance, if it was a heat sensor which was originally fitted and she was driving perfectly, but a lambda sensor is now fitted and she isn't, what is the difference?
Cheers eunosfan
Thanx for the quick and helpful reply.
I've got her booked in to two different garages to see if they can work together to diagnose and resolve the issue.
The noise and how she is driving is exactly the same as when the heat sensor first came off, hence am not sure it's the ECU, but am more than happy for this to be eliminated. It's as if there is still a hole in the exhaust somewhere.
Am by no means an expert but have owned my baby for nearly 16 years so I know enough to get by and maintain and change the basics.
In my ignorance, if it was a heat sensor which was originally fitted and she was driving perfectly, but a lambda sensor is now fitted and she isn't, what is the difference?
Cheers eunosfan
MX5parts call it an oxygen sensor and Autolink call it a lambda oxygen sensor:
https://www.mx5parts.co.uk/oxygen-sensor-aftermark...
http://www.autolinkmx5.com/oxygen-lambda-sensor-ma...
Might be worth a call to the guy at Autolink, he knows his stuff and might have a better idea what needs replacing based on the symptoms.
Also they sell a fault code reader for £5.80 which might be of use:
http://www.autolinkmx5.com/diagnostic-fault-code-r...
However if it's making a lot of exhaust noise that wasn't there before then it sounds like there is a leak or crack somewhere, any garage with a lift should be able to check the entire exhaust and locate the source of the increased noise.
https://www.mx5parts.co.uk/oxygen-sensor-aftermark...
http://www.autolinkmx5.com/oxygen-lambda-sensor-ma...
Might be worth a call to the guy at Autolink, he knows his stuff and might have a better idea what needs replacing based on the symptoms.
Also they sell a fault code reader for £5.80 which might be of use:
http://www.autolinkmx5.com/diagnostic-fault-code-r...
However if it's making a lot of exhaust noise that wasn't there before then it sounds like there is a leak or crack somewhere, any garage with a lift should be able to check the entire exhaust and locate the source of the increased noise.
Edited by anonymous-user on Sunday 13th May 19:32
The heat sensor is supposed to indicate an issue with the cat. However, most of the time, all it indicates is an issue with the heat sensor. The ecu does not use it at all. It contributes nothing at all to how the engine runs. It’s a simple circuit that lights a light on the dashboard when the sensor is overheated and fused by excessive exhaust heat supposedly due to a cat failure. It rarely is to do with a cat failure.
It will not be the cause of the error. It also can’t be replaced with a lambda/o2 sensor. Better to just disconnect it. Snip off the sensor and tie the cave up out of the way.
The first thing you need to check on your car is for dampnaround the ecu. It’s located under the carpet in the passenger footwell. It’s very common for the ecu to be damaged by water.
It will not be the cause of the error. It also can’t be replaced with a lambda/o2 sensor. Better to just disconnect it. Snip off the sensor and tie the cave up out of the way.
The first thing you need to check on your car is for dampnaround the ecu. It’s located under the carpet in the passenger footwell. It’s very common for the ecu to be damaged by water.
Hi all,
So the CAT, spark plugs and HT Leads were replaced but she is still over idling like mad - I got about a mile down the road and she over idled and then dropped. They checked the ECU and it isn't that. Started her up again a few hours later, sat stationary in a car park and she over idled again.
I needed the N/S window regulator replacing but apparently the original switch wouldn't work with it, so they replaced the switch with one they had, but this meant they had to adapt the O/S too. A few miles down the road the switch stopped working and I couldn't wind the window back up, I just had to keep trying until it worked.
I had to drive to Northampton so a good run, and she was parked for about 3.5 hours, I got back in her to leave and turned the key and nothing, she was dead, but the lights and radio worked. I also noticed that the warning light for the rear heated windscreen was on on the dash, it has never come on in 16 years as I don't actually have one, and the switch for it was lit up permanently. I checked the battery cables and the basics under the bonnet, tried again and she fired up. Again she over idled and dropped back down.
The radio also stops working when I use the wipers...
As the garage worked on electrics today (Fri) is tonights problem anything to do with the work they've done? They can't have her back in until next week and I am so p'd off with what has happened.
Any ideas please?
Thanx Eunosfan
So the CAT, spark plugs and HT Leads were replaced but she is still over idling like mad - I got about a mile down the road and she over idled and then dropped. They checked the ECU and it isn't that. Started her up again a few hours later, sat stationary in a car park and she over idled again.
I needed the N/S window regulator replacing but apparently the original switch wouldn't work with it, so they replaced the switch with one they had, but this meant they had to adapt the O/S too. A few miles down the road the switch stopped working and I couldn't wind the window back up, I just had to keep trying until it worked.
I had to drive to Northampton so a good run, and she was parked for about 3.5 hours, I got back in her to leave and turned the key and nothing, she was dead, but the lights and radio worked. I also noticed that the warning light for the rear heated windscreen was on on the dash, it has never come on in 16 years as I don't actually have one, and the switch for it was lit up permanently. I checked the battery cables and the basics under the bonnet, tried again and she fired up. Again she over idled and dropped back down.
The radio also stops working when I use the wipers...
As the garage worked on electrics today (Fri) is tonights problem anything to do with the work they've done? They can't have her back in until next week and I am so p'd off with what has happened.
Any ideas please?
Thanx Eunosfan
When you say "they checked the ECU" - is that just a normal garage checking that it's not wet or physically damaged, or was it removed and sent to a specialist?
Are the battery cables intact and making good contact? You say it started after fiddling with those.
My 1.6 used to have a high idle and also rev-down a lot slower for a while after the battery was disconnected, IIRC it required a few on-off cycles and journeys before it settled back down to idle at about 800rpm and the revs would drop back quickly. If always felt like a different car for a while after I'd disconnected the battery.
Given the amount of sensor and electrical issues perhaps take it to a dedicated auto-electrician?
Are the battery cables intact and making good contact? You say it started after fiddling with those.
My 1.6 used to have a high idle and also rev-down a lot slower for a while after the battery was disconnected, IIRC it required a few on-off cycles and journeys before it settled back down to idle at about 800rpm and the revs would drop back quickly. If always felt like a different car for a while after I'd disconnected the battery.
Given the amount of sensor and electrical issues perhaps take it to a dedicated auto-electrician?
Hi,
Thanx very much for the reply and help.
Yes a normal garage and they checked to see if it was wet.
I checked the battery cables last night and they seemed ok, albeit they didn't need to check the battery at all yesterday while working on electrics. They told me this after I commented on the heated rear windscreen lights because they said the relay for it is in the boot, with the battery, and they didn't need to go in the boot.
I will check everything again later.
She started again after checking the battery and checking the HT Leads, one of which was not on properly and I was advised it had 'popped' off earlier.
The idle issue, in fact all of these problems, have only started post the heat sensor coming off of the CAT, the work done on this, and the air filter housing and water temp sensor being changed by the garage.
The problems last night started after they replaced the window switch as my original switch wouldn't work with the new window regulator they replaced, which was the N/S. I am now having problems with the O/S as the replacement switch doesn't work properly and the window does / doesn't wind up or down.
Am so annoyed. I have her booked in to another garage next week who are also experienced with auto electrics.
Any other ideas in the meantime please?
Cheers Eunosfan
Thanx very much for the reply and help.
Yes a normal garage and they checked to see if it was wet.
I checked the battery cables last night and they seemed ok, albeit they didn't need to check the battery at all yesterday while working on electrics. They told me this after I commented on the heated rear windscreen lights because they said the relay for it is in the boot, with the battery, and they didn't need to go in the boot.
I will check everything again later.
She started again after checking the battery and checking the HT Leads, one of which was not on properly and I was advised it had 'popped' off earlier.
The idle issue, in fact all of these problems, have only started post the heat sensor coming off of the CAT, the work done on this, and the air filter housing and water temp sensor being changed by the garage.
The problems last night started after they replaced the window switch as my original switch wouldn't work with the new window regulator they replaced, which was the N/S. I am now having problems with the O/S as the replacement switch doesn't work properly and the window does / doesn't wind up or down.
Am so annoyed. I have her booked in to another garage next week who are also experienced with auto electrics.
Any other ideas in the meantime please?
Cheers Eunosfan
Where are you based?
It sounds like you need someone experienced with MX5's if you want a garage to fix this.
Honestly, it's worth having a go yourself. The cheap diagnostic reader mentioned above is a good starter otherwise try the ECU. For £50 from autolink it will probably be about the same cost as another garage diagnosing the issue and it might just fix it. Fitting is seriously easy, they are plug and play and need no special tools.
It sounds like you need someone experienced with MX5's if you want a garage to fix this.
Honestly, it's worth having a go yourself. The cheap diagnostic reader mentioned above is a good starter otherwise try the ECU. For £50 from autolink it will probably be about the same cost as another garage diagnosing the issue and it might just fix it. Fitting is seriously easy, they are plug and play and need no special tools.
If it started after checking the battery and fiddling with the HT leads, but was totally dead before (ie. not even turning over on the starter) then the HT lead was probably just coincidence as even with the HT leads off it should still turn over on the starter. Also probably best to sort the intermittent dead electrics before replacing parts for minor systems such as the windows as there might be nothing wrong with them after all.
Have you checked for wetness or corrosion in the under-bonnet fuse box?
Does it have any form of immobilizer?
Seeing as the running issues started after the garage changed the AFM I'd check that again as I can find a load of google results about mk1s that wont start or run really badly or have an unstable idle after people have fiddled with the AFM or unscrewed the black socket and damaged the internals etc...
eg : https://www.miata.net/garage/afm_fix.html
Have you checked for wetness or corrosion in the under-bonnet fuse box?
Does it have any form of immobilizer?
Seeing as the running issues started after the garage changed the AFM I'd check that again as I can find a load of google results about mk1s that wont start or run really badly or have an unstable idle after people have fiddled with the AFM or unscrewed the black socket and damaged the internals etc...
eg : https://www.miata.net/garage/afm_fix.html
Edited by anonymous-user on Saturday 19th May 16:38
Evening,
So the problems with the electrics only started last night after the window switch was replaced. The regulator died on me weeks ago but I only got round to having it replaced yesterday. There was no problem with the O/S window until after the switch was replaced.
The N/S window regulator has been replaced twice now, and the O/S once, no problems with the switches.
The rear window defogger light has never ever come on on the dash before as I don't have one, and the switch for this has never stayed lit up before. I have a soft top with a plastic rear window.
When I got her started there was a high pitch shorting noise, this happened yesterday as well but I forgot to mention it, again post this switch being installed.
When the heat sensor initially broke off, this will have left cables dangling and disconnected under the car as the sensor was basically ripped off bouncing along hitting the road and car - how do I know this has all been fixed correctly with the new CAT and heat sensor? Where does the wiring go and what else might it be connected to?
I get most of my parts from Autolink who are brilliant, and they recommended the current garage and BBR. They also commented on getting the AFM checked as the air filter housing was changed. Thank you for the link.
Yes she has an immobliser and from what I can tell all is working correctly, and the light on the dash is working.
I've checked the under bonnet fuse box and that seems fine.
And tonight the same thing happened - parked up for a few hours, turned the key in the ingnition and nothing bar the heated rear windscreen light on the dash. I wiggled the battery connections and the relay in the boot for the rear heated windscreen and she started again, and the light went off of the dash.
I was sat in the car for a good 5/6 mins with the engine running and once again she started to over idle, the RPM goes up to 3/4000 and then fluctuates between 0-4000, I have to press the accelerator to stop her from doing this and she goes back to normal but upon pressing the accelerator she sounds as though she's misfiring or as if the exhaust still has a hole in it. Eventually this stops and the upside is she's not doing it all the time now.
As you can appreciate all very annoying. I think I'll have to wait until I can take her to BBR.
Cheers!
So the problems with the electrics only started last night after the window switch was replaced. The regulator died on me weeks ago but I only got round to having it replaced yesterday. There was no problem with the O/S window until after the switch was replaced.
The N/S window regulator has been replaced twice now, and the O/S once, no problems with the switches.
The rear window defogger light has never ever come on on the dash before as I don't have one, and the switch for this has never stayed lit up before. I have a soft top with a plastic rear window.
When I got her started there was a high pitch shorting noise, this happened yesterday as well but I forgot to mention it, again post this switch being installed.
When the heat sensor initially broke off, this will have left cables dangling and disconnected under the car as the sensor was basically ripped off bouncing along hitting the road and car - how do I know this has all been fixed correctly with the new CAT and heat sensor? Where does the wiring go and what else might it be connected to?
I get most of my parts from Autolink who are brilliant, and they recommended the current garage and BBR. They also commented on getting the AFM checked as the air filter housing was changed. Thank you for the link.
Yes she has an immobliser and from what I can tell all is working correctly, and the light on the dash is working.
I've checked the under bonnet fuse box and that seems fine.
And tonight the same thing happened - parked up for a few hours, turned the key in the ingnition and nothing bar the heated rear windscreen light on the dash. I wiggled the battery connections and the relay in the boot for the rear heated windscreen and she started again, and the light went off of the dash.
I was sat in the car for a good 5/6 mins with the engine running and once again she started to over idle, the RPM goes up to 3/4000 and then fluctuates between 0-4000, I have to press the accelerator to stop her from doing this and she goes back to normal but upon pressing the accelerator she sounds as though she's misfiring or as if the exhaust still has a hole in it. Eventually this stops and the upside is she's not doing it all the time now.
As you can appreciate all very annoying. I think I'll have to wait until I can take her to BBR.
Cheers!
Yeah it sounds like a few issues combining to make a whole load of trouble. If wiggling the battery leads restores the electrical system then there must be a break or dodgy contact in something back there - I assume you've removed the battery leads and cleaned the connectors and the battery terminals?
Sounds like the best course of action is to take it to BBR and see what they find, it's probably a couple of simple fixes as there's not that much on a mk1 to go wrong really.
Sounds like the best course of action is to take it to BBR and see what they find, it's probably a couple of simple fixes as there's not that much on a mk1 to go wrong really.
Hi all, so we went to BBR and they were great, very thorough. We found that the new CAT hadn't been put on correctly so the flanges / pipes didn't line up and only one bolt, which was the wrong size, had been forced in to one of the holes. As a result the exhaust was still leaking which is what I could hear and feel aiding to the ongoing problems. The wrong water temperature sensor had been replaced as this was still coming up as an error on the diagnostics. And an electrical connection was left shorting, can't remember which one now. The exhaust was corrected and now has two bolts sealing the pipes. The ECU and coil pack were thoroughly checked and tested, including footwell area, and reset, no further fault codes found. Correct water temperature sensor replaced. The battery was reset. Centre console removed and the windows and window switch were corrected. They even fixed my O/S door panel speaker which had been left hanging by previous garages ;-) Agreed to see how she goes and report back with any issues. So am very happy to report that the over idling and loss of power is resolved, yay so pleased! Unfortunately on low idle she has almost stalled a few times and the 'shorting' is still happening when I turn the key and start the engine. As of Sunday when I put my foot down on the accelerator there is a high pitch coming from the exhaust, and it sounds as though there is movement, as well as the gear stick vibrating and the car slightly shuddering, which I can't feel via the steering wheel. Then as of today the anti lock warning light came on and what I think is the ABS pump stays on even after the engine is turned off and the key removed. The unit gets hotter and noisier the longer it is on so some helpful colleagues showed me how to disconnect it while I'm not driving. BBR informed and my pride and joy is going back to them tomorrow. I have no idea if this is related to any of the works done regarding the ECU, sensors and electrics or just a coincidence, but so flippin' annoying - anyone? Cheers
Ah, just had my water temp sensor replaced. I had fitted a new one along with HT leads and a loom I had wired up as an extension for a Jackson cold air induction.
Since then I had all kinds of revving and misfires/ cuts happening.
Thought it might have been my lack of wiring skills but turned out to be a faulty new sensor.
Got an original one from mx5 parts and now all good.
Hope you get the rest of the issues sorted. Like another person here commented sometimes a couple or more things happen simultaneously just to confuse!
Since then I had all kinds of revving and misfires/ cuts happening.
Thought it might have been my lack of wiring skills but turned out to be a faulty new sensor.
Got an original one from mx5 parts and now all good.
Hope you get the rest of the issues sorted. Like another person here commented sometimes a couple or more things happen simultaneously just to confuse!
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