Please please help. Still having problems with this 1.6 roadster 1993, it continues to misfire when hot. Have tried coil packs, ecu temp sensor, cleaned out throttle body checked TPS, changed leads, plugs and o2 sensor. Today I checked ECU for evidence of water damage and its dry and clean. After plugging the ECU back in the car ran perfectly without misfire for about 40 mins, then but then the dreaded misfire was back. Checked the diagnostics again and its thrown up a code 3. Would the CAS cause the car to misfire when hot only, it only apperars to be when the car is under load at around 2.5-3k rpm. It starts and idles no problem, even when the engine is hot it just sits and purrs away, ask it to do some work it coughs and splutters. Tacho needle is bouncing all over when it exceeds 2000rpm. Could it be a problem with the ECU? I checked the spark plugs and Cyl 3 shows carbon deposits and the rest are normal. I have took it to my local garage and he’s scratching his head no one seems to have any idea what could be causing this problem. No loss of coolent or oil good sparks at all the plugs. At the present moment in time I feel like freewheeling it into a field with a can of petrol lighting it and running away. Any ideas greatfully received. Thanks
Your symptoms mostly point to things you’ve already either checked or changed. If we assume the things you’ve changed are not at fault what remains ?
If your problem was originally caused by water ingress the WD-40 is your friend, but you need to get it in the right place The inability to rev beyond 2k or so is often an indication of a problem with the TPS. How carefully have you checked this? Can you take the cover off and squirt some WD inside?
Try taking off the plug on the ignitor and giving it a squirt of WD-40, Ditto the CAS. If you need to replace the CAS let me know, I have a spare.
Check the ground connections under the wiper motor, thre is a lot of anecdotal evidence from the US that a poor ground connection here can cause a myriad of problems. Don’t just undo the bolt and clean the connection, you also need to undo the plastic cover and remove/replace the connections to the ‘strip’ (this will make sense when you do it).
The tacho signal comes from the ignitor, indirectly from the CAS via the ECU. It shouldn’t be feasible for water to get into the CAS, but I suppose anything is possible if enough high pressure water is sprayed around. If you take the CAS off mark the position relative to the head with a scribed mark. The cover can then easily be removed and checked for any water ingress, though unlikely.
Keep us up to date with what you’ve checked/changed, and any changes in your situation. There is a lot of expertise on this forum and I’m sure someone will come up with the right answer soon.
Good Luck
I would change the CAS, at least you will be starting with no errors. I understand the ECU compensates very well for defectice CAS etc but it would be best to replace it first.
This may sound strange but check the pivot bolt for the alternator, this is how the alternator grounds and it has to be a clean tight connection otherwise symtoms such as yours can be seen.
Thanks for your helps guys. I checked the CAS today and its looks brand new, so other than replace the CAS I took your advice and sprayed WD40 everywhere there was a connection including the TPS (which also looks brand new). However when spaying the Coil pack connector I noticed the wiring loom that houses the CAS, coil and other sensor wiring was badly taped up. After stripping the old tape away I noticed the blue wire that runs into the coil pack connector was joined by a crimp. Further down this loom the red and white wires that also run into the coil pack connector disappeared into grey insulation. Sticking out of the top of this insulation shared with the red and white wires was a thick bare wire. Not connected to anything and hidden with yards of electricans tape. My car is an L reg 1.6, so could this be the source of the mystery misfire that no one can track down? It seems very strange after replacing everything that could have caused this misfire I find this. Im i getting my hopes up here or could we have found a solution. Any suggestions will be greatfully recieved. Thanks again for your help and support. Oh forgot to mention the rev counter responds as normal but starts to bounce around over 2000 revs just before the car starts to misfire…a type of early warning indicator. Thanks again.
You can get the wiring diagrams here:-
http://www.madracki.com/miata/wiring.html Though these are for the US model they’re generally close enough.
To be honest, it sounds as though your car may have had this problem for some time, and the ‘funny’ wiring you’re finding could be the result of earlier attempts to fix it. I would certainly strip the old insulation back and do some thorough investigating.
FWIW crimp connections, when done properly with ratchet or hydraulic crimping tools, produce a better and more robust connection than soldering and sleeving.
If you still believe that it’s the pressure washing that caused the original problem then why not take off the possible culprits,
CAS, TPS, Coil packs, Ignitor; and put them in a WARM place (airing cupboard or similar) for 24 hours to dry out thoroughly. While they’re drying you could check out the wiring.
Good Luck
I
Thanks for that, well today i’ve cleaned the gunk off the crimped wire (old tape adhesive) cleaned it and insulated bare wire. Have retaped the wiring loom and ran the car for an hour. Up to now no misfire but rev counter still bouncing around intermittently over 2.5-3000 rpm. No change in engine sound when whis is occurs though. I’ve checked again today and the ignitor looks to be brand new and so does the TPS and CAS. So I think your right about this car having this problem for some time. But on positive note this time last week car would only run 10-15 mins before misfiring, and today no misfire at all up to now. Will keep you posted with developments its into a mazda specialist tomorrow. Its a lovely vehicle so worth getting to the bottom of this. Thanks you for your help
B
Just a quick update, two days now without a misfire!! Not even a cough!! I cleared the codes out of ECU have given the car a good 12 mile run today and no problems other than a rattle from exhaust at 3000 rpm. It seems much quicker and not using excessive fuel either! Rev counter behaving itself too. Still early days but fingers crossed it seems to have gone.
Thank you so much to all those who have helped and offered solutions, your help and support has been tremendous.
B