Tekforums

When Im driving at a steady pace such as in traffic or on the motorway at slowish speeds, or have taken my foot off the accelerator, Ive noticed that on odd occasions between 3k and 4k rpms the tachy blips between either of the two, as though it cant quite work out where it should be. Its been becoming more frequent lately, does anyone know what this could be?

There is no audible difference in the engine, the car doesnt kick back or anything either. If I wasnt catching the tachy out the bottom of my vision I wouldnt have noticed anything at all.

I think theres a "knock sensor" that is linked with the rev counter... the sensor might be on its way out? or I could be talking rubbish... :)

Electronic Spedo sensor on the gearbox?  My old Ibiza used to do that until i replaced it.  

It only happens for a second, say it will blip from 3k up to 4k, or it might swing back down to 3k for a second or two then go back up to 4k. Its very odd.

Ive been suspecting problems with either my thermostat or o2 sensor so Im having them replaced this Saturday during its MOT, Im wondering if this might be related.

It s a 17 year old Mazda, so Ive no idea if it has electronic speedo gearbox trickery or anything like that, I dont recall ever seeing mention of anything like that on the mx5oc forums or the enthusiasts manual.

Knock sensor will have nothing to do with it, a knock sensor is there to detect knock and allow the ecu to retard the timing if knock is detected to prevent detonation.

O2 sensor failing will give you violent jerking when acelerating at certain rev ranges, or generally pish running

thermostat will see your temperature behaving oddly, or the heaters never getting warm when driving if its stuck open

What drives the rev counter on them - is it a pickup on the crankshaft or is it impulses from the coil. could be a faulty sensor. The speedo will prob be driven by pulses from the ecu from a sensor in the gearbox

Ive no idea what drives the rev counter and I dont even know how to find out.

As for the thermo and o2 sensor, the car takes an age to warm up so I figured its worth swapping for a tenner. My mileage is very poor and I think a combination of a poor sensor and it being two wire maybe be part of the reason for this, so Im having that changed too for a new four wire. The car seems to open right up as soon as I touch 4200rpm regardless of how far I press the pedal.

The opening up at 4200rpm will prob be the start of the powerband (As its a 16V motor)

Well its always done that as far as I know, I didnt know if it was related or not but there we go.

My fuel consumption is high even when Im not driving it hard in the high revs. Ill suppose Ill have to let you know how it runs on Saturday when its been swapped around.

take your plugs out and inspect them to see if it looks like its running rich etc

Dont you need esoteric tools to take out spark plugs? Should I just ask the garage to take a look at it. I havnt a clue what Id be looking for quite frankly.

You only need a plug spanner, and a wrench.

Take a photo and show it to mark.

I dont have either, I guess I could ask the garage to take a look. Although Im changing the plugs anyway, should I ask them if I can keep the old set to look at?

Have you asked on the mx5oc forums?

No, Ive had a good read on there and not found anything about it though. Ive only just noticed the problem and thought I would ask the knowledgable gents here first :)

I did have the same prob in one of my minis, it was a loose wire but it sounds like you got something different going on. If the engine isnt doing anything odd I wouldnt worry too much - its 17yrs old like you say.

I couldnt get all the work done, only the lambda sensor as they found I had a leaky rear caliper and had to replace it :o

Everything else will be done Tuesday now. It seemed a bit smoother on the drive home, but that was probably because the engine had warmed up properly.

Well, in a shady turn up for the books the garage I was praising and using before somehow passed my cars MOT without a rear fog (I thought they had fitted it to the rear high level brake light, it now turns out that they didnt but still charged me for it). So thats £20 for light & switch + labour... but now I have a rear fog lamp in my bumper; praise to MX5 City theyve done a really good cutout job in the bumper, its very neat.

Second, the previous garage I was using appear to have arsed up installing a new cambelt at the same time last year - its missing a spoke. I had my timing stepped up to 14 degrees BTDC and now its running even worse than before, the garage said this was likely down to the cambelt as when they were using the timing gun to check it it was totally off, so of course theyd have to strip everything down to take a proper look at it and now my car feels like someone has poured treacle in the engine, I put my foot down and it makes a lot of noise but sod all happens :(

Im really quite angry with it all, Ive had a whole day off sat in the reception while they sort everything out and give me a new MOT, to find Im paying for work that should have already been done last year and my car has come off running worse. I really dont want to have to fork out for more labour stripping off the cam, etc to get the belt checked properly and get my timing sorted :( :disappointed:

welcome to the shady world of english MOTs

Id put my neck out and say 4/10 cars in England that passed their MOT TODAY would fail here tomorrow.


Is there a tooth off the belt or one of the camshaft pulleys? If so you should NOT BE DRIVING IT AT ALL!!!!!

It will need at least a new belt, immediately if not sooner - and if you absolutely have to drive it, I would drive it as slowly as is possible with very little revs

Its actually ridiculous that they let you drive off with a damaged belt/pulley

Actually, when i move to the North East in a couple of years, Im opening a garage that does proper MOTs, with the work actually being done to standard.

Its "missing a tooth" I think is what he said, but Ive been driving it with it like that for a year now it must be? I would have thought it would be gone already if it was due to break. Thankfully if it does go they are non-interference on the MX-5s... do you think this could be related to my tachy problem?

Other than lack of power now the car is actually running smoother, but Im putting that down to the new lambda sensor.

Id get it off to someone who will change the timing belt for you, and degree the cams correctly - most garages will do this the half assed way as theyre either too lazy, or dont know how to find proper TDC and how to use a degree wheel

Timing belt isnt worth gambling on - the chances are it will still be a disaster if it failed

I can get it back to them to strip it down and fix it/change the belt as necessary, its going to be expensive though isnt it? :(

How come it has lasted so long without a problem and going unnoticed?

pure luck, or it has just broke before getting it to them and is now on its last legs - hard to say

You will notice some difference when the cams are set right

I should think so, I cant believe how sluggish it feels like its running now the timing has been adjusted. I guess Im going to have to take it back to them to fix on Monday then...


 :rage:

Im booked in for Monday. £170 its going to cost me - if they swap the belt - which they might as well. Just opening up the engine is going to be £150. Im so pissed off...

Do I have any recourse with the previous garage? Its been over a year and I suspeect theres not even a guarantee I can claim off.

Quote from: Clockd 0NeIm booked in for Monday. £170 its going to cost me - if they swap the belt - which they might as well. Just opening up the engine is going to be £150. Im so pissed off...

Do I have any recourse with the previous garage? Its been over a year and I suspeect theres not even a guarantee I can claim off.

?

Quote from: Clockd 0NeIm booked in for Monday. £170 its going to cost me - if they swap the belt - which they might as well. Just opening up the engine is going to be £150. Im so pissed off...

Do I have any recourse with the previous garage? Its been over a year and I suspeect theres not even a guarantee I can claim off.

Id say yes take it back, why have you gone to another garage? The belt should have a longer life expectancy than 1 year.

Ive moved further north, hence taking it to the nearby MX5 specialist Mx5 City rather than just the local garage. Plus I was starting to feel the other garage were not doing that good a job, this has proved it. Its all the NVQ wasters they take on board Im sure, as soon as I see a 17 year old working on a car Im certain they wont have a clue what they are doing now and will be lazy and do a half arsed job. You want someone in their 50s, with the filthiest overalls youve ever seen and hands like a bears working on your car - someone you know could rebuild your engine blindfolded.

tell me about it !

I ended up with a £1700 bill to replace an exhaust gasket !

(van needs to be checked by a garage every 6 weeks for the opperators liscence or Id have done it myself!)

im not following this at all?

you had your cambelt changed at one garage last year? and the car was running fine ?

now recently youve gone to another garage, theyve told you the belt is missing a tooth, adjusted your timing and now the car is running like a bag of nails?

Precisely DEViANCE.

Honestly I wish I was a mechanic and knew a thing or two, Id know who was full of sh*t and trying to fleece me. Its actually starting to annoy me how useless I feel when it comes to car mechanics.


The long story to the timing is:

Last year when I had my MOT and servicing done at the previous garage (who changed the cambelt for me) I asked them to check/adjust the timing to 10 degrees BTDC which is standard for the MX-5. The 1.6s can generally be cranked up to 12/14 degreees BTDC no problem for a minor performance boost, and as the car had been running well/great I figured why not get it done this time around and see if it was even sharper off the mark.

When the bloke at the new garage came to inform me of the bad news, he said they couldnt track it properly wih the timing gun as it was way off due to the belt missing a tooth, so they put it where 14 BTDC should have been and said if its driving like crap bring it back in, well probably need to open up it and look more thoroughly at the cam.

i could be well off here..

...but it sounds to me like the 2nd garage is the problem, your car was running fine before it went there and now it isnt, that would be my starting point.

why where they looking at the timing belt anyway, how did they notice it was missing a tooth?

i doubt it was installed like that by the 1st garage (would be very very very bad practice) the belt can strip a tooth if incorrectly installed (to much/little tension) but it will give poor performance immediatly and eventually fail, i couldnt see it lasting a year.

^ yeah.

Well I was inclined to think that way at first. But I know the first garage has not done other things right on the car, furthermore I cant see why or how an MX-5 specialist would bodge up a simple timing change and blame the cambelt when they work on these cars every day of the year.

I forking hate garages. :(

fair enough, if the belt is definatly missing a tooth it HAS to be changed asap.

the fact the garage let you have the car back after discovering it baffles me to be honest, they may aswell have emptied your engine oil and told you to go for a drive.

you seem to know more about the mx5 timing stuff than me but if it safe to play around with a few degrees then its trail and error to see what feels best really.

your probably abit too late to complain to the 1st garage about the timing belt, its worth a go tho, but you can definatly complain to them if they falsely MOTd your car, they can get in serious poo poo for that.

Thats the thing, I read plenty theory about these things so I can go out armed with a bit of knowledge and understand everything a bit better, but I wouldnt have a clue how to check any of it for myself. Youd think it would help me avoid getting into this kind of situation but sadly not.

Its rather a grey area with what the other garage did for it to pass the MOT, the wiring to the high level clearly had been used at some point for a fog and then later switched back to a brake light so it would be difficult to go back a year and claim they duffed the MOT.

Im wondering if whent he belt was changed they did a poor job of it following my instructions to be careful of disturbing the short-nose crankshaft. Having said that though they seemed to ignore all my other instructions like flushing the coolant before replacing it with OAT.

Im guessing the belts a tooth out, not a tooth missing.
If its a tooth out on the cam that drives the dizzy, that would sound about right.

Hmm. Thats probably what they said actually thinking about it. What does that mean in real world terms? It still has to all come out and be sorted at my expense doesnt it? Do you think its likely the first garage was responsible if thats the case?

if its a tooth out, it just means the cog is turned round 1 tooth on the belt ;)

and maybe the old garage bodged the timing to get it running right ?

it really depends where its a tooth out...

p.s. cowboy mechanics suck ass... youre moeny is gone, and theres nothing you can do about it now :(

lucky for me I now have a reputation with the ones local to work after I tried to hit one with a shovel and then chased him down the street with it.... (its a long story)

Yeah a tooth out is way better than a tooth off, phone up tomorrow and ask.

One thing to bear in mind is softtop season is coming up soon - really you could ask the garage to bodge it for selling on or have them sort it properly for keeping another 12 months.

Id really like to keep it, Im happy with the money Ive spent elsewhere on it and want to keep it running for a few years until I can afford something bigger and better :)

If its a tooth out then yes 1st garages fault, the belt could be left on and the adjuster slackened to allow the cam to be turned 1 tooth. New belt fitted is about 2 hours, this will be a bit quicker but not much.
A new garage would want to fit a new belt as its bad practise to refit an old one.

Is it distributor or distributorless ignition

Theres no distributor.

Funny story, I went to drive home in the dark and found my dashboard no longer lights up, so I had to drive home with no clue what speed I was doing.

Yay for mechanics! :bowdown:

Do you know which cam is off, or is it both ?

Ive no idea Mark, to be honest I didnt think there was more than one cam :wtf:

Its finally been sorted, now its running how it should have all along, and a slightly bit more pickup thanks to the timing advance.

Happy day. :bounce:

Quote from: Clockd 0NeIve no idea Mark, to be honest I didnt think there was more than one cam :wtf:

Yup, therell be an exhaust and an inlet camshaft

I thought about getting a 4-2-1 manifold fitted to replace the OEM, then saw the cost... not worth it!

DIY

but first, save up and get a daily hack like an ax derv

then you can afford to not finish it at the weekend.