NB RUnning Poorly...any ideas?

hamish71 · Postby **hamish71** » Wed Jan 16, 2008 3:28 pm

I have a 2001 NB. I am about to rebuild it, in the next 4-8 weeks, but Id like to go into that knowing what is currently wrong with my car. By way of background, it is a 2001 NB, with SVT, 150000km (93000miles) on the clock. It had the timing belt changed at 100000km as per OEM recommendations. DUring this change, the key in the crank was left loose, and I have a visible bend in the end of the crankshaft, but everything has worked ok for about the last 40000km. The car is serviced regularly.

Right, symptoms, of which I have a few:

1. Starting about 15000km ago, on cold mornings, (by which I mean below about 15 degrees celcius or about 60F)the car will start, and sound like a bridge port rotary \"blapping\" about 3 times a second. This will continue until the gauge shows operating temperature, at which point, the car has been fine to drive. Until it reaches operating temperature, any attemp to push the accelerator is met by an engine which coughs and splutters, like it is being overfueled, or starved. It is possible to goose the throttle a few times, and once the revs get to about 2000, then it seems to rev clean. If you let the revs drop below this, you have the same problem....until it achieves operating temperature.

I have had this problem for about 18 months. In that time, the car has been serviced three times. Plugs have been changed, O2 sensor changed, codes checked (none), injectors cleaned. The plugs were quite fouled. A different MAF has been tried. When I get it back from a service, it is good for a week, and then problem resurfaces.

2. About 2 months ago, the car started to stall, intermittently at traffic lights. Pull up, and the car would be at idle, and then it would dip low. It felt like the ecu would try and catch it, and sometimes it did, and sometimes it didnt. This is an intermitttent fault, it doesnt happen at every set of lights. Also, on starting the car, sometimes it fires, and then stalls about 2 seconds later. Turn the key and it starts straight away.

3. In the last couple of weeks, it has felt like I am driving with the hand brake on. The car runs, it just doesnt feel like it is running hard under acceleration...whats more, it \"feels like\" the VVT is kicking in much later. By that, I mean under full acceleration, u have what feels like retarded accelration, and then at about 6000+rpm, it takes off.

So, diagnosing by text is not easy, but I am all ears!

bigdog · Postby **bigdog** » Wed Jan 16, 2008 3:42 pm

I take it you have a 'professional' servicing the car Hamish and that you are not responsible for the crank issue personally? I would insist that the engine rebuild was paid for by said 'professional' on that basis (preferably by someone who knows what they are doing!) A 'visibly bent crankshaft' is a major problem, notwithstanding your continued use of the car. Given that the car has had 3 services and that they have failed to diagnose the problem, I would suggest taking the car to a recognised specialist in your area for proper diagnosis forthwith.

Steampunk · Postby **Steampunk** » Wed Jan 16, 2008 3:50 pm

bigdog wrote: I would suggest taking the car to a recognised specialist in your area for proper diagnosis forthwith.

X2 BIG TIME!

hamish71 · Postby **hamish71** » Wed Jan 16, 2008 3:51 pm

Yes, the faultily installed key was by a Mazda dealer in Sydney. I have been through the process of trying to have them cover the cost of repairs. Difficulty was that it was done whilst car was with previous owner. It had done a further 20k km before I bought the car, and my mechanic spotted it immediately. At the time, the operation of the car was perfect. The bend is slight, external to the block, and is probably machinable \"in place\" should I wish to go down that path. The car had done another 10k km in my possession before the problems above had surfaced. I have taken this up with Mazda, armed with photos and a letter from my mechanic as the most likely cause. Mazda refused, claim that \"anyone else\" could have replaced the pulley and key since? Like I pull the engine out for kicks on weekends.

hamish71 · Postby **hamish71** » Wed Jan 16, 2008 3:52 pm

Oh, and my mechanic is the MX5 Factory in Melbourne, who have been outstanding....except they havnt found the core problem yet. I dont blame them....no codes...intermittent fault....

JBT · Postby **JBT** » Wed Jan 16, 2008 4:07 pm

Your symptoms of sluggish performance are just like those found with a worn crankshaft pulley keyway. :frown:

Steampunk · Postby **Steampunk** » Wed Jan 16, 2008 4:11 pm

short nose crank problem

I thought it was just a very very small percentage of NA6's

hamish71 · Postby **hamish71** » Wed Jan 16, 2008 4:40 pm

OK, I dont have the problem described in this article, but I have the result. When (in all likelihood) the pulley was put back on after the timing belt replacement, it was not done up firmly. It worked its way loose, and has worn the key, and the key way. The pulley, now not quite square on the shaft, has provided assymetrical force to the crankshaft, causing it to bend, slightly. The MX5 Factory diagnosed the problem, and replaced the key, and the pulley, and torqued it up. The pully is just perceptably not square (caused by the slight bend). It is one of the possible things that is causing this problem, that the CPS is not quite working as it should. I was aware of the early NA problem, but had not read an article like that one....whilst the cause is different, the symptoms, or at leat some of them, sound perfect:

...Usually a worn keyway will result in a poor running engine as the crankshaft loses its position relative to the camshafts...

...Some owners experienced poor performance as the slipping sprocket allowed relative crankshaft and camshaft timing to wander...

JBT · Postby **JBT** » Wed Jan 16, 2008 5:19 pm

hamish71 wrote:OK, I dont have the problem described in this article, but I have the result....................The MX5 Factory diagnosed the problem, and replaced the key, and the pulley, and torqued it up. The pully is just perceptably not square (caused by the slight bend).

Sounds horrible from that description. You say that the sluggishness started a few weeks ago. Well maybe the pulley moved. How can you be certain that it hasn't? It only has to move a couple of millimetres to completely stuff performance.

Craig · Postby **Craig** » Wed Jan 16, 2008 8:06 pm

hamish71 wrote:1. Starting about 15000km ago, on cold mornings, (by which I mean below about 15 degrees celcius or about 60F)the car will start, and sound like a bridge port rotary "blapping" about 3 times a second. This will continue until the gauge shows operating temperature, at which point, the car has been fine to drive. Until it reaches operating temperature, any attemp to push the accelerator is met by an engine which coughs and splutters, like it is being overfueled, or starved. It is possible to goose the throttle a few times, and once the revs get to about 2000, then it seems to rev clean. If you let the revs drop below this, you have the same problem....until it achieves operating temperature.

I have had this problem for about 18 months. In that time, the car has been serviced three times. Plugs have been changed, O2 sensor changed, codes checked (none), injectors cleaned. The plugs were quite fouled. A different MAF has been tried. When I get it back from a service, it is good for a week, and then problem resurfaces.

Gearbox neutral switch.

Steampunk · Postby **Steampunk** » Thu Jan 17, 2008 9:00 am

Craig wrote:Gearbox neutral switch.

Huuuhhhh? please explain :roll:

sirbob · Postby **sirbob** » Thu Jan 17, 2008 9:16 am

Maybe something less obvious like a dodgey coil pack?

Its a known problem with NB's of similar km's to yours and would give the same symptoms you're describing?

Just a thought...

hamish71 · Postby **hamish71** » Thu Jan 17, 2008 11:11 am

OK, there are two things to explore there.

Lets start with Gearbox neutral swith....Id explore it, except I dont have the faintest reason what that has to do with my problem....please explain.

Secondly, coil pack. Is it possible for the coil pack to provide the symptoms I have described? When I have the start problem, it goes away when it is warm. When it is warm, and running, it alomost feels like it has a restrictor over the air intake...the car is running, but just not freely, until it gets to about 6000rpm, then it just goes. When it is at idle, and warm, and NOT diplaying the stall problem, it seems to idle perfectly, and adjust for the a/c coming on no problem.

It is going back into the MX5 factory on Monday, and I am having both O2 sensors changes, and will have the pulley and crank checked again. I am also going to put a new air filter on it (I live on a dirt road, and possibly the filter is just \"full\") new plugs, new leads. I will ask about having the coil pack checked. I also, myself, am going to pull the fuel pump and clean it. Any recommendations for how to ensure the tank is clean, or how to remove it and clean it?

Craig · Postby **Craig** » Thu Jan 17, 2008 7:03 pm

1red5 wrote:
Craig wrote:Gearbox neutral switch.

Huuuhhhh? please explain

OK

I'll

explain

it

for

you

Craig · Postby **Craig** » Thu Jan 17, 2008 7:09 pm

hamish71 wrote:Lets start with Gearbox neutral swith....Id explore it, except I dont have the faintest reason what that has to do with my problem....please explain.

Right...the early NB8B's that had the shuddering clutches replaced are prone to this error as the neutral switches wiring is clipped to the under chassis of the car, and when the clutches are replaced the dealers just cut the ties and never bother to replace them, which in time leads to the wire breaking internally from vibration and fatigue.

Now...what happens is the car thinks you just sitting there stationary and revving the crap out of your car, and not actually in gear, hence it never actually uses the readings from the O2 sensor and it drives like sh*t until it warms up and goes into a default setting.

Craig

P.S. I'll type up a novel next time perhaps or maybe you can just trust me!