mx5cartalk.com

Hey Guys,
Been a while since I've been active here.
Need a little help now.
The SE's now done 150,000 k. Regularly serviced, as you'd expect from me.
Did a long drive last weekend and experienced severe power loss in the twisties between Bairnsdale and Omeo.
It's now 3 tanks of fuel later and it's still occuring at then of a 30km freeway trip to work (engine now hot). So bad that when I go to take off at the lights, I have to hold the clutch in and the guys behind me have to go around. Threatens to stall all the time. On the freeway leading up to this it's a bit down on power, but no more than a normally aspirated NB (my previous '5). Another symptom is occasional surging btw 500 and 1500 RPM. This tends to happen when just off cold.
Suspected plugs, leads and coil packs. These have all been changed with no effect. I'm getting the dealer to change the coil packs back to the old ones (objected to paying $800 to change something that didn't need changing).
Any ideas? I'm guessing a sensor or injectors. Cant imagine it's the pump as surely that's working pretty hard at 100kph (gove or take ;o) ) on the freeway.
It's going back in tomorrow to have the coil packs swapped back out.
Don't the dealers have access to diagnostic equipment that at least tells them whether it's spark, fuel or air that's deficient and which cylinder may be misfiring.

Any help appreciated,
Cheers,
Alf

I hate to suggest it, but check for crankshaft pulley wobble while idling... My NB8B is in the throws of having a new crank fitted due to the infamous "short nose crank issue", which yes, happens on long nose cranks too if the timing belt change was not done correctly - crank pulley bolt must be replaced and tightened correctly. The timing belt change on mine was done at a Mazda dealer

Mine was showing the same symptoms as you've outlined, and was at its worst when the a/c was on. The car was woeful below 3000rpm, and would struggle to get off the line on even the slightest incline. I changed coils, leads, plugs, CAS, ran injector cleaner through it, all to no avail. The problem was not always very obvious, it would come and go. As I have since found out, probably because the crank/cam belt pulley had a couple of degrees of play to work with.

Check for boost leaks too - a loose connection or even a hole in the cooler will do it. Check the turbo and manifold bolts are all tight as well.

NMX516 wrote:My NB8B is in the throws of having a new crank fitted

No, not the SP?

bruce wrote:

NMX516 wrote:My NB8B is in the throws of having a new crank fitted

No, not the SP?

Yep, but it will be coming back better and meaner than ever

Thanks, guys.

I have a horrible, horrible feeling that NMX516 is on the money (and I'm guessing there's lots of it involved). A couple of months ago my son had borrowed my car when it had an exhaust whstle (gasket gone). He was looking for the source and rang me saying the pulley was wobbling a little. Didn't pay much attention at the time, though did mention it to the dealer when it was in getting the exhaust repaired. Every service and repair has been done at the same dealer including the timing belt replacement, so if that's the cause, I'm hoping the dealer feels obliged to replace it, perhaps after the lease company leans on him a bit.

Cheers,
Alf

Well, we found the problem. NMX516 pointed to it. However, in this case, thankfully the crank was fine.
Have a look at this picture of the inside of the harmonic balancer. You will see that the balancer was only on the shaft by about 4mm out of about 20. The pulley was then wobbling on the shaft by about 7 degrees as it machined itself out on one side of the crank. The keyway was damaged on the pulley, but not on the crank.

Replacing the pulley did the job. I paid for parts, but the dealer covered the labour, recognising that the problem was caused at the timing belt service. The SE hasn't run like this for a long while. In fact I'm half regretting that it's time to update in another 5 weeks or so.



Thanks all,
Alf

Alf, good to hear you got it sorted reasonably painlessly.