Mx5, Chapter 2

The American · Postby **The American** » Mon Apr 20, 2015 9:42 am

There's another possibility. After the car was tuned, and in fact before the install of the new ECU, the light throttle was very sensitive, and had a hesitation/stumble immediately on first crack of the throttle.

I'd talked to the tuner about it and he told me that the ECU was seeing the TPS indicate a jump from 0% to 50% before falling back to about 30%. He said he'd filtered the TPS signal as much as he could (when I checked in the ECU manager, the filter level was set to 7). I picked up a replacement TPS from mx5plus and swapped it in. All the light throttle issues disappeared immediately and the ease of changing gears smoothly improved out of sight, but the car overall did feel less responsive.

At the Hillclimb on Saturday morning, the first thing I noticed is that I struggled to control wheel spin in the launch off the start line. Reducing my throttle inputs did not seem to reduce power levels, and I had to get almost right off the throttle to stop the wheels spinning. On my second run I warmed the tires in the staging area hoping for more grip off the line, which I got, but the same issue saw the car just about overshoot the first corner (which is a tight right hander quite close to the start line).

The next clue was that at any point on the course where I was using part throttle halfway through the rev range (3.5 - 5k rpm), as I backed off the throttle while attempting to maintain the same speed, it felt like it continued to boost and then hit some kind of cut. This happened going both up hill and down hill and for a few moments on the flat over the finish line. Going WOT or backing off completely brought it back to running 'normally'.

All of this happened pretty quickly on a track where you really can't afford to make a mistake or be staring at your tachometer, so may not be a perfect description of what happened. As per the post above, I twice drive up Mt Glorious and was able to replicate it the first time with a low fuel level, and then couldn't the second time with a full tank, but this problem first occurred on the track with a little over 1/2 tank in the car - fuel surge seems unlikely (filter sock maybe? 1500km of e85 dislodged some gunk clogging the filter?)

So here's the theory: the tuner tuned around the failing TPS, and now that a fully functioning TPS is fitted, the throttle signal for a given position has changed. As a result, boost is not being modulated by the throttle position as it was with the original, causing boost to continue rising on part throttle until it leans out, triggering a boost cut.
I’m sure someone who knows these things could immediately tell me if this explanation is even possible!
In any case, the difficulty modulating power, and the cut on part throttle is new since the ECU was repaired, and the TPS replaced.

The American · Postby **The American** » Tue May 12, 2015 9:27 am

After attempting to go for a drive on the weekend and making it less than 10 minutes from home before the engine cut out, and then cut out again, it has gone back to the tuner.

On the drive to the tuners workshop this morning, it died and would not restart at traffic lights. That's not fun at 7:30am on a week day! It died again rolling into the workshop, and then - annoyingly - it restarted second try for the tuner, only to cut out a minute later while we were standing there.

The theory is that the trouble is still internal to the ECU.

The American · Postby **The American** » Fri May 15, 2015 5:57 pm

The tuner swapped the ecu out with a spare, and the fault presented again, ruling out the ECU. The data log showed a trigger failure of the Crank Position Sensor (which was new, but apparently non-genuine). He replaced the CPS with second hand genuine item, and the car has not faulted again. My job is now to drive the car for the weekend to be sure that no other issue exists, and then return the car for some fine tuning that's needed after replacing the faulty TPS.

The CPS beginning to fail was apparently the cut-like feeling I was experiencing during the hillclimb event.

**SIGH**

Magpie · Postby **Magpie** » Fri May 15, 2015 7:29 pm

Interesting, we have the same tuner, engine and fuel (E85) yet different issues. Our only real difference is forced vs natural and base car model. Mine was a NA6 with a NB motor inserted. Curious if the issue is that for mine none of the original ECU wiring was used?

Good to hear your issues are getting resolved.

The American · Postby **The American** » Fri May 15, 2015 10:48 pm

Hi Mark,
At this stage, a random ECU fault, a faulty TPS, and now a faulty crank sensor, but no identified issues with the factory wiring (sensors excluded!). Frustratingly, the most recent cut out issue appears to be associated with a sensor that I'd replaced while chasing the original fault. Apparently the sensor I installed is non-genuine (tut, tut) and may not be of OME quality. If I'd left it alone....

I've had no E85 issues and no non-electrical problems with the car. It drove home fine (that e85 disappears fast!) and for a 30 minute drive this evening with no issues other than the evident need for throttle fine tuning that will happen on its next visit.

Maybe I will make it to the Aust Hillclimb comp in a fortnight! I'd also like to get to the Morgan Park day that MattR is facilitating.

Magpie · Postby **Magpie** » Sat May 16, 2015 5:42 am

I agree on the E85 falling out of the tank fast. Between Eastern Creek and QR mid week sprints went through about 140 ltrs. It has a tank of 98 at the moment but I will swap for E85 before the club day.

Morgan Park is a great day, lots to learn and great instructors.

The American · Postby **The American** » Fri May 22, 2015 9:45 pm

Picked it up this evening. Drove home. No hesitation. Running normally.

Many thanks to GT Autogarage for persisting with it!

The American · Postby **The American** » Sat Jul 04, 2015 12:33 am

11 July Morgan Park and then 25-26 July Noosa Hill

I think I'll be needing some new semi slicks by the end of this month!

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The American · Postby **The American** » Thu Jul 09, 2015 10:35 pm

I found some Russian goodness!

luzinit · Postby **luzinit** » Thu Jul 09, 2015 11:18 pm

Nice!! What size?

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The American · Postby **The American** » Thu Jul 09, 2015 11:47 pm

15x6.5 +45

The American · Postby **The American** » Thu Jul 16, 2015 11:30 pm

Morgan Park Raceway 11 July 2015

What an awesome track, and a very well run day by the SDT team.

In spite of the NB8B brakes, by lap 3, when braking down the hill after the bridge, I was experiencing significant fade. Magpie was easily out braking me with his modified NA6. I think some alternative pads are in order.

It's a small world - the brother of the previous owner of my car was also at the track with his modified Mini. His Mini was also out braking me!

One of the activities of the day was a 'horizontal Hillclimb' that was being roughly timed by stopwatch. I managed a 41.something and was quite chuffed to have picked up the fastest time of the morning in my little 'hairdryer' as they called it.

Halfway through the day, a momentary puff of white popped out the passenger side of the car (not out the exhaust) and an inspection under the bonnet showed a small spray of oil on the hood and in other spots near the turbo. Very clean oil, that I thought at the time was engine oil, possibly blowby from the dipstick.

It wasn't until I was heading home after lunch that I noticed the air conditioning was not kicking in. On inspection when I arrived home, it appears the a/c hose that passes down by the turbo to the compressor may have ruptured. I suspect the really clean oil is actually compressor lubricant.

Finally, all my slipping and sliding in the corners has put the passenger rear a050 at the end of its life, or almost.

All in all, it was a great day, and it was good to finally meet some local mx5 people in person (Magpie, Gslender, and Red_bullet)

Postby **Okibi** » Fri Jul 17, 2015 1:15 am

Thanks for the update, great to hear you're having so much fun. Gotta love boost. :mrgreen:

ManiacLachy · Postby **ManiacLachy** » Fri Jul 17, 2015 8:06 am

Nice write up. I'm disapointed I missed this SDT day, but there's another in October I' aiming for. By all accounts it's a great day out. Did you just go it alone, or did you get one of the instructors to give you some pointers?

Magpie · Postby **Magpie** » Fri Jul 17, 2015 8:53 am

Good to catch up likewise. We have the same brakes (NB8B) but I have no boost, thanks for the feedback that I was out braking you. By the way I'm running a Winmax W5/W3 combination however changing to a W6.5/W3 for the next track session.

I'll go through my videos and see if I have got any from behind you or you overtaking me.