K Series Brise Starter - Another Odd Failure Mode

[revilla]

I have recently been helping somebody get to the bottom of some really odd running issues on a 1.8 K SuperSport. After trying to diangnose over WhatsApp for a while, he brought the car to see me today.

Symptoms were: Each time you starter the car (hot or cold), you either got a "good start" in which case it would run normally, or you got a "bad start" after which i) the shift light in the tacho remained solidly lit, ii) the engine would run if you kept giving it throttle but it would not idle (this was a persistent state, it never recovered and ran normally until you stopped the engine and started again, in which case you either got a "good start" or a "bad start" again), iii) the short term fuel trim went to +19.53% and stayed there solidly but the long term trim stayed at 0.00%, iv) the throttle response was sluggish and the engine tended to deteiorate and started bog down after a while running with throttle.

If you got a "good start", the engine would then continue to idle and run reasonably normally, indefinitely. It would not malfunction again unless you switched off and started again.

While it was running badly, other than the odd fuel trim to full rich there was nothing remarkable to see in terms of DTCs (only a cam sensor fault which was unrelated, genuine and resolved with a replacement sensor) or live data. Fuel pump was running normally, MAP was normal, IACV appeared to be recycling and operating normally.

Given that the continued running issues or otherwise seemed to be determined by the start, and knowing the previous issues I'd seen with Brise starter motors causing low voltage transients (which usually led to failure to idle for a few seconds while the IACV recycled followed by normal running) I put an oscilloscope on the battery when starting and this is what I saw:

On some starts, the starter motor was pulling the battery down to as low as 4.3V!

The owner had been starting repeatedly whilst trying to get to the bottom of this over several days and the battery was definitely somewhat discharged, but the voltage settled to about 12.35V when left standing so it was probably still around 60% charged. It was a little slow to recover to this voltage after a starting transient. The fluid levels were a tiny bit down so we topped up and he will continue to monitor, but even with jump leads across from my car we still had the same strange "good start" / "bad start" behaviour.

So we swapped the Brise starter motor out for a spare Magneton I had to hand.

All of the "bad start" issues disappeared immediately. The engine started first time, every time and settled into a much smoother idle straight away. The shift light was extinguished. Fuel trim was still quite high (more info below) but a lot more normal, it was wavering up and down and the long term trim started to adjust as the ECU adapted to it. We had many more starts during the afternoon as we were working on other issues, and not once did we see the "bad start" problem return. The owner had commented that although it had done the "bad start" thing sometimes since he got the car, it had deteriorated significantly over the last few days. I think this was probably due to the battery charge state going down with repeated stop-start during testing potential causes and fixes.

With the battery state being as it was the voltage drop on the Magneton was still rather more than I would have liked to see but it was a lot better with a minimum voltage of about 7.5V seen.

The owner will continue to monitor the battery to see if a replacement is in order.

So it seems that the initial 4.3V transients were throwing the ECU into some kind of error state in which it would continue to struggle along running the engine, but from which it would not recover until the ignition was cycles off and on again. The Magneton was not triggering this behaviour with the drop to 7.5V. Although I've seen instances where the initial transient from a Brise starter would trigger the ECU to recycle the IACV leading to a failure to idle for a few seconds after starting, I've not seen it trigger the ECU to fall into some kind of persistent poor running state before. We did try swapping out the ECU but the behaviour was exactly the same. 4.3V is about the deepest transient I've observed.

The car had an FIA master cutoff switch but the voltage measurements were taken directly across the battery terminals so voltage drops across resistances in the extended wiring or across the switch were not a factor.

We did find some other issues with the car:

1. I read the map off the ECU and compared it maps that I had read previously from other cars. It was conclusively a 1.6 SuperSport map on a 1.8 SuperSport engine. The older style fuel rail with an adjustable fuel pressure regulator had been fitted; I believe this was done on earlier EU2 SuperSport engines where the same map was used and the fuel pressure was increased to compensate in a crude fashion. We took the rail and injectors off a spare manifold and swapped it back in to restore standard fuel pressure setup. I flashed an 1.8 SuperSport map onto the ECU. This all made a big difference to running, the idle was smooth, throttle response was sharp and return to idle was was well controlled. The engine suddenly felt really happy for the first time. We also upgraded from a 48mm throttle body with the response-damping wedge to a 52mm throttle body while we were at it, and made some map tweaks including an immobiliser delete, sharpened throttle response and some pop and crackle.
2. The cam sensor had failed. We replaced it and the cam sensor DTCs were resolved.
3. There were some poor crimps in the wiring loom which we tidied up.
4. Oil level was very low (despite a very recent service by someone who apparently knew Caterhams. New owner, I explained the "hot and running" check technique).

He came over from South Wales on a trailer but after a quick test drive put a massive smile on his face he decided he was definitely driving it all the way back, even in the rain!

I forgot to take a photograph of the offending starter motor with part number but I will ask the owner to take one for me and I'll post it up here for future reference.

[SM25T]

So, another happy customer .... and you win a tow car and trailer too !!

[K7 VCT]

Well done Revilla, another one for your biography.

[John Vine]

...another one for your biography.

And his CV.  Well played, Andrew!

JV

[revilla]

For the record, the offending starter was a Brise C890510PGR.

https://brise.co.uk/Caterham-C890510PGR.html

[Nick Bassett]

I too had starting issues with my old Brise 'AX' starter fitted to my 7 - thought it was going to be a useful upgrade, but I quickly removed it again...

IIRC correctly, on starting the Emerald kept tripping out - the car was always a pig to start from cold, but I just thought it was the car being difficult. It was only when a friend mechanic who knows 7s, pointed out to me that on cranking the Emerald kept clicking out - you could hear it, although I hadn't really noticed it before. Anyway, cutting a long story short, I did a bit of research online and found some articles stating the problems some Brise starters cause with 7s. Thankfully I had kept my original Magnetron starter which I refitted tout suite and all the problems went away!

I don't begin to understand what was causing the issue, only glad it went away. Also made me realise why the second-hand Brise starter I had bought was in such good condition - I suspect the previous owner had the same issues I experienced.