1.6 K series EU2 losing power/cutting out - ecu overheating?

[LazerBrain]

Some engine woes took the edge off a fab weekend at the 60th.

1.6K series SuperSport. No changes to engine other than servicing for last 5 years (when plastic throttle body was changed to metal one.) ECU is EU2 MEMS SuperSport. I think this is my rebuilt ecu (probably around 8+ years ago I had an ecu fault where the injector relay in the MFRU stayed on forever, even with the keys out. The ecu was sent away and they changed the timeout on this output, possibly changed the pcb too.) Battery is PowerVamp and could be 11 years old, always on a decent conditioner when in my garage.

Friday morning was pretty warm and I got stuck in traffic after about 40 miles (few miles of motorway, 40-50 on busy A roads) whilst heading to a meeting point. Water/oil temps and oil pressure were normal for my car. The engine stuttered, and misfired as I blipped the throttle, but then seemed ok. A couple of traffic light junctions later it stuttered and died, but restarted immediately on the starter. There were a couple more occasions where it stuttered, but cleared when I dipped the clutch and blipped the throttle.

Once I got to the meeting point I had the bonnet off and had a look around. I checked the HT leads on the dizzy cap and rotated them forward/back a quarter turn; and pushed the inertia switch (it did feel like it could click slightly.) I left the bonnet off for ~15 mins and the engine restarted at the first attempt. The cooling fan switched on and off as normal and all seemed generally ok when I joined the ReHaB convoy.

Around 40 miles later, similar behaviour started again. It cut out, but restarted a few times. At one point it cut out at ~60mph in 6th, the rev counter dropped to zero and it bump started itself after 2-3 seconds without any change. I limped into the lunch stop and did the same checks as before. After lunch, I think we drove about 60-70 miles to Donington and there was no issue. I was taking it easier, changing up earlier, but the weather had cooled a bit, was less sunny and there were fewer traffic holdups too.

I only took part in the Tarmac Lake/Heritage Loop events - but even waiting in the queue on the latter didn't cause an issue.

When I came to head home yesterday it was cooler in the morning, and I didn't notice any issues on the first ~70 miles to the lunch stop. I was taking it fairly easy to start with (sorry Chris!) but was driving normally for most of that section. After lunch, the sun came out and it was hotter again. I got to around 10-15 miles from home when there was a brief misfire, then it cut out a few miles later. It cut out again at speed and wouldn't restart for several seconds. A couple of miles later I got stopped at 3 sets of lights and it misfire again, before cutting out completely at a roundabout. It wouldn't start at all, and I got a push across the roundabout before parking in a side road in the shade with the bonnet off. After 10 mins I touched the cable to the TPS which looked quite taut, and then restarted the engine. It ran, but blipping the throttle from the throttle body resulted in the revs taking ages to drop back to idle.

I drove the last few miles home from here without ear plugs and the engine sounded different on very small throttle opens for the first mile or so. Can't really explain it - like a higher pitch of air rushing in. I left the engine running on the driveway whenm I got home & stuck a thermocouple on the ecu top cover after a few mins which read about 40C. The outside temperature was probably around high 20s. I tried testing moving the TPS cable around at the connector, but it made no difference to the engine running.

With the engine running, there was 14.0v across the battery, dropping to ~13.9v when the fan cuts in. Alternator light is out, except when the engine is off.

Common points: engine running for >1/2 hour, ~40 miles, slow driving in traffic after faster driving. Engine oil/waters temps ok, oil pressure ok. V. sunny.

Thinking back, it has had a very slight misfire in the last few years in similar situations - but has cleared pretty quickly.

So, where to start troubleshooting? I think it has to be something electrical, as surely most other things would take longer to recover (especially the fact that it misfires a bit, recovers, then gets worse and cuts out.) Are there any non-electrical issues which cause this problem?

The loom is a bit tight at the back of the engine - so I can check connections to the TPS. Would a connection on the TPS going open circuit stop the engine from restarting when the engine is warm (or would it just prevent it being revved?) I can also disconnect and reseat the ecu /immobiliser and the couple of main loom plugs in case there is a connection which is a bit oxidised.

I have another SuperSport MEMS with immobiliser, but this problem is intermittent and does seem to need the combination of ambient temperature and heat build up from traffic. I'd like to eliminate stuff that can be tested rather than just swap out the ecu if possible, especially as reseating connections when swapping ecus could clear the fault.

Anyone else seen this type of issue before?

[Jonathan Kay]

That looks better. ;-)

Are there any non-electrical issues which cause this problem?

It doesn't sound like the classical story, and it isn't top of my list, but how about fuel starvation because of deficient tank breathing? That could even explain the unusual sound. But not the association with slow driving.

Test by removing the filling cap the next time it happens and listening for a rush of air and observing whether the running improves.

Jonathan

[Jonathan Kay]

At one point it cut out at ~60mph in 6th, the rev counter dropped to zero and it bump started itself after 2-3 seconds without any change.

That indication was with the ignition on and the engine not declutched from the road... suggesting an electrical problem rather than a stopped engine? Any other instruments affected, and do you have an electronic speedometer?

Jonathan

[LazerBrain]

Hi JK,

Correct - car in gear, clutch up, ignition on, rev counter off, and the engine had temporarily died.

Good point about the fuel cap - I had released it when I stopped at the first meeting point and it didn't have a problem. Ditto on the last fill up on the way home (tank was filled from 1/4 to 1/2 full.) The problem has appeared when I've had varying levels of fuel in the tank.

[Shaun_E]

Possibly the coil is breaking down. Sounds very similar to the symptoms I had years ago.

[John Vine]

Hmmm...could be a whole host of things.  But starting with the simple electrical stuff:

Are the relays all properly seated?

Are the spade connections at the back of the ignition switch fully pressed home?

Are the contacts in the various harness connectors clean:

• ECU plug (36-pin)
• MFU plugs (2) under the ECU (6-pin and 8-pin)
• Big grey plug under the plenum (13-pin)

Good point about the coil.  Also worth checking the rotor arm in the dizzy. The retaining bolt has been known to short to the camshaft.

JV

 

[Garf]

My tuppence .... many years ago I had a crank position sensor do funny things with the revs when the engine got hotter. Took a while to pin-point but changing it sorted it out (after doing the coil first) - maybe it was already breaking down and some resistance changed when hot.....

Anyway after more recent CPS related irregular starting issues these last weeks (and improved electrical knowledge) I suggest you check the following on the CPS:

1) Resistance - should be 12,000 - 14,000 Ohm  (recent non-starter was 0.022 Ohm and problem fixed with new one )

2) Voltage on cranking - mine was about 0.35V which was deemed normal

Hope you get there as appreciate the pains of having an electrical issue - mine is 1.4K SS on EU2

[LazerBrain]

Thanks all - will hopefully get a chance to do some checks over the weekend.

 

At 20 years old, it's probably sensible to replace coil and CPS. Any recommendations on where to get them from?

[SM25T]

Start with Red Line Components 01883 346515

[m1 se7en]

Not sure if you've bought one yet but markiebabes has a coil for sale here:

https://www.lotus7.club/forum/sale/garage-clear-out-k-series-bits-and-pieces

[LazerBrain]

cheers Steve - have already dropped him a line.  If I'd realised, I could have joined your K-series parts collecting spree!