Poor running 1600 K-series Supersport

[Jon Ward]

Hi All,

 

Is anyone able to help me apply some logic to my running problem, as my current search/best guess method isn’t working?

 

When the car is hot it will not tick over or run properly under 4500rpm. If I hold the car on part throttle (to keep it running) the rev’s climb to around 3500rpm and then drop to around 800rpm before climbing again to 3500rpm and so on. I don’t think this is a ‘traditional’ misfire - if the car was running on three the engine would run rough, but run consistently (wouldn’t it?). In the split second that the rev’s drop it’s like the car is running on none. The problem isn’t intermittent, and the car is significantly louder when playing up. To reiterate, I did Donnington yesterday and the problem wasn’t noticeable on track, as it doesn’t occur at high rev’s. In the pits it was cutting out and kangarooing as ever. On the road it’s almost impossible to drive. If I don’t drive the car, but leave it stationary to warm up the problem still occurs

 

The car is a 1600 K-series Supersport EU2, ported head, verniers, standard plenum (but blanked off/no IACV), 52mm throttle body. I’ve swapped the rotor-arm, coil and lambda sensor, but that made no difference

 

Naturally, I’m happy to answer any questions as this is becoming a bit of a pain in the 🙆🏻

 

Thanks,

 

Jon

[TomB]

Have you an Emerald? It could be a duff sensor on the engine. If you look at the engine through the Emerald software, you should be able to see which key data, if any, is missing from a broken sensor on the live adjustments screen.

[CageyH]

Check the voltage across the throttle pot as well.

Not sure what it should be, but a dodgy connection there may give some of the symptoms.

[Mick Day]

I had a misbehaving K series for 3 or so years. Misfire symptoms would come & go along with poor starting, TPS passed all tests. Recommissioning after the winter & misfire back with a vengeance. New TPS cured all symptoms.

[Jon Ward]

The car is running on a standard Rover ECU (supersport)

 

I'm not great with electrics, but I've just tried to test the TPS. All three wires have continuity from the TPS plug to the ECU plug. There is a 5v feed to pin 1. I can't see how to test the voltage output as the plug needs to be connected to the TPS. Resistance across pins 1 and 2 varies from 385 ohms shut to 70 ohms open

 

I'm not sure if the 'test' tells me anything anyway, as it never fails to start and only plays up when hot

[Klunk]

Hi Jon ,

 

I think you may have just answered your own question. Have you tried changing the ECU coolant temperature sensor? Somewhere I've got the resistance values at given temperatures - will try and find them and post back.

 

Regards,

 

Giles

 

Edited by - Klunk on 11 Jul 2013 23:28:53

[Klunk]

Can't find my info but sensor testing can be found here. The ECU coolant temp sensor is the brown one (top of the page).

 

If you want to measure the voltages/resistance of the TPS whilst in situ, fold back the rubber plug cover.

 

Regards,

 

Giles

[Jon Ward]

Hi Giles,

 

I did think it could be the ECU temp sensor, but I just couldn't see how it would cause the symptoms. I've tested the temp sensor and I get...

 

Ambient 2630 ohms

40 deg 790 ohms

60 deg 400 ohms

80 deg 250 ohms

 

The TPS plug doesn't have a rubber cover, it's just a hard plastic plug

 

OK what next? Test the TPS in situ - how? (my concern being - it may only break down at high temp). Swap the TPS and try it (anyone got a spare I can borrow?). Look elsewhere (advice much appreciated)

 

Thanks,

 

Jon

[Mark Durrant]

Jon

 

I think there might be a TPS in the Speed Champ spares box you could try. I suggest you drop Simon an email.

[TomB]

Be careful, there are two kind of TPS out there. Earlier cars (my 1996 original 1.4k) had a different TPS to the newer one I got on a set of SLR throttle bodies.

[Jon Ward]

Thanks Mark, I'll drop Simon an e-mail

 

OK I've just been out on a blat to wiggle a few wires etc. I don't want to lead anyone, but does this help. I did around 8 miles with the car up to temp before setting off. The problem occurred twice. The first time I parked up and held the car on part-throttle to keep it running. Got out to take the bonnet off, and the car cut out. Re-started it and couldn't get the symptoms back. Second time, approx. 2 miles up the road, properly kangarooing at around 40mph, depressed the clutch and restarted while coasting - the problem went way

 

Any suggestions much appreciated

 

Jon

[apjenkins]

Jon,

 

I have a spare TPS I'll bring to Loton on Sunday if you haven't sorted the problem out by then. You can have it for as long as you like, may take one variable out of the equation.

 

@ndrew

 

[charlie_pank]

Hi Jon,

 

From what you've described, I'd be looking at either the TPS (best test is to swap in another one from a friend) or the ECU coolant temp sensor - they are very cheap, you could probably just buy another one to try it. If the coolant sensor is giving duff information, then it's probably telling the ECU that the engine is cooler than it is, and as a result you're getting bogged down by too much fuel - how's your MPG? Does the exhaust stink of petrol?

 

 

In terms of logical diagnostic tests, I always start from the basic premise that the engine needs 3 things (in the right proportions, at the right time) to run:

 

fuel

air

spark

 

 

Now it sounds like you can reproduce the problem whenever you want, so presumably you can reproduce it once the engine is warm with the bonnet off by rotating the throttle spindle with your hand.

 

Test #1: reproduce the problem as described above, then try doing it again while spraying Easistart into the air-intake (remove air-filter). Does the problem disappear?

 

If the problem disappears then you have too-little fuel going in (or too much air - air leak?), if it doesn't then the problem is either caused by too much fuel, or lack of spark... if you report back the results, we can try and devise the next test...

 

 

[Mr Locust]

Jon,

 

trust you are well.

 

Have you re routed the centre ht lead at all? Or is it in a poor state?

 

Trish's SLR went through an odd spell a few years ago when the lead was repositioned closer to the crank sensor on the back of the flywheel. It appeared to be a noise / interference issue. Routing the lead further away sorted it.

[Jon Ward]

Hi All,

 

Thanks for the replies to date. I've replaced rotor-arm, coil and lambda sensor. I've tested the ECU temp sensor and the tps. I've checked the feed to the ECU (spade connector) and carefully routed the king lead

 

To recap, the symptoms are...on part throttle (to keep it running) the rev’s climb to around 3500rpm and then drop to around 800rpm before climbing again to 3500rpm and so on. In the split second that the rev’s drop it’s like the injectors aren't firing, or the plugs aren't sparking

 

I've just been out on a test drive, and had the problem 3 times. On each occasion I turned the ignition off, re-started the car, and the problem went away

 

Is this indicating an ECU fault?

 

Cheers,

 

Jon