Attn all K-series with idle/running problems!

[caterhamnut]

There are a lot of threads about this sort of thing at the moment, so thought I would start a new one because at last, after months and months of trying this and that, replacing parts and leads, I THINK we have sorted our missing/rough idle problem, which has been extensively covered here!

😬 😬 😬 😬 😬 😬 😬 😬 😬 😬 😬 😬 😬 😬 😬 😬 😬 😬 😳 😬 😬 😬 😬 😬

Not saying that the other solutions/problems were not relevant, our MFU was corroded and our HT leads were leaking and giving me shocks, so they needed replacing. But a process of elimination has meant that we canlimit the causes of our problems.

 

Right - symptoms - car just about started, rough idle, lots of popping and spitting when increased throttle, accompanied with relay clicking in the MFU.

On the road we could trickle along at less than 3000rpm, any more and the backfiring would start, along with sudden drops in power and stalling until the throttle was eased off.

I was always convinced it was something to do with the coil, or HT lead, or one of the leads found under the inlet manifold. Well, tonight Mark 355GTS, 'Caterham Valet service and trouble shooting', solved the problem.

 

Drum role please. Here it is.

 

The coil is mounted on the engine block under the manifold. Just along the block behind this is the crankshaft sensor. The wire from the sensor passes up and into the main loom, passing close to the HT lead that runs from the coil. It would seem that interference or 'noise' from the HT lead was disrupting the signal from the crankshaft sensor. If you look at the wires from this sensor on our car they seem to have a length of braided tube along some of their length, which I reckon is some sort of shield. Normally the HT lead is routed up and above the crank sensor wiring - there is a clip just under the throttle body that holds it up in fact. Ours was not in this clip, simply because I had replaced the leads, was taking them on and off etc.

We re-routed both wires so that they were as far apart as possible. Car started instantly - with NO clicking, hunting or missing. Nothing. Went for a quick blast - did not miss a beat - full revs, max speed etc, all fine. Back in garage, we moved the wires back together again - engine coughed, starved and MFU clicked. Back apart - engine runs cleanly. This is repeatable.

Just driven back the 15 miles from Marks - car was perfect. I think we cracked it.

 

Thinking about it makes sense - low throttle openings/low revs the signal from the HT lead is less, or slower pulses - higher throttle, more revs, greater interference from coil and HT lead.

Apparently the a lot of the engine running is taken from the crank sensor - such as fuel pump operation - engine dying at full throttle inputs was no fuel getting through.

I think we (Mark!) have cracked it. It all makes sense. Everytime I fiddled with the wires and thought I had fixed it, I was proberbly just re-arranging them -sometimes closer together, sometimes further apart.

Well - it is another thing to check if you have similar problems. May not always be the answer, but in this case it has totally restored an engine which would not run at all this morning.

(Incidently, the non starting bit which came later in the day was a lose wire in the relay bypass circuit - not related!)

Hope this helps someone - now at last I can go and play with my new dampers!

It goes without saying that we are massively indebted to Mark for all his help. He deserves a medal for solving this problem, but will probably just have to accept a cartoon of his 355!

 

Also a big thank you to Adam M who had offered to come and help with some fancy pieces of electronic equipment - I am hoping we don't need you, but we should still meet up and have a celebratory drink!

 

cheers

 

NEW Nurburgring Pictures posted

here

55,000miles in 2.5 years

 

Edited by - angus&tessa on 23 Feb 2004 22:45:33

[Chris__]

Congrats. I had similar running problems with an old Golf GTI I had. Fantastic feeling when it all gets solved!

 

[O/T]Another for your website too, it's a girlfriend converter. (wasn't convinced about the bootspace; showed her your photographic evidence) :) /thread hijack.

 

Chris.

 

Edited by - Chris__ on 23 Feb 2004 22:57:30

[caterhamnut]

Thanks Chris - amazing what you can get in the boot with photoshop!

Only joking - all the pics are real!

 

Amazing how something as simple as 2 wires being so close together can cause the car to be unusable.

 

NEW Nurburgring Pictures posted

here

55,000miles in 2.5 years

[Michael_E]

Glad to hear its been sorted, Mark is a top bloke and goes out of his way to help.

 

The only engine problem I've had was with sensors, but mine was on the induction (air preasure) side and the wires where loose. It gave me somebloody awful kangarooing (not to sure on that spelling 😬) and really unsettled me at Llandow .

 

If you didn't spot my comment on another thread - cheers for the warm up coffee break and really nice to meet you both.

 

C7 MLE

The Furry Fast Car

Currently wondering what colour fur for 2004?

[Noel Mclaughlin]

Kangarooing spelt correctly 10/10 go to the top of the class

😬 😬 😬 😬 😬 😬 😬 😬 😬 😬 😬 😬 😬 😬 😬 😬

 

We will make an Aussie out of you yet then the rest of these Blatchatters can pick on someone else for a change

[caterhamnut]

Additional info from Adam who had emailed me with some more elcetronic info - all very clever stuff!

 

'Sounds like a result :-) Marks a very helpful & wise chap!

 

As part of a project to learn how the ECU works I made a device that

generated the same pulse train as the K-series crank sensor does. The

crank sensor basically generates a pulse for each tooth (edge) on the

flywheel. I was learning how the MBE ECU works, but it too was very

sensitive to the pulses being in the correct "order". This isn't

surprising when you think of how the ECU works out where TDC is. It

basically needs to see a series of pulses and when it see a special

sequence of missing pulses in knows where TDC is. If these sequences get

messed up - eg by the addition of HT pulses, or a lose connection - the

ECU may well get TDC wrong and fire the spark at the wrong time, ie

pops-n-bangs or misfires etc.'

 

Fingers crossed it is all sorted now

 

NEW Nurburgring Pictures posted

here

55,000miles in 2.5 years

[Don Cook]

I wonder if this could also cause problems on the VX engine. The crank sensor lead passes through the plug cover with the HT leads ?.

Don

[caterhamnut]

I guess if the cxable from the sensor is well shielded then it should be ok, and if the VX cable path is normal, then its obviously deemed ok. Still, worth a look I suppose.

I think that in all my fiddling with the engine I had moved the 2 wires closer together. Be interested to see if when you actually hold the 2 wires together you can hear a change in the engine note - on ours the engine actually stopped when the wires were held tightly together - an artificial situation but it proved the point.

Its interesting that I do not recall ever having read anything about this on techtalk before.

 

NEW Nurburgring Pictures posted

here

55,000miles in 2.5 years

[fordy]

I had a problem on my 1.4KSS with a sudden high (>3000rpm) scary idle !!! Solved it when I had the engine out by re-lagging all the engine loom (it was all a bit knackered and oily). Totally solved the problem. Clearly a case of interference from the HT side of the coil. I'd been through all the same red herrings (replace MFU as corroded tracks, new leads, plugs, various sensors etc....).

 

My coil is mounted off the chassis. No idea if this is non-standard or not though.

[Nifty]

Excellent news Angus.

 

My loom sits on the livingroom floor as we speak so I'll ensure I sort some serious insulation out before it goes back on the car.

 

I too have a 1.4SS and have had the high idle intermittently.

Also suffered from engine running on after a serious belt to overtake. Pull in behind a car and the 7 wants to ram it from behind!!!

Hope this will solve this permanently.

 

Thank very much for highlighting it. *thumbup*

 

Keep off the straight and narrow 😬

[caterhamnut]

Hope it helps Nifty - worth pointing out that in this particular case the wires from the crank sensor are insulated with a RF shielded cable/tube.

Can someone go and have a look at their car (or loom) and see if it is obvious on their cable as well - just out of interest. No idea if this has anything to do with the over-running bit - I suspect not but you never know.

 

NEW Nurburgring Pictures posted

here

55,000miles in 2.5 years

[fordy]

both K's I've had in the garage had insulated leads on the crank sensor. A grey braided sock type thing ISTR. Doesn't covered the whole length of the current car adequately I don't think though.

[caterhamnut]

yep - that sounds like the one, and ours is certainly about 2 inches too short as well (and black through age and dirt!)

 

NEW Nurburgring Pictures posted

here

55,000miles in 2.5 years

[CHRIS CLARK]

A & T.

Congrats. Ain't it annoying though when you find out it is a 'that's-all-it-was' sort of problem. Glad you could reproduce it too. So easy to disturb something and think you've fixed the fault while working on another theory only for it to fall back and re-create the problem.

Good one 😬 😬

 

Clamshell Club Founder Member.