K series misfire - RESOLVED

[AntonyH]

Hi all,

 

I should start by saying, 1.8 K, 140bhp, has run trouble-free for the last 12 months (since we bought it).

 

Couple of days back we had a misfire, sounded like she was occasionally running on three cylinders. Tried the IT solution (turned it off and on again - you sort of have to when fuelling!) and that made no difference - the idle was unsteady and under acceleration she'd power, hiccup, power etc. not the normal smooth shouty engine we're used to.

 

Stopped again, armed and disarmed the immobiliser, and she then seemed entirely fine (barring one tiny hiccup about 30 minutes later).

 

Today, same thing - hiccups on tickover and under load; tried the immobiliser trick a few times, no joy. After about 15 minutes driving she seemed to clear whatever the problem was, so we went on with a test drive. Mostly fine but still the occasional splutter at higher revs under harder acceleration.

 

Any ideas?

 

Edited by - AntonyH on 18 Jul 2013 19:02:21

[tbird]

Don't suppose you had washed her with a hose just before misfire, could it be water in the spark plug sockets

 

Tim

[Stationary M25 Traveller]

Unplug connector in lambda sensor and try it.

[AntonyH]

@tbird - nope. She does get hosed as a rinse before washes, but it's been a while and I'm always careful to not point it into the bonnet vents.

 

I do suspect it's something electrical though.

 

@sm25t - I am now off to research where that is on my particular car, thanks for the suggestion.

[tin duck dave]

Could be throttle position sensor - try the reset procedure

[AntonyH]

OK, update:

 

Tried the *other* IT fix, i.e. unplugging and plugging back in, of both the lambda and throttle sensors. The contacts looked clean enough but repeated a couple of times just in case.

 

Left her to cool and had dinner.

 

Took her out for a test, seemed fine! :s

 

Only differences were, it's now much cooler (ambient) (but was only high 20s earlier); this evening we didn't run her up first to dip the oil - however she came to temperature soon enough and had no problems.

 

Ran her over the Snake in both directions, just had the one minor cough towards the end, under hard acceleration, towards the upper end of the rev range (5,000? Wasn't looking at the dials particularly!) whilst overtaking.

 

So, possibly just a tired connection?

 

Not sure, need to do more testing this week to try to replicate...

[Stationary M25 Traveller]

With the lambda ..... unplug it and leave it unplugged. If it drives ok (it is fine without), you know it was the problem.

[Barbarossa.]

In 16 years, my 2 k-series missfires turned out to be;

 

Blocked injector, when was the fuel filter changed last? By the way, anyone remember the service interval for the fuel filter?

 

Failed ECU - Came on suddenly with difficult starting and poor low speed running. Got quickly worse.

[jackb_ms]

Barbarossa, how did you clean the injector?

 

Jack

[elie boone]

Fuel filter every 24.000 mls

[Barbarossa.]

Sent the injectors away to a specialist. I think that they clean them ultrasonicaly.

 

In both cases, I ended up getting the garage to diagnose the problem. Without the right tset equipment, you are just shooting in the dark.

[AntonyH]

Quoting Stationary M25 Traveller: 

With the lambda ..... unplug it and leave it unplugged. If it drives ok (it is fine without), you know it was the problem.

 

Thanks - that was the plan last night, to set off with it connected (to be sure she was spluttering), disconnect, and have proof.

 

Only problem was, she didn't splutter. So we went a bit further. Still didn't splutter. In the end we "had" to do the Snake Pass, then turn around and do it again*. Still no splutter.

 

Ah well, the only thing for it is more testing this evening...

 

:)

 

 

*Well, it was a nice night and the doors were off. So I've got some classic GoPro footage of Mrs H's hair doing all sorts of interesting dancing!

[AntonyH]

Well... had a lovely run to Malton yesterday, just the occasional hiccup under hard acceleration (not confidence-inspiring whilst overtaking!).

 

Turned around at Malton, disconnected the lambda, set off back. Initially the whole engine reponse felt better, smoother, crisper; like the car was breathing easier. Thought that was "obviously" the issue, so pressed on.

 

Unfortunately, on the second (or third?) overtake after the restart, the same hiccup. It happened after a few minutes of low-rev ticking along (40mph in 6th) followed by a rapid application of throttle to make the pass (when a safe and sensible opportunity arose, of course). Seems to be around the 4,500-5,000 rpm range.

 

Ah well, I think a trip to Dave at Kimberworth is calling.

[Stationary M25 Traveller]

Hope you get it sorted soon.

[AntonyH]

Resolved - new plugs, HT leads and coil.

 

And an advisement to steer clear of the less expensive supermarket petrol. Three of the plugs looked like they'd got frost or white furry mold on them...

[Al7]

Hoorah!!

[Roadsport06]

Odd that you have diagnosed poor super market fuel for your white furry mold electrodes. There are many reasons for white electrodes including the wrong plugs for the engine. Why do you think it is poor quality fuel?

[AntonyH]

Quoting Roadsport06: 

Odd that you have diagnosed poor super market fuel for your white furry mold electrodes. There are many reasons for white electrodes including the wrong plugs for the engine. Why do you think it is poor quality fuel?

 

To be clear, it's not my diagnosis. I've always thought that "petrol is petrol" and never bought into the fuel brands' claims about how their hydrocarbons are "better".

 

However, fuel quality (from one particular supermarket) is what the expert (Dave at Kimberworth, Seven owner and trusted MOTer and servicer of a great many local Sevens) suggested as the most likely cause.

 

If the plugs had been of the wrong type he'd have pointed that out, I have no doubt. However any other possible causes, I'm more than willing to hear and take heed of.