Hola,

Having a bit of a mare here...

Bought this back in Sept, had a rough idle, hesitation and a drink problem.

I've put the following on:

• New crank sensor
• New MAP / air temp sensor (it's combined on this engine)
• New water temp sensor
• New NGK lambda sensor
• NGK iridium plugs
• Magnecor KV85 leads
• New coil packs

Also thoroughly cleaned the the throttle body / idle control valve.

After all that, it was still drinking and the idle, while better, was still hunting a bit. I figured the ICV was causing the hunting - it wasn't too bad so I left it. The hesitation was gone and it was accelerating a lot harder.

It's been leaking oil since I got it and I'd been topping it up every so often until I got time to track it down properly. The other week I over filled it - I didn't realise what I had done until I was in a bit of a hurry, the power dropped off and a puff of smoke came out the back. Instantly backed off and all was fine.

...until about a week later when it started to miss. Did a compression test today and I'm getting around 180psi (+/-5psi) on each cylinder - although they took a couple of cranks to get up to 180psi. I forgot to run the fuel out before doing the test so that might be why it didn't go to 180 instantly?

The miss is getting quite bad now but only seems to start when its up to temp and it only happens under load at low revs and the longer it runs, the worse it gets - it'll happily pull from 3500 revs under load tho.

The last time I had this happen (on another car), it was the crank sensor but it made it miss at high revs when hot.

So, given that I've changed everything that matters - bar the fuel pump, filter and injectors - and the head gasket seems fine, anyone got any ideas? I just find it odd that it's only at low revs, under load when hot...

When hot and at lumpy idle, remove and replace each injector connector in sequence.

If one of them makes no difference to the lumpiness, you might have found the culprit.

Remove and test further.

Cheers

SPD

unfortunately, it only really happens under load - on the rare occasion that it does it with no load, a quick rev cures it so it's difficult to replicate to test the injectors

mine and my mates sporting misfire under load from about 2000 - 3500 revs when under hardish acceleration.

no idea what it is iv replaced temp sensors, plugs, leads, lambda sensor, gave up now.

lol thanks

forgot to mention, when i turn the ignition on, the fuel pump "groans" into life.

might try another compression test when hot just to rule it out fully.

It has been known for a burnt valve to cause this.

However, harder to spot is a cracked valve seat!

I am leaning towards the valve seat though, because it may not show up during a compression test, but more when the engine is hot/under load.

Turbo charged engines are slightly more prone to such a sneaky fault due to the extreme pressures involved.

Ok, just did a hot compression test - I don't know if I read it wrong yesterday but compression was up 10psi on each cylinder to 190psi.

Pulled each HT lead in turn while it was rough idling, made it worse each time.

Went for a drive with the lambda disconnected, no change.

Unplugged pretty much all the sensors, made it run rougher.

I can't get at all the injectors due to the arrangement of the inlet manifold so I decided to spray some carb cleaner, no real change.

It also sounds really tappetty but it has plenty (a bit too much) oil in it - I don't have a hex key big enough to drop the oil out at the moment.

So, thoughts?

Ok, to update, it only happens up to 2000RPM DEAD. As soon as it goes past 2000RPM, it stops missing...

Now, the only thing I know of that is working up to that rev range is the ICV....but it rough idles even with it disconnected - although I haven't tried driving with it disconnected, yet.

Is there anything that only works up to 2000RPM? Any kind of ECU condition that anyone is aware of? I know after 4000RPM the ECU disregards a couple of the sensors (I forget which now), read it in the 16F docs (very similar to the 18FD ECU).

Solved

Right, seeing as everyone seems stumped on this, I bit the bullet and took it for a diagnostic. On the off chance (and now knowing a bit more about how the 18FD ECU works), I took it to a local garage who were able to read it with their Snap-On tool! Last garage I went to couldn't with theirs....

ANYWAY

The ECU flagged up almost everything because I'd been fiddling but once cleared, didn't flag up anything. Game over I thought, back to square one. Until he ran the engine and almost instantly I could hear something arcing - something that it hadn't done before. A closer look revealed that the No.4 terminal on the coil pack had started arcing from its base onto one of the coil pack bolts!

Now, this coil pack was brand new less than 1000 miles ago and it took two weeks of intermittent misfiring for a very small hole to appear at the base of the terminal and that literally happened when I got to the garage and he started revving the tits off it because the car was almost undrivable on the way home - I had hazzards on most of the time and had to keep pulling over...luckily was only a short drive!

So, moral of the story, even if you've replaced everything and it works fine for a bit then screws up again, try your old parts and check for a difference. It's running fine with my old coil packs now!

I'll take a pic of the coil pack later, it came from a motor factor, brand is Cambiare.

Pics:

I have a W reg 1.2 16v from new. It's been a great car to date. Seems now to hit a problem very similar to what's already said in this thread with some small differences.

Essentially, only on cold, a small misfire at low revs started 2 weeks back. Decided to check plugs & HT leads. Didn't replace anything and now it is very much bigger issue. Engine starts OK when cold and only just when hot, although sometimes not at all. It's misfiring lightly at low revs. The big problem though - even on standstill it will not rev quickly at all, and the same when under a light load - almost causes a stall. I can though (again on standstill) build revs very slowly and appears to run OK through the full range.

I've seen the great advice re replacing plugs, HT leads & coil pack etc. Before spending ££, though I'd check to see if anyone had exact same problem & what cure was i.e. replaced only one of the parts mentioned.

Thanks In Advance.

The old tricks are the best. Run the car at night (or in the dark -- an old blanket works wonders) with the bonnet up. Any blue flashes from the coils or leads indicate the issue. And it costs nowt.

old HT's will appear to be fine
But when they need to fire - they arc instead

Not all the time

Ziggy

Thanks guys for your help. You're correct, replaced the HT leads, problem sorted.

Out of interest, the small breather leading off the main air intake ducting is completely split. I'm going to replace anyway, just wondering what would happen if I didn't?

if its air ducting itll suck air in where it shouldn't

if its connected to the engine its the crankcase breather and recycles the fumes

ziggy

Not sure where it goes on a 16v. But it will serve some useful function, so, replace.