Miss Firing Between 1k - 2k Rpm.

[The Arch Bishop 0]

I've been enjoying my 1.6 for a month now and it's been a great drive but there's one thing spoiling it a bit. I have miss-fires between 1000 and 2000 rpm which makes getting away cleanly from junctions akin to a Friday night Halfords car park burnout. If I drive normally, the miss-fire is slap bang in the middle of the ideal pull away rpm which can leave me limping away bunny-hopping as it attempts to clear its throat. The only way to drive around it is to pin the throttle at about 2000+ rpm and do a clutch frying getaway. Not ideal!

 

I can also feel a slight jerking when I'm trundling through town at low revs on a light throttle load. With the throttle nailed she pulls really well and cleanly all the way to the redline and the tick over is as smooth as any 8 valve.

 

The car has new plug leads, dizzy cap and rotor. The connections to the coil are pretty clean and tight and the earths are ok also.

 

I've swapped out the AFM, and tried three separate good bosch ignition amps (with new paste each time) and checked all the plugs between them but still no improvement.

 

Before I go splashing out on a new coil, can anyone suggest anything else that would cause these symptoms? Could it be a air-leak problem (I have been over it all and can't see anything obvious but these things seldom are) or is it more likely a failing electrical item?

 

I'd be pleased for any ideas chaps!

Edited October 11, 2009 by The Arch Bishop

[Gman 29]

I had a similar problem years ago in my old 1.9. It was the HT lead so I was wondering if you have changed that as well. It certainly sounds ignition related so coil pack is the next thing to change.

[The Arch Bishop 0]

Yep, HT lead was changed with the plug leads. Are these symptoms synonymous with a coil breaking down?

[kyepan 291]

check for air leaks too, as they show up much more around idle and low revs than they do when the AFM goes open circuit at higher revs. It could be something like the dizzy vac hose, or any one of the re-circulating breathers.

 

Try putting your hand over the intake and see if it still manages to run, or you may be able to hear it.

 

other than that low rev high load misfires, look at the rotor arm, dizzy cap for poor or corroded contacts, they should be fairly cheap to fix, dizzy o-ring leaking oil into the distributor is another favourite.

[The Arch Bishop 0]

check for air leaks too, as they show up much more around idle and low revs than they do when the AFM goes open circuit at higher revs. It could be something like the dizzy vac hose, or any one of the re-circulating breathers.

 

Try putting your hand over the intake and see if it still manages to run, or you may be able to hear it.

 

other than that low rev high load misfires, look at the rotor arm, dizzy cap for poor or corroded contacts, they should be fairly cheap to fix, dizzy o-ring leaking oil into the distributor is another favourite.

The rotor arm, cap and the like are all spanking new so I'm ruling those out for the mo. The dizzy o-ring is interesting though. I have a new one waiting to go on just been too lazy to fit it! Would it cause such a consistent miss-fire though? I think I'll sort that anyway and check all the breathers over again. I know this is daft, but a loose dipstick wouldn't have any effect would it?

[steve@cornwall 100]

Inner wing mounted coils can arc between the king lead and negative LT connectors - Try some insulating tape wrapped around the LT spades to test. I've also had cheap HT leads arc against the expansion bottle pipe if they run close to king lead!

[Galifrey 1]

Inner wing mounted coils can arc between the king lead and negative LT connectors - Try some insulating tape wrapped around the LT spades to test. I've also had cheap HT leads arc against the expansion bottle pipe if they run close to king lead!

 

Mine did this, the only cure I found was replacing all the HT leads as one was clearly breaking down.

 

I tried all sorts of insulator on the coil top, including tape and a length of hose, it just arced thru them both as well!

 

[The Arch Bishop 0]

Well, it's developed a little although it's difficult to say whether it's related or another issue. After a good thrash back from work last night, it started having the odd big misfire. It would jolt the car pretty badly when it happened and seemed random (once when half way through a keen overtake!!). Happened about three times within 5 miles. It's also started ticking over lower and occasionally cutting out. The other problems are still there also.

 

I had a look under the bonnet last night in the the dark to see if there was anything arcing but all seemed well so I'm ruling out leads as the problem. Suppose this narrows things a little but still don't know what next. Again, does this hint at a coil on its last legs?

 

Edit: Just took the dizzy cap on to find there's a lot of oil residue in the distributor. Could be it so nice one kyepan! Will give it a good clean up and replace the seal. Would explain the hot oil smell that it suffers from as well...

Edited October 17, 2009 by The Arch Bishop

[The Arch Bishop 0]

Meh. Well after fitting another coil this morning and cleaning up the elderly spark plugs, I thought I'd take her for a spin this morning. All was very well and she was running really nicely until I hit the 60 limit and floored it... Then a complete loss of power and a gentle coast to a halt. The obligatory peer under the bonnet showed nothing has come loose or dropped off. Managed to get her started and limped home at about 20mph with a very poppy exhaust and my foot to the floor.

 

Well I thought game over, dropped valve or something equally awful. Looking at the oil pressure gauge shows I still have normal pressure but the dizzy was VERY hot as was the engine.

 

So my question is, engine or dizzy? I had the dizzy off to sort out the knackered oil seal and clean out the oil and disturbed the (already shot) vacuum advance thingy. Would the above symptoms point to the vacuum advance arm having come off the dizzy internals and if so, what can I do to keep it on there? Or is my engine muffed?

 

EDIT: I ought to point out that I haven't the time to check the dizzy today coz I'm being dragged to a fookin' wedding fair in Worthing. I'm not just being lazy but I don't want to spend the next few days worrying that the engine's shagged!

Edited October 25, 2009 by The Arch Bishop

[Tom Fenton 1,583]

Sounds like classic air flow meter fooked to me.

[The Arch Bishop 0]

Cheers Tom, I'll swap it out today as the Fair didn't take too long to go round! The one I have in it at the moment looks like it's been tinkered with in the past as it has sealant round the lid. It did sound a bit like if you try to start it with it with the AFM off the throttle body (don't ask me how I know that...).

[24seven 104]

It did sound a bit like if you try to start it with it with the AFM off the throttle body (don't ask me how I know that...).

 

you wouldn't be the first!

[The Arch Bishop 0]

..Or the last! Anyway, the AFM wasn't the problem in the end. The vacuum advance arm had indeed come adrift of the advance plate in the dizzy. Put it back on again and we're in business. Phew!

 

Anyway, I can't help but think it's going to do this again as soon as I floor it so I've put a spanner and a screw-driver in the boot for some roadside maintenance. To be honest, I was kicking myself this morning that I'd taken my tool kit out of the boot a few weeks ago. Does anyone know how to stop the flipping thing coming off again?!?

[m@ttc 30]

..Or the last! Anyway, the AFM wasn't the problem in the end. The vacuum advance arm had indeed come adrift of the advance plate in the dizzy. Put it back on again and we're in business. Phew!

 

Anyway, I can't help but think it's going to do this again as soon as I floor it so I've put a spanner and a screw-driver in the boot for some roadside maintenance. To be honest, I was kicking myself this morning that I'd taken my tool kit out of the boot a few weeks ago. Does anyone know how to stop the flipping thing coming off again?!?

Decellier types are just held on by one bolt. dont know about bosch types.