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        General >> Problems >> Engine misfire under acceleration.
        
(Message started by: NICKDICK on May 29^th, 2010, 5:27pm)

Title: Engine misfire under acceleration.
Post by NICKDICK on May 29^th, 2010, 5:27pm

Hi guys. I wonder if anyone can help me with a misfire problem. I have the 2.3. The car accelerates fine under light acceleration, but when you put your foot down to overtake for example there is a sudden loss of power and bad misfire, especially betweem 3 and 4 thousand rpm. I don't know if this is part of the problem but a couple of months ago one of the wires from the ecu to the first coil pack wore through and started shorting so nothing was getting to this coil pack causing the car to only run on two cylinders. I replaced the loom but the short must have been as it came through the bulkhead after the ecu. In the end I took her to an auto electricians who from what I can tell spliced in a completely new wire. This meant that she ran on all cylinders but I have had the misfire problem ever since. The electrician couldn't help any further. Could the length of the wire he put in cause any problems or is it more likely to be something else? Cheers, Nick.

Title: Re: Engine misfire under acceleration.
Post by Mike H on May 29^th, 2010, 6:35pm

Coil pack wiring comes from the distributorless ignition amplifier gizmo box, not the ECU direct

Does it only happen when accelerating as described, no other circumstances?

And, if you persevere and keep your foot down does it suddenly "clear" after a second or two and resume working properly?

Title: Re: Engine misfire under acceleration.
Post by Jonnycab on May 29^th, 2010, 6:57pm

Sounds like one or both coil packs breaking down under load.....or maybe spark plugs are past their best :)

Title: Re: Engine misfire under acceleration.
Post by NICKDICK on May 29^th, 2010, 9:44pm

Hi Mike, thanks for getting back to me. It only misfires under medium to hard acceleration. I haven't tried keeping the power on yet. I will try tomorrow and get back to you. Thanks very much. Hi Johnnycab. I put new plugs in a couple of months ago and got some other coil packs from a breakers so I suppose they could be faulty. Thanks.

Title: Re: Engine misfire under acceleration.
Post by Mike H on May 30^th, 2010, 1:18pm

on 05/29/10 at 18:57:13, Jonnycab wrote:

Sounds like one or both coil packs breaking down under load.....or maybe spark plugs are past their best :)

On the basis that acceleration increases density of the air in the combustion chamber, more difficult to make a spark in. Deffo aggravate weaknesses elsewhere or too big a spark gap can't make it

Title: Re: Engine misfire under acceleration.
Post by Mike H on May 30^th, 2010, 1:25pm

What I was trying to get at was whether it's same as what I was having, viz apparent misfiring under acceleration sort of around 40 - 50 mph (between 3,000 - 4,000 ish), if you "force it" it kind of sorts itself out after a couple of seconds and then seems to go properly.

Tres inconvenient if you're overtaking I can tell you ;D

Plus, worse in Summer than Winter.

Like you new plugs and the dodgy coil pack wiring renewed.

Turned out, renewing air / fuel filters and the MAF sensor cured it (the air filter was excessively overdue!)

Title: Re: Engine misfire under acceleration.
Post by NICKDICK on May 30^th, 2010, 4:58pm

Cheers Mike. Sounds exactly the same. Like you say overtaking was scary to say the least. Will try the MAF sensor. Nice one.

Title: Re: Engine misfire under acceleration.
Post by Tompion on May 30^th, 2010, 5:48pm

Try disconnecting the MAF first before buying another, the engine should run fine without it.
Just tried my 2.3 with it disconnected – went like the clappers, definitely not “limp home mode” although probably in drink even more petrol mode:D

Title: Re: Engine misfire under acceleration.
Post by Dave2302 on May 30^th, 2010, 7:27pm

Sounds like a classic case of spark breaking down under load. Don't assume the plugs are good just because they been changed, don't forget the HT leads either, if it has them.

If it was missing for a while before the guy sorted the wiring issue it could well be a plug, they get knacked by excessive fuel when they're not firing.

Or coil pack.....

Change the cheapest first, or if the leads haven't been done in a while do them first.

HTH Dave

Title: Re: Engine misfire under acceleration.
Post by Mike H on May 31^st, 2010, 11:29am

on 05/30/10 at 17:48:34, Tompion wrote:

Try disconnecting the MAF first before buying another, the engine should run fine without it.

^ What he said, it's a good test, forces the PCM to do without it and use a different method for the fuelling

Title: Re: Engine misfire under acceleration.
Post by Mike H on May 31^st, 2010, 11:31am

on 05/30/10 at 19:27:11, Dave2302 wrote:

If it was missing for a while before the guy sorted the wiring issue it could well be a plug, they get knacked by excessive fuel when they're not firing.

Is that right?

Title: Re: Engine misfire under acceleration.
Post by faffi on May 31^st, 2010, 12:56pm

Yes. Wet soaked spark plugs will die sooner or later - sooner if they have NGK stamped onto them ;)

Title: Re: Engine misfire under acceleration.
Post by Mike H on Jun 1^st, 2010, 1:01pm

How does that work?

Title: Re: Engine misfire under acceleration.
Post by faffi on Jun 1^st, 2010, 1:20pm

I don't know, but they short out in some way. My first motorcycle was a 1974 Suzuki A100 that was given a bit more fuel and oil than it needed, and it ate spark plugs like people eat candy. Bosch were far better than NGK, the latter never making it past 200 miles. Later, I had a coil issue with a Kawasaki Z400, and NGK spark plugs would simply self-destruct before I could get it started. Champions, however, didn't seem to be affected.

I've had it on other machines as well, more than enough to know that wet soaking spark plugs can easily destroy them, even though nothing can be seen on the outside.

Title: Re: Engine misfire under acceleration.
Post by Mike H on Jun 1^st, 2010, 6:03pm

OK, problee then, 'cause it leaves carbon on the ceramic (whatever it's made of) insulator which can become conductive. (?)

Title: Re: Engine misfire under acceleration.
Post by Dave2302 on Jun 1^st, 2010, 6:43pm

No, there wont be any carbon cos it aint firing.

It is because the fuel gets up inside the plug insulator and shorts the plug internally. You cannot dry them out, just bin em and fit new.

And I personally, wouldn't buy anything other than NGK or Bosch for certain applications, try buying a set of Champions for a V12 or V8, and you'll be sending at least 2 or 3 back cos it's got a missfire or 2.

Any plug will "juice up" if it gets soaked with unburnt fuel. ;)

Oh and BTW you cannot clean platinum plugs with a wire brush either lmao :)