Misfires on acceleration

[alinton]

Hey all - my '99 4.5 is having this problem, when I accelerate, at between 3,000 - 4,000 revs it often misfires, often with a huge BANG.

Sometimes this is enough to stall the engine.

I changed both coil packs a couple of months ago, checked HT leads were seated etc.

Any ideas please?

Thanks

Andy.

[ancol]

hi mate i had similar problem under hard acceleration under close inspection found it was the plug caps arcing across onto block this was after a service had to have new leads then problem was solved. not saying that is your problem but worth further inspection regards andy

[baztvr]

Mine did that a couple of weeks ago.then died. got home and found the alternator was'nt chargeing the battery, therefore the engine was running on a dying battery. changed the alt. only to find it was the dreaded 'Big fuse'. worth a look. hope I'm right, it's cheap!

[HarryW]

Assuming the leads are OK.
I went through a couple of coil packs myself only to find the low voltage plug/lead feeding one of the packs had corroded internally, worth a look. Do a continuity check between the ECU and these plugs. The other thing is the ECU itself, there are 4 driver amps each firing pairs of plugs (inners and outers together - 1&7, 3&5, 2&8 4&6), but you would need a spare ECU to prove that one fully.

[jonbarrett]

coils, leads and plugs fixed this on mine.

[VPower]

Have you checked the big fuse for cracks?

ECU's do not like low voltages and can often go loopy when they get it.

Just a thought and simple thing to check.