Misfire at 5000 revs

[Tomm3]

Hi all was there a definitive answer to the misfire/backfire at around 5000 revs? I saw a thread when I googled it from a few years back where an Ecu change worked but hadn't previously but I think someone also fixed it with a new coil.
My 4.0 has started having this problem a few wks back, would obviously be nice not to replace stuff unnecessarily

[Steve_D]

You don't say if the 5000 is under load on the road or free reving. If free then this could just be an off-load misfire.
If under load and it only starts at those revs then a weak coil could well be the cause as it is working its hardest at this point.

Steve

[Tomm3]

Thanks, it's under load. Looks like I'll try a new coil.

[Hedgehopper]

....or perhaps a blocked fuel tank vent. My Opel Manta tank was sucked flat when this happened to me.

[FlipFlopGriff]

Ignition amplifier
FFG

[QBee]

Tomm3 said:

Thanks, it's under load. Looks like I'll try a new coil.

I have a new spare, as well as a known working one. I must have the ignition amplifier too, as I recently changed to coil packs
I see you live in Cambs and will be in Cambs myself on Monday and Wednesday, if you fancy trying one without having to lash out the cash. .

Email me if you want to meet up.

[Tony91]

Tomm3 said:

Hi all was there a definitive answer to the misfire/backfire at around 5000 revs? I saw a thread when I googled it from a few years back where an Ecu change worked but hadn't previously but I think someone also fixed it with a new coil.
My 4.0 has started having this problem a few wks back, would obviously be nice not to replace stuff unnecessarily

I had that on my previous Grif it was cam lobe worn pulled ok up to about 5000 then broke down with a misfire.
Hope for you its just electrical and a cheap fix.

[Tomm3]

Many thanks to QBee for the coils to try but unfortunately no change.
Maybe leave it awhile, run about keeping revs below 5 😊.

[Rako]

Have a look at the fuel pressure regulator as that what the issue was on mine, can't remember the figs now but on tinternet somewhere?

I've also had issues with the battery breaking down internally as the accumate charger seemed (used) to fry them after 2 winters on trickle charge?? No probs since swapped to very clever CTEK unit......

Cheers

E

[Tomm3]

Result! The coil ht lead connection on the cap was corroded/burnt slightly so I put on the lead, arm and nice new cap that the very kind Mr Qbee lent me and the engine ran through 5k like it should.
Not that much happens past 5500 anyway....

[Classic Chim]

So the moral of the story is the system requires perfect connection when at its highest demands as in 5500 revs and anything that creates resistance is likely to be found out.
A partial connection will cause sparks and burn off the coating on plug lead ends. Often seen because they have gone rusty which always suggests a bad connection. if this arcing has damaged the leads they should be changed.

[Tomm3]

Yep. Loads of different fixes for a spark reduction it seems.
Thanks for all your replies.