v8 misfire

[shawser]

Cheers mate, thats what i needed to hear. When i first put on new leads i may have put them on wrong and caused the backfire, once i knew they were correct, then it was more a spitting back through carb, but defo not a backfire. It was like excess fuel coughing back up through carb and you could smell it too. cheers Dennis

[DEVONMAN]

Cheers mate, thats what i needed to hear. When i first put on new leads i may have put them on wrong and caused the backfire, once i knew they were correct, then it was more a spitting back through carb, but defo not a backfire. It was like excess fuel coughing back up through carb and you could smell it too. cheers Dennis

Once you have removed and checked the carb I would remove the plugs and clean and dry them and spin the engine a few times before you replace the plugs. Remove the supply to the coil before you do. Then refit the carb and supply and try again.

Regards Denis

[SuperV8]

On my last v8 i had a few big missfires due to a timing problem. I figured out the timing was wrong but it still wouldn't start, coughed and sputtered. Tried drying and cleaning the plugs but still nothing. In the end fitted new plugs and fired straight away. Seems the backfire damaged the plug so the spark was earthing down tiny cracks in the porcelain. I would try cranking checking the spark at each plug by earthing it on the block, obviously keep your fingers well clear should get a nice fat spark at each plug electrode.

Tom

[jefferybond]

My money is still on the leads being in the wrong order ;-)

[ramon alban]

When i first put on new leads i may have put them on wrong and caused the backfire, once i knew they were correct, then it was more a spitting back through carb, but defo not a backfire.

Hello Dennis, just to be sure, the leads are not only in the right order but they start in the right place, is your layout like this on my Vitesse?

[DaveEFI]

Here's the one from the Rover manual:-

[DEVONMAN]

When i first put on new leads i may have put them on wrong and caused the backfire, once i knew they were correct, then it was more a spitting back through carb, but defo not a backfire.

Hello Dennis, just to be sure, the leads are not only in the right order but they start in the right place, is your layout like this on my Vitesse?

Unlikely to be anything to do with this problem but leads 5 & 7 should not be run parallel through any of the clips and should be positioned as shown in the Rover manual drawing posted by DaveEFI.
This is prevent crossfiring between 5 & 7 which are next to each other in the firing order.
Regards Denis

[shawser]

good point mate. Noted.

[ramon alban]

Thanks for the heads-up Dennis, I'll change things around and see if it makes a detectable difference.

Assuming that is, that cross-firing is actually occurring, because everything I ever read on the subject has the liberal use of the words "possible" and "possibly".

Not that I'm questioning the science, you understand, just the reality of it occurring.

As a matter of technical interest, can anyone advise:-

Under what actual conditions of lead proximity does the induction induced cross fire actually occur?

I read that as long as the separators were used liberally along the whole run of the wires the phenomenon does not occur.

After all, all the HT wires are running parallel to at least one other wire and sometimes two other wires, so the the induction induced cross-firing MIGHT be happening all the while in all the wires.

So, if in actuality, it is happening all the time but only becomes critical between 5 and 7 what would be the symptoms of a cross-firing ignition system?

Expressed another way - Apart from the possible eventual long term damage, how would I know if it were happening when driving?

[DEVONMAN]

Thanks for the heads-up Dennis, I'll change things around and see if it makes a detectable difference.

Assuming that is, that cross-firing is actually occurring, because everything I ever read on the subject has the liberal use of the words "possible" and "possibly".

Not that I'm questioning the science, you understand, just the reality of it occurring.

As a matter of technical interest, can anyone advise:-

Under what actual conditions of lead proximity does the induction induced cross fire actually occur?

I read that as long as the separators were used liberally along the whole run of the wires the phenomenon does not occur.

After all, all the HT wires are running parallel to at least one other wire and sometimes two other wires, so the the induction induced cross-firing MIGHT be happening all the while in all the wires.

So, if in actuality, it is happening all the time but only becomes critical between 5 and 7 what would be the symptoms of a cross-firing ignition system?

Expressed another way - Apart from the possible eventual long term damage, how would I know if it were happening when driving?

As soon as I finished writing i was convinced that you would furnish a lengthy reply.

I am merely going on the cautious advise from Rover, who saw that if crossfire does occur between leads 5 & 7, some damage is possible if cylinder 7 gets an induced spark from lead 5 when 7 it is half way up the compression stroke.
But why take a chance when it is so easy to avoid the possibility.

Regards Denis