Misfire!

discomark10 · Jun 5, 2010

So I went out for a lil spin in my 3.5 92 v8 disco, to my local green-lane.
15min in it starts misfiring when over 2000rpm, I noticed the battery light is on too, so I pulled over to check for any loose connections- all seemed ok from what I could see at least.
I thought it might of been dodgy fuel as I had just filled up before coming out and last time I used it, it was fine.
So I gave it a few rev's to see if I could clear any possible gunk in my fuel and my bloody rad went pop and sprang a leak! so I limped her home!

So any body got any thoughts on the misfire, and is it possible to re-core my rad, or is that only when the fins have gone ( from what I can see a new rad isn't cheap! ).

Disco-Steve · Jun 5, 2010

As to the misfore, id start with the plugs, and work back from there, when were thay last changed cleaned or gapped?

With that rad, it is possible to recore, BUT, from i found when i had mine done, a recore was only a couple of quid cheaper than getting a new rad, shop around a little..

discomark10 · Jun 6, 2010

So, Ive decided as the hole looked prety small im goin to have a go at soldering the hole with Lead! wish me luck

discomark10 · Jun 16, 2010

Update - ive now checked:
- my plugs (gap and condition) they looked in good condition, and black coaked with a lil bit of brown, so ok.
- my ht leads, checked the resistance was the same on all of them and they look in good condition as well.
- changed my fuel filter
- changed my distributor cap and cleaned the rotor

Next I think I will pressure test each cylinder.

Is there anything else I could test, without spending too much money?

classic kev · Jun 17, 2010

Check ignition amplifier, check output from the coil. check output from the alternator, check battery condition. Check vac advance and mechanical advance, check ignition timing.

discomark10 · Jun 17, 2010

classic kev said:
Check ignition amplifier.

What / where is this?

classic kev said:
check output from the alternator, check battery condition.

Ive checked them, the batt was about 12v the alternator took it up to about 14v.

classic kev said:
Check vac advance and mechanical advance.

How do u check for this?

Is it possible that the chain can slip or is that pretty unlikely?

Thanks!

discomark10 · Jun 18, 2010

Update-

I checked my compression today: left side all were about 140 psi, right 135 but 1 was 105, but when i put oil in there it went up to match the rest at 130, so all that's wrong is a piston ring. FYI this was on a cold engine... only found out after that it should really be done on a warm engine!

Also i checked that each spark plug is sparking :/

classic kev · Jun 19, 2010

discomark10 said:
What / where is this?

Ive checked them, the batt was about 12v the alternator took it up to about 14v.

How do u check for this?

Is it possible that the chain can slip or is that pretty unlikely?

Thanks!

Get yourself into the V8 section and do a search, I recently posted the test procedures for most of the ignition circuit. As for the timing chain slipping this is unlikely BUT if the chain is worn and a bit slack the ignition timing can wander a bit; testing for a slack chain is not really possible unless you have made up a tool to be able to feel for slack. I have one made out of an old dizzy. Sometimes if the chain is very slack you will hear it clanking away but if it is that bad I suspect the engine would barely run.

discomark10 · Oct 26, 2010

-Update-

so now i have replaced...

Spark plugs
HT leads
Dizzy cap
Rotor arm
Coil
Fuel filter

And yet the missfire is still there... 2000-3000 rpm.

Misfire!

discomark10

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