3K - Intermittent Misfire

[LukeAE71]

Ok lads here's one for you.

 

I installed a new 3K about 6 weeks ago. I replaced the points as they were a bit worn etc and they burnt out within about a week.

 

When this occurred I took the car to a place to get tuned as it was running like a three legged dog anyway. They replaced the points, set timing etc but didn't replace the condensor as they didn't have any in stock. He said to me at the time I 'should' replace the condensor also as that might be why the points burnt out.

 

I forgot to replace said condensor - there goes another set of points.

 

I have since replaced condensor and new set of points, all gapped to factory spec etc. No worries burned away from the car shop feeling very proud.

 

My issue is I have an intermittent misfire but only when the weather is cold. I drive 40 kms to work every day through the hills. When I drive the car to work in the morning (6am) the weather is cold. It makes a misfire noise similar to what it was making when the points were rooted. This makes me think I have a problem with my points. I gapped them a little further apart and the problem went away only slightly more.

 

When I get the car down the hill to the flat the air temperature is quite a bit warmer and the misfire disappears.

 

When I drive the car home in the afternoons it is quite a bit warmer and no misfire at all. The drive home is quite pleasant.

 

Sorry for the big blurb and history lesson but I thought it might help.

 

Any suggestions?? :wink:

[Felix]

Sounds like it could be running a bit lean.

 

No air leaks at all?

[LukeAE71]

No air leaks.

 

Could it have something to do with the air temperature plus the altitude? This might indicate a mixture issue.

 

But then in saying that it runs fine in the afternoons up the hill :blush:

[Felix]

Could it have something to do with the air temperature plus the altitude? This might indicate a mixture issue.

 

Could do.

 

I'd be experimenting with upping the primary main jet size a little.

[LukeAE71]

Thanks for the tip :y:

 

In the meantime do you think I would have damaged my engine at all?? :blush:

[ke70dave]

how much altitude are we talking here?

 

cooler temps = denser air

 

higher altitude = less dense air.

 

you would think they may cancel each other out..

 

but i can't image you are talking about to much altitude here? few hundred meters wont make much difference at all.

 

are you running cold air induction?

 

on carby cars if the intake air is to cold then it can play with how the carby works. fuel wont atomise properly possibly?

[crunk81us]

could it have something to do with the actual temp of the engine? whats the water temp doing?

[LukeAE71]

Water temp is fine - running thermostat etc.

 

The air temperature we are talking about here is sometimes 1 - 2 degrees when I leave in the mornings. So.... its cold :lolcry:

 

There can be (at times) between 5 and 10 degrees air temperature difference between top of the hill and bottom of the hill. If its hotter (ie 40 degrees) the difference is more likely to be higher between the two areas.

 

I left later in the morning yesterday, after daybreak and no misfire at all :bash:

[crunk81us]

just as something to try.. just to be sure..

blank off part of your radiator say half with a piece of cardboard, watch temps make sure it doesn't overheat. Could definitely rule that out then.

 

How about carby icing? whats the humidity like there? Is there a pipe on k series from factory that heats the intake air? i can't remember. maybe try running the intake to somewhere near the exhaust manifold?

[TRD ke70]

Could be a crook coil!!

[altezzaclub]

blank off part of your radiator say half with a piece of cardboard, watch temps make sure it doesn't overheat.

 

In theory this shouldn't have any effect, as the thermostat does that work. Once it has warmned up and the thermostat has opened then the cardboard wil run the motor hotter than usual if the radiator is struggling to cope.

 

Coil would be a suspect for sure, that would link into the electrical misfire.

 

Can you pull out the choke when its missing to richen the mixture and that will sort out if it is too lean.

[LukeAE71]

Thanks guys for all your suggestions.

 

The coil and ballast resistor will be the only parts I haven't replaced so might give them a shot if it keeps happening. It has all new leads, plugs, points, rotor button, cap, etc.

 

I had thought of pulling the choke out to see if it goes away, but alas the last two mornings it has been a little warmer and the misfire has not shown up.

 

Next time it happens though I am going to test it with the choke.

[ke30nut]

my 3k was misfiring badly just yesterday all it was was dirty spark plugs took them out cleaned then and hay presto it's running better than it has in months but my god to sounded like a Subaru :lolcry:

[LukeAE71]

Yesterday morning it was misfiring like crazy!!!

 

Tried the choke - no luck.

 

Bit the bullet and replaced the coil when I got home in the afternoon. Awesome town :dance:

 

Even in the warmer weather the car feels more responsive, sounds beefier and just all round better. Oh what a feeling :laff: It pulls hard up a hill in 5th that I used to have to drop back to 4th for :wink:

 

This morning was cold and no misfire. Fingers crossed that was the issue.

 

Thanks for the help lads :yes: