Only does this when it's cold

Only does this when it's cold - 04/30/12 01:59 AM

After I fire up my 67 Coronet it only runs on 7. As it warms up it picks up the other cylinder and runs great after that. I've put in a new set of plugs and it still does it. What could it be? Plug wire?

Posted By: ralphie361

Re: Only does this when it's cold - 04/30/12 02:06 AM

Sounds like it could be the start of a head gasket. After it warms up it burns the coolant out and runs okay. When it is cold you might pull the plug and see if there is any traces of coolant in the cylinder. Hopefully I am wrong.

Posted By: Coronet-R/T-Rag

Re: Only does this when it's cold - 04/30/12 02:09 AM

Quote:

Sounds like it could be the start of a head gasket. After it warms up it burns the coolant out and runs okay. When it is cold you might pull the plug and see if there is any traces of coolant in the cylinder. Hopefully I am wrong.

I've also been worried about this. I put a set of CnC'd Stealth heads on it last year and now I'm wondering if I've got a gasket going or a CRACK?

Posted By: RodStRace

Re: Only does this when it's cold - 04/30/12 02:12 AM

Any valvetrain noise? I've seen older engines have lifters bleed down and take a while to fully pump up.
Also, a vacuum leak on one cylinder could be the cause.

Posted By: Coronet-R/T-Rag

Re: Only does this when it's cold - 04/30/12 02:16 AM

Quote:

Any valvetrain noise? I've seen older engines have lifters bleed down and take a while to fully pump up.
Also, a vacuum leak on one cylinder could be the cause.

It's got a solid lifter cam. Maybe a intake gasket leak on one cylinder that seals as the engine warms? It seems to start harder when It's cold than it used to....Hmmmm.

Posted By: ralphie361

Re: Only does this when it's cold - 04/30/12 02:19 AM

Youre right, maybe a small intake manifold gasket leak, when it warms it swells. When its cold try and spray some carb cleaner around the gaskets and see if it smooths out.

Posted By: Coronet-R/T-Rag

Re: Only does this when it's cold - 04/30/12 02:22 AM

Quote:

Youre right, maybe a small intake manifold gasket leak, when it warms it swells. When its cold try and spray some carb cleaner around the gaskets and see if it smooths out.

A couple of times it's really ran crappy and I get a "popping" in the mufflers. That sounds like unburnt fuel? That's why I thought ignition.

Posted By: Coronet-R/T-Rag

Re: Only does this when it's cold - 04/30/12 02:50 AM

Quote:

Quote:

Youre right, maybe a small intake manifold gasket leak, when it warms it swells. When its cold try and spray some carb cleaner around the gaskets and see if it smooths out.

A couple of times it's really ran crappy and I get a "popping" in the mufflers. That sounds like unburnt fuel? That's why I thought ignition.

Buuut it could be coolant not letting the plug fire and loading the mufflers with fuel. Hey, this is just like therapy. I'm answering my own questions.

Posted By: ralphie361

Re: Only does this when it's cold - 04/30/12 02:53 AM

We'll save you therapy money so you can fix your car

Posted By: RodStRace

Re: Only does this when it's cold - 04/30/12 03:00 AM

"anything' that causes a misfire is going to as an after-effect also cause popping in the exhaust.

You can swap in new plugs and wires if you are about due. If you have the opportunity, you can also start it and allow it to run for a bit while it's rough, then shut it off and compare plugs to determine which cylinder(s) are missing.
If it's a coolant leak, the exhaust will have a sweet smell.

Posted By: Coronet-R/T-Rag

Re: Only does this when it's cold - 04/30/12 11:45 PM

Quote:

"anything' that causes a misfire is going to as an after-effect also cause popping in the exhaust.
You can swap in new plugs and wires if you are about due. If you have the opportunity, you can also start it and allow it to run for a bit while it's rough, then shut it off and compare plugs to determine which cylinder(s) are missing.
If it's a coolant leak, the exhaust will have a sweet smell.

\

That's the thing, no sweet smell or white smoke. Last time I adjusted the valves I tightened the lash a little more than I have in the past but that was last fall and it ran good after that. I'm thinking I've got a valve that's too tight and not sealing until it warms up but lash loosen over time not tightens?