Time for another swap?

**steelholder** · 12-03-2018

So I'm cruising around 75mph and notice the check engine light is flashing, I feel a slight vibration when accelerating. I pulled over and ran the OBD, I got the misfire 300 code. Very rough idle but decided to go on then boom, a super loud knocking sound that increases with acceleration.

I swapped out my engine once before about 3 years ago with some help from you fine gents. Is my engine gone? Could something else cause a misfire and that dreadful sound? This website has changed a bit since then, I hope all the informative threads carried over here.

**QUICKSILVER462** · 12-03-2018

Check to see if the flexplate is cracked first.

**Scottydoggs** · 12-03-2018

post a vid if you can. idle, then hold it at 3000 rpm and then just drop the throttle drop.

**steelholder** · 12-03-2018

Wouldn't I need to remove the engine to check the plate?

Here's a vid, rev to 3000 then let go
3.8 knocking - YouTube

**steelholder** · 12-03-2018

Also gives off the smell of gasoline.

**Fivefingerdeathpunch** · 12-04-2018

Jesus that is one huge exhaust leak.

Sounds like the rear manifold broke somewhere or at the downpipe connection.

**steelholder** · 12-04-2018

Originally Posted by Fivefingerdeathpunch

Jesus that is one huge exhaust leak.

Sounds like the rear manifold broke somewhere or at the downpipe connection.

Sounds like good news, hope you're right

**steelholder** · 12-04-2018

Going under later, any places to check besides the obvious?

**BillBoost37** · 12-04-2018

If that's an exhaust leak it should be very obvious and have a lot of carbon around the leak.

I'm not so sure it's a leak, but start there since that's as good as anywhere else.

**steelholder** · 12-05-2018

Thought it sounded like an engine knock plus the misfire code, didn't get a chance to check yesterday will do today

**Scottydoggs** · 12-05-2018

or it could be a busted rocker arm or bent or broken push rod and that sound is the valve not opening. hoping for the exhaust leak.

**steelholder** · 12-05-2018

Originally Posted by Scottydoggs

or it could be a busted rocker arm or bent or broken push rod and that sound is the valve not opening. hoping for the exhaust leak.

I looked under, around the catalytic and could feel a strong airflow in my face coming from manifold/down pipe area but couldn't locate a crack or where it was coming from, it even tore up that fabric material (heat shield insulation?) around the down pipe area. It's raining hard so couldn't get a great look but it's def coming from behind the lower engine area, crossing my fingers for anything but a busted engine.

**steelholder** · 12-08-2018

One of the spark plugs had popped off somehow, screwed it back in and back to normal, thanks guys.

**SgtMarshal** · 12-08-2018

Originally Posted by steelholder

One of the spark plugs had popped off somehow, screwed it back in and back to normal, thanks guys.

that's crazy, i'm wondering how that would happen

**Scottydoggs** · 12-08-2018

damn i knew that was a odd sound lol

**Fivefingerdeathpunch** · 12-08-2018

Originally Posted by BillBoost37

If that's an exhaust leak it should be very obvious and have a lot of carbon around the leak.

I'm not so sure it's a leak, but start there since that's as good as anywhere else.

Bill, doubting me are you??

Hmmmmmmmmmmmmm.

Exhaust leak, spark plug blown out = same thing right?

I was damn close to real problem.

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