Daily driven 71 now runs like crap after a 700 mile trip (and WTF is this sound?)

[BigTopGT]

Super frustrated, fellas.

I've got a 71 with a basic SBC 350/700R4 combo and I'd been daily driving it in south florida for literally 2+ years without any issues. (Hedman mid lengths, Erson 1.5 rockers, edelbrock intake manifold, Holly 650 carb, full Magnaflow exhaust, etc...)

With little more than occasional maintenance, the truck always started on the first hit of the key and idled/ran/drove like a champ the entire time.

After a long drive from Florida to central NC, the truck hasn't run right since.

Now, when I start it, it runs rough & I've got to give it a little gas until it warms up. If I don't, it'll stall any time I even put it in drive.

I'm not even sure where to START looking, since it seems so random and out of the blue.

If anyone has some advice, I can't tell you how much I appreciate it.

It's also had a knocking sound that's been nagging me for months. It comes and it goes and I thought a new crank balancer would resolve the issue, but no such luck. (it's loudest when the truck is cold and it's quiet when it's warm)

Really trying to not pull my hair out here...


Video of the noise I've been chasing

https://youtu.be/mC7LzL19K6g?si=v_HAxJV4iIsbzDkD

[Dead Parrot]

Knock sounds like exhaust leak. Those can be hard to chase. Don't overlook the intake exhaust crossover. Yes, a bad intake gasket can cause an exhaust leak.

Take all the belts off and give it a short run. Possible the 'knock' is one of the accessories being EOL. If things get quiet with no belts, go through the process of elimination until you find the noisy accessory. May also be easier to track down the leak or internal noise without the fan and other noises. Just don't get lost in noise tracking that you forget the short run part.

Rough running could be a simple as it needs a tune up.

[leegreen]

probably two things going on.

On the rough startup, I'd check choke is coming on properly, check timing and pull plugs for a look.

your knock is hard to hear, is there a lifter tick or a knock?
Things DP suggested and also look at the flex plate.

I had a van I thought had a bad main, but the noise was only at low unloaded RPM. Finally figured out the flex plate was cracked all the way around the bolt circle at crank and the noise was the torque converter banging around. the noise went away when the TC had power applied as the crack jammed into itself. It was a high mileage van (250k+miles), the knock came on suddenly for no apparent reason. I could wiggle the TC & flex plate around from the inspection cover

[BigTopGT]

Originally Posted by leegreen

probably two things going on.

On the rough startup, I'd check choke is coming on properly, check timing and pull plugs for a look.

your knock is hard to hear, is there a lifter tick or a knock?
Things DP suggested and also look at the flex plate.

I had a van I thought had a bad main, but the noise was only at low unloaded RPM. Finally figured out the flex plate was cracked all the way around the bolt circle at crank and the noise was the torque converter banging around. the noise went away when the TC had power applied as the crack jammed into itself. It was a high mileage van (250k+miles), the knock came on suddenly for no apparent reason. I could wiggle the TC & flex plate around from the inspection cover

Thanks, man!

I'll get her up in the air tomorrow and start turning over some stones.

I'll report back as I start ruling things out.

[Grounded63]

I'd also check the valve lash/preload/rockers. Make sure you don't have some that have loosened up.

[cadillac_al]

Hmmm, sounds pretty bad. It doesn't sound quite like a rod knock but it does seem to come from the bottom. It does not sound like a lifter tick to me. Those flexplate knocks can be kinda tricky. I think I would bet my money on a bad flexplate.

[Grounded63]

I bought a steel crank 454 from some friends once. They thought it had a rod knock, and pulled it. Crank was fine. But, a couple of cam lobes and lifters were wiped out.

[kaycee]

Has it ever been over heated, had one do that and warped a cyl (rod) thing ran great after it happened.I actually ran it for a couple years with not one issue besides the knock.

[kaycee]

Has it ever been over heated, had one do that and warped a cyl (rod) thing ran great after it happened.I actually ran it for a couple years with not one issue besides the knock.

[kaycee]

Has it ever been over heated, had one do that and warped a cyl (rod) thing ran great after it happened.I actually ran it for a couple years with not one issue besides the knock.

[AcampoDave]

A bad fuel pump can make a knocking sound.

[dmb]

flex plate cracked or loose , converter bolts loose
ez to check david

[Ziegelsteinfaust]

This happened to me, and killed a motor. Or atleast the symptoms sound very much the same.

Get the engine started, and check each plug with a timing light.

What happened to me was plugs would drop in&out when the engine got hot, and especially under load. Meaning driving down the freeway at 75/80 or going up the Cajon pass. Causing all sorts of headaches.

[BigTopGT]

Originally Posted by kaycee

Has it ever been over heated, had one do that and warped a cyl (rod) thing ran great after it happened.I actually ran it for a couple years with not one issue besides the knock.

No, it's never been overheated since ve owned it and it's been with me 4 or 5 years.

I'll be back in town this week and I'll start digging in.

[HO455]

Having issues after a long road trip makes me suspect a burnt valve. Especially if the noise is an exhaust leak.

Make sure your ignition system is all good. Cap, rotor, plugs, & wires. If that checks good then my next step would be a leak down test.

Good luck and keep us posted.

[dmb]

Originally Posted by dmb

flex plate cracked or loose , converter bolts loose
ez to check david

maybe you did not see my post. I worked for Chevrolet for years, my money is on a cracked flex plate or lose converter. You can check it in 15 min The flywheel can be installed without taking the trans all the way out.