knocking/tapping sound when cold

theFastone · 04-27-2009, 03:25 PM

i get this wierd knocking sound from the engine compartment when i start cold. it goes away as it warms up.

8589 · 05-23-2009, 03:16 PM

...as it warms up.

are you talking about minutes of knocking?

mine knocks-then-ticks for a full second on cold start up, I do attribute to oil pump leaking overnite (dry cold start)

Jackstand Queen · 05-25-2009, 10:44 AM

Weird . . . I am getting the exact opposite. Relatively smooth running when cold, but after the 15 minutes of driving . . . . it starts knocking seriously bad.

I have diagnosed my issue as fuel injector related.

Your problem could be the same as mine, or it could be your O2 sensor sending a faulty signal. What year is your car again?

theFastone · 05-27-2009, 03:02 PM

1988. actually its like a ticking poping sound. and it stays on when its hot.

Jackstand Queen · 05-27-2009, 03:12 PM

Popping sounds like its a small exhaust leak. The leak gets bigger as the exhaust parts get hotter and expand.

You could use a small mirror and light and look around the head where the exhaust comes out. Look for a discolored blackened area.

Jack it up and check where the pipes go from 4 to 1 pipe flange. Get close and look first, then listen. Be careful burns hurt like the ****ens. Also check the bung where the O2 sensor screws in. Good luck!

Jackstand Queen · 06-22-2009, 11:17 AM

Researching engine sounds produced some more information.

Knocking on start up is a good indication of piston slap. The piston is too loose inside the cylinder and is slamming against the cylinder wall. As the aluminum piston heats up, it expands more than the iron block around it, and begins to fit in better.

A diagnostic test goes like this . .. . isolate the knocking cylinder, squirt in a table spoon of motor oil . . . if the sound does not occur or is greatly reduced . . . its piston slap.

You probably don't have enough reason to tear into the engine and fix it, or spend thousands on a (probably incompetent) rebuild at a local machine shop. Piston slap means your engine will fail long before an engine without piston slap. But it probably won't blow up tomorrow, or even next month.

04-27-2009, 03:25 PM	#1 (permalink)
theFastone No Skills Join Date: Mar 2009 Posts: 21 Thanks: 1 Thanked 0 Times in 0 Posts iTrader Rating: (0/0% )	knocking/tapping sound when cold i get this wierd knocking sound from the engine compartment when i start cold. it goes away as it warms up.

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode

05-23-2009, 03:16 PM	#2 (permalink)
8589 No Skills Join Date: Mar 2009 Location: Florida Posts: 43 Thanks: 2 Thanked 2 Times in 2 Posts iTrader Rating: (0/0% )	...as it warms up. are you talking about minutes of knocking? mine knocks-then-ticks for a full second on cold start up, I do attribute to oil pump leaking overnite (dry cold start)

05-25-2009, 10:44 AM	#3 (permalink)
Jackstand Queen Cage Fighter Join Date: May 2008 Posts: 677 Thanks: 52 Thanked 56 Times in 53 Posts iTrader Rating: (1/100% )	Weird . . . I am getting the exact opposite. Relatively smooth running when cold, but after the 15 minutes of driving . . . . it starts knocking seriously bad. I have diagnosed my issue as fuel injector related. Your problem could be the same as mine, or it could be your O2 sensor sending a faulty signal. What year is your car again?

05-27-2009, 03:02 PM	#4 (permalink)
theFastone No Skills Join Date: Mar 2009 Posts: 21 Thanks: 1 Thanked 0 Times in 0 Posts iTrader Rating: (0/0% )	1988. actually its like a ticking poping sound. and it stays on when its hot.

05-27-2009, 03:12 PM	#5 (permalink)
Jackstand Queen Cage Fighter Join Date: May 2008 Posts: 677 Thanks: 52 Thanked 56 Times in 53 Posts iTrader Rating: (1/100% )	Popping sounds like its a small exhaust leak. The leak gets bigger as the exhaust parts get hotter and expand. You could use a small mirror and light and look around the head where the exhaust comes out. Look for a discolored blackened area. Jack it up and check where the pipes go from 4 to 1 pipe flange. Get close and look first, then listen. Be careful burns hurt like the ****ens. Also check the bung where the O2 sensor screws in. Good luck!

06-22-2009, 11:17 AM	#6 (permalink)
Jackstand Queen Cage Fighter Join Date: May 2008 Posts: 677 Thanks: 52 Thanked 56 Times in 53 Posts iTrader Rating: (1/100% )	Researching engine sounds produced some more information. Knocking on start up is a good indication of piston slap. The piston is too loose inside the cylinder and is slamming against the cylinder wall. As the aluminum piston heats up, it expands more than the iron block around it, and begins to fit in better. A diagnostic test goes like this . .. . isolate the knocking cylinder, squirt in a table spoon of motor oil . . . if the sound does not occur or is greatly reduced . . . its piston slap. You probably don't have enough reason to tear into the engine and fix it, or spend thousands on a (probably incompetent) rebuild at a local machine shop. Piston slap means your engine will fail long before an engine without piston slap. But it probably won't blow up tomorrow, or even next month.