Motor sounds weaker after driving? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Reziel_1983 · 06-23-2011, 12:32 AM

Whenever I first start my truck up after the motor has been sitting for a while and is cold, it sounds really nice and it runs really good. However, after it has been running for a while and is hot, it doesn't lope nearly as much and it tries to die if it's in drive, ever whenever it is idled higher. It just sounds weaker and feels weaker in general. It has a 350 with the stock quadrajet that has been rebuilt less than 500 miles ago. Any ides of what could be causing this?

rwhit57 · 06-23-2011, 03:42 AM

I assume you're not leaking or using any oil or anything like that? First I would check to see if it's losing vacuum somewhere, hoses, carb, intake, etc. Then if that's ok then I would run a compression test.

sumran · 06-23-2011, 08:52 AM

I would look for carb adjusment, choke adjusment and function and vacuum leaks. If the valve lash was not properly adjusted in the rebuild you can get odd behavior.

geeforcem · 06-23-2011, 10:32 AM

Does the truck still have the original catalytic converter? It could be clogging.

jeff

Cherub · 06-23-2011, 10:50 AM

Im thinking something simple like getting heat soaked.

Reziel_1983 · 06-23-2011, 05:44 PM

Thanks for all the replies guys. I do not think I am leaking any oil, but I will double check to make sure. And no geeforcem it doesn't have catalytic converters on it at all. I will check all the suggestions, thank you!

1LowToy · 06-23-2011, 08:15 PM

After 500 miles on the motor you may need to run the valve adjustment again. Make sense?

rayfinseats · 06-23-2011, 08:58 PM

Do you have a return line to the gas tank? Maybe it's vapor lock.

rwhit57 · 06-23-2011, 09:04 PM

Quote:

Originally Posted by 1LowToy

After 500 miles on the motor you may need to run the valve adjustment again. Make sense?

Man, Might be a good catch on that. I didn't think of that. The other thing is if whoever broke the cam in didn't use an oil with the Zinc additive, you could be already showing cam wear. Pull the dipstick and inspect the oil for any signs of metal.

Pyrotechnic · 06-24-2011, 02:07 AM

I had a motor that sounded better and felt more powerful when cold. My conclusion was the heat crossover under the intake. Having an aluminum intake with all that hot exhaust gas passing under was just not good for power. It was also hard starting when ever you would park it and come back a few minutes later. Not in the sense of a slow starter, but more in the sense of the fuel being boiled out of the carb. Should have blocked off those passages.

06-23-2011, 12:32 AM	#1
Reziel_1983 Registered User Join Date: Feb 2011 Location: Brownwood, Texas Posts: 421	Motor sounds weaker after driving? Whenever I first start my truck up after the motor has been sitting for a while and is cold, it sounds really nice and it runs really good. However, after it has been running for a while and is hot, it doesn't lope nearly as much and it tries to die if it's in drive, ever whenever it is idled higher. It just sounds weaker and feels weaker in general. It has a 350 with the stock quadrajet that has been rebuilt less than 500 miles ago. Any ides of what could be causing this? __________________ 1983 Chevy lwb: 400 sbc destroked to 377, comp cams xe 268, Holley Street Dominator Intake, Holley Street Avenger 670 cfm, headers, flowmasters. SOLD 1998 Trans am, mostly stock with magnaflow catback My build thread: http://67-72chevytrucks.com/vboard/s...d.php?t=454329

06-23-2011, 03:42 AM	#2
rwhit57 Registered User Join Date: Jan 2011 Location: Tulsa,Okla Posts: 590	Re: Motor sounds weaker after driving? I assume you're not leaking or using any oil or anything like that? First I would check to see if it's losing vacuum somewhere, hoses, carb, intake, etc. Then if that's ok then I would run a compression test.

06-23-2011, 08:52 AM	#3
sumran Registered User Join Date: Feb 2011 Location: Gainesville, FL Posts: 406	Re: Motor sounds weaker after driving? I would look for carb adjusment, choke adjusment and function and vacuum leaks. If the valve lash was not properly adjusted in the rebuild you can get odd behavior. __________________ Randy Summers Never brake in the learning curve! 1984 GMC Sierra project truck http://67-72chevytrucks.com/vboard/s...d.php?t=446737

06-23-2011, 10:32 AM	#4
geeforcem Registered User Join Date: Oct 2003 Location: houston, texas Posts: 26	Re: Motor sounds weaker after driving? Does the truck still have the original catalytic converter? It could be clogging. jeff __________________ Jeff 1986 Chevy C10 Custom Deluxe swb 1983 Chevy Silverado swb stepside, factory 6.2/700r4 2002 GMC Sierra SLT 1979 GMC Jimmy High Sierra 1978 Chevy C10 Big 10 lwb Scottsdale

06-23-2011, 10:50 AM	#5
Cherub Registered User Join Date: Feb 2008 Location: Houston Posts: 970	Re: Motor sounds weaker after driving? Im thinking something simple like getting heat soaked. __________________ 2014 LTZ Z71 Silverado 82 C15 LQ4/4L80E Conversion 78 Suburban build (SOLD) 83 4x4 Suburban(SOLD) 82 C15 (my first truck)

06-23-2011, 05:44 PM	#6
Reziel_1983 Registered User Join Date: Feb 2011 Location: Brownwood, Texas Posts: 421	Re: Motor sounds weaker after driving? Thanks for all the replies guys. I do not think I am leaking any oil, but I will double check to make sure. And no geeforcem it doesn't have catalytic converters on it at all. I will check all the suggestions, thank you! __________________ 1983 Chevy lwb: 400 sbc destroked to 377, comp cams xe 268, Holley Street Dominator Intake, Holley Street Avenger 670 cfm, headers, flowmasters. SOLD 1998 Trans am, mostly stock with magnaflow catback My build thread: http://67-72chevytrucks.com/vboard/s...d.php?t=454329

06-23-2011, 08:15 PM	#7
1LowToy Registered User Join Date: Nov 2009 Location: Sonora California Posts: 860	Re: Motor sounds weaker after driving? After 500 miles on the motor you may need to run the valve adjustment again. Make sense?

06-23-2011, 08:58 PM	#8
rayfinseats Registered User Join Date: Dec 2010 Location: sioux city, iowa Posts: 619	Re: Motor sounds weaker after driving? Do you have a return line to the gas tank? Maybe it's vapor lock.

06-24-2011, 02:07 AM	#10
Pyrotechnic Registered User Join Date: Feb 2007 Location: Austin, TX Posts: 3,930	Re: Motor sounds weaker after driving? I had a motor that sounded better and felt more powerful when cold. My conclusion was the heat crossover under the intake. Having an aluminum intake with all that hot exhaust gas passing under was just not good for power. It was also hard starting when ever you would park it and come back a few minutes later. Not in the sense of a slow starter, but more in the sense of the fuel being boiled out of the carb. Should have blocked off those passages. __________________ 1977 GMC Sierra Grande

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