Engine Detonation - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Caymandave · 08-20-2011, 01:24 PM

Hi All,
I have a 454 C-20 with automatic. I just had new plug wires,plugs,rotor cap,rotor, modula installed.
I am seeing soome detonation when I stop the truck. What do you think is causing this and how do I get that stopped?
Thanks in Advance

RustyBucket · 08-20-2011, 01:35 PM

not a real fix, but shut it off in gear and THEN put it in park....

1970 Bowtie · 08-20-2011, 01:48 PM

Quote:

Originally Posted by Caymandave

Hi All,
I have a 454 C-20 with automatic. I just had new plug wires,plugs,rotor cap,rotor, modula installed.
I am seeing soome detonation when I stop the truck. What do you think is causing this and how do I get that stopped?
Thanks in Advance

You say you just had these parts installed,so I assume that someone else did the work?

Caymandave · 08-20-2011, 02:08 PM

Yes a mechanic who did the new transmission.

ChevLoRay · 08-20-2011, 02:18 PM

Could be a timing issue, but the engine run-on issue could be related to carbon build-up within the combustion chamber. Did it do it before the work was done? If not, I'd be checking the timing. Still, a hot-spot on the top of a piston could be igniting some fuel vapors that may be present within the intake due to some other fault. What year engine/carb do you have? During the mid-Seventies, engine run-on was not uncommon. GM had an anti-dieseling solenoid on a lot of carbs that was designed to close the throttle plate and prevent fuel mixture from entering the intake. If you're running a Q-Jet, there could be some fuel leaking from the plugs beneath the float bowls. That's not uncommon, either.

RustyBucket · 08-20-2011, 02:22 PM

maybe the carb is loose/leaking around the base gasket or intake gaskets. While the engine's idleing squirt some spray start along the manifold gaskets and carb base. If you've got a leak the idle will speed up.

1970 Bowtie · 08-20-2011, 02:26 PM

Have you spoke to him about the problem you are having,and if so what did he tell you?

DT1 · 08-20-2011, 02:28 PM

Quote:

Originally Posted by Caymandave

Hi All,
I have a 454 C-20 with automatic. I just had new plug wires,plugs,rotor cap,rotor, modula installed.
I am seeing soome detonation when I stop the truck. What do you think is causing this and how do I get that stopped?
Thanks in Advance

Detonation or dieseling after the engine is shut down is usually a result of hot chambers and raw fuel. Fuel can percolate from the bowel vent and enter the throttle body. It the chambers are hot enough, it can cause dieseling. Check to see if your throttle plates are fully closed when the engine is off. Some carburetors are equipped with a solenoid actuated throttle stop (Anti-Dieseling Solenoid)that will retract when the ignition is off, allowing the throttle plates to completely shut. If, as you state, you had a mechanic install the parts, I assume he set the timing properly. It wouldn't hurt to check it. Too much advance will cause the engine to run hotter.

Caymandave · 08-20-2011, 05:31 PM

Have not seen any indication of a hotter engine. I will have him check timing and check the throttle body to see if it is tight. All great ideas, thanks a million.

Lee H · 08-20-2011, 06:17 PM

What is you idle RPM set at. Sounds like it is set to high.
Posted via Mobile Device

Caymandave · 08-21-2011, 10:24 AM

No tack so don't know the RPM but it does not sound high. No higher than it ever has been. Going to the shop on Monday Morning.
Thanks

konasummit · 08-21-2011, 01:39 PM

Quote:

Originally Posted by Lee H

What is you idle RPM set at. Sounds like it is set to high.

ya i was having problems with the dieseling and it was just because my idle was set too high, but just try turning down the idle a bit and see if that does the trick

08-20-2011, 01:24 PM	#1
Caymandave Registered User Join Date: Jun 2011 Location: Miramar Beach Florida Posts: 30	Engine Detonation Hi All, I have a 454 C-20 with automatic. I just had new plug wires,plugs,rotor cap,rotor, modula installed. I am seeing soome detonation when I stop the truck. What do you think is causing this and how do I get that stopped? Thanks in Advance

08-20-2011, 01:35 PM	#2
RustyBucket Registered User Join Date: Jul 2009 Location: Space Coast, Fl. Posts: 1,050	Re: Engine Detonation not a real fix, but shut it off in gear and THEN put it in park.... __________________ Dad always said, "Son, WISH IN ONE HAND, and ......." -------------------------------------- -------------------------------------- Current toy trucks: '71 GMC 1500 SUPER CUSTOM short/step, orig. dk. blue, 350/700r, ps,pb, A/C '72 Blazer 2wd, ochre & white, 454, tremecTKO 500 5spd. ps, pb, A/C, tilt Last 10yrs of hobby vehicles, had a FEW more in the 50yrs. before these: '66 Plymouth Belvedere City of Miami cop car clone. '70 Nova 406"sb, 13.5-1, solid roller, Brodix, p.glide/t.brake, back halved, 9" Ford, spool 4.88, cage,ladder bar/coilover, 10.5 tire....... SOLD!! '67 C10 short/step side mount spare -- SOLD!! '72 Jimmy 2wd, 350/350, ps, pb, fun driver, lots of bondo & a shiny red paint job..... SOLD!! '69 Nova 350, 4spd, A/C, ps, p.b, ...SOLD!!

08-20-2011, 02:08 PM	#4
Caymandave Registered User Join Date: Jun 2011 Location: Miramar Beach Florida Posts: 30	Re: Engine Detonation Yes a mechanic who did the new transmission.

08-20-2011, 02:18 PM	#5
ChevLoRay Old Skool Club Join Date: Jun 2001 Location: Benton, AR "The Heart of Arkansas" Posts: 10,880	Re: Engine Detonation Could be a timing issue, but the engine run-on issue could be related to carbon build-up within the combustion chamber. Did it do it before the work was done? If not, I'd be checking the timing. Still, a hot-spot on the top of a piston could be igniting some fuel vapors that may be present within the intake due to some other fault. What year engine/carb do you have? During the mid-Seventies, engine run-on was not uncommon. GM had an anti-dieseling solenoid on a lot of carbs that was designed to close the throttle plate and prevent fuel mixture from entering the intake. If you're running a Q-Jet, there could be some fuel leaking from the plugs beneath the float bowls. That's not uncommon, either. __________________ Member Nr. 2770 '96 GMC Sportside; 4.3/SLT - Daily driven....constantly needs washed. '69 C-10 SWB; 350/TH400 - in limbo The older I get, the better I was.

08-20-2011, 02:22 PM	#6
RustyBucket Registered User Join Date: Jul 2009 Location: Space Coast, Fl. Posts: 1,050	Re: Engine Detonation maybe the carb is loose/leaking around the base gasket or intake gaskets. While the engine's idleing squirt some spray start along the manifold gaskets and carb base. If you've got a leak the idle will speed up. __________________ Dad always said, "Son, WISH IN ONE HAND, and ......." -------------------------------------- -------------------------------------- Current toy trucks: '71 GMC 1500 SUPER CUSTOM short/step, orig. dk. blue, 350/700r, ps,pb, A/C '72 Blazer 2wd, ochre & white, 454, tremecTKO 500 5spd. ps, pb, A/C, tilt Last 10yrs of hobby vehicles, had a FEW more in the 50yrs. before these: '66 Plymouth Belvedere City of Miami cop car clone. '70 Nova 406"sb, 13.5-1, solid roller, Brodix, p.glide/t.brake, back halved, 9" Ford, spool 4.88, cage,ladder bar/coilover, 10.5 tire....... SOLD!! '67 C10 short/step side mount spare -- SOLD!! '72 Jimmy 2wd, 350/350, ps, pb, fun driver, lots of bondo & a shiny red paint job..... SOLD!! '69 Nova 350, 4spd, A/C, ps, p.b, ...SOLD!!

08-20-2011, 02:26 PM	#7
1970 Bowtie It's all in the timing Join Date: May 2009 Location: Lake Mary,Florida Posts: 600	Re: Engine Detonation Have you spoke to him about the problem you are having,and if so what did he tell you? __________________ The Dude Abides. ---------------------- I aint sayin, I'm just sayin.

08-20-2011, 05:31 PM	#9
Caymandave Registered User Join Date: Jun 2011 Location: Miramar Beach Florida Posts: 30	Re: Engine Detonation Have not seen any indication of a hotter engine. I will have him check timing and check the throttle body to see if it is tight. All great ideas, thanks a million.

08-20-2011, 06:17 PM	#10
Lee H Registered User Join Date: Jun 2010 Location: Upland Ca Posts: 4,143	Re: Engine Detonation What is you idle RPM set at. Sounds like it is set to high. Posted via Mobile Device __________________ 1972 C10 SWB, Air, PS, PB, 350/350THM. Second owner. 1965 Corvette roadster, 44K miles, 327/365 SHP, 4 speed, side exhaust, knockoffs, teak, second owner (bought in 1970), Have ALL numbers matching components. My frame off restoration thread: http://67-72chevytrucks.com/vboard/s...d.php?t=556703

08-21-2011, 10:24 AM	#11
Caymandave Registered User Join Date: Jun 2011 Location: Miramar Beach Florida Posts: 30	Re: Engine Detonation No tack so don't know the RPM but it does not sound high. No higher than it ever has been. Going to the shop on Monday Morning. Thanks



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