Sudden Acceleration and loud Backfire - The 1947 - Present Chevrolet & GMC Truck Message Board Network

rennalds · 03-19-2010, 06:48 PM

My son was driving his 71 Chevy and all of the sudden it started to accelerate on its own, he shifted it to nuetral and turned off the ignition and it backfired. He said even when he got out of the truck it sounded like it was running? Any ideas? We had just put a different carbuerator on earlier this week, but everything seemed to be running real good up until now.

**68 Stepside** · 03-19-2010, 07:23 PM

The backfire could be related to the carburetor venturis being open when the key was turned off, and that could also most definitely be why it sounded like it continued to run after he shut it off. It was probably dieseling. As far as accelerating on its own, check the throttle return springs and be sure the linkage isn't binding anywhere.

big mike71 · 03-19-2010, 08:54 PM

It sounds like it has a bad case of Toyota-itis

hayhauler71 · 03-19-2010, 09:02 PM

Quote:

Originally Posted by big mike71

It sounds like it has a bad case of Toyota-itis

I was thinking the same thing big mike

*beechd18* · 03-19-2010, 09:01 PM

See if it's on any of the recent recall lists

neba · 03-19-2010, 10:27 PM

was he turning left? chevy used to have a problem with broken motor mounts. when you would turn left, the engine would torque to the right and pull the throttle linkage with it causing it to accelerate. that recall was to install a cable restricting motor movement. they wouldnt replace the bad motor mounts.

OhOneWS6 · 03-19-2010, 10:33 PM

Quote:

Originally Posted by neba

was he turning left? chevy used to have a problem with broken motor mounts. when you would turn left, the engine would torque to the right and pull the throttle linkage with it causing it to accelerate. that recall was to install a cable restricting motor movement. they wouldnt replace the bad motor mounts.

Just Because Neba mentioned it.
http://67-72chevytrucks.com/vboard/s...3&postcount=13

I'm betting your problem is binding linkage.

**Boog** · 03-20-2010, 09:32 AM

Oh man. Mike you beat the rest of us to it. You know we are all thinking the same thing with this title what with all the media coverage of the ongoing Toyota runaway probs.

I agree. Make sure the carb linkage is not binding. As far as run on after key off it does sound like dieseling due to high engine speed.
Good thinking on the boys part to shove it in neutral.
Some of these unfortunate Toyota owners should be doing that when they experience the runaway deal.

Tx Firefighter · 03-20-2010, 01:12 PM

He has a 71 so throttle linkage should be a non issue.

**leddzepp** · 03-20-2010, 01:18 PM

Sounds like the throttle cable is binding. If so, that's an easy fix.

Too bad fixing a Toyota isn't that simple.

1-PU70 · 03-20-2010, 02:08 PM

Check the return spring on the carb. U should use a double one for safety.

gkesseru · 03-20-2010, 10:33 PM

Agree with the broken left engine mount as a possibility but that wouldn't explain the dieseling.
BTW, I had one problem with a Quadrajet on an aluminum intake (don't remember the brand). Everything looked good when assembled, ran fine. On my first test drive I decided to punch it going into second and the throttle stuck full open. Turned out that the intake got in the way of the throttle linkage and "held" it open when fully depressed. It was pretty exciting for a few seconds since this happened with tires spinning in full acceleration about 50 yards before a hard 90 degree left turn. I needed two hands to make the turn so I had to ride it out until after the turn when I could finally reach down and turn the key off.
I switched to a Holley and never had that problem again.

powell72 · 03-20-2010, 10:44 PM

The truck could definitely diesel if he shut it off while the RPM's were up.

03-19-2010, 06:48 PM	#1
rennalds Registered User Join Date: Nov 2009 Location: vacaville california Posts: 109	Sudden Acceleration and loud Backfire My son was driving his 71 Chevy and all of the sudden it started to accelerate on its own, he shifted it to nuetral and turned off the ignition and it backfired. He said even when he got out of the truck it sounded like it was running? Any ideas? We had just put a different carbuerator on earlier this week, but everything seemed to be running real good up until now.

03-19-2010, 07:23 PM	#2
68 Stepside huh? Join Date: May 2000 Location: Washington, Illinois Posts: 5,692	Re: Sudden Acceleration and loud Backfire The backfire could be related to the carburetor venturis being open when the key was turned off, and that could also most definitely be why it sounded like it continued to run after he shut it off. It was probably dieseling. As far as accelerating on its own, check the throttle return springs and be sure the linkage isn't binding anywhere. __________________ Someday when I'm lonely, Wishing you weren't so far away, Then I will remember Things we said today. RIP El Jay

03-19-2010, 08:54 PM	#3
big mike71 Registered User Join Date: Mar 2009 Location: independence mo Posts: 2,111	Re: Sudden Acceleration and loud Backfire It sounds like it has a bad case of Toyota-itis __________________ I'm not as good as I once was, But I'm as good once as I ever was.

03-19-2010, 09:01 PM	#5
beechd18 Account Suspended Join Date: Nov 2009 Location: Ninnekah,OK Posts: 376	Re: Sudden Acceleration and loud Backfire See if it's on any of the recent recall lists

03-19-2010, 10:27 PM	#6
neba Registered User Join Date: Feb 2010 Location: duluth mn Posts: 108	Re: Sudden Acceleration and loud Backfire was he turning left? chevy used to have a problem with broken motor mounts. when you would turn left, the engine would torque to the right and pull the throttle linkage with it causing it to accelerate. that recall was to install a cable restricting motor movement. they wouldnt replace the bad motor mounts.

03-20-2010, 09:32 AM	#8
Boog laying low Join Date: Mar 2001 Location: Searcy, Ark. USA Posts: 13,448	Re: Sudden Acceleration and loud Backfire Oh man. Mike you beat the rest of us to it. You know we are all thinking the same thing with this title what with all the media coverage of the ongoing Toyota runaway probs. I agree. Make sure the carb linkage is not binding. As far as run on after key off it does sound like dieseling due to high engine speed. Good thinking on the boys part to shove it in neutral. Some of these unfortunate Toyota owners should be doing that when they experience the runaway deal. __________________ Boog 69 Chevy stepside, 358/T350, 4.11 posi, 4.5/4 drop, rallys, poboy driver primer is finer 91 Chevy sportside, Tahoe, Yukon & GMC Crewcab All GM..'nuff said. I stand for the flag and kneel at the cross

03-20-2010, 01:12 PM	#9
Tx Firefighter Watch out for your cornhole ! Join Date: Jun 2003 Location: Azle, Texas Posts: 14,162	Re: Sudden Acceleration and loud Backfire He has a 71 so throttle linkage should be a non issue. __________________ I'm on the Instagram- @Gearhead_Kevin

03-20-2010, 01:18 PM	#10
leddzepp Moderator Join Date: May 2007 Location: Southern Cal Posts: 20,020	Re: Sudden Acceleration and loud Backfire Sounds like the throttle cable is binding. If so, that's an easy fix. Too bad fixing a Toyota isn't that simple. __________________ 1972 C/10 Cheyenne Super SWB. Restored, loaded, slammed. 1968 C/10 50th Anniversary LWB. Unrestored, stock, daily driver/work truck. RIP ElJay RIP 67ChevyRedneck RIP Grumpy Old Man RIP FleetsidePaul

03-20-2010, 02:08 PM	#11
1-PU70 Registered User Join Date: Apr 2000 Location: Bradenton, FL Posts: 1,036	Re: Sudden Acceleration and loud Backfire Check the return spring on the carb. U should use a double one for safety. __________________ 1970 CST/10 402,700R4,3:73 posi,AC,PS,PB,TLT,PW,Buckets with heaters

03-20-2010, 10:33 PM	#12
gkesseru Registered User Join Date: Dec 2009 Location: California, Maryland Posts: 544	Re: Sudden Acceleration and loud Backfire Agree with the broken left engine mount as a possibility but that wouldn't explain the dieseling. BTW, I had one problem with a Quadrajet on an aluminum intake (don't remember the brand). Everything looked good when assembled, ran fine. On my first test drive I decided to punch it going into second and the throttle stuck full open. Turned out that the intake got in the way of the throttle linkage and "held" it open when fully depressed. It was pretty exciting for a few seconds since this happened with tires spinning in full acceleration about 50 yards before a hard 90 degree left turn. I needed two hands to make the turn so I had to ride it out until after the turn when I could finally reach down and turn the key off. I switched to a Holley and never had that problem again. __________________ 72 Fleet (died) 78 Step (sold) 55 Step named Fred (sold) 00 F150 68 Step (named El Scorcho by PO) Build thread for the new El Scorcho http://67-72chevytrucks.com/vboard/s...d.php?t=392932

03-20-2010, 10:44 PM	#13
powell72 Senior Member Join Date: Jan 2005 Location: Loveland Co. Posts: 3,098	Re: Sudden Acceleration and loud Backfire The truck could definitely diesel if he shut it off while the RPM's were up. __________________ Chris 74 Custom Deluxe SWB 350/350/3.73’s 99 2wd Silverado RCSB 5.3/4L60/3.90’s http://www.classictrucks.com/feature...short_bed.html



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