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Topic: Engine Stutter

in Forum: C3 Engines

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Engine Stutter

Posted: 3/4/07 7:29pm Message 1 of 14
thargrav
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Huntsville, AL - USA
Joined: 3/4/2007
Posts: 17
Vette(s): 1977 Black on black

I have a problem with my 1977 Vette - the engine ruins great around town but as soon as I get on the highway, it randomly stutters. The symptoms feel like a back fire to me. I've driven wioth the problem enough to know that it starts at about 62 MPH RPM & gets worse as the speed increases. Any ideas?

The car is a 1977 L48 with a Turbo Hydromatic 350 transmission, original carb & factory tune.
 
Thanks in advance, Tom
 

Engine Stutter

Posted: 3/4/07 7:54pm Message 2 of 14
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Gunslinger
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Frederick, MD - USA
Joined: 9/8/2003
Posts: 3398
Vette(s): 1969 convertible L71 427/435 4-speed black interior
It could be a lot of things...ignition breakdown, vacuum leak, carb out of adjustment or leak, a clogged fuel filter. A lot of stuff.

You need to narrow it down...does it idle smoothly or break down while revving the engine in neutral? How old are the spark plugs and plug wires? Make sure all the plug wires are on tight and routed correctly...they could be in a crossfire condition if not routed correctly. If the wires aren't on tight one could be grounding out.

Attach a vacuum gauge to a source on the intake manifold...that can tell you a lot.

It does sound like either an ignition breakdown at higher rpm's or a carburetor issue as the most likely, but down't overlook anything as basic as a fuel filter (even back inside the gas tank).

Engine Stutter

Posted: 3/4/07 8:14pm Message 3 of 14
thargrav
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Huntsville, AL - USA
Joined: 3/4/2007
Posts: 17
Vette(s): 1977 Black on black
The car idles fine & runs great until I reach 62 - 65 MPH. I've also run the engine hard at lower speeds to see if the symptoms appear - they don't, unless they are being covered up under load. I did hear some pinging & I topped off with 93 octane gas & the pinging went away. The engine has run trouble free for over a year.
 
The wires are routed correctly - I still need to look at the plugs. The plugs & wires have about 5K miles on them.
 
I've done the following so far:
Rebuilt & recalibracted the Q-jet carb.
Replaced the fuel filter (part of rebuild).
Replaced the ignition module.
Checked for vacuum leaks.
 
I have not rev'd the engine in neutral but it's getting late & I don't need to disrupt the neighbors.
 
I bought a replacement coil & planned on installing it tonight but I just found out that the passenger side latch won't release. I guess this is something else to chase in the morning.
 

Engine Stutter

Posted: 3/4/07 9:26pm Message 4 of 14
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Adams' Apple
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Duncanville, TX - USA
Joined: 11/8/2003
Posts: 20213
Vette(s): #1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas
How many miles are on it? You may have a timing chain about to take a dump. Those years have nylon covered teeth on the cam gear, and that stuff will break over time, and cause the cam timing to fluctuate. If you take the dist. cap off, turn the engine by hand, and see how far it moves before the rotor in the dist. starts to move. If it's more than a degree or two, the timing chain needs to be inspected/replaced.
It could also be the sock filter in the tank, as Bruce suggests. So many possibilities..

Joel Adams
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Engine Stutter

Posted: 3/5/07 2:58am Message 5 of 14
thargrav
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Huntsville, AL - USA
Joined: 3/4/2007
Posts: 17
Vette(s): 1977 Black on black
The car has 63,000 miles on the clock.

Engine Stutter

Posted: 3/5/07 5:55am Message 6 of 14
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Adams' Apple
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Duncanville, TX - USA
Joined: 11/8/2003
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Vette(s): #1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas
See if the new coil helps. It may be the problem. Make sure the new coil has the same color wires on it...there are several different ones.
Most of the nylon style cam gears are only good for about 40-50,000 miles, if that. The 4spd cars are harder on the gears than the automatics, tho.
Keep us posted.

Joel Adams
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Engine Stutter

Posted: 3/5/07 6:02am Message 7 of 14
OlrustysGhost
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Spotsylvania, VA - USA
Joined: 1/20/2007
Posts: 293
Vette(s): 1977 Silver Coupe

When I bought mine. I had to go to Pennsylvania to get it. on the test drive the guy drove and I had shotgun. He was always flooring it and saying how got it ran.  My wife liked it , so I gave him the cash he requested. The thing Idled fine in his driveway. But when I got it on the superslab at cruising speed , it would sputter just like you are talking about . He had let the car set and it had a water build up in the tank. It took about 4 tanks of fuel just to get the moisture out. I always do a complete fill-up if It going to set for a while. 

Engine Stutter

Posted: 3/6/07 5:49am Message 8 of 14
thargrav
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Huntsville, AL - USA
Joined: 3/4/2007
Posts: 17
Vette(s): 1977 Black on black
I did some more troubleshooting - the new coil seemed to help some, but it could be my imagination.
 
I did get a chance to rev the engine in the driveway - it starts missing at 2700 RPM, no load. This says "ignition problem" to me.

Engine Stutter

Posted: 3/6/07 5:58am Message 9 of 14
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Adams' Apple
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Duncanville, TX - USA
Joined: 11/8/2003
Posts: 20213
Vette(s): #1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas
You may need to verify that you have a good, solid 12v going to the dist. Use a volt-meter for this, as a test light will only tell you if there IS voltage, not how much. You may have a connector problem somewhere that is keeping the dist. from getting the clean voltage it needs to operate properly. Just another idea/theory...

And another...have you looked at the wires for the pick-up/pole piece in the dist? The wires are subject to a lot of heat, and can fail intermittently. If the wires are brittle, or mushy(mostly mushy), and the insulation falls off when you move them around, that could be the source of the miss/surge. Adams' Apple2007-03-06 06:02:53

Joel Adams
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Engine Stutter

Posted: 3/6/07 7:18am Message 10 of 14
thargrav
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Huntsville, AL - USA
Joined: 3/4/2007
Posts: 17
Vette(s): 1977 Black on black
I already looked at the wiring & it seems to be in great shape. I ordered a replacement condenser - it will be in wednesday. I've not yet checked the voltage at the distributor.
 
Thanks, Tom

in Forum: C3 Engines

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