'72 ls5 problems
Thread Starter
Pro
Joined: Jan 2014
Posts: 566
Likes: 163
From: Earleton Fl
'72 ls5 problems
I have a '72 454, Auto, Air, PS, PB and the car has a miss we can't find.
I had it in the shop-second time, and they did: new battery, ignition wires, points, condenser, rotor, distributor cap, as well as rebuilding the distributor. Found several vacuum leaks, and replaced a lot of vacuum hoses. Set timing, and dwell. I put a new rebuild carburetor on several months ago.
The car seems to idle OK. But when you get up to 40 MPH plus you can feel it miss. The tach also fluctuates 75-100 rpm. If you put it in neutral and rev up the engine you can see the tack bounce, and hear it miss.
Several questions:
How can I check for vacuum leaks? The car is a real nightmare of vacuum hoses. How can I check for leaks without doing each hose one at a time? How much vacuum should I have at idle?
Could this miss be coming from someplace other than the ignition? Could a slipping transmission cause the same feeling, and change in RPMs? If yes, how can I isolate it?
How about the jetting in the carb? Any thoughts on jet size? We are just a little above sea level.
I'm at the end of my rope with this! Any ideas or thoughts will help!
THANK YOU ALL!
I had it in the shop-second time, and they did: new battery, ignition wires, points, condenser, rotor, distributor cap, as well as rebuilding the distributor. Found several vacuum leaks, and replaced a lot of vacuum hoses. Set timing, and dwell. I put a new rebuild carburetor on several months ago.
The car seems to idle OK. But when you get up to 40 MPH plus you can feel it miss. The tach also fluctuates 75-100 rpm. If you put it in neutral and rev up the engine you can see the tack bounce, and hear it miss.
Several questions:
How can I check for vacuum leaks? The car is a real nightmare of vacuum hoses. How can I check for leaks without doing each hose one at a time? How much vacuum should I have at idle?
Could this miss be coming from someplace other than the ignition? Could a slipping transmission cause the same feeling, and change in RPMs? If yes, how can I isolate it?
How about the jetting in the carb? Any thoughts on jet size? We are just a little above sea level.
I'm at the end of my rope with this! Any ideas or thoughts will help!
THANK YOU ALL!
Le Mans Master
Joined: Jan 2001
Posts: 6,692
Likes: 1,366
Try swapping in a generic coil. I had an intermittent miss that took me forever to find.....Just "happened" to find it late one evening while spacing-out as I pondered what to do as the car was idling and I was continuously flashing flashing the timing light on the wall...... when I suddenly noticed a "skip"...hmmm.... then as I paid attention I noticed that it was "skipping" in a non-routine manner. I had an old Datsun back then and I just swapped in it's coil..... immediately fixed that.
PS-It also eliminated a problem I had with the car suddenly dying in really hot weather.....which, as soon as I opened the hood, would cool down the coil, and it would just restart.....that was a pain.
You can pick up a cheap coil at autozone for under 20 bucks:
https://www.autozone.com/ignition-tu...9_576402_17367
PS-It also eliminated a problem I had with the car suddenly dying in really hot weather.....which, as soon as I opened the hood, would cool down the coil, and it would just restart.....that was a pain.
You can pick up a cheap coil at autozone for under 20 bucks:
https://www.autozone.com/ignition-tu...9_576402_17367
I have a '72 454, Auto, Air, PS, PB and the car has a miss we can't find.
I had it in the shop-second time, and they did: new battery, ignition wires, points, condenser, rotor, distributor cap, as well as rebuilding the distributor. Found several vacuum leaks, and replaced a lot of vacuum hoses. Set timing, and dwell. I put a new rebuild carburetor on several months ago.
The car seems to idle OK. But when you get up to 40 MPH plus you can feel it miss. The tach also fluctuates 75-100 rpm. If you put it in neutral and rev up the engine you can see the tack bounce, and hear it miss.
Several questions:
How can I check for vacuum leaks? The car is a real nightmare of vacuum hoses. How can I check for leaks without doing each hose one at a time? How much vacuum should I have at idle?
Could this miss be coming from someplace other than the ignition? Could a slipping transmission cause the same feeling, and change in RPMs? If yes, how can I isolate it?
How about the jetting in the carb? Any thoughts on jet size? We are just a little above sea level.
I'm at the end of my rope with this! Any ideas or thoughts will help!
THANK YOU ALL!
I had it in the shop-second time, and they did: new battery, ignition wires, points, condenser, rotor, distributor cap, as well as rebuilding the distributor. Found several vacuum leaks, and replaced a lot of vacuum hoses. Set timing, and dwell. I put a new rebuild carburetor on several months ago.
The car seems to idle OK. But when you get up to 40 MPH plus you can feel it miss. The tach also fluctuates 75-100 rpm. If you put it in neutral and rev up the engine you can see the tack bounce, and hear it miss.
Several questions:
How can I check for vacuum leaks? The car is a real nightmare of vacuum hoses. How can I check for leaks without doing each hose one at a time? How much vacuum should I have at idle?
Could this miss be coming from someplace other than the ignition? Could a slipping transmission cause the same feeling, and change in RPMs? If yes, how can I isolate it?
How about the jetting in the carb? Any thoughts on jet size? We are just a little above sea level.
I'm at the end of my rope with this! Any ideas or thoughts will help!
THANK YOU ALL!
Race Director
Joined: Apr 2011
Posts: 11,183
Likes: 3,334
From: North of Toronto - Ontario
Double check your intake bolts for tightness
Maybe treat the car like any other chevy and disconnect the "extra" vacuum systems so you only have the power brake and transmission lines and even the pcv (need one of those push in valve cover breathers to replace it. Cap off the other fittings and "T's"
Then try that and see if the miss is still there. If nothing else it might separate the "everything else" from the equation
A fuel line leak, especially where it doesn't drip but will suck air when under load is usually more dramatic and causes the car to fall pretty flat on it's face once you hit the point where it starts to suck more air than fuel and then goes back to OK once the rpm drop back down to where it can keep up
Rebuilt carb (just ask Lars) might not be correct or the choke is set incorrect
Just some WAGs
M
Maybe treat the car like any other chevy and disconnect the "extra" vacuum systems so you only have the power brake and transmission lines and even the pcv (need one of those push in valve cover breathers to replace it. Cap off the other fittings and "T's"
Then try that and see if the miss is still there. If nothing else it might separate the "everything else" from the equation
A fuel line leak, especially where it doesn't drip but will suck air when under load is usually more dramatic and causes the car to fall pretty flat on it's face once you hit the point where it starts to suck more air than fuel and then goes back to OK once the rpm drop back down to where it can keep up
Rebuilt carb (just ask Lars) might not be correct or the choke is set incorrect
Just some WAGs
M
Is my vette stock?? HAHA
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From: Im not allowed to tell you
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pull one plug wire at a time and see if all 8 change at idle. If its just one plug it could be a bad lobe on your cam or a bent valve or something along those lines. If all 8 are the same then its a random thing and your looking at the coil, a shorting plug wire, bad points, crack in the cap, cracked plug, bad gap....... If its random, when was the last major tuneup done?
Last edited by Rescue Rogers; Jun 17, 2018 at 02:00 PM.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,114
From: Crossville TN
Two ideas:
1. What plug gap did you use? If you have a points ignition, you should gap at .035", REGARDLESS of the coil you have installed.
2. If you did some painting on the intake manifold, you need to be certain that the metal-to-metal contact areas between the distributor housing, metal hold-down clamp, and the engine block are FREE of paint. You only need small contact areas which are paint-free. That pathway is the ground connection for the distributor.
1. What plug gap did you use? If you have a points ignition, you should gap at .035", REGARDLESS of the coil you have installed.
2. If you did some painting on the intake manifold, you need to be certain that the metal-to-metal contact areas between the distributor housing, metal hold-down clamp, and the engine block are FREE of paint. You only need small contact areas which are paint-free. That pathway is the ground connection for the distributor.
Last edited by 7T1vette; Jun 17, 2018 at 04:18 PM.
Thread Starter
Pro
Joined: Jan 2014
Posts: 566
Likes: 163
From: Earleton Fl
72 LS5 problems
Thanks for everyone's idea. Heres what I did:
Manifold bolts are tight
The car has had a complete tune up twice in last 6 months..New dist, points, condenser, rotor, dist cap, one new set of plugs and wires.
Measure Vacume-about 20 inches at idle.
Removed fuel filter...still runs rough
put in new fuel filter-no change
Put on another coil-no change
Removed fuel tank cap-no change-thinking maybe not venting?
I put my timing light on the high voltage wire from the coil to the distributor. You can "see" the miss as the timing light flashes. It seems totally random.
I took a piece of wire and went directly from the battery to the plus side of the coil-hopefully eliminating any possible loose connections. No change.
AGAIN THANKS for the thoughts and ideas...Keep them coming...
George
Manifold bolts are tight
The car has had a complete tune up twice in last 6 months..New dist, points, condenser, rotor, dist cap, one new set of plugs and wires.
Measure Vacume-about 20 inches at idle.
Removed fuel filter...still runs rough
put in new fuel filter-no change
Put on another coil-no change
Removed fuel tank cap-no change-thinking maybe not venting?
I put my timing light on the high voltage wire from the coil to the distributor. You can "see" the miss as the timing light flashes. It seems totally random.
I took a piece of wire and went directly from the battery to the plus side of the coil-hopefully eliminating any possible loose connections. No change.
AGAIN THANKS for the thoughts and ideas...Keep them coming...
George
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,114
From: Crossville TN
But you didn't run a jumper ground wire from some metal on the distributor housing to metal on the engine block. You also didn't mention what plug gap you used.
If all you do is check the things that you think are the problem, you'll likely not find the cause.
If all you do is check the things that you think are the problem, you'll likely not find the cause.
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Drifting
Joined: Jul 2004
Posts: 1,556
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From: Skiatook. Oklahoma.
"Try swapping in a generic coil. I had an intermittent miss that took me forever to find.....Just "happened" to find it late one evening while spacing-out as I pondered what to do as the car was idling and I was continuously flashing flashing the timing light on the wall...... when I suddenly noticed a "skip"...hmmm.... then as I paid attention I noticed that it was "skipping" in a non-routine manner. I had an old Datsun back then and I just swapped in it's coil..... immediately fixed that.
PS-It also eliminated a problem I had with the car suddenly dying in really hot weather.....which, as soon as I opened the hood, would cool down the coil, and it would just restart.....that was a pain."
That's exactly what's happening to my 1969 Camaro now. You just confirmed what I suspected.
Thanks.
PS-It also eliminated a problem I had with the car suddenly dying in really hot weather.....which, as soon as I opened the hood, would cool down the coil, and it would just restart.....that was a pain."
That's exactly what's happening to my 1969 Camaro now. You just confirmed what I suspected.
Thanks.
Last edited by orourke; Jun 19, 2018 at 01:49 PM.
Le Mans Master
Joined: Jan 2001
Posts: 6,692
Likes: 1,366
Let us know if the coil swap works for you..... that would be cool. Sure hope so.
"Try swapping in a generic coil. I had an intermittent miss that took me forever to find.....Just "happened" to find it late one evening while spacing-out as I pondered what to do as the car was idling and I was continuously flashing flashing the timing light on the wall...... when I suddenly noticed a "skip"...hmmm.... then as I paid attention I noticed that it was "skipping" in a non-routine manner. I had an old Datsun back then and I just swapped in it's coil..... immediately fixed that.
PS-It also eliminated a problem I had with the car suddenly dying in really hot weather.....which, as soon as I opened the hood, would cool down the coil, and it would just restart.....that was a pain."
That's exactly what's happening to my 1969 Camaro now. You just confirmed what I suspected.
Thanks.
PS-It also eliminated a problem I had with the car suddenly dying in really hot weather.....which, as soon as I opened the hood, would cool down the coil, and it would just restart.....that was a pain."
That's exactly what's happening to my 1969 Camaro now. You just confirmed what I suspected.
Thanks.
Le Mans Master
Joined: Jan 2001
Posts: 6,692
Likes: 1,366
From what I recall placing the timing light on the coil wire makes it flash very rapidly....
Try placing it on an individual plug lead and see if you can still observe the skipping (it should be a bit slower).
You may also have a bad plug, or 2..... I would check each plug lead if the first one I check doesn't show a skip.
Also ensure the good adequate ground as mentioned earlier.
Try placing it on an individual plug lead and see if you can still observe the skipping (it should be a bit slower).
You may also have a bad plug, or 2..... I would check each plug lead if the first one I check doesn't show a skip.
Also ensure the good adequate ground as mentioned earlier.
Thanks for everyone's idea. Heres what I did:
Manifold bolts are tight
The car has had a complete tune up twice in last 6 months..New dist, points, condenser, rotor, dist cap, one new set of plugs and wires.
Measure Vacume-about 20 inches at idle.
Removed fuel filter...still runs rough
put in new fuel filter-no change
Put on another coil-no change
Removed fuel tank cap-no change-thinking maybe not venting?
I put my timing light on the high voltage wire from the coil to the distributor. You can "see" the miss as the timing light flashes. It seems totally random.
I took a piece of wire and went directly from the battery to the plus side of the coil-hopefully eliminating any possible loose connections. No change.
AGAIN THANKS for the thoughts and ideas...Keep them coming...
George
Manifold bolts are tight
The car has had a complete tune up twice in last 6 months..New dist, points, condenser, rotor, dist cap, one new set of plugs and wires.
Measure Vacume-about 20 inches at idle.
Removed fuel filter...still runs rough
put in new fuel filter-no change
Put on another coil-no change
Removed fuel tank cap-no change-thinking maybe not venting?
I put my timing light on the high voltage wire from the coil to the distributor. You can "see" the miss as the timing light flashes. It seems totally random.
I took a piece of wire and went directly from the battery to the plus side of the coil-hopefully eliminating any possible loose connections. No change.
AGAIN THANKS for the thoughts and ideas...Keep them coming...
George
Thread Starter
Pro
Joined: Jan 2014
Posts: 566
Likes: 163
From: Earleton Fl
Burning Brakes
Joined: Jan 2017
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From: The Buckle of the Bible Belt. Joplin Mo
I think you nailed it in your first post. Vacuum is a killer in the Corvette. Just experienced something similar with my 69.
Locate the vacuum block on the intake. find your main vacuum line for the cars headlights and wiper door. Disconnect and cap. if you lose the miss, your leak is in the system. My 454 did not like the low vacuum signal and was running as you indicated. Now its running great, I just have to find the pin hole
Locate the vacuum block on the intake. find your main vacuum line for the cars headlights and wiper door. Disconnect and cap. if you lose the miss, your leak is in the system. My 454 did not like the low vacuum signal and was running as you indicated. Now its running great, I just have to find the pin hole
Thread Starter
Pro
Joined: Jan 2014
Posts: 566
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From: Earleton Fl
Pro
Joined: Oct 2000
Posts: 558
Likes: 22
From: Vancouver, B.C., Canada
When looking for ignition misses I like to run the car in a very dark, blacked out garage. If there's a short somewhere you'll usually see a lovely blue light show. Doesn't take long to see. If you try it, make sure your exhaust is piped to the outside.
Le Mans Master
Joined: Jan 2001
Posts: 9,240
Likes: 221
From: Dryden MI
http://performancetechnician.com/pdf...ion-System.pdf