Shakes really bad at idle
Thread Starter
Racer
Joined: Jun 2015
Posts: 315
Likes: 20
From: Vasteras, Sweden
Thread Starter
Racer
Joined: Jun 2015
Posts: 315
Likes: 20
From: Vasteras, Sweden
Really confused....the shakes are back again!
Feels good first 15-20 minues of driving, then it starts to shake when it`s hot...WTF!!!
Pulled all the plugs, looks god, a bit of oil residue on cyl 8, but no oilconsumption.
Could a bad compression on one cylinder be the cause when it gets reel hot??
Feels good first 15-20 minues of driving, then it starts to shake when it`s hot...WTF!!!
Pulled all the plugs, looks god, a bit of oil residue on cyl 8, but no oilconsumption.
Could a bad compression on one cylinder be the cause when it gets reel hot??
Racer
Joined: Aug 2006
Posts: 330
Likes: 3
From: Wellington, New Zealand
Sounds like a timing issue to me, pull your initial back to around 8 or 10 degrees and test drive. You may be suffering from either too much mechanical advance or too much vacuum advance or a combination of the two at idle and off idle.
The car will run very rough and miss fire with too much advance. A good timing light will let you diagnose where the fault lies.
The car will run very rough and miss fire with too much advance. A good timing light will let you diagnose where the fault lies.
Thread Starter
Racer
Joined: Jun 2015
Posts: 315
Likes: 20
From: Vasteras, Sweden
Sounds like a timing issue to me, pull your initial back to around 8 or 10 degrees and test drive. You may be suffering from either too much mechanical advance or too much vacuum advance or a combination of the two at idle and off idle.
The car will run very rough and miss fire with too much advance. A good timing light will let you diagnose where the fault lies.
The car will run very rough and miss fire with too much advance. A good timing light will let you diagnose where the fault lies.
Why does it not shake at idle before it gets really hot.
Starts to shake like after 30 minutes or so...
Thread Starter
Racer
Joined: Jun 2015
Posts: 315
Likes: 20
From: Vasteras, Sweden
I had 8 initial to start with, now it is 14, runs better with that, the shake is there regardless. New 180 thermostat, new rebuilt Quadrajet by Kent here in Sweden ( he is a reel pro at this ) I have been thinking about the fuel boiling issue...
I am going to increese idle mixture and see what happens.
I am going to increese idle mixture and see what happens.
Racer
Joined: May 2013
Posts: 421
Likes: 6
From: Chicago IL
When you shut your car off, take the air cleaner off and listen for the fuel boiling. If it is, trying running a richer mix and/or add a spacer under the carb if space permits. Can you record a video of the shake? Maybe the tach as well?
Melting Slicks
Joined: Jul 2006
Posts: 2,292
Likes: 494
From: Salmon Arm, BC
Some things to check.....
Does the module in the HEI have dielectric grease between it and the housing? If the module can't transfer heat the module will break down and cause misfires, or just stop functioning at all. A dropped on the floor plug could have a cracked insulator, check them. Make sure you have a solid 12v to the HEI at all times.
Does the module in the HEI have dielectric grease between it and the housing? If the module can't transfer heat the module will break down and cause misfires, or just stop functioning at all. A dropped on the floor plug could have a cracked insulator, check them. Make sure you have a solid 12v to the HEI at all times.
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Thread Starter
Racer
Joined: Jun 2015
Posts: 315
Likes: 20
From: Vasteras, Sweden
Full voltage to the HEI, new plugs.
"dielectric grease between it and the housing"
Not sure what this means, have never disassembled a HEI.
I increased the idle mixture and now it runs a bit smoother.
Will do more adjustments and testdriving if it only stops raining here in Sweden...
"dielectric grease between it and the housing"
Not sure what this means, have never disassembled a HEI.
I increased the idle mixture and now it runs a bit smoother.
Will do more adjustments and testdriving if it only stops raining here in Sweden...
Burning Brakes
Joined: Dec 2008
Posts: 971
Likes: 45
From: Middlesex NJ
Who is the maker of the HEI?
Sounds like your module is getting funny when hot? Not sure what year car you have or how you wired up the HEI. Early C3's had a yellow/white cloth wrapped resistor wire that feed the + of the coil and it dropped the voltage down to about 6-7 volts..you cant use that wire for HEI. HEI needs 12v all the time.
Odd thing though is that you say it will smooth over if you bring it up above 1000rpm?? this doesnt sound like ignition unless when you are idling your voltage is getting too low and when you rev it you get 12v+.
My friend got an inexpensive HEI off ebay and while the distributor itself works well ... they put the cheapest ignition module in it you could find and almost no dielectric grease. The engine would run fine when cold and then once it got hot enough it would just cut out. It would start again and cutout when hot. Module was crap.
Try a new quality ignition module and make sure you have a good coating of dielectric grease on it. Also, get two modules... keep one in the car. They do go bad.
Sounds like your module is getting funny when hot? Not sure what year car you have or how you wired up the HEI. Early C3's had a yellow/white cloth wrapped resistor wire that feed the + of the coil and it dropped the voltage down to about 6-7 volts..you cant use that wire for HEI. HEI needs 12v all the time.
Odd thing though is that you say it will smooth over if you bring it up above 1000rpm?? this doesnt sound like ignition unless when you are idling your voltage is getting too low and when you rev it you get 12v+.
My friend got an inexpensive HEI off ebay and while the distributor itself works well ... they put the cheapest ignition module in it you could find and almost no dielectric grease. The engine would run fine when cold and then once it got hot enough it would just cut out. It would start again and cutout when hot. Module was crap.
Try a new quality ignition module and make sure you have a good coating of dielectric grease on it. Also, get two modules... keep one in the car. They do go bad.
Last edited by mysixtynine; Jun 18, 2015 at 11:32 AM.
Thread Starter
Racer
Joined: Jun 2015
Posts: 315
Likes: 20
From: Vasteras, Sweden
Can not find a brand on the HEI, but it looks like one from Summit.
Forgot to mention this, i also have a MSD unit.
I am with you on the ignition part, i don`t think it is ignition related.
Forgot to mention this, i also have a MSD unit.
I am with you on the ignition part, i don`t think it is ignition related.
Burning Brakes
Joined: Dec 2008
Posts: 971
Likes: 45
From: Middlesex NJ
Guess you have to shoot this when its misbehaving.
Need more info on the ignition. Do you have one of those correct-a-caps on it to make the plug wire routing look better? maybe an email out to MSD tech support would help you? Make sure your voltages are correct at your ignition components when hot.
When its running rough.... you still need air, gas and spark in the right proportions.
You could use a timing light on each plug wire to see if the flashes are rythmic on each and every wire. Would tell you if the ignition is breaking up.
You could also short out each plug wire one at a time with a pin and jumper wire to the carb stud and see if each one makes the shaking worse or has no effect. The NON effect (if there is one) is the cylinder acting up. Then you need to determine why. Just did this on a buddies car to find two bad plug wires.
I see you put another post out there about hard starting..... black smoke is either too much gas or missing ignition events. Maybe when its hot the float level is too high?
Need more info on the ignition. Do you have one of those correct-a-caps on it to make the plug wire routing look better? maybe an email out to MSD tech support would help you? Make sure your voltages are correct at your ignition components when hot.
When its running rough.... you still need air, gas and spark in the right proportions.
You could use a timing light on each plug wire to see if the flashes are rythmic on each and every wire. Would tell you if the ignition is breaking up.
You could also short out each plug wire one at a time with a pin and jumper wire to the carb stud and see if each one makes the shaking worse or has no effect. The NON effect (if there is one) is the cylinder acting up. Then you need to determine why. Just did this on a buddies car to find two bad plug wires.
I see you put another post out there about hard starting..... black smoke is either too much gas or missing ignition events. Maybe when its hot the float level is too high?
Last edited by mysixtynine; Jun 18, 2015 at 12:02 PM.
Thread Starter
Racer
Joined: Jun 2015
Posts: 315
Likes: 20
From: Vasteras, Sweden
The voltage is good at all times, checked every plugwire, no issues.
Tried to short out every plugwire, no issues there either..
Will do the timinglight thing and see if there is any issues.
The start thing pussels me, when it sits 2 days it starts fine, but after 5-6 days it is a reel pain in the *** to start...ignition should not be the case and there is gas..
Tried to short out every plugwire, no issues there either..
Will do the timinglight thing and see if there is any issues.
The start thing pussels me, when it sits 2 days it starts fine, but after 5-6 days it is a reel pain in the *** to start...ignition should not be the case and there is gas..
Thread Starter
Racer
Joined: Jun 2015
Posts: 315
Likes: 20
From: Vasteras, Sweden
Tried to increese the idle mixture, no change...only change is poore milage..
Tried to unhook distributor vacumm to get less advance at idle, no change there either.
The odd thing is that it does not shake before it gets reel hot i.e crusing in town.
Guess i have to bring it to the shop and see what they say.
Tried to unhook distributor vacumm to get less advance at idle, no change there either.
The odd thing is that it does not shake before it gets reel hot i.e crusing in town.
Guess i have to bring it to the shop and see what they say.
Burning Brakes
Joined: Dec 2008
Posts: 971
Likes: 45
From: Middlesex NJ
What trouble shooting have you done when the car is hot, running and shaking? You say you shorted out each plug wire to see if you could isolate each cylinder while it is shaking? The engine should shake worse when you short out a cylinder that is firing and there should be no change when you short out a cylinder that is NOT working.
Do you still have the heat riser valve on the passenger side exhaust manifold? Is it opening fully?
What is the engine vacuum like prior to the issue occurring, and what is it when the issue is occurring?
I am a little puzzled that you said the gap change on the plug being made smaller helped initially.... making the gap smaller will also have an effect on how hard the coil and the module are being stressed for the arc. So it could still be that you have some odd ignition issue that is increased with heat and time.
Do you still have the heat riser valve on the passenger side exhaust manifold? Is it opening fully?
What is the engine vacuum like prior to the issue occurring, and what is it when the issue is occurring?
I am a little puzzled that you said the gap change on the plug being made smaller helped initially.... making the gap smaller will also have an effect on how hard the coil and the module are being stressed for the arc. So it could still be that you have some odd ignition issue that is increased with heat and time.
Last edited by mysixtynine; Jun 22, 2015 at 11:09 AM.
Thread Starter
Racer
Joined: Jun 2015
Posts: 315
Likes: 20
From: Vasteras, Sweden
The shake got worse when i shorted out each cylinder, but i could not find one were the shake was the same when i shorted it out,..maybe it is hard to detect?
It feels like it`s not missing one every cycle and the longer i drive it the worse it gets, it`realy visible on the tach.
Stock exhaust manifolds are replaced with Hedman LT:s
Engine vac is 15 Hg, have not done a messure between hot and cold.
Heat and time is key i think, have to consult a shop and get a second opinion.
Like you said, this puzzels me to.
I am more and more convinced that the solution is ignition related.
Thanx for your input, appreciate it!
It feels like it`s not missing one every cycle and the longer i drive it the worse it gets, it`realy visible on the tach.
Stock exhaust manifolds are replaced with Hedman LT:s
Engine vac is 15 Hg, have not done a messure between hot and cold.
Heat and time is key i think, have to consult a shop and get a second opinion.
Like you said, this puzzels me to.
I am more and more convinced that the solution is ignition related.
Thanx for your input, appreciate it!
Race Director
Joined: Jan 2000
Posts: 12,399
Likes: 247
From: San Jose CA
Have you disconnected every vacuum hose other than the mandatory ones (pcv, vac brakes, choke pull-off and dist) to see if the issue persists?
My suspicion is that something on the other side of a TVS switch has a vac leak.
My suspicion is that something on the other side of a TVS switch has a vac leak.
Thread Starter
Racer
Joined: Jun 2015
Posts: 315
Likes: 20
From: Vasteras, Sweden
Plugged every vacuumconection and started the car...it ran soo smoth!
I let it sit 20 minutes at idle, still ran smooth
Started to connect vacuumlines one by one, when i connected the one to the autotrans the shake was there again...Eureka!!...i hope this is the solution.
Done this part before and did not get this result??
Old cars can be a reel PITA, but when they work, there is nothing that compares
I let it sit 20 minutes at idle, still ran smooth
Started to connect vacuumlines one by one, when i connected the one to the autotrans the shake was there again...Eureka!!...i hope this is the solution.
Done this part before and did not get this result??
Old cars can be a reel PITA, but when they work, there is nothing that compares
Burning Brakes
Joined: Dec 2008
Posts: 971
Likes: 45
From: Middlesex NJ
Are there any TCS vacuum switches on a 72 454? maybe its on the trans and not the intake?
Is there transmission fluid in the line running up to the intake from the modulator?
Maybe when it was getting hot the oil was expanding or thinning enough to suck oil out of the trans via a perforated vacuum modulator diaphragm or at the least here it seems to be causing a vacuum leak?
Just looked at zip... there are TCS switches but I cant pinpoint anything for a 72/454 seems only on 350's?
http://www.zip-corvette.com/catalogs...lt/?cat=&q=tcs
Not sure if the TCS was 4spd or auto or both?? Some folks seem to kill it off due to it causing issues with leaking and hurting performance... you would have to decide on that.
some searching on the forum https://www.corvetteforum.com/forums...d-testing.html
Is there transmission fluid in the line running up to the intake from the modulator?
Maybe when it was getting hot the oil was expanding or thinning enough to suck oil out of the trans via a perforated vacuum modulator diaphragm or at the least here it seems to be causing a vacuum leak?
Just looked at zip... there are TCS switches but I cant pinpoint anything for a 72/454 seems only on 350's?
http://www.zip-corvette.com/catalogs...lt/?cat=&q=tcs
Not sure if the TCS was 4spd or auto or both?? Some folks seem to kill it off due to it causing issues with leaking and hurting performance... you would have to decide on that.
some searching on the forum https://www.corvetteforum.com/forums...d-testing.html
Last edited by mysixtynine; Jun 23, 2015 at 02:56 PM.
Thread Starter
Racer
Joined: Jun 2015
Posts: 315
Likes: 20
From: Vasteras, Sweden
Are there any TCS vacuum switches on a 72 454? maybe its on the trans and not the intake?
Is there transmission fluid in the line running up to the intake from the modulator?
Maybe when it was getting hot the oil was expanding or thinning enough to suck oil out of the trans via a perforated vacuum modulator diaphragm or at the least here it seems to be causing a vacuum leak?
Just looked at zip... there are TCS switches but I cant pinpoint anything for a 72/454 seems only on 350's?
http://www.zip-corvette.com/catalogs...lt/?cat=&q=tcs
Not sure if the TCS was 4spd or auto or both?? Some folks seem to kill it off due to it causing issues with leaking and hurting performance... you would have to decide on that.
some searching on the forum https://www.corvetteforum.com/forums...d-testing.html
Is there transmission fluid in the line running up to the intake from the modulator?
Maybe when it was getting hot the oil was expanding or thinning enough to suck oil out of the trans via a perforated vacuum modulator diaphragm or at the least here it seems to be causing a vacuum leak?
Just looked at zip... there are TCS switches but I cant pinpoint anything for a 72/454 seems only on 350's?
http://www.zip-corvette.com/catalogs...lt/?cat=&q=tcs
Not sure if the TCS was 4spd or auto or both?? Some folks seem to kill it off due to it causing issues with leaking and hurting performance... you would have to decide on that.
some searching on the forum https://www.corvetteforum.com/forums...d-testing.html
Well.. i am a newbe on old muscle cars, had an `07 Mustang GT before, so i am a bit in the dark here and "Learning all the time"
The TCS, if there is one, were is it located if so?
And what is the function?
I will fix the vacuum line to the trans and see what happens.