454, unstable idle when hot
Thread Starter
Racer
Joined: Jun 2015
Posts: 315
Likes: 20
From: Vasteras, Sweden
454, unstable idle when hot
`72 454, when engine gets real hot the idle gets rough.
It seems like when the oilpressure goes down the idle gets more and more rough, could it be a lifter that`s gone bad, when cool idle is good.
There is a knocking sound from one off the lifters i suspect.
Rockers are not stock, got rollers, i have heard they can make some noise....
Oilpressure is 35 when hot, 60-70 Cold, not sure if meter is right.
It seems like when the oilpressure goes down the idle gets more and more rough, could it be a lifter that`s gone bad, when cool idle is good.
There is a knocking sound from one off the lifters i suspect.
Rockers are not stock, got rollers, i have heard they can make some noise....
Oilpressure is 35 when hot, 60-70 Cold, not sure if meter is right.
Last edited by clwi; Aug 5, 2015 at 12:15 PM.
Melting Slicks
Joined: Apr 2009
Posts: 2,632
Likes: 112
From: Great Plains Iowa
`72 454, when engine gets real hot the idle gets rough.
It seems like when the oilpressure goes down the idle gets more and more rough, could it be a lifter that`s gone bad, when cool idle is good.
There is a knocking sound from one off the lifters i suspect.
Rockers are not stock, got rollers, i have heard they can make some noise....
Oilpressure is 35 when hot, 60-70 Cold, not sure if meter is right.
It seems like when the oilpressure goes down the idle gets more and more rough, could it be a lifter that`s gone bad, when cool idle is good.
There is a knocking sound from one off the lifters i suspect.
Rockers are not stock, got rollers, i have heard they can make some noise....
Oilpressure is 35 when hot, 60-70 Cold, not sure if meter is right.
Your idle mixture might be a tad lean so try opening up your mixture screws another 1/8th to 1/4 turn.
There isn't any relationship between hot oil pressure and idle quality.
As the 454's use push rod guide plates they do create more noise.
Your oil pressure is normal for the cold and hot temperatures.
Thread Starter
Racer
Joined: Jun 2015
Posts: 315
Likes: 20
From: Vasteras, Sweden
Your idle mixture might be a tad lean so try opening up your mixture screws another 1/8th to 1/4 turn.
There isn't any relationship between hot oil pressure and idle quality.
As the 454's use push rod guide plates they do create more noise.
Your oil pressure is normal for the cold and hot temperatures.
There isn't any relationship between hot oil pressure and idle quality.
As the 454's use push rod guide plates they do create more noise.
Your oil pressure is normal for the cold and hot temperatures.
The knocking sound confuses me..
I do have an Edelbrock 2162 cam, 218/228@0,50, 0,500"/0,500" LSA 114, but that is a very mild cam and should not be the issue..
Last edited by clwi; Aug 5, 2015 at 02:18 PM.
Melting Slicks
Joined: Apr 2009
Posts: 2,632
Likes: 112
From: Great Plains Iowa
Roller tip rockers DO make more noise as the roller clicks against the side of the rocker arm casting. So between the guide plates and roller tip rocker arms they do make more noise. Quite often you'll notice the clicking goes away as the rpm increases. And I have also found rocker arms will often hit the oil baffles in the valve covers and I had one in which the rocker arm was actually striking the underside of the OEM valve cover that was about 5/16" shorter than aftermarket valve covers.
Thread Starter
Racer
Joined: Jun 2015
Posts: 315
Likes: 20
From: Vasteras, Sweden
[QUOTE=toobroketoretire;1590205999]Roller tip rockers DO make more noise as the roller clicks against the side of the rocker arm casting. So between the guide plates and roller tip rocker arms they do make more noise. Quite often you'll notice the clicking goes away as the rpm increases. And I have also found rocker arms will often hit the oil baffles in the valve covers and I had one in which the rocker arm was actually striking the underside of the OEM valve cover that
Yes, i have roller tip rockers, but there is just on one cylinder i can hear the knocking...
Had a car years ago with a bad piston and i made a similar noise.
At cruise with light throttle there is almost no knocking, but when i add a little throttle the knocking increse..
Yes, i have roller tip rockers, but there is just on one cylinder i can hear the knocking...
Had a car years ago with a bad piston and i made a similar noise.
At cruise with light throttle there is almost no knocking, but when i add a little throttle the knocking increse..
Thread Starter
Racer
Joined: Jun 2015
Posts: 315
Likes: 20
From: Vasteras, Sweden
Drifting
Joined: Jul 2011
Posts: 1,697
Likes: 139
From: Syracuse NY
Nobody has suggested vacuum leak? When the intake gets good and hot it may be warping enough to create a intake or carb base leak. Its as simple as re-torquing all your manifold fasteners......worth 15 minutes of your time just to check it.
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Thread Starter
Racer
Joined: Jun 2015
Posts: 315
Likes: 20
From: Vasteras, Sweden
No vacuum leak or ignition issues, checked all this.
Thread Starter
Racer
Joined: Jun 2015
Posts: 315
Likes: 20
From: Vasteras, Sweden
Previous owner did the cam swap when he renovated the heads and did a new grind on crank with new bearings.
What puzzels me is when it`s cold idle is very stable....
Carb, ignition and vacuum is checked.
Last edited by clwi; Aug 6, 2015 at 12:48 PM.
Le Mans Master
Joined: Apr 2011
Posts: 6,284
Likes: 1,171
From: Hermosa
Your corvette is doing what most do when they get hot. When the engine bay is saturated with heat so is the intake. The mixture setting on the carb is too rich for 130*-140* air. Leading to a rich mixture at that moment making your idle worse. Also your intake may be hot enough to be causing some percolation in the carb. Both of these things are detrimental to idle quality.
Oil pressure is absolutely connected to idle quality. I would expect toobroke to know that. The oil pump is driven by the distrubitor which is driven by the cam. Lower rpm = lower oil pressure. So your low or loping idle is affecting your oil pressure not the other way around.
Could also be that you are on the edge of what your vacuum advance can accept for minimum vacuum. Go even 100 rpm lower and you vacuum can stops advancing your timing leading to an even worse idle. Probably contributing to why you can't idle lower than 700 RPM.
Oil pressure is absolutely connected to idle quality. I would expect toobroke to know that. The oil pump is driven by the distrubitor which is driven by the cam. Lower rpm = lower oil pressure. So your low or loping idle is affecting your oil pressure not the other way around.
Could also be that you are on the edge of what your vacuum advance can accept for minimum vacuum. Go even 100 rpm lower and you vacuum can stops advancing your timing leading to an even worse idle. Probably contributing to why you can't idle lower than 700 RPM.
Thread Starter
Racer
Joined: Jun 2015
Posts: 315
Likes: 20
From: Vasteras, Sweden
Your corvette is doing what most do when they get hot. When the engine bay is saturated with heat so is the intake. The mixture setting on the carb is too rich for 130*-140* air. Leading to a rich mixture at that moment making your idle worse. Also your intake may be hot enough to be causing some percolation in the carb. Both of these things are detrimental to idle quality.
Oil pressure is absolutely connected to idle quality. I would expect toobroke to know that. The oil pump is driven by the distrubitor which is driven by the cam. Lower rpm = lower oil pressure. So your low or loping idle is affecting your oil pressure not the other way around.
Could also be that you are on the edge of what your vacuum advance can accept for minimum vacuum. Go even 100 rpm lower and you vacuum can stops advancing your timing leading to an even worse idle. Probably contributing to why you can't idle lower than 700 RPM.
Oil pressure is absolutely connected to idle quality. I would expect toobroke to know that. The oil pump is driven by the distrubitor which is driven by the cam. Lower rpm = lower oil pressure. So your low or loping idle is affecting your oil pressure not the other way around.
Could also be that you are on the edge of what your vacuum advance can accept for minimum vacuum. Go even 100 rpm lower and you vacuum can stops advancing your timing leading to an even worse idle. Probably contributing to why you can't idle lower than 700 RPM.
I am running with manifold vac to distributor, tried to plug it to only get initial timing, same rough idle still...
Le Mans Master
Joined: Apr 2011
Posts: 6,284
Likes: 1,171
From: Hermosa
And it wouldn't make a difference if the vacuum advance has already dropped out, right? Try putting a longer hose on there and advancing the timing by sucking on the hose. If you get improvement then you just proved that the vac advance is dropping out at idle due to insuffecient vacuum.
Melting Slicks
Joined: Apr 2007
Posts: 3,189
Likes: 111
From: Tolland CT
How "hot" is hot? What temps are you reaching?
Does the idle smooth out if you rev the engine several times, then eventually start to idle rough again?
I'm having a similar issue with my 70 454 which I suspect is partly attributable to ethanol in modern gas, possibly percolation in the carb, too much heat. Like yours, my 454 idles great until it has been run for about an hour on a hot day.
Does the idle smooth out if you rev the engine several times, then eventually start to idle rough again?
I'm having a similar issue with my 70 454 which I suspect is partly attributable to ethanol in modern gas, possibly percolation in the carb, too much heat. Like yours, my 454 idles great until it has been run for about an hour on a hot day.
Thread Starter
Racer
Joined: Jun 2015
Posts: 315
Likes: 20
From: Vasteras, Sweden
And it wouldn't make a difference if the vacuum advance has already dropped out, right? Try putting a longer hose on there and advancing the timing by sucking on the hose. If you get improvement then you just proved that the vac advance is dropping out at idle due to insuffecient vacuum.
Thread Starter
Racer
Joined: Jun 2015
Posts: 315
Likes: 20
From: Vasteras, Sweden
How "hot" is hot? What temps are you reaching?
Does the idle smooth out if you rev the engine several times, then eventually start to idle rough again?
I'm having a similar issue with my 70 454 which I suspect is partly attributable to ethanol in modern gas, possibly percolation in the carb, too much heat. Like yours, my 454 idles great until it has been run for about an hour on a hot day.
Does the idle smooth out if you rev the engine several times, then eventually start to idle rough again?
I'm having a similar issue with my 70 454 which I suspect is partly attributable to ethanol in modern gas, possibly percolation in the carb, too much heat. Like yours, my 454 idles great until it has been run for about an hour on a hot day.
My conclusion is that it has something to do with oilpressure..
As soon pressure drops to 35 when hot the problem starts.
Does not smooth out after reving.
This drives me crazy
On a really hot day it goes up and down 50-100rpm at idle and shakes way to much.
Melting Slicks
Joined: Jul 2009
Posts: 2,091
Likes: 40
I'm confused as to the development of this issue.
I take it , the engine was running fine for years , months , days ?
When did you first notice the issue....it must have been fine at some point.
Is the problem totally new to the car? Or did you buy it with this issue ?
I take it , the engine was running fine for years , months , days ?
When did you first notice the issue....it must have been fine at some point.
Is the problem totally new to the car? Or did you buy it with this issue ?
Safety Car
Joined: Jan 2009
Posts: 4,000
Likes: 299
From: New York
Oil pressure is an unlikely event to cause any running issues . .
I would say the choke is staying slightly closed And I derive this opinion based on your statements "idles fine cold but when warm not so good" . .
Also turn that idle up, 700 in drive for a bb with a better cam then stock should shoot for 750 or better at idle when warm in drive .
I would say the choke is staying slightly closed And I derive this opinion based on your statements "idles fine cold but when warm not so good" . .
Also turn that idle up, 700 in drive for a bb with a better cam then stock should shoot for 750 or better at idle when warm in drive .
Le Mans Master
Joined: Apr 2011
Posts: 6,284
Likes: 1,171
From: Hermosa
I'm confused as to the development of this issue.
I take it , the engine was running fine for years , months , days ?
When did you first notice the issue....it must have been fine at some point.
Is the problem totally new to the car? Or did you buy it with this issue ?
I take it , the engine was running fine for years , months , days ?
When did you first notice the issue....it must have been fine at some point.
Is the problem totally new to the car? Or did you buy it with this issue ?