Need help diagnosing [Video]
Thread Starter
Safety Car
Joined: Dec 2008
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From: North New Jersey
Need help diagnosing [Video]
Hey guys,
My buddy's Corvette is having a problem. When you drive it normally, going easy, it is completely fine. Once you step on the gas hard, it stumbles or something... If you gradually accelerate, the car is fine... It is only when you punch it.
When you punch it, it accelerates until the "stumbling" happens then it stops accelerating as fast, the rpms dont go up as quick, and then it all of a sudden "grabs" and accelerates normally...
It is a 94 Automatic with 60k miles and at redline it wont shift under full throttle. The videos below give you an idea of what the engine sounds like when it is happening... The torque converter is locking up (I tested that).
I think it might be something to do with the tranny but even in neutral when you rev the engine quickly, it "stumbles"
Additionally, the fuel pressure is running perfect. Even with the car "stumbling" the pressure is steady.
Any help would be appreciated!
http://www.youtube.com/watch?v=SOjOsgow2bY
http://www.youtube.com/watch?v=8b7bcBCQBQo
My buddy's Corvette is having a problem. When you drive it normally, going easy, it is completely fine. Once you step on the gas hard, it stumbles or something... If you gradually accelerate, the car is fine... It is only when you punch it.
When you punch it, it accelerates until the "stumbling" happens then it stops accelerating as fast, the rpms dont go up as quick, and then it all of a sudden "grabs" and accelerates normally...
It is a 94 Automatic with 60k miles and at redline it wont shift under full throttle. The videos below give you an idea of what the engine sounds like when it is happening... The torque converter is locking up (I tested that).
I think it might be something to do with the tranny but even in neutral when you rev the engine quickly, it "stumbles"
Additionally, the fuel pressure is running perfect. Even with the car "stumbling" the pressure is steady.
Any help would be appreciated!
http://www.youtube.com/watch?v=SOjOsgow2bY
http://www.youtube.com/watch?v=8b7bcBCQBQo
Last edited by dogfish246; Sep 28, 2012 at 08:22 AM. Reason: added 60k miles
Pro
Joined: Aug 2012
Posts: 663
Likes: 1
From: Nashville TN
Distributor, plugs and wires are the first places to start. Mine was just like that and these parts were worn out.
Run it in the dark and see it you see sparks flying around the plug wires.
Run it in the dark and see it you see sparks flying around the plug wires.
Last edited by bassackwards; Sep 27, 2012 at 11:26 PM.
Thread Starter
Safety Car
Joined: Dec 2008
Posts: 3,588
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From: North New Jersey
Any other ideas?
Safety Car
Joined: Apr 2011
Posts: 3,660
Likes: 22
do the obvious...
get the fuel pressure gauge out and see what FP is at key on...idle, and as the eng revs to 4-5000. Note the ability of the FP to keep up with the demand.'
is it getting knock counts? is the EGR stuck open>?
Is the FSM open to the drivability & emissions section?
get the fuel pressure gauge out and see what FP is at key on...idle, and as the eng revs to 4-5000. Note the ability of the FP to keep up with the demand.'
is it getting knock counts? is the EGR stuck open>?
Is the FSM open to the drivability & emissions section?
Thread Starter
Safety Car
Joined: Dec 2008
Posts: 3,588
Likes: 10
From: North New Jersey
do the obvious...
get the fuel pressure gauge out and see what FP is at key on...idle, and as the eng revs to 4-5000. Note the ability of the FP to keep up with the demand.'
is it getting knock counts? is the EGR stuck open>?
Is the FSM open to the drivability & emissions section?
get the fuel pressure gauge out and see what FP is at key on...idle, and as the eng revs to 4-5000. Note the ability of the FP to keep up with the demand.'
is it getting knock counts? is the EGR stuck open>?
Is the FSM open to the drivability & emissions section?
How can I check for knock counts?
Le Mans Master
Joined: Dec 2006
Posts: 5,139
Likes: 482
From: H-Town Texas
I'm thinking spark issues as well. Without knowing type and mileage on plugs and wires it's hard to say. But coil, icm could be going as well.
As far as fuel, my first thought is fuel pressure regulator, if the gauge is reading good pressure.
Also, and maybe you have, but leave the gauge on and turn it off. See how long it takes for the pressure to drop. As in leaking injector(s)
Third, and long shot, perhaps he has a cat going out. Exhaust flow at idle good, then sudden build up of back pressure on acceleration?
But it really sounds like a misfire to me, so I'm sticking with spark issue. Probably not the opti, however, if it runs well under all other conditions than rapid throttle increase.
As far as fuel, my first thought is fuel pressure regulator, if the gauge is reading good pressure.
Also, and maybe you have, but leave the gauge on and turn it off. See how long it takes for the pressure to drop. As in leaking injector(s)
Third, and long shot, perhaps he has a cat going out. Exhaust flow at idle good, then sudden build up of back pressure on acceleration?
But it really sounds like a misfire to me, so I'm sticking with spark issue. Probably not the opti, however, if it runs well under all other conditions than rapid throttle increase.
Drifting
Joined: Feb 2008
Posts: 1,537
Likes: 177
From: NE Ohio
2024 C4 of the Year Finalist - Unmodified
I had a prolem about the same. Turned out to e plug wires. Sprayed water on wires no change, no llight show in dark garage. Put timing light on one wire at a time and on 6 I got a radical flashing. New wires and new plugs and wow smooth and it runs like a mad bear.
Drifting
Joined: Dec 2007
Posts: 1,672
Likes: 8
From: Sumter South Carolina
+1 for ignition prob, sounds like the timing isnt advancing... if the other stuff fails id put a light on it and watch your timing when you rev it and see if it moves from base but you have the opti so im not familiar with that system. If it was an L98 id say that timing wire might be disconnected or something. Also make sure your TPS (throttle position sensor) is tight and set correct and working right. I have had simmilar symptoms and turned out the thing was loose. But id do wires and plugs first!
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Thread Starter
Safety Car
Joined: Dec 2008
Posts: 3,588
Likes: 10
From: North New Jersey
I'm thinking spark issues as well. Without knowing type and mileage on plugs and wires it's hard to say. But coil, icm could be going as well.
As far as fuel, my first thought is fuel pressure regulator, if the gauge is reading good pressure.
Also, and maybe you have, but leave the gauge on and turn it off. See how long it takes for the pressure to drop. As in leaking injector(s)
Third, and long shot, perhaps he has a cat going out. Exhaust flow at idle good, then sudden build up of back pressure on acceleration?
But it really sounds like a misfire to me, so I'm sticking with spark issue. Probably not the opti, however, if it runs well under all other conditions than rapid throttle increase.
As far as fuel, my first thought is fuel pressure regulator, if the gauge is reading good pressure.
Also, and maybe you have, but leave the gauge on and turn it off. See how long it takes for the pressure to drop. As in leaking injector(s)
Third, and long shot, perhaps he has a cat going out. Exhaust flow at idle good, then sudden build up of back pressure on acceleration?
But it really sounds like a misfire to me, so I'm sticking with spark issue. Probably not the opti, however, if it runs well under all other conditions than rapid throttle increase.
I was thinking it could be a cat but it is interesting that it wont shift at redline... Thanks for the idea!!!
Thread Starter
Safety Car
Joined: Dec 2008
Posts: 3,588
Likes: 10
From: North New Jersey
Thread Starter
Safety Car
Joined: Dec 2008
Posts: 3,588
Likes: 10
From: North New Jersey
+1 for ignition prob, sounds like the timing isnt advancing... if the other stuff fails id put a light on it and watch your timing when you rev it and see if it moves from base but you have the opti so im not familiar with that system. If it was an L98 id say that timing wire might be disconnected or something. Also make sure your TPS (throttle position sensor) is tight and set correct and working right. I have had simmilar symptoms and turned out the thing was loose. But id do wires and plugs first!
Le Mans Master
Joined: Dec 2006
Posts: 5,139
Likes: 482
From: H-Town Texas
I added the mileage in the first post but it is 60k miles... I tried all of the fuel pressure tests and it is not the fuel pressure regulator and not leaky injectors...
I was thinking it could be a cat but it is interesting that it wont shift at redline... Thanks for the idea!!!
I was thinking it could be a cat but it is interesting that it wont shift at redline... Thanks for the idea!!!
Just start with the basics, ignition from the plugs backward to the coil and icm. Of course air filter, and make sure the maf is clean, as well as the throttle body. Check the PVC, if this is clogged it can cause some stumbling. Vacuum hoses etc. But I still can't help but think there's a misfire there.
The cat is a longshot, and really no way to know until the insides start shooting 'glitter' out of the tail pipe.
As far as shifting at redline, maybe it's related or maybe a seperate deal. The only experience I have with this trans was the 4l60 in my
98 Z28, and it never had that problem, so I didn't have to learn about it.
Team Owner
Joined: Dec 2000
Posts: 90,675
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From: SE NY
Cruise-In II Veteran
To test for a clogged fuel filter:
-remove vac line from FPR & plug it
-start engine; fuel pressure should be at max value
-pop the accelerator; fuel pressure should remain rock steady, else replace fuel filter.
-remove vac line from FPR & plug it
-start engine; fuel pressure should be at max value
-pop the accelerator; fuel pressure should remain rock steady, else replace fuel filter.
Thread Starter
Safety Car
Joined: Dec 2008
Posts: 3,588
Likes: 10
From: North New Jersey
Thread Starter
Safety Car
Joined: Dec 2008
Posts: 3,588
Likes: 10
From: North New Jersey
Sorry, I meant the mileage on the plugs and wires.
Just start with the basics, ignition from the plugs backward to the coil and icm. Of course air filter, and make sure the maf is clean, as well as the throttle body. Check the PVC, if this is clogged it can cause some stumbling. Vacuum hoses etc. But I still can't help but think there's a misfire there.
The cat is a longshot, and really no way to know until the insides start shooting 'glitter' out of the tail pipe.
As far as shifting at redline, maybe it's related or maybe a seperate deal. The only experience I have with this trans was the 4l60 in my
98 Z28, and it never had that problem, so I didn't have to learn about it.
Just start with the basics, ignition from the plugs backward to the coil and icm. Of course air filter, and make sure the maf is clean, as well as the throttle body. Check the PVC, if this is clogged it can cause some stumbling. Vacuum hoses etc. But I still can't help but think there's a misfire there.
The cat is a longshot, and really no way to know until the insides start shooting 'glitter' out of the tail pipe.
As far as shifting at redline, maybe it's related or maybe a seperate deal. The only experience I have with this trans was the 4l60 in my
98 Z28, and it never had that problem, so I didn't have to learn about it.
Le Mans Master
Joined: Dec 2006
Posts: 5,139
Likes: 482
From: H-Town Texas
I bought my car with 24K on the clock, by 60K I was on my third set of plugs. They say platinums are good for 100K, but I don't believe so. Get the tune up stuff done and then see where you're at.
Thread Starter
Safety Car
Joined: Dec 2008
Posts: 3,588
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From: North New Jersey
Safety Car
Joined: Apr 2011
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Thats should be OBD-II.....or a mid-stream hybrid ecm...so it can easily be scanned with the parts store type scan tools.
Have ANY flash codes been detected or read?
spark advance/timing is one possible place to explore, but the OPTI is certainly a leading suspect. Anyone been under the hood with the water hose? or a pump leak? OPTIs go south and misfire, or cause stumble when they get wet. 7 of 10 times they get replaced. They are not as easy to "refresh" and dry with a bowl of rice as a cell phone...OPTIs are a little more fragile. They hate water, bottom line. You might try blowing out the cap with air as best you can, and see if that changes anything. I've seen dirty or corroded connections in the harness plugs cause these same symptoms.
Have ANY flash codes been detected or read?
spark advance/timing is one possible place to explore, but the OPTI is certainly a leading suspect. Anyone been under the hood with the water hose? or a pump leak? OPTIs go south and misfire, or cause stumble when they get wet. 7 of 10 times they get replaced. They are not as easy to "refresh" and dry with a bowl of rice as a cell phone...OPTIs are a little more fragile. They hate water, bottom line. You might try blowing out the cap with air as best you can, and see if that changes anything. I've seen dirty or corroded connections in the harness plugs cause these same symptoms.
Thread Starter
Safety Car
Joined: Dec 2008
Posts: 3,588
Likes: 10
From: North New Jersey
UPDATE!!!!
So we checked it out at night and both sides of the engine are sparking like crazy!!!! The wires and plugs are definitely shot then!!! Thanks everyone for all your help diagnosing! If this doesnt fix it then I will post back up!
So we checked it out at night and both sides of the engine are sparking like crazy!!!! The wires and plugs are definitely shot then!!! Thanks everyone for all your help diagnosing! If this doesnt fix it then I will post back up!
Le Mans Master
Joined: Dec 2006
Posts: 5,139
Likes: 482
From: H-Town Texas
Find a chart on what to look for when looking at old plugs. I have some old Haynes manuals that have color pics of old plugs in different conditions, and explain what issues in the cylinder cause this. Can be real helpful in getting a clue on what's going on inside the engine.