Engine stumbles as RPMS drop.
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Engine stumbles as RPMS drop.
As the title says (it's a 1992 LT-1 automatic with about 161k miles)
Say I have it in park or neutral, I'll rev the motor to around 4-5k, it'll be a smooth rev.
Now on the way down, when the RPMS drop to 2k and below(around that range) The engine seems to stumble and it shakes the car a bit. I always had a thought in the back of my head that this isn't normal.
My question is, what would cause this stumble? Could it be the damn opti spark?
Thanks.
Say I have it in park or neutral, I'll rev the motor to around 4-5k, it'll be a smooth rev.
Now on the way down, when the RPMS drop to 2k and below(around that range) The engine seems to stumble and it shakes the car a bit. I always had a thought in the back of my head that this isn't normal.
My question is, what would cause this stumble? Could it be the damn opti spark?
Thanks.
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It runs nice when I drive it.
My idle seems a bit too shaky for me, makes my tires wiggle a bit and I can feel it in my steering wheel. For some reason "EGR" valve comes to my head. Now as for the second question, I'll have to do it when I'm in the car cause I forgot lol.
I know my charcoal canister line to the intake manifold might be clogged( I took out some carbon bits before but didn't clean the entire line or the canister) But I don't know if that would affect my performance???
I know my charcoal canister line to the intake manifold might be clogged( I took out some carbon bits before but didn't clean the entire line or the canister) But I don't know if that would affect my performance???
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Melting Slicks
Joined: Dec 2008
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From: Mystic CT
If you have a scanner that can get real time data while doing this with a warmed up engine look at the following and see if it makes sense and moving as you think they should
TPS voltage it should be a smooth increase with no delays or jumps
MAF g/sec should smoothly increase with rpm
O2 sensor cross counts should be actively chamging and not slowly
BLM what are the numbers looking like?
When is the last time it got a real tune up? Plugs wires cap rotor filters PCV etc.. at 161k it would not be a bad idea to send the injectors out to be checked or replaced.
Dave
TPS voltage it should be a smooth increase with no delays or jumps
MAF g/sec should smoothly increase with rpm
O2 sensor cross counts should be actively chamging and not slowly
BLM what are the numbers looking like?
When is the last time it got a real tune up? Plugs wires cap rotor filters PCV etc.. at 161k it would not be a bad idea to send the injectors out to be checked or replaced.
Dave
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Joined: Jun 2011
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If you have a scanner that can get real time data while doing this with a warmed up engine look at the following and see if it makes sense and moving as you think they should
TPS voltage it should be a smooth increase with no delays or jumps
MAF g/sec should smoothly increase with rpm
O2 sensor cross counts should be actively chamging and not slowly
BLM what are the numbers looking like?
When is the last time it got a real tune up? Plugs wires cap rotor filters PCV etc.. at 161k it would not be a bad idea to send the injectors out to be checked or replaced.
Dave
TPS voltage it should be a smooth increase with no delays or jumps
MAF g/sec should smoothly increase with rpm
O2 sensor cross counts should be actively chamging and not slowly
BLM what are the numbers looking like?
When is the last time it got a real tune up? Plugs wires cap rotor filters PCV etc.. at 161k it would not be a bad idea to send the injectors out to be checked or replaced.
Dave
Last time I did a tune up was not even 3k miles ago lol...I changed spark plugs, wires, opti spark, ignition coil. (I've only changed the grommet to valve cover on the PCV system) Alternator, it's got new bosch 3 injectors( 26 LB HR and not the stock 24 LB HR, just incase I did some mods in the future) new fuel pump, fuel filter. One of these days soon I'm going to take out my injectors and fuel rail and clean it out with some carb. cleaner.
I haven't touched the EGR valve. My charcoal canister line may be clogged, don't know if that would affect anything?
Additional info, Mods on the car I currently have a factory header/ catless exhaust, X-pipe with Borla Stinger mufflers and a cold air intake(VORTEX AIR RAMMER....I don't like the quality of it)
Thanks for the reply to my thread.
Last edited by VetteAholicC4; Nov 16, 2011 at 01:44 PM.
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I will put the scanner on it and see the real data, I'll post the results for the most concerned sensors.
Last time I did a tune up was not even 3k miles ago lol...I changed spark plugs, wires, opti spark, ignition coil. (I've only changed the grommet to valve cover on the PCV system) Alternator, it's got new bosch 3 injectors( 26 LB HR and not the stock 24 LB HR, just incase I did some mods in the future) new fuel pump, fuel filter. One of these days soon I'm going to take out my injectors and fuel rail and clean it out with some carb. cleaner.
I haven't touched the EGR valve. My charcoal canister line may be clogged, don't know if that would affect anything?
Additional info, Mods on the car I currently have a factory header/ catless exhaust, X-pipe with Borla Stinger mufflers and a cold air intake(VORTEX AIR RAMMER....I don't like the quality of it)
Thanks for the reply to my thread.
Last time I did a tune up was not even 3k miles ago lol...I changed spark plugs, wires, opti spark, ignition coil. (I've only changed the grommet to valve cover on the PCV system) Alternator, it's got new bosch 3 injectors( 26 LB HR and not the stock 24 LB HR, just incase I did some mods in the future) new fuel pump, fuel filter. One of these days soon I'm going to take out my injectors and fuel rail and clean it out with some carb. cleaner.
I haven't touched the EGR valve. My charcoal canister line may be clogged, don't know if that would affect anything?
Additional info, Mods on the car I currently have a factory header/ catless exhaust, X-pipe with Borla Stinger mufflers and a cold air intake(VORTEX AIR RAMMER....I don't like the quality of it)
Thanks for the reply to my thread.
Damn code 41 popped up, EST....electronic spark timing is open.
On another hand, I unplug the vacuum source to the EGR valve and nothing happens. I push the diaphragm in the EGR and it shuts the car down, when I do this it takes a few seconds for the car to restart and the idle sucks, it shakes too much, like if the valve gets stuck open(or closed?)
Melting Slicks
Joined: Aug 2008
Posts: 2,082
Likes: 50
From: Palmdale CA
Damn code 41 popped up, EST....electronic spark timing is open.
On another hand, I unplug the vacuum source to the EGR valve and nothing happens. I push the diaphragm in the EGR and it shuts the car down, when I do this it takes a few seconds for the car to restart and the idle sucks, it shakes too much, like if the valve gets stuck open(or closed?)
On another hand, I unplug the vacuum source to the EGR valve and nothing happens. I push the diaphragm in the EGR and it shuts the car down, when I do this it takes a few seconds for the car to restart and the idle sucks, it shakes too much, like if the valve gets stuck open(or closed?)
The engine should stumble, or die off when you force the valve open, this indicates that the exhaust passages are open. You might have a valve thats not fully closeing..maybe carbon build up? I would at least remove it for inspection.
