Seville Runs Rough/Sputters Between 1500rpm and 2500rpm???

[CadillacGibbs]

Hey guys, I am having a hell of a time figuring this one out here, hopefully someone can help.

I have a 1992 Seville w/ 137k miles on the all stock 4.9

All of a sudden I noticed it was running rough and sputtering alittle between 1500 rpm and 2500 rpm. it runs perfect under or over mentioned rpm. I did the basics including Fuel filter, Air Filter, PCV, and coil and no results... My next thought was cap and rotor possibly???

Has anyone out there had this issue or heard of this issue in the past? Thanks Guys!

[Cadillac Jim]

I would definitely change the distributor cap and rotor. Look at the centrifugal advance if there is one, and you can see it, and make sure that it's free of debris and isn't sticking.

Have you run the OBD codes yet?

[rockfangd]

I was thinking that also. OR possibly egr problem. but more likely sounds like ignition problem

[barczy01]

centrifugal advance wow thats been gone for a while.. Pull the EGR supply tube and drive it, see if the sputter goes away.

[CadillacGibbs]

[CadillacGibbs]

centrifugal advance wow thats been gone for a while.. Pull the EGR supply tube and drive it, see if the sputter goes away.

Where is this tube and how do I do that??? Thanks

[CadillacGibbs]

I would definitely change the distributor cap and rotor. Look at the centrifugal advance if there is one, and you can see it, and make sure that it's free of debris and isn't sticking.

Have you run the OBD codes yet?

I have ran the scan but It says "NO ECM CODES" I dont know if I am doing this right or what its supposed to tell me, I havent been able to find anything online other than how to initiate the scan...

[Cadillac Jim]

If you are getting "NO ECM CODES" then, you have no ECM codes that can be displayed without a Tech II, and you can say that yes, you have run the ECM codes.

Here's what I have from the FSM and my experience with my old 1997 ETC. Once the scan has been initiated, the car's computer (actually the IPC module, which "hosts" the OBD connector) is in the diagnostic mode. It polls the car's main modules, beginning with the PCM/ECM, for OBD codes. When it is done, it stops with the prompt "PCM?"

At this point, some of the buttons on the A/C console operate the diagnostic mode:

OFF backs out one level, like the <Esc> key on your computer. Press it at the "PCM?" prompt and it will repeat the codes.

FAN UP is like "YES"

FAN DOWN is like "NO"

AUTO terminates the diagnostic mode. You can also press "Info Reset" or turn off the key.

There are others that I don't recall right now.

You can press FAN DOWN and step through all the modules, getting a succession of prompts like "PZM?". The list will then repeat, beginning with "PCM?". At any one of them, you press FAN UP and enter the diagnostic mode for that particular module. Pressing FAN DOWN will give you a succession of prompts that will always include "CODES?" which, if you press FAN UP, will read out the codes for that module, and "CLEAR CODES" which, if you press FAN UP, will clear the codes for that module. I suggest that you do not enter FAN UP at any of the other prompts until you know more about the diagnostic mode. These other prompts include "DATA?" and "OVERRIDES?". Information that is available through the "DATA" mode us usually very difficult to interpret even with a FSM. A mistake in the "OVERRIDES" section can result in an embarrassing and expensive trip to the dealer, and it's even possible to brick the IPC/IPM, a very serious problem because that module has all your car's options coded into it and must be used for that data to program a new IPC/IPM.

[CadillacGibbs]

If you are getting "NO ECM CODES" then, you have no ECM codes that can be displayed without a Tech II, and you can say that yes, you have run the ECM codes.

Here's what I have from the FSM and my experience with my old 1997 ETC. Once the scan has been initiated, the car's computer (actually the IPC module, which "hosts" the OBD connector) is in the diagnostic mode. It polls the car's main modules, beginning with the PCM/ECM, for OBD codes. When it is done, it stops with the prompt "PCM?"

At this point, some of the buttons on the A/C console operate the diagnostic mode:

OFF backs out one level, like the <Esc> key on your computer. Press it at the "PCM?" prompt and it will repeat the codes.

FAN UP is like "YES"

FAN DOWN is like "NO"

AUTO terminates the diagnostic mode. You can also press "Info Reset" or turn off the key.

There are others that I don't recall right now.

You can press FAN DOWN and step through all the modules, getting a succession of prompts like "PZM?". The list will then repeat, beginning with "PCM?". At any one of them, you press FAN UP and enter the diagnostic mode for that particular module. Pressing FAN DOWN will give you a succession of prompts that will always include "CODES?" which, if you press FAN UP, will read out the codes for that module, and "CLEAR CODES" which, if you press FAN UP, will clear the codes for that module. I suggest that you do not enter FAN UP at any of the other prompts until you know more about the diagnostic mode. These other prompts include "DATA?" and "OVERRIDES?". Information that is available through the "DATA" mode us usually very difficult to interpret even with a FSM. A mistake in the "OVERRIDES" section can result in an embarrassing and expensive trip to the dealer, and it's even possible to brick the IPC/IPM, a very serious problem because that module has all your car's options coded into it and must be used for that data to program a new IPC/IPM.

Thank you Jim! I'll try to do that tonight. I appreciate the help and will let you know what comes of it.

[Cadillac Jim]

I gave you the procedures to get into the car's computer for your information and future reference. Right now, there is no reason to do that. I would get back to looking for problems that don't throw codes.

Given compression and valve timing, there are three elements of automotive four-stroke combustion: air, fuel, and spark. One of these three is disrupted over the 1500-2500 RPM range. Since things are OK above 2500, a problem with air seems unlikely. You have throttle-body injection, which would likely throw a code if there was a problem. This leaves spark, the most unreliable element of automotive engines to this day, in my opinion.

Your car has the traditional distributor drive: chain-driven cam, 45-degree distributor gears on the cam to effect a 90 degree rotation axis change with 1:1 rotation rate to the distributor shaft that has the distributor on one end of the driven shaft and the oil pump on the other end, centrifugal advance between the distributor shaft and the ignition pickup (points cam on cars before solid state ignition), vacuum advance on the "stationary" part of the ignition pickup that goes to the module, a module, and finally a distributor rotor that points to the towers of the distributor caps at TDC firing for each cylinder. Plug wires then go through a loom to the individual spark plugs.

Places to look for a strange problem like this are a worn spot on the distributor pickup wire, which is under the HEI module under the distributor cap, the HEI module itself which includes the module and the HEI ignition coil, then the usual parts: cap and rotor, wires, and plugs. There are other things, like missing or broken springs on the centrifugal advance, perforated diaphragm on the vacuum advance, vacuum advance tubing bad or missing, etc. but these seem less likely based on what you are describing.

[CadillacGibbs]

I gave you the procedures to get into the car's computer for your information and future reference. Right now, there is no reason to do that. I would get back to looking for problems that don't throw codes.

Given compression and valve timing, there are three elements of automotive four-stroke combustion: air, fuel, and spark. One of these three is disrupted over the 1500-2500 RPM range. Since things are OK above 2500, a problem with air seems unlikely. You have throttle-body injection, which would likely throw a code if there was a problem. This leaves spark, the most unreliable element of automotive engines to this day, in my opinion.

Your car has the traditional distributor drive: chain-driven cam, 45-degree distributor gears on the cam to effect a 90 degree rotation axis change with 1:1 rotation rate to the distributor shaft that has the distributor on one end of the driven shaft and the oil pump on the other end, centrifugal advance between the distributor shaft and the ignition pickup (points cam on cars before solid state ignition), vacuum advance on the "stationary" part of the ignition pickup that goes to the module, a module, and finally a distributor rotor that points to the towers of the distributor caps at TDC firing for each cylinder. Plug wires then go through a loom to the individual spark plugs.

Places to look for a strange problem like this are a worn spot on the distributor pickup wire, which is under the HEI module under the distributor cap, the HEI module itself which includes the module and the HEI ignition coil, then the usual parts: cap and rotor, wires, and plugs. There are other things, like missing or broken springs on the centrifugal advance, perforated diaphragm on the vacuum advance, vacuum advance tubing bad or missing, etc. but these seem less likely based on what you are describing.

Okay thats a whole lot of info I did not know...lol I appreciate all the help, Im going to do the cap and rotor first and see if it helps. Also above in the post above barczy01 said to pull the vaccum line going to the EGR valve and try driving it then??? Is there any chance that will screw anything up and if it does work is that telling me my EGR valve needs replacing? and is it even worth trying since you beleive my problem is spark not air?

[Cadillac Jim]

The EGR sometimes gets clogged, causing tuning problems. All post-1972 cars need the EGR passages cleaned out eventually. Sometimes the EGR valve sticks open, closed, or in an intermediate position, also causing tuning problems. Most cases require cleaning of the EGR passages and EGR valve. Only if the EGR solenoid has an open circuit or short, or if it is damaged and can't be cleaned, does the EGR valve need to be replaced.

[barczy01]

the egr vacuum tube is behind the throttle body, in between the throttle body and blower motor on the firewall . It goes from a solenoid to the brass color egr valve. Unhook the valve and try it when the car is warm . let me know .

[CadillacGibbs]

the egr vacuum tube is behind the throttle body, in between the throttle body and blower motor on the firewall . It goes from a solenoid to the brass color egr valve. Unhook the valve and try it when the car is warm . let me know .

I tried this last night and it only made it worse. If I am understanding you right... I pulled the vacuum tube out of the the egr valve (there was only one tube) and ran it while it was already hot. Does this tell us anything? Does this mean the EGR is bad??? Thanks I appreciate the support.

[Logan]

centrifugal advance wow thats been gone for a while.. Pull the EGR supply tube and drive it, see if the sputter goes away.

Yeah...no vacuum advance since about the early 80's....no centrifugal advance about the same time. All controlled by the computer.

Used to hunt for the late 70's GM HEI distributors that did have the vacuum and mechanical advance. They were kinda rare..

Can be the wiring inside the distributer. The pick up coil can go green after 10-20 years. Also the pins and connectors and related wires on the IC control module can turn green too.

At some point...if you are reving the car in park or netural...you will hit a rev limiter at some point. You may think there is a problem when none really exists.

I attached a pic of a 'green' rotted pick up coil.

[KHE]

the egr vacuum tube is behind the throttle body, in between the throttle body and blower motor on the firewall . It goes from a solenoid to the brass color egr valve. Unhook the valve and try it when the car is warm . let me know .

I tried this last night and it only made it worse. If I am understanding you right... I pulled the vacuum tube out of the the egr valve (there was only one tube) and ran it while it was already hot. Does this tell us anything? Does this mean the EGR is bad??? Thanks I appreciate the support.

Did you plug the vacuum line when you removed it? If not, you had a substantial vacuum leak which would tend to affect performance.

[Cadillac Jim]

Thanks, Logan. I was assuming that the TBI controlled the mixture and that the ignition was straight HEI.

[CadillacGibbs]

the egr vacuum tube is behind the throttle body, in between the throttle body and blower motor on the firewall . It goes from a solenoid to the brass color egr valve. Unhook the valve and try it when the car is warm . let me know .

I tried this last night and it only made it worse. If I am understanding you right... I pulled the vacuum tube out of the the egr valve (there was only one tube) and ran it while it was already hot. Does this tell us anything? Does this mean the EGR is bad??? Thanks I appreciate the support.

Did you plug the vacuum line when you removed it? If not, you had a substantial vacuum leak which would tend to affect performance.

No, That would make sense to do so...haha I'll try it again and let you know what happens. Thanks

[barczy01]

By pulling the EGR vaccum supply, your not going to pull that much vacuum to make a driveability issue. Check the cap and rotor and if there are numbers on the plug wires then i would replace plugs and wires and cap and rotor. Numbers on the plug wires indicate factory wires.

[CadillacGibbs]

By pulling the EGR vaccum supply, your not going to pull that much vacuum to make a driveability issue. Check the cap and rotor and if there are numbers on the plug wires then i would replace plugs and wires and cap and rotor. Numbers on the plug wires indicate factory wires.

Thanks Barczy01! Ive ordered all my parts including the EGR valve. I noticed the top was covered in corrosion so regardless of if its bad or not, I'm going to replace it anyway. I'll be doing all the work on her this weekend so I'll give you guys an update on Monday! Cross your fingers...

[CadillacGibbs]

Forgot to update on this guys, but it was indeed the EGR valve.... The Service Engine light came on before I did the tune up and when I ran the code it was the EGR valve. $70 dollar part and she purrs like a kitten!!! Thanks for all the great support!!!