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misfire under load but no CEL

2004CSOTP

New member
8
3
3
Buick Ownership
2004 Buick Lesabre Custom
I have on 04 Lesabre with 110,000 miles on it. There is a misfire under slight load (about 20% according to Torque Pro). It clears up under heavier load. It doesn't happen at low speeds. I notice it most at highway speeds. The CEL is not on. I have tried holding the throttle at the point where it happens attempting to trigger a code without success. I have been researching online but found that the solutions are all over the place. If anybody has had this issue before, I would appreciate some guidance. Thank you.
 

Alan 55

Buick Newbie
Sustaining Member
327
110
43
Florida
Buick Ownership
2001 Buick Park Avenue, previously owned 1997 Park Avenue
I have on 04 Lesabre with 110,000 miles on it. There is a misfire under slight load (about 20% according to Torque Pro). It clears up under heavier load. It doesn't happen at low speeds. I notice it most at highway speeds. The CEL is not on. I have tried holding the throttle at the point where it happens attempting to trigger a code without success. I have been researching online but found that the solutions are all over the place. If anybody has had this issue before, I would appreciate some guidance. Thank you.
Welcome to the group!
Concerning your 04 LeSabre, there are some basic maintenance items to be considered. These items may or may not be the actual cause of your problem. However we need to establish a baseline on certain things.
What is the age/ condition of your battery? Spark plugs; When were they last changed? Type of plug.
Spark plug wires; when we’re they last changed? Type of wires. Fuel filter; When was it last replaced?
Sorry for these questions but without this info, it will be difficult to assist.
 

2004CSOTP

New member
8
3
3
Buick Ownership
2004 Buick Lesabre Custom
Thank you for your response. This vehicle appears untouched for the most part. The spark plug wires look like the original. I've looked at a couple of spark plugs and they look good although that can be deceiving. I'm not sure how old the fuel filter is, but I tried to change it and it's corroded into place to the degree that I began rounding the nut on the fuel line. I stopped trying after that.

I don't know how old the battery is, but it tests as good. I noticed that one coil looked worse than the others so I changed it which helped a little. I thought I was on the right track, so I changed the other two without any benefit.

Other than this problem, the car runs great. It starts easily and runs smooth. On hard acceleration, I notice it feels like something is holding it back slightly.
 

Frisbee

Member
50
26
8
The CEL is not on. I have tried holding the throttle at the point where it happens attempting to trigger a code without success.
Don't wait for a CEL to check for DTCs (Diagnostic Trouble Codes). You could have one or more "pending" DTCs without ever seeing a CEL.
______________________________
 

Frisbee

Member
50
26
8
Thank you. I tried that, but no codes.
OK, good.

In addition to Alan55's wise advice above, and since you have Torque Pro, if you have not considered this already, you might want to monitor some misfire-related PIDs. I suspect that the PCM on a 2004 LeSabre will support both "historic" and "current" misfire PIDs on all 6 cylinders (EDIT: With 2 PIDs for each cylinder). I'd check to see what GM-related misfire PIDs Torque Pro offers.
 

imidazol97

Top Dog
1,534
59
48
2004
Replace the spark plugs with the AC Delco recommended plug.
I bought AC Delco OEM wires on rockauto.com. I believe there were two levels and I bought the
ones that were "slightly better" quality.

I too had that kind of feeling of a miss on a 2003 at something of the same mileage. I fussed around
after checking plugs, coils, wires, spark control module... and changed the injectors around. I would
get an occasional misfire on #3 showing up. My shadetree neighbor mechanic helped me with pulling
the gas lines off the injectors. He said the #3 injector had "gunk" in the screen on the input. That seemed to
help at first, but then I recall I still had an uneven firing.

I had used injector and fuel system cleaners off and on, but gave it extra to try to clear the problem. No joy.

I wondered if it is the torque converter lockup transmitting engine unevenness under light load. On my 1993 leSabre Buick put in a new chip that changed the lockup speed for the torque converter to a higher speed to get away
from a more definite transmission of uneven firing that was normal engine operation.

On the 03 I tried slight upgrades where the slight extra tip in on the accelerator gave the feeling of misfire going in 3rd gear and the torque converter lockup trying to analyze the sensation.

Short of replacing all the injectors, I gave up and just enjoyed the ride up to 200K miles and traded it.
 

2004CSOTP

New member
8
3
3
Buick Ownership
2004 Buick Lesabre Custom
2004
Replace the spark plugs with the AC Delco recommended plug.
I bought AC Delco OEM wires on rockauto.com. I believe there were two levels and I bought the
ones that were "slightly better" quality.

I too had that kind of feeling of a miss on a 2003 at something of the same mileage. I fussed around
after checking plugs, coils, wires, spark control module... and changed the injectors around. I would
get an occasional misfire on #3 showing up. My shadetree neighbor mechanic helped me with pulling
the gas lines off the injectors. He said the #3 injector had "gunk" in the screen on the input. That seemed to
help at first, but then I recall I still had an uneven firing.

I had used injector and fuel system cleaners off and on, but gave it extra to try to clear the problem. No joy.

I wondered if it is the torque converter lockup transmitting engine unevenness under light load. On my 1993 leSabre Buick put in a new chip that changed the lockup speed for the torque converter to a higher speed to get away
from a more definite transmission of uneven firing that was normal engine operation.

On the 03 I tried slight upgrades where the slight extra tip in on the accelerator gave the feeling of misfire going in 3rd gear and the torque converter lockup trying to analyze the sensation.

Short of replacing all the injectors, I gave up and just enjoyed the ride up to 200K miles and traded it.

That makes sense. I'll do that and check back. Thank you.
______________________________
 

imidazol97

Top Dog
1,534
59
48
BTW. When I said I tried to duplicate the slight feeling of a miss at a certain tach speed on very light upgrade load in the 03 leSabre by putting it in 3rd with the torque converter locked up (which is not 100% but close), I never could get the car to give the same feeling. It was strictly a 4th gear behavior.

I switched coils and the ISC from my 98 leSabre and that didn't fix the problem.

That's why I related the story about the 93's lockup speed being raised with a new computer chip to avoid that year's engine uneven running at low tach speeds with light loads.
 

HotZ28

Full Member
7,531
548
113
Buick Ownership
1996 Roadmaster Limited Collectors Edition 58k - 1996 PAU
Ignition wire(s) are the most likely suspect! I don't care of they are new, but low quality, the can fail out of the box on the DIS ignition system!
 

2004CSOTP

New member
8
3
3
Buick Ownership
2004 Buick Lesabre Custom
Hello all,

I changed the spark plugs and wires today and that solved the problem. It went as expected. The front plugs took five minutes. The back three were a pain in the butt.

I used AC Delco plugs and wires. It was surprisingly easy for a transverse mounted six.
 

Alan 55

Buick Newbie
Sustaining Member
327
110
43
Florida
Buick Ownership
2001 Buick Park Avenue, previously owned 1997 Park Avenue
Hello all,

I changed the spark plugs and wires today and that solved the problem. It went as expected. The front plugs took five minutes. The back three were a pain in the butt.

I used AC Delco plugs and wires. It was surprisingly easy for a transverse mounted six.
Great news! Thanks for sharing this information ! Yes, the back three plugs are a test of your mechanical skills. This requires working by feel only as the plugs are practically out of sight. Glad you used quality AC Delco parts.
______________________________
 

imidazol97

Top Dog
1,534
59
48
You can see the rear plugs if you put a large piece of foam on top of the engine to protect your knees and carefully kneel on top to look over the back. I had trouble reaching the center plug; the two outer ones were difficult to break the seal on the wire ends against the porcelain. I took off the motor lift bracket that was in the middle close to the plug as well. Two small taps.

Taller folks can easily reach over. I used to have my shadetree expert two houses up do them for me. LOL
 

Waiex191

Active member
208
74
28
Poplar Grove, IL
Buick Ownership
2000 Century
Here is my giant piece of foam. I don't kneel on it, I lie on it. I also popped off the front mounts and used a ratchet strap to pull the engine forward. Not absolutely necessary but gives some extra room.
 

2004CSOTP

New member
8
3
3
Buick Ownership
2004 Buick Lesabre Custom
Great ideas. Wish I thought of the foam. I laid down on top of the engine and bruised myself up pretty good.
 

HotZ28

Full Member
7,531
548
113
Buick Ownership
1996 Roadmaster Limited Collectors Edition 58k - 1996 PAU
Here is my giant piece of foam. I don't kneel on it, I lie on it. I also popped off the front mounts and used a ratchet strap to pull the engine forward. Not absolutely necessary but gives some extra room.
The original thread was about a LeSabre, not a Century, which are two different animals!
______________________________
 

imidazol97

Top Dog
1,534
59
48
Abouve the foam I used: it was a fairly stiff foam rubber. It was a large triangle for holding a knee up in the air to facilitate healing and reduce swelling after a knee replacement.

It would be a like a stiff foam for a seat cushion on a couch.

I like the surf board looking device which is likely a styrofoam product?
 
Last edited:

Waiex191

Active member
208
74
28
Poplar Grove, IL
Buick Ownership
2000 Century
Abouve the foam I used: it was a fairly stiff foam rubber. It was a large triangle for holding a knee up in the air to facilitate healing and reduce swelling after a knee replacement.

It would be a like a stiff foam for a seat cushion on a couch.

I like the surf board looking device which is likely a styrofoam product?
I think it's poly foam. I bought it from a packaging place in Connecticut. Here is a company that sells it.
The Foam Factory, Packaging Foam, Polyethylene
 
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