To put everything into perspective: Vehicle in question is a 1998 Buick LeSabre with 166k Mileage still using original Catalytic Converter.
I bought this LeSabre when it had 148k Mileage. It idled just a little rough right at the day I bought it.
I drove it till 160k when on came the Check Engine Light stating a Random Engine Misfire. We guessed the Plugs and Wires may still be original so we put in new Wires & Plugs. That did not fix the Misfire Code.
With my Uncle's Vehicle know how He eventually narrowed down the Misfire Problem to a Bad Ignition Module. We replaced the Ignition Module with a used one from a junk yard, that fixed the Misfire and eliminated the Check Engine Light.
A few days later on came the Check Engine Light, this time stating "P0420 OBD-II Trouble Code: Catalyst System Efficiency Below Threshold (Bank 1)"
So we figured then a Clogged/Bad Cat. Converter.
While searching online for New Cat. Converters I ran across a Fuel Additive called "CRC Guaranteed to Pass". I used the Guaranteed to Pass as directed on the Bottle. By the time the Fuel Tank was nearly empty nothing much had changed and the Check Engine Light was still on.
I then decided to try Seafoam Motor Treatment https://seafoamsales.com/sea-foam-motor-treatment/
I used the Seafoam pretty close to as directed on the Can (1 ounce (US) Seafoam per Gallon (US) of gasoline.
The 1st Tank of Gasoline I had right about 16 Gallons in the Tank along with the Seafoam. Began using the LeSabre as usual. I Deliver Pizza so my Mileage Tacks up pretty quickly.
Within in the first 100 miles I already noticed the Engine starting to Idle Better, plus the engine hesitations at stoplights becoming less severe. I went thru the rest of the Tank and the Engine kept slowly running better.
Tank Empty, figured I'd try it again. Put in a full can of Seafoam into the very next tank full, this time I filled it to 18 Gallons.
Again all thru this Tank Full with Seafoam the Engine slowly ran better and better.
2nd Seafoam Tank Empty, figured I'd try it again. Put in the 3rd Can and added Gas to about 16'ish Gallons in the Tank.
With the Tank about 3/4 of Full of the 3rd Consecutive Tank with Seafoam Added, the Check Engine Light suddenly Disappeared.
When this All began I really believed it would not work, but it did work. The Seafoam removed the P0420 Check Engine Light.
The Engine now Idles smoother then when I bought it.
The Engine still hesitates slightly when cold, runs fine when warm. The Check Engine has not yet returned.
One thing odd, when doing a pizza delivery last evening, a few hours after the Check Engine Light had disappeared, I left the Car running when handing the Pizza to the Customer, I then noticed that very obvious Catalytic Converter Smell coming from the Exhaust, Had never smelt that from this car before.
To be on the safe side I plan to run 1 maybe 2 more Tank Fulls with Seafoam in it.
If you get a P0420 Bank-1 Code this Seafoam is Definitely worth a Try.
I bought this LeSabre when it had 148k Mileage. It idled just a little rough right at the day I bought it.
I drove it till 160k when on came the Check Engine Light stating a Random Engine Misfire. We guessed the Plugs and Wires may still be original so we put in new Wires & Plugs. That did not fix the Misfire Code.
With my Uncle's Vehicle know how He eventually narrowed down the Misfire Problem to a Bad Ignition Module. We replaced the Ignition Module with a used one from a junk yard, that fixed the Misfire and eliminated the Check Engine Light.
A few days later on came the Check Engine Light, this time stating "P0420 OBD-II Trouble Code: Catalyst System Efficiency Below Threshold (Bank 1)"
So we figured then a Clogged/Bad Cat. Converter.
While searching online for New Cat. Converters I ran across a Fuel Additive called "CRC Guaranteed to Pass". I used the Guaranteed to Pass as directed on the Bottle. By the time the Fuel Tank was nearly empty nothing much had changed and the Check Engine Light was still on.
I then decided to try Seafoam Motor Treatment https://seafoamsales.com/sea-foam-motor-treatment/
I used the Seafoam pretty close to as directed on the Can (1 ounce (US) Seafoam per Gallon (US) of gasoline.
The 1st Tank of Gasoline I had right about 16 Gallons in the Tank along with the Seafoam. Began using the LeSabre as usual. I Deliver Pizza so my Mileage Tacks up pretty quickly.
Within in the first 100 miles I already noticed the Engine starting to Idle Better, plus the engine hesitations at stoplights becoming less severe. I went thru the rest of the Tank and the Engine kept slowly running better.
Tank Empty, figured I'd try it again. Put in a full can of Seafoam into the very next tank full, this time I filled it to 18 Gallons.
Again all thru this Tank Full with Seafoam the Engine slowly ran better and better.
2nd Seafoam Tank Empty, figured I'd try it again. Put in the 3rd Can and added Gas to about 16'ish Gallons in the Tank.
With the Tank about 3/4 of Full of the 3rd Consecutive Tank with Seafoam Added, the Check Engine Light suddenly Disappeared.
When this All began I really believed it would not work, but it did work. The Seafoam removed the P0420 Check Engine Light.
The Engine now Idles smoother then when I bought it.
The Engine still hesitates slightly when cold, runs fine when warm. The Check Engine has not yet returned.
One thing odd, when doing a pizza delivery last evening, a few hours after the Check Engine Light had disappeared, I left the Car running when handing the Pizza to the Customer, I then noticed that very obvious Catalytic Converter Smell coming from the Exhaust, Had never smelt that from this car before.
To be on the safe side I plan to run 1 maybe 2 more Tank Fulls with Seafoam in it.
If you get a P0420 Bank-1 Code this Seafoam is Definitely worth a Try.