I have a 1991 F250 4x4 with the 7.5 liter (460 cid). The catalytic converter has a hole in it, and I want to have it removed. The engine is fuel injected. The O2 sensor wire goes into the manifold BEFORE the converter. Will it adversely affect the performance of my truck to remove the catalytic converter

There is no such thing as a 2.3 Liter 8 Cyl. Ford Engine. You must be counting Spark Plug wires because the 4 Cyl engine has 2 Spark Plugs per Cylinder. I would check the Fuel Pressure first then if that is not the problem check the Catalytic Converter to see if it is plugged.

built into the fuel pump

I doubt removing the cat will cause any major problems with the truck. At some point the check engine light will come on and that may cause it to run richer than normal.
It is a federal offense to remove it with up to a $10,000 fine, but only if you get caught. So keeping it on the farm is probably safe.

I knew someone with a 92 Lumina who had the same problem and it turned out to be a bad fuel pump. If she has had the car for a long time and never had it changed, then it's definitely a good place to start. If the filter hasn't been changed in a while or possibly ever, then it should be changed. When it's a fuel related problem, it's usually worse when the engine is cold. If it's a catalytic converter problem, then it usually gets worse the longer you drive it.
Fuel system problems are usually checked with a fuel pressure gauge. the injectors must have a constant supply of fuel delivered at a certain pressure at all times for proper engine operation.
Catalytic converter problems can be checked by removing the converter and installing a test pipe. If the problem goes away, then the converter should be replaced. I hope this information has been helpful.

SECTION 309-00: Exhaust System 2003 Focus Workshop Manual DESCRIPTION AND OPERATION Procedure revision date: 01/24/2003 Exhaust System Printable View (214 KB) Vehicles with 2.0L Zetec-E engine
Item Part Number Description 1 - Bracket 2 - Gasket 3 - Catalytic converter 4 - Bracket 5 - Gasket 6 - Front muffler 7 - Rear muffler 8 - Hanger 9 - Flexible pipe

Vehicles with 2.0L SPI engine
Item Part Number Description 1 - Gasket 2 - Catalytic converter 3 - Bracket 4 - Gasket 5 - Front muffler 6 - Rear muffler 7 - Hanger 8 - Bracket 9 - Flexible pipe

Vehicles with 2.3L PZEV Engine
Item Part Number Description 1 5G232 Catalytic converter 2 5K222 Mounting bracket 3 5K282 Head shield 4 9451 Gasket 5 5A262 Insulator 6 5E292 Converter and muffler assembly 7 9448 Gasket 8 5G203 Flex Pipe NOTE: The exhaust systems shown in this section are production systems.
The exhaust systems are of a two-piece construction for production and five-piece construction for service.
Catalytic Converter
The catalytic converter fitted to the Focus range resembles a small muffler. Because of the high temperatures at which the catalytic converter operates, the vehicle body areas around the catalytic converter are protected by heat shields. The catalytic converter controls three emissions; Hydro carbons (HC), carbon monoxide (CO) and oxides of nitrogen (NOx).
Catalyst deactivation due to poisoning
Sulphur (S) in the fuel can cause deactivation of the catalyst.
Lead (Pb) in fuel can cause a severe deactivation at levels above 5 mg per liter of fuel. It is therefore essential that vehicles with catalytic converters always operate on unleaded fuel.
Zinc (Zn) and phosphorus (P) present in some oils, can cause deactivation if oil consumption is high.
The effect of sulphur is felt most if it is released from the catalytic converter as hydrogen sulphide (H2S). This has an unpleasant odor similar to rotten eggs. Changing the fuel manufacturer may help in reducing this phenomena.
To minimize H2S emissions, it is essential that the idle CO level is within specification and that the engine emission system is functioning correctly. For additional information, refer to Section 303-08A or Section 303-08B.
CAUTION: If temperatures exceeding 900°C are achieved the catalyst substrates will start to deteriorate. It is important that the cause is defined and rectified if subsequent melts are to be prevented.
Catalyst melts are normally accompanied by loss of power due to excessive back pressure. For additional information, refer to Section 303-07A or Section 303-07B.
High substrate temperatures are caused by the ignition or the fuel systems. For additional information, refer to Section 303-07A or Section 303-07B.
Misfires at high engine speed may result in an almost instantaneous melt.

I think this TSB will solve your problem even know your car is older.



NO: 18-05-96 Rev. A
GROUP: Vehicle Performance
DATE: May 24, 1996
SUBJECT: **Intermittent Rough Idle**
NOTE: This bulletin supersedes technical service bulletin 18-05-96 dated February 16, 1996 which should be removed from your files. The subject description was printed incorrectly and is marked with **ASTERISKS**
MODELS: 1991 - 1995 Acclaim/Spirit/LeBaron Sedan 1991 - 1993 Dynasty/New Yorker/New Yorker Salon 1991 - 1993 Daytona 1991 - 1995 LeBaron Coupe/LeBaron Convertible 1991 - 1994 Sundance/Shadow/Shadow Convertible 1991 - 1995 Caravan/Voyager/Town & Country NOTE: This bulletin applies to vehicles equipped with 2.2 liter and 2.5 liter engine and high pressure throttle body fuel injection.
SYMPTOM/CONDITION:
An intermittent rough idle may occur during cold engine operation, within 3 minutes after engine start up, in rainy weather and temperatures of approximately 30° to 50°F.
PARTS REQUIRED:
Quantity Part Number Part Name 1 4288298 Idle Air Control Motor (IAC) REPAIR PROCEDURE:

1. Remove A/C motor.
2. Install new IAC motor (P/N 4288298) and rubber O-ring, torque to 2 Nm (17 in. lbs).

CAUTION: The rubber o-ring must be installed with the IAC motor for proper operation.

I would also recommend doing a fuel pressure test to see if it loses fuel pressure overnight.

The catalytic converter may be fried. Very poor design of the restricted exaust ports.
And the fuel pumps are junk straight from the box. Around 94 Ford had to change the design of the fuel pumps.
I am not a mechanic but had the same issues.
I removed the catalytic converter and get the inspection done by a freind.
Your alternative is to change the entire exaust system to say a "Banks". Which is about $3000 for the paRTS.

CODE PO420 CATALTYLIC CONVERTER SYSTEM FAULT.ITS SAYING FAULTY CATALTYLIC CONVERTER.IF IT BEEN A WHILE IF YOUR CAR HAS A WHOLE LOT OF MILES ON IT.YOUR SPARK PLUG CHANGE IS DUE AT 120000 MILES. DUE A LITTLE TUNE UP CHANGE AIR FILTER AND FUEL FILTER.SEE IF YOU HAVE ANY ENGINE FAULTS BAD PLUGS DIRTY INJECTORS ANY THING UP SET FUEL SYSTEM CAUSE CAR TO RUN RICH.EXCESSIVE UNBURN FUEL WILL GATHER IN CATALYTIC CONVERTER CAUSE IT TO BURN OUT.SHORTING LIFE OF THE CATALYTIC CONVERTER.

if you follow your exhaust system you will find the o2 sensors they could have one right off the exhaust manifold and your second o2 is going to be behind the catalytic converter. so you will have a o2sensor before and after the catalytic converter on the exhaust hope this helps you out.
please rate me if you would
thank you
Aaron

Adjust idle speed back down
Clean fuel filter and check fuel pump