P0420 code 1 day after replacing Fuel pump

Hey all....I have a 99 silverado 5.3 Z71 with 144,000 miles on it. I finally had to replace the fuel pump (replaced it with a Delphi) a few days ago. All is fine other than this. A day after replacing the fuel pump, my CEL light came on. I have a elm327 reader and have it hooked up to my laptop to read the code. I now get a P0420 code. I reset it and get it back within 5 miles of normal highway driving. I have replaced the plugs (with AC Delco Iridium) at 90,000 miles. Other than fluids, tires, and 2 "U" joints. Everything is still stock. I plan on keeping the truck for a while (just bought 4 new Michelin LTX's). I have been reading of a catalytic converter to be replaced, but need some input. Ihave been reading that at this mileage, the cat is probably bad. also told that the o2 sensors are not usually bad.

I have an elm 327 reader and scantool. I can read levels of the o2 sensors and such. What should I look for next to conferm that my cat needs to be replaced??

Also, where should I look for a replacement cat? I do all of my own work.
Should I try to replace just one cat or get the "Y" cat and replace both at the same time?

If I get just the cat, do I have to weld the new cat in, or could I use clamps? Just asking, I have not even crawled underneath to see what this is going to entail for labor.

Thanks for reading this, and thanks for looking.

You need to find the cause of code befor throwing cats at it.
Main cause of cat codes is missing /missfir /engine running rich.

http://www.troublecodes.net/articles/catfailure/

DTC P0420, P0421, and P0430 & P0431: Check Possible Cause Of Misfire DTC P0420 and P0421 indicate bank one catalyst system efficiency is minimum requirement. DTC P0430 and P0430 indicate bank 2-catalyst system efficiency is minimum requirement. Possible causes are as follows: Use of leaded fuel. Oil contamination. Cylinder misfire. Fuel pressure too high. HO2S sensor improperly connected. Damaged exhaust system component. Faulty ECT sensor. Faulty HO2S. Ensure ignition timing is correct. Retrieve all Continuous Memory DTCs. If misfire code is not present, go to next step. If misfire code is present, isolate cylinder and repair as necessary. Check HO2S Monitor DTCs If DTCs P0136, P0138, P0140, P0141, P0156, P0158, P0160, or P0161 were present in step 1), service as necessary before continuing. If none of these codes are present in step 1), go to next step. Check ECT Sensor DTCs If DTCs P0117, P0118, P0125 or P1117 were present in step 1), service as necessary before continuing. If none of these codes are present in step 1), go to next step. If any codes except P0420, P0421, P0430 and/or P0430 were present in step 1), service as necessary before continuing. If no codes except P0420 and/or P0430 were present in step 1), go to next step. Check Rear HO2S Wiring Harness Turn ignition off. Ensure HO2S wiring harness is correctly routed and connectors are tight. Repair or replace as necessary. If wiring harness and connectors are okay, go to next step. Check Fuel Pressure Turn ignition off. Release fuel pressure. Install fuel pressure gauge. Start engine and allow to idle. Note fuel pressure gauge reading. Increase engine speed to 2500 RPM and maintain for one minute. For fuel pressure specifications, see FUEL PRESSURE SPECIFICATIONS article. If fuel pressure is as specified, go to next step. If fuel pressure is not as specified, go to CIRCUIT TEST HC. Check For Exhaust System Leaks If exhaust system leaks, it may cause catalyst monitor efficiency test to fail. Inspect exhaust system for cracks, loose connections or punctures. Repair or replace as necessary. If exhaust system is okay, go to next step. Check For Exhaust System Restrictions Inspect exhaust system for collapsed areas, dents or excessive bending. Repair or replace as necessary. If exhaust system is okay, go to next step. Check Manifold Vacuum Install tachometer. Connect vacuum gauge to intake manifold vacuum source. Start engine and raise engine speed to 2000 RPM. Manifold vacuum should rise to more than 16 in. Hg. If manifold vacuum is okay, go to next step. If manifold vacuum is low, go to step 11). Leave tachometer and vacuum gauge connected. Start engine and raise engine speed to 2000 RPM. On a non- restricted system, manifold vacuum should quickly rise to normal range as increased RPM is maintained. On a restricted system, manifold vacuum will slowly rise to normal range as increased RPM is maintained. If manifold vacuum is okay, no indication of exhaust leak or restriction has been detected and testing is complete. If manifold vacuum is low or slow to respond, go to next step. Leave tachometer and vacuum gauge connected. Remove exhaust pipe from exhaust manifold. Start engine and raise engine speed to 2000 RPM. If manifold vacuum is now okay, fault is downstream from exhaust manifold. Reconnect exhaust pipe to exhaust manifold and go to next step. If manifold vacuum is still low or slow to respond, fault is in exhaust manifold or intake manifold gasket. Repair or replace as necessary and repeat QUICK TEST. Leave tachometer and vacuum gauge connected. Disconnect muffler/tailpipe assembly from rear of catalytic converter. Start engine and raise engine speed to 2000 RPM. If manifold vacuum is now okay, fault is in muffler/tailpipe assembly. Repair or replace as necessary and test-drive vehicle to verify elimination of symptom. If manifold vacuum is still not okay, fault is in catalytic converter. Repair or replace as necessary. Check tailpipe/muffler assembly for debris from catalytic converter. Test drive vehicle to verify elimination of symptom.


Let us know how it goes.

Just to give you some more info....The P0240 is the only code that is stored.
I do not get any misfire codes (I did before I changed out the Fuel pump, but all are cleared now).

I will check the fuel pressure this weekend and post. Thansk for the info. I will read and read and read. Thanks

Cleared my P0420 code and comes on after 30+ miles of normal highway driving then 10 mins of stop and go. there are no other codes. No misfire codes... nothing. I cleared the code then I have ready my fuel pressure. It is running at 48-49 lbs at idle and drops to about 47 when revved at 2500 RPM for 1 minute. I have no oil in my coolant nor any coolant (or water bubbles) in my oil. I checked the dipstick. All looks normal.

I left my Chilton's manual at work...Does 48lbs at idle and 47lbs at 2500 RPM sound normal for a 99 silverado?

Just to let you know, there has been no difference in gas mileage nor performance with the check engine light on.

I could not find the "see FUEL PRESSURE SPECIFICATIONS article" that is in MT-2500's article.

Thanks for the help.

http://www.obd-codes.com/p0420

matter of fact, let me add something. inlaw's celica threw same code about 2 weeks ago. replaced fuel tank cap, made her add a can of seafoam to a tankful, and go 70 on freeway for about half an hour. so far so good.
but because you messed with fuel pump area, you might have something leaking air into the tank now. just like that infamous cap.

Cleared my P0420 code and comes on after 30+ miles of normal highway driving then 10 mins of stop and go. there are no other codes. No misfire codes... nothing. I cleared the code then I have ready my fuel pressure. It is running at 48-49 lbs at idle and drops to about 47 when revved at 2500 RPM for 1 minute. I have no oil in my coolant nor any coolant (or water bubbles) in my oil. I checked the dipstick. All looks normal.

I left my Chilton's manual at work...Does 48lbs at idle and 47lbs at 2500 RPM sound normal for a 99 silverado?

Just to let you know, there has been no difference in gas mileage nor performance with the check engine light on.

I could not find the "see FUEL PRESSURE SPECIFICATIONS article" that is in MT-2500's article.




Thanks for the help.


Specs. are 55/62 lbs. on a 5.3

On a 5.3 check the vacuum line to fuel pressure regulator for gas in it.

If your scanner can show pre and post catalityc converter o2 readings, then you want to look at a graph of both at the same time. If the post-cat. o2 sensor is showing the same reading as the pre-cat sensor, then your catalytic converter is bad. Take a look at the post cat. o2 sensor readings and see if they are fluctuating between rich and lean like the pre-cat o2 is. If it is, then your cat. is bad. The post cat o2 should show a basically flat lean o2 reading.

On a 5.3 check the vacuum line to fuel pressure regulator for gas in it.

There is no gas in the Vacuum line to the fuel regulator

If your scanner can show pre and post catalityc converter o2 readings, then you want to look at a graph of both at the same time. If the post-cat. o2 sensor is showing the same reading as the pre-cat sensor, then your catalytic converter is bad. Take a look at the post cat. o2 sensor readings and see if they are fluctuating between rich and lean like the pre-cat o2 is. If it is, then your cat. is bad. The post cat o2 should show a basically flat lean o2 reading.

I have an ELM 327 OBD usb cord. I have a few programs that were free and I could get some values. but some other programs are demo versions (shows the pre o2 and post o2 graphs). Could somebody point out a good Windows based program for the elm either free or pay. I don't want to pay for a junk program. I would rather get some input from somebody that has a good experience with them.

There is no gas in the Vacuum line to the fuel regulator


Is this normal...or should there be gas in the vacuum hose to the regulator???

Is this normal...or should there be gas in the vacuum hose to the regulator???

No, that means the regulator diaphram ripped and excess fuel is in the intake.I would prob quess that you are looking at a cat and they are part of the y pipe($$$). Before you throw that money down look at the o2 readings. You dont really need a graph. The upstrem should be bouncing all over the place trying to balance the engine, the down stream should be slow moveing.

Let me know