1999 GMC Sonoma fuel mileage

GUYONTHEMTA

MEMBER
1999 GMC SONOMA
4 CYL
2WD
AUTOMATIC
94,000 MILES

I have been getting very bad mileage lately about 16 mpg. I just replaced the fuel pressure regulator because it went bad cut out the catalytic converter but kept the o2 sensor section and put on straight pipe. All new wires and plugs and tire pressure is good, I change oil regularly. All new o-rings on the fuel injectors and new intake gasket. There is a trouble code P0420 but even though, it is a 2.2L and should be getting much more. Please help!

5 Replies

RACEFAN966

MECHANIC
5,029 POSTS

Ok what you have here is a code that now can not be fixed. The code is a Cat low flow code. So now that there is no cat the truck is running on preset information not on sensor information. The only way to make it run right again is to put a cat back in it. Now the down stream O2 sensor which monitors cat flow is seeing to many emissions because the temp in the exhaust is to low because of no cat so it just can't run as it should. So tell me why did you remove it in the first place?

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Wednesday, July 15th, 2009 AT 10:03 AM

GUYONTHEMTA

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I removed it because it was rattling the piece inside had broken off. There is no way I can put another one back on at this point the flanges are cut off and it would be a mess. Is there anything else I could do?

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Wednesday, July 15th, 2009 AT 3:35 PM

RACEFAN966

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You need to replace it inorder for the computer to work as it should with the sensors. There are universal ones that can be bought that don't use the flanges and cost less too. I am sorry for the bad news but until the cat is replaced and the codes are cleared after that you can't get it run and get the mileage it should.

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Thursday, July 16th, 2009 AT 9:26 AM

GUYONTHEMTA

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Ok thanks

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Thursday, July 16th, 2009 AT 3:42 PM

RACEFAN966

MECHANIC
5,029 POSTS

Let me know how it ends up ok. If there are any more problems when it is back to correct let me know and we will go through what ever tests may be needed. Thanks again and have a great day.