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#1
03-16-2008, 04:44 PM
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Short term fuel trim question
I have a P0420 on this van. Both O2's are good and the van runs great but I can't seem to get rid of this DTC.
Looking thru my Auto-tap diagnostic I noticed I have 1- Short term fuel trim bank-1 0% @ idle 2- Short term fuel trim bank-1 from O2 Bank 1 Sensor 1 0% @ idle 3- Short term fuel trim bank-2 from O2 Bank 1 Sensor 2 is 99% @ idle. Any ideas on what this means and what do I need to do to fix it? Thx
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03 GMC Sierra 100k 05 Infiniti G35 150K 10 Mazda 3 Hatchback 110K 16 Infiniti Q50 Red Sport 34K Last edited by Headnsouth; 03-16-2008 at 05:35 PM. 
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#2
03-17-2008, 08:29 AM
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Re: Short term fuel trim question
Fuel trim numbers are corrections to the length of injection time in order to match emission/performance targets.
HOw 1 is 0% and the other 99% seems somewhat arkward ...I've no immediate explanation. Ideally, both should be near 50%. Any possibility that the cat would be shot?.. But..I'd measure fuel pressure at fuel rail just to verify if correction is related to abnormal pressure..should be near 40 psi at idle. DO you have long term trim readings?
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'93 Ponty Transport 3.8; 2011 SUzuki SX4 AWD (wife's) ; 2015 Sorento 2.4 AWD 1928 Graham Paige Model 629 I don't believe in miracles.
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#3
03-17-2008, 08:37 AM
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Re: Short term fuel trim question
The more reading I'm doing the Cat appears to be shot @172K miles and I drove 25k with a misfire from new bosch plugs. GRRR! I NEVER suspected new plugs.
Both O2 sensors pretty much mirror the response's. Considering its a cat I can get a direct fit with gaskets for about $200. I'll have to see if I can get a fuel rail reading. I don't have a adapter to screw on to the rail. No long term trim reading either but I'm learning more about this auto-tap diag. tool it maybe listed. thx for the help.
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03 GMC Sierra 100k 05 Infiniti G35 150K 10 Mazda 3 Hatchback 110K 16 Infiniti Q50 Red Sport 34K
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#4
03-17-2008, 04:10 PM
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Re: Short term fuel trim question
Got hold of a infrared thermometer and let the van run about 20 minutes @ idle and got these temps if it tells anyone anything.
Before cat 250-260F @ cat 140-145F After cat 6" away 175F I ordered a new cat today cause I think it probably poisoned from the misfire. Unless that can be fixed?
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03 GMC Sierra 100k 05 Infiniti G35 150K 10 Mazda 3 Hatchback 110K 16 Infiniti Q50 Red Sport 34K
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