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Short term fuel trim question

03-16-2008, 04:44 PM
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

03-17-2008, 08:29 AM
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?

03-17-2008, 08:37 AM
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.

03-17-2008, 04:10 PM
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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