Short term fuel trim question

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Headnsouth

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Short term fuel trim question
I have a P0420 on this 98 Pontiac van with 172k miles. Its been recently tuned new plugs, wires, filters. 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
 
Catalyst System Efficiency Below Threshold (Bank 1) indeed.

You have two problems, a bad catalyst on bank one, and a likely vac leak on bank 2 (possible manifold gasket or leak in the vac system that goes to one of the Bank 2 runners.)

Short trims don't set codes till they get bad enough to be long term codes.
 
Originally Posted By: punisher
Catalyst System Efficiency Below Threshold (Bank 1) indeed.

You have two problems, a bad catalyst on bank one, and a likely vac leak on bank 2 (possible manifold gasket or leak in the vac system that goes to one of the Bank 2 runners.)

Short trims don't set codes till they get bad enough to be long term codes.

Whats a Bad catalyst? A bad CC?
What exactly is bank 2 runner?
 
Originally Posted By: mechtech2
Could also be a bad second [downstream ] o2 sensor.

Just replaced it same DTC.
frown.gif


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?
 
Originally Posted By: mechtech2
Could also be a bad second [downstream ] o2 sensor.


Not for that code. A bad secondary will set a code specific to that sensor and not a cat efficiency code. A bad cat monitor will likely ignore a faulty cat.
 
I had the same code when one of my cats was emptied temporarily until the new one could be installed. The code would throw the CEL at constant speeds of 45mph. I had a custom tune made by BAMA chips for my SCT programmer, and I told him before he wrote the tuning file that I was having that problem. Once I loaded the new firmware into my computer the CEL quit coming on for good. I've since changed the cat and noticed a HUGE drop in power and mileage, but at least the epa should be happy.
 
Installed the new Cat. I can manually clear the SES light but if I do that I'll have to drive it about 200 miles in order to have all the monitoring completed and I can't really drive it cause its failed emissions.
How many drive cycles will it take to clear on its own and what constitutes a "drive cycle"?
 
First hit in Google for "OBDII drive cycle":

Performing a GM OBDII Driving cycle:


Cold Start. In order to be classified as a cold start the engine coolant temperature must be below 122°F (50°C) and within 11°F (6°C) of the ambient air temperature at startup.
Do not leave the key in prior to the cold start or the heated oxygen sensor diagnostic may not run.

Idle. The engine must be run for two and a half minutes with the air conditioner on and rear defroster on. The more electrical load you can apply the better. This will test the O2 heater, Passive Air, Purge "No Flow", Misfire, and - if closed loop is achieved- Fuel Trim.

Accelerate. Turn off the air conditioner and all the other loads and apply half throttle until 55mph (88km/hr) is reached. During this time the Misfire, Fuel Trim, and Purge Flow diagnostics will be performed.

Hold Steady Speed. Hold a steady speed of 55mph (88km/hr) for 3 minutes. During this time the O2 response, air Intrusive, EGR, Purge, Misfire, and Fuel Trim diagnostics will be performed.

Decelerate. Let off the accelerator pedal. Do not shift, touch the brake or clutch. It is important to let the vehicle coast along gradually slowing down to 20 mph (32km/hr). During this time the EGR, Purge and Fuel Trim diagnostics will be performed.

Accelerate. Accelerate at 3/4 throttle until 55-60mph (88-96 km/hr). This will perform the same diagnostics as in step 3.

Hold Steady Speed. Hold a steady speed of 55mph (88km/hr) for five minutes. During this time, in addition to the diagnostics performed in step 4, the catalyst monitor diagnostics will be performed. If the catalyst is marginal or the battery has been disconnected, it may take 5 complete driving cycles to determine the state of the catalyst.

Decelerate. This will perform the same diagnostics as in step 5. Again, don't press the clutch or brakes or shift gears.
 
The catalyst efficiency monitor test in Ford vehicles will not run unless you drive at a steady speed of 50-55MPH or so for several miles. I expect other manufacturers catalyst efficiency tests will run under the same conditions.
 
Originally Posted By: brianl703
The catalyst efficiency monitor test in Ford vehicles will not run unless you drive at a steady speed of 50-55MPH or so for several miles. I expect other manufacturers catalyst efficiency tests will run under the same conditions.


Jeeps (and I assume other DC offerings) need a cold start to initiate the readiness tests. That is, if you reset a code, you can't just drive. We're allowed one readiness test to not be performed. If your tank is too full or empty, it won't perform the EVAP PURGE test. If the CAT EFF readiness test has not been performed, and all the others have (it's must take a while to set the CEL), then the OBDII test works here in PA for getting your sticker.
 
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