A/F ratio, takes 30+ min to get to 14.7

[SnowLizard]

Usually don't have to drive for 30 min, everything is dang close... like 3 miles from work/store/shops/etc... and I'm always watching my A/F ratio and it's always on the rich side, 9-13.5 (oddly 9 is cold, and 13.5 is accelerating, where as 12.5 is coasting/stopping)

I drove around in stop/go traffic today to watch the A/F FINALLY got to 14.7

I'm thinking a few things...

A) Catalytic converters (yes I have the P0420 code) <--- I have ordered them today
B) faulty O2 (a/f) sensor <--- less than 1 month old denso
C) injectors/FPR/gas pump

anyways, I'm a consistant 14.9-15.3mpg for city, and freeway, I'll see 16.5-17.1 so I know something is up....

I'm gonna replace the CC's next sat (ordered today from rock auto), but just wondering if anyone else has experienced these symptoms.

 

[AZBub]

Gas mileage seems bad considering you're mostly stock. I WAS getting 19.5-21 mpg until about 2 weeks ago. My culprits were bad spark plugs, an intake elbow with tears allowing air in past the MAF and a gummed up IAC. I fixed the other stuff but had mechanic clean out the IAC.

I also leaned that is usually the O2 sensor at the back end of the cat(s) that needs replaced. I replaced the front thinking that was problem but read on here its common for the back O2 to become "lazy".

Have you ran a can of seafoam through it at all?

 

[JayRolla]

You run rich when in open loop. So until the motor hits a certain temp it wont switch to closed loop. Once in closed loop you will be on the leaner fuel map giving you the 14.7 you are looking for. Guess maybe 30 minutes is a little long but I dont see your issue really. Also your mileage seems fine for city. I get 14-15 city, 17-19 hw.

 

[SilverRidgeRunner1]

Your Long term and short term Fuel trim could be the key to knowing what your ecm is doing and could help determine specifically the problem weather it a sensor or vacuum leak.. Have u attempted to monitor these values

 

[sjwelna]

You run rich when in open loop. So until the motor hits a certain temp it wont switch to closed loop. Once in closed loop you will be on the leaner fuel map giving you the 14.7 you are looking for. Guess maybe 30 minutes is a little long but I dont see your issue really. Also your mileage seems fine for city. I get 14-15 city, 17-19 hw.

This. While the car is warming up, the ecu intentionally targets richer a/f ratios to help things along. Unless you are cruising at constant throttle/load or sitting idling with the car hot, it probably won't be hitting 14.7 consistently. As soon as you crack the throttle all kinds of corrections like tip-in enrichment, LTFT/STFT and the A/F targets all start moving things away from 14.7. Your gas mileage looks normal.

 

[csp]

Mine is in closed loop before I can get it backed out of the garage, typical with a heated oxygen sensor.

 

[98OzarksRunner]

Mine is in closed loop before I can get it backed out of the garage, typical with a heated oxygen sensor.

Yep. I'd check the O2 heater circuit (though it should throw a code if it's not working) or an engine temp sensor (probably also throw a code though). It sounds like it's not going into closed loop or the O2 sensor isn't getting hot enough. Unless it's -20 outside, you should go into closed loop in 5 to 10 minutes.

 

[Skinfaxi]

If you're monitoring with a ScanGauge or similar, you can watch the open/closed loop flag. If your O2 heater is failing, it can slow the response. The car should set the engine light at some point, but that was still the early days of OBDII and the window for setting the light could be pretty big.

 

[Ruiner]

a somewhat obvious thing to check that may be easily overlooked is are you using the correct/functioning Tstat, and/or is something wrong with your fan-clutch. If its taking to long to get to operating temp, then those could be a reason why.

 

[SnowLizard]

Gas mileage seems bad considering you're mostly stock. I WAS getting 19.5-21 mpg until about 2 weeks ago. My culprits were bad spark plugs, an intake elbow with tears allowing air in past the MAF and a gummed up IAC. I fixed the other stuff but had mechanic clean out the IAC.

I also leaned that is usually the O2 sensor at the back end of the cat(s) that needs replaced. I replaced the front thinking that was problem but read on here its common for the back O2 to become "lazy".

Have you ran a can of seafoam through it at all?

I'm hoping I can get up to that mpg... not even close yet... I have replaced the rear sensor too (denso) from previous codes hoping to find these gremlins... I have ran a tank of seafoam, I have not run an 'intake' of seafoam yet, still debating if I need that. new MAF, I haven't thought of IAC, As far as I know I don't have a vacuum leak but I am going to be replacing many of the hoses here soon as preventive maint.

You run rich when in open loop. So until the motor hits a certain temp it wont switch to closed loop. Once in closed loop you will be on the leaner fuel map giving you the 14.7 you are looking for. Guess maybe 30 minutes is a little long but I dont see your issue really. Also your mileage seems fine for city. I get 14-15 city, 17-19 hw.

I started monitoring last night, I'm in open loop for about 1-2 min, then goes to closed, it will go back open if I floor the pedal. so it seems to be getting the signal right away, and acting as expected. one think I want to note, I'm stock, no lift/armor/extra weight, and you're getting better than me on HW. I'm lucky if I get 17.1 HW

Your Long term and short term Fuel trim could be the key to knowing what your ecm is doing and could help determine specifically the problem weather it a sensor or vacuum leak.. Have u attempted to monitor these values

I'll have to look up those codes, I haven't been monitoring.

 

[SnowLizard]

a somewhat obvious thing to check that may be easily overlooked is are you using the correct/functioning Tstat, and/or is something wrong with your fan-clutch. If its taking to long to get to operating temp, then those could be a reason why.

it gets to operating temp the same time as my 97 4runner does... almost no difference.

 

[SnowLizard]

... a gummed up IAC. I fixed the other stuff but had mechanic clean out the IAC.

I had to search more on this, looks like my IAC might also be gummed up.. gonna tackle it here soon, maybe before cat's... or after, I wanna know which 'fixes' my issues best.

Thing's I've noticed, my truck goes closed loop within 10-20 sec's of starting cold, granted I'm starting it at 80*+ weather for 730am.. but it is what it is...

just drove 166 miles, 9.5 gallons, that's 17.5mpg.... but that was all freeway (gilbert to flagstaff az @ 75mph) still took 30+min to get to 14.7 a/f... I think if I went 65-70 it would be up... gonna get my return mpg tomorrow.

sorry nothing else to report but my observations... want to document for other's

 

[SnowLizard]

changed both cats
cleaned my IAC and TB no difference
I also did spark plugs thinking that could be part of my 'rich' issue...

when I pulled the old ones they were horribly warn, and the middle cyl drivers was LOOSE, freaked me out as I thought it might have been stripped. but the new one went in like the other 5 just fine. took maybe 1.5hr. I also did OEM plug wires, figure another 50k+ out of them.

I'm still seeing rich after all this. I'm thinking maybe fuel regulator? or possible injector cleaning.

If anyone can, post thier A.F ratio please, I want to know what is should be. IDK if it's supposed to get to 14.7 now.

oh and my P0420 code hasn't come back.

 

[Bstrom]

You run rich when in open loop. So until the motor hits a certain temp it wont switch to closed loop. Once in closed loop you will be on the leaner fuel map giving you the 14.7 you are looking for. Guess maybe 30 minutes is a little long but I dont see your issue really. Also your mileage seems fine for city. I get 14-15 city, 17-19 hw.

That's what I was gonna say too. Until the whole block and exhaust are at full temp you won't see the best MPG available. I learned this on my Mercedes E320. It takes at least a half hour of driving to get any fuel mileage out of it - and it improves after that as the computer leans out the fuel/air mix for optimum burn. Kinda cool...

 

[SnowLizard]

That's what I was gonna say too. Until the whole block and exhaust are at full temp you won't see the best MPG available. I learned this on my Mercedes E320. It takes at least a half hour of driving to get any fuel mileage out of it - and it improves after that as the computer leans out the fuel/air mix for optimum burn. Kinda cool...

I hear you, I know it take some time to warm up and get optimum, but at that time it was 100* outside and 130 in the sun (157 in the car) so I know warm up time is small... now is different with the winter season... it's cold.

So this past Saturday, I drove up to cottonwood az, never hit my 14.7 A/F desire, granted it was up hill most of the way.
on the way back coming down hill, (7k to 2.5k elev) I still never saw my 14.7, it's a 2.5hr drive, so the 5hr's I drove saturday, I never saw it in the 14's... every once in a while it saw it in the 13.2-13.5 but never saw it higher than that. I'd saw majority of the time I saw it hoovering around 12.8 for a high.

 

[BlackCat914]

It's never going to run at perfect stoich. Its ALWAYS going to fluctuate. The numbers you posted seem totally within reason.

 

[sjwelna]

One other thing, is the reading from the O2 sensor even reliable on these cars? I know a lot of cars use narrowband O2 sensors that aren't worth much more than essentially a "too high!" or "too low!" reading. If the o2 sensors are basically a factory wideband then the readings hold more weight. I still think there isn't anything wrong with the OP's truck though, especially if there aren't any CEL's showing.

-Steve

 

[4eigner]

Did you replace the front O2 sensor or only the rear. It's my understanding that the front sensor is the one that controls the fuel trim

 

[JRZEE2000TR4LTD]

Did you replace the front O2 sensor or only the rear. It's my understanding that the front sensor is the one that controls the fuel trim

This is true assuming the truck is Cali emissions. Federal emissions only have an o2 sensor (and one cc)