Detonation, Bad Gas Mileage, P0171

4Runnin2000

4Runnin2000

New member
Ok. I have been searching for a couple weeks on how to fix this. Nobody seems to have my same problem. After the lift and slightly bigger tires 265/75/16 I expected a slight drop in mpgs. But I have been hearing what I think is detonation. Beacause It gets better when I fill up with 91 octane but is still pretty bad. Like marbles in a coffee can Threw the P0171 code. Too lean bank one. And have been getting maybe 170 to the tank city and maybe 200 all highway. Used to get close to 300 highway. I'm lost. Put in new plugs and wires about 6 months ago. Replaced fuel filter 3 months ago. Ran Lucas fuel system cleaner and does nothing. Trying to get this fixed because I feel like when I drive it I'm damaging it. Any help would be appreciated! Thanks!
 
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The tires is completely a coincidence. Tires won't make your engine run bad!

Try removing your MAF from the air intake and spraying carb or MAF clean on the large wire and the small one tucked inside real good until it's clean. One of your sensors is starving the engine of fuel and it's most likely the MAF sensor. Takes all of 10 min and can even improve your MPG's.
 
I have cleaned the MAF sensor pretty good a couple times with MAF cleaner and have also clean the wires with the electronic cleaner. forgot exactly what it was called. Then I'll delete the code and see if it comes back. And it comes back pretty quickly still. unless it's bad enough to need replacing.
 
Ok, 2 more things to check.

1. With a cold engine, start it up. Spray the cleaner on each vacuum hose and gasket (especially around the throttle body) and listen for a raise in idle speed. That indicates a vacuum leak. Just be careful... it is flammable... you can use an unlit propane torch too and that is safer.

2. Replace your front O2 sensor if all else fails.
 
Ok. I will do that as soon as I get the plugs back in. What do you guys think? Maybe 3k miles on them. They look normal?

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Okay I put the plugs back in. I change the PCV valve because it was looking pretty rough and the grommet. cleaned the MAF sensor again along with the connectors . sprayed the carb cleaner around all the vacuum hoses while it was running so I'm good there. Still have the detonation and the check engine light...
 
Plugs look good. Nice mocha color on the insulator and no damage or shiny black gas/oil deposits.

Here's what the FSM says for a P0171:

Air induction system
Injector blockage - Not likely since plugs are good.
Mass air flow meter
Engine coolant temp. sensor
Fuel pressure
Gas leakage on exhaust system - Highly unlikely.
Open or short in O2 sensor (bank 1 sensor 1) circuit
O2 sensor (bank 1 sensor 1)
PCV valve and hose

I bolded the ones you've already done. Keep knocking away at that list!

O2 sensors don't last forever though, usually around 100k miles. If you've had it a long time and it's never been replaced then I'd think that's your issue.
 
Thank you for the list. I will knock one out at a time (hopefully hit the one that fixes it first). I will probably start with the o2 sensor. I'm thinking that might be the cause of a couple of my problems. 140k on the odo. It would be a good maintenance item anyway. I will look up the part number for non cali emission one. Unless someone has it conveniently next to them?
 
Okay so this morning after doing an oil change and a little bit of seafoam, I started it up and heard a rattle from the alternator pulley area. is it possible that this can sound like detonation? I'll have to investigate more. But what would cause it to rattle like that? Bearings going bad? Alternator going bad? Just curious if anybody has heard of this before
 
4Runnin2000 said:
Okay so this morning after doing an oil change and a little bit of seafoam, I started it up and heard a rattle from the alternator pulley area. is it possible that this can sound like detonation? I'll have to investigate more. But what would cause it to rattle like that? Bearings going bad? Alternator going bad? Just curious if anybody has heard of this before
Click to expand...

The pulley or bracket might just be loose. Wouldn't throw a P0171 though.
 
4Runnin2000 said:
Nothing yet. Been busy at work. But tomorrow I am going to pop the hood and check it out.
Click to expand...

Been having a similar issue lately. P0171. Poor gas mileage but otherwise runs fine, no real signs of detonation though. Going to change front o2 sensor on Saturday.
 
GSPRunner said:
Been having a similar issue lately. P0171. Poor gas mileage but otherwise runs fine, no real signs of detonation though. Going to change front o2 sensor on Saturday.
Click to expand...
Oh really? Yeah that's going to be my next move I think. Not sure what else would cause this. Let me know if that helps
 
Well I will say that the new pcv valve has helped my gas mileage a little bit. Still have detonation and CEL came back on. Gonna take it to Auto zone and pull the code and make sure it's the same one. Bracket for my alternator is tight and belts are tight and aligned right. So I don't think that's the noise. It just sounds too much like detonation. So the o2 sensor will probably be next. Found it on Amazon for 45 dollars. Gotta wait 5 days for it though! Dammit!
 
I have been chasing this code for some time now... Truck stumbles and falls on its face above 3500 and just won't go more than 4500rpms. I have replaced the coils with new ones from Toyota, along with wires and plugs, all OE from Toyota. I have replaced the coolant temp sensor (from Toyota) and a denso o2 sensor from Amazon. New fuel and air filters (Toyota), new injectors (Toyota) swapped MAFS with a known good one. "Improved" the cat, replaced the fuel pump (airamotive)... What I have not done is the PVC valve, of the fuel pressure regulator... It is entirely possible I got a bad o2 sensor, but highly unlikely. I have also been getting a hard start when warm, like its being flooded.

I'm totally stumped with this. According to my fuel gauge I'm getting maybe 100miles to a tank. Yes 100... I have not run the truck dry to find out, and I might just do that Monday on my way to Seattle (I got 10 extra gallons in the back bumper).

If I find any info I'll be sure to post up as well
 
My p code was the result of a cracked/deteriorated intake inlet hose at the t.b.. The crack was bad enough to cause the truck to almost stall out. Couldn't see the rip cause it was on the bottom , I guess the computer sees it as a vacuum leak. Truck felt like it had no power. I also cleaned out the MAF sensor, but you already did that. So I did the repairs, cleared the and no problem since.
 
the great him said:
I have been chasing this code for some time now... Truck stumbles and falls on its face above 3500 and just won't go more than 4500rpms. I have replaced the coils with new ones from Toyota, along with wires and plugs, all OE from Toyota. I have replaced the coolant temp sensor (from Toyota) and a denso o2 sensor from Amazon. New fuel and air filters (Toyota), new injectors (Toyota) swapped MAFS with a known good one. "Improved" the cat, replaced the fuel pump (airamotive)... What I have not done is the PVC valve, of the fuel pressure regulator... It is entirely possible I got a bad o2 sensor, but highly unlikely. I have also been getting a hard start when warm, like its being flooded.

I'm totally stumped with this. According to my fuel gauge I'm getting maybe 100miles to a tank. Yes 100... I have not run the truck dry to find out, and I might just do that Monday on my way to Seattle (I got 10 extra gallons in the back bumper).

If I find any info I'll be sure to post up as well
Click to expand...

Your issue definitely sounds like a fuel related issue. Could be dumping way too much fuel in the engine causing it to lose power. I'm not entirely sure how to check for fuel delivery issues beyond injectors though...
 
gamefreakgc said:
Your issue definitely sounds like a fuel related issue. Could be dumping way too much fuel in the engine causing it to lose power. I'm not entirely sure how to check for fuel delivery issues beyond injectors though...
Click to expand...

P0171 is a lean code
P0172 is a rich code.

most likely an o2 sensor failure or a vacuum leak somewhere in the intake system
 
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