4 codes after heavy acceleration(P2197,P2195,P0174,P0171)

I did a search but I haven't found anything similar to my situation. Here's what's going on:

2005 Prerunner 4.0L
235,000 miles

Truck runs great overall but if I go out onto the highway and stomp on it, the OBD will show the above 4 codes pending and eventually it'll throw the CEL. The truck seems to accelerate normally. No stuttering or hesitation. I'd recently replaced the upstream 02 sensors due to P0171/0174. Admittedly, they're Amazon specials but all codes came right back. Also, both OEM upstream sensors "failed" about the same time which isn't likely. If I keep it below highway speeds or accelerate slowly at highway speeds, I'll never get the codes. I've checked all vacuum lines and can't see any cracks/splits/deterioration/loose hoses. I've also replaced the MAF sensor.

So this is leading me to the fuel pump and the possibility the pickup/filter is very slightly blocked which slightly restricts fuel delivery under heavy acceleration. Additionally, the autostart won't start because manual starts requires one more crank than the autostart cranks. I'd put a fuel pressure tester on it but I'm sure once running at idle it'll read normal. Again, it's only at high speeds and heavy acceleration. I just don't believe it's an injector because acceleration is smooth, I simply will get the codes.

Anyone with guesses or insight, feel free to chime in. Also, if anyone has changed the fuel pump, let me know what you think is the best way to go about it. Right now I plan to take the box off for ease of access instead of laying on my back and dropping tools on my face.

 

These trucks operate the fuel system on 2 speeds.
Low and High. The high speed is operated at “high speeds and heavy acceleration”, just as you describe.
It may be that the fuel pump is weak? A fuel pressure test would be a great place to start here.

And it’s not just me that’s said this before.
Take it from a Toyota Tech.
https://www.tacomaworld.com/threads/horribly-degraded-performance.628800/#post-21527521

 

16 yr old truck, original pump and filter. 235k miles....

Replace the pump n filter and i bet it all stops

Your fuel pump cant keep up with the demands for fueling at higher rpms and loads. The truck likely runs just fine under WOT conditions as stock they demand SUCH a rich fuel mixture that when they do go "lean" due to fuel pump problems, they are likely still plenty rich.

That stated, i wouldnt risk it. replace that fuel pump.

 

Thanks guys

 

Update: well, the pump didn’t fix it. For having 235,000 miles, that pump was impeccably clean which was impressive. So I’m still getting all four codes only when I’m at highway speeds and stand on it. The pending codes had actually gone away because my son never got over 50 for a few days. So now what? Injectors maybe slightly plugged? Or should I try putting in OEM O2 sensors first? This one is really a head scratcher.

 

Maybe the fuel pump relay isn’t switching to high speed?
Could it be that it’s stuck on Low Speed?
You could jump it temporarily and see.
The fuel pump is supposed to operate on High speed when starting the truck.
But it very well may start just fine even if the relay is stuck on low?

To be honest, I doubt that’s the problem.
As the resistor usually fails. I can’t say I’ve seen a relay fail?
But there’s a first time for everything!
It’s certainly something I’d be tempted to check if it were my truck.

@Jimmyh did a great job of explaining the relay and resistors purpose here.
https://www.tacomaworld.com/threads/fuel-pump-resistor-symptoms.632838/#post-21729932

Here are pictures to the location of the resistor.
https://www.tacomaworld.com/threads/07-tacoma-fuel-and-vacuum-line-diagram.693109/#post-24511272

 

I simply disconnected it. It started fine and then died a few seconds later. Plugged it back in and started and ran fine. I don’t know, everything looks OK physically. Also, the codes are all gone again. It just doesn’t like highway speed.

 

OP. I'm a bit confused here. Did you replace the fuel pump and if so was it an aftermarket pump?

 

Most recent part was an aftermarket fuel pump. I’ve also replaced the MAF and both O2 sensors(also aftermarket). I’ve inspected all vacuum hoses and they look good. I’m showing lean in both banks but only after hard acceleration at highway speeds.

 

Thats what it should do if you disconnect the resistor.
The truck starts on High speed, then switches to low speed shortly after start up.
If the relay we’re stuck stuck on low speed, the truck probably wouldn’t have started.

So, the mystery remains.
I mean, it’s not likely both the A/F Sensor and the O2 Sensor went out at the same time.
Do you have a scan tool capable of monitoring A/F and O2 voltages?

 

Look for any exhaust leaks upstream or around the oxygen sensors

 

Look for cracked/loose intake side parts too

 

These Amazon special upstream sensors. They weren't Denso, correct? What brand did you choose? That could be a major part of the problem.

As in the OE were old and beyond their lives, but the new ones aren't quality enough to perform properly. Lazy or Faulty signals.

 

Bank 1 and 2 Sensor 1 both showing 3.3V

 

Correct, not Denso but I forget the brand.

 

It could have been residual fuel pressure it was running on for a few seconds.

What you need to do is:

1.) Disconnect the fuel pump Resistor.
2.) Jumper across the harness side connector terminals. This is the high speed mode for the pump.
3.) Test it under a full load and see if it is still running like crap when you drive it hard.

If it still craps out you know it isn't the resistor. If it runs as it should then it is the resistor.

 

But it doesn’t run like crap, ever. I simply get codes. That’s what’s so annoying.

 

It seems you visually checked potential vacuum leaks. You need to use brake cleaner and spray it around all possible leaks to see if the engine stumbles. It's a great way to check for leaks.

 

OK

Test it under a full load and see if it is still Getting the codes when you drive it hard.

If it still Gets the codes you know it isn't the resistor.

If it runs without getting the codes then it is the resistor.

 

All indicators if all above are ruled out. 235k. Wouldn't be unreasonable to question the FPR and or injectors. I don't know what they run $ wise, would be easier to diagnose if something was following a specific cylinder. I dislike part hanging, but there's not a real DIY way I'm aware of to see how functional they are. If you could borrow a set somehow, that would be great. I've had witch-hunter rebuild some of mine in the past. They will show you pre tests and flow rates vs post tests etc.

Edit:

I should have formatted / specified better. I was mainly talking about the injectors. You could get a set of noid lights, but I would suspect based on what's known that it would be a flow issue, not an electrical issue. The FPR on the other hand, run the truck a while, shut it down, pop the vac line to it, and see if gas comes out. However with the low/high fuel delivery system, you may want to try starting the truck, unplug the vac line, then pull a vacuum with a standard hand pump so it opens up more, then see if gas shoots all over. Get ready to shut down quick!