1997 4runner 3.4L engine running to lean

Instead of thread jacking I decided to create my own post this is my 1st time posting so go a little easy on me. My engine upon heavy acceleration starts to sputter and almost cuts out but never fully cuts out, when the heavy throttle is eased off..... it returns to driving fine. I replaced the MAF, THEN it threw the "engine running lean" code. This code wasn't thrown BEFORE I swapped the MAF, just had the "hickup" upon heavy acceleration (the "hickup" is why I changed the MAF in the first place)
Description of heavy acceleration: as if you need to speed up onto an entrance ramp, going from 40mph-60mph. Trying to catch up to speed. I took it to toyota and spent $1000 and they did
Combustion test (passed)
Fuel pressure test at idle (pass)
They replaced plugs and wires.

Parts I've replaced (tips from reading other threads)
MAF
both 02 sensors
Fuel filter
Throttle Position sensor
Plugs
Wires
Pcv valve
SOME vaccum lines (did the starter fluid test ALL around the engine ....engine never idle up) ‍♂️
Parts I am considering replacing next without testing is
Fuel pump, then Injectors. Any help will be appreciated, I am at your mercy.

 

My first thought is Fuel pump. It's due. Probably weak.

Consider replacing the sending unit too since it's in the same spot. It's probably due and they burn out consistently at 200k miles.

Don't know if you have the large black check valve like my 2002 4Runner has but I'd do that too while there along with all gaskets/grommets for anything that is plugged into the tank. They dry and crack and leak.

If it was a bad injector...I would think a misfire code may happen and it won't cutout like that either.

 

Okay! I'll get this replaced and see what happens

 

Wait. Check the CAT. Could be the cheaper route.

If clogged, that also will cause loss of power at acceleration.

(Did the Combustion Test cover that?)

 

Well, I'm not to sure but there's tons of exhaust coming out the tail pipe

 

Just wanted to state, this 4runner has 171k miles

 

Well, a cat won't be clogged shut...so at idle you won't see anything out of the ordinary. However, if it's clogged enough then trying to push more exhaust through won't work and the engine stalls. I don't think you will get a lean code on that though, but hard to say. I'm still thinking fuel pump.

If you read up on how to test for a clogged cat, I think you can run the car for a bit and then check the temperature of it and if it's super hot...it's plugging up.

 

Okay, update.
Got my thermo gun, around 422F on top and bottom side of CAT, gonna replace fuel pump this week and see if anything changes.

 

That seems like a normal Temp. Internet says 400-600F is normal.

I found a good guide on testing:

https://www.2carpros.com/articles/how-to-test-a-catalytic-converter

I have never needed to do it...but I would definitely follow their instructions. The back of the cat (toward rear of car) should be hotter than the front. (the chemical reaction of the CAT heats up the exhaust)

If you disconnect the exhaust or remove the O2 sensors, you should see a performance improvement as the gas can escape easier.

If it all checks out, I would definitely consider it a fuel problem.

Just would hate for you to drop the fuel tank which is a PITA if it's not the pump.

 

I understand that very well, I'm also looking at all the "wasted money " (on parts, not labor) as preventive maintenance. Lol
A symptom I forgot to mention is when I crank it..... it takes a little bit to crank up, like grunnnnn, grunnnn,grunnnnn, *vrooom makes me think....... fuel pump. ‍♂️ but I'm not a mechanic.....and I did the right thing and took it to "the man" got burnt, now it's up to me, which I dont mind..... I know it'll be done right.

 

I any intake pieces are loose from air/filter/MAF to throttle body. It will not run right....

 

He said he did the starter spray test around the engine and it "never idles up".

Also, OP, make sure you get a Denso pump. No cheap aftermarket stuff. Denso runs ~$100 and it's the same manufacturer that TOYOTA uses. TOYOTA will want $250 for the same thing. One of very few parts I didn't source from the dealer.

 

Update.... I went under th back seat to see if MAYBE this year, I could remove the fuel pump without dropping the gas tank, and found all wires just like in this picture
(I just bought this 4runner about a month ago) my rear window doesn't work BUT, one thing at a time, I plugged that white plug in and the ABS light (which has been on) actually went off. I really thought the car was going to explode when I plugged it in

 

God bless that mess.

You're going to find out why it was disconnected at some point.

I would get a schematic and rip out all that aftermarket crap.

People who cut wiring for aftermarket crap like that need to be drawn and quartered.

 

I dont even know where to start

 

Well turns out I replaced body harness to fix those wires and BAM!







SAME PROBLEM. So what's next go with the fuel pump?
I changed the crank sensor in the front bottom of engine, still same problem, I also cut my cat/exhaust all of it off and looked inside the cat and it literally looked brand new. Still haven't fixed this problem and probly have close to 1500$ invested

 

Cutting out under heavy acceleration is often the Fuel Pump or maybe Fuel pressure regulator. You changed the MAF (hopefully with a quality one) and you aren't getting codes, so my best internet guess is the pump.

 

I have simular issue and replaced all 6 injecters. The engine runs great fuel consumption is down but now mass sensor says running lean. Lurches when hard take off. I imagine something in plenum or intake hose isn't right. Will be checking all vachoses and clamps. Ordered a new intake hose keeping stock since it's just a daily driver. Getting a P0172 code. May reseat injecters seeing if one has bad o ring or seal. Idles better that b4. Slight fuel smell once in a while.