01 Tundra 5vzfe Running lean
 

Hello everyone, I'm hoping that someone has come across this before.. I am at wits end and don't want to part ways with my tundra.
I've owned this truck since brand new, it currently has 185K on it. I'm good about keeping up with all the maintenance on it as well.
Here's what happens, under load in 3rd or 4th gear from 1/8th to 3/4 throttle the engine pings like a diesel, I often reset my foot on the accelerator pedal to stop it, which means just barely touching it on the highway to stop the ping. If I go past 3/4 throttle the truck will not accelerate that much but will start to buck like it's starving out of fuel. I do have a CEL, the code is a P0171 Bank 1 too lean. It's not indicating bank 1 sensor 1 which I have had in the past and replaced the A/F sensor (march of this year). End of last year I replaced the Rear O2 sensor. My neighbor is a mechanic of over 20 years of experience and we took it for a ride with his Solus connected to watch the sensors in real time to see if anything was way out of range, and they are not. The injector pulse is widening according to throttle position, the A/F, rear O2, MAS/MAF and TPS are all reading within specs. I have also replaced my fuel filter and fuel pump within the last 2 months, and the problem is only getting worse. Now, when I first start it in the morning, it runs extremely rough, like I've disconnected the battery and it's re-learning everything for that first time. If I smell the exhaust at this time.. it's the only time the exhaust is very very rich and loaded with fuel. Within a few minutes, it leans way out to the point of you can tell by just smelling the exhaust that she's running way too thin.
My thought, is that it's the Fuel Pressure Regulator... but my mechanic buddy says when these units go they flood the vacuum line with gas which in turn it would run in the port in the back of the plenum causing it to run rich / rough.. which its not. I've gone through and checked / replaced all the vacuum lines which there were some cracked lines but none causing a bad leak. The only thing I can think of that's left is the FPR is stuck in single position and not adjusting like it should, Or the supply line from the fuel filter to the fuel rail is clogged or my ecm is messed up somehow.
I can't see all 6 injectors being clogged either.
Has anyone come across a problem like this?
We also swapped the MAS out the other day just to be sure and nothing changed. A clogged CAT has been ruled out as well, the exhaust is flowing normal.

I'm open to any ideas / suggestions at this point just shy of pouring gasoline on it and having a bond fire... which I don't want to do to my truck.

thanks in advance,
Rapt0r

So, I've narrowed it down to the TPS. Doesn't kick any tps codes but if I disconnect the TPS the truck runs alot better and no longer pings and runs lean. I went and got a new TPS sensor and connected it up and it's doing the same thing, so now I know it's in the tps wiring somehow / someway. Now I just need to find out what should be at those three connections that plug into the TPS sensor. I bet I've got a wire grounding itself out... now to trace it out... uck...

40 + views and nothing... really?

Ever get that figured out?

No I haven't, I've gone through everything one could go through... I'm thinking of trying to find an aftermarket adj. fuel pressure regulator so that I can up the pressure to the injectors slightly.
Still tossing a P0171 code, but it's a new a/f sensor, new Maf sensor, new TPS sensor, all other sensors are sweeping within normal ranges, cat isn't clogged, timing belt hasn't jumped, No vacuum leaks. I don't see how multiple injectors could get clogged all at once, which is what it seems like. And I'm not in the market to dish out that kind of dough... I've read they are expensive new...How ever, strange thing, if I disconnect the TPS while hot, the truck stops pinging and runs much better... yes there's a little bog.... I've even checked the relays for the EFI... I'm at a loss.

:dunno:bump

Can anyone recommend a good adjustable fuel pressure regulator for this truck? I search and find a couple dozen that look like they'd work just fine. Is there a particular that's better for the 5vzfe?

thanks

Is there a reason why nobody has chimed in? are you considered dirt here until you have 1000 posts or something? Such a helpful board, such insight.
I remember when it used to be a helpful place...but I guess those days have come and gone.

Bad spark plugs or spark plug cables? Check all your ground wires. A loose/corroded ground can do weird things. Check the air intake tube for cracks too.

Here is a thread on low idle and on page 4 the importance of good grounds:
https://www.yotatech.com/forums/f2/1...43/index4.html

Have you gone through the dianostic section of the FSM?

I've gone over and cleaned all the grounds.... If I had any bad plugs or wires wouldn't it be running noticably fat? You smell the exhaust it's really lean... but the plugs / could explain the past half throttle breakup..

thanks for some input sir.

I don't know the 3.4, but TPS was my first thought. You've probably been over the feeler clearances a few times though. Seems to be related if it affects the problem though. Do you have an altitude sensor between the TPS and ECU on that one? Just another variable in the circuit to eliminate if so.

Otherwise it does sound like an ECU thing, they're supposed to sense pinging and run in failsafe mode (knock sensor OK?) Maybe a slow leak over the pass side windshield (or wherever it is on that rig) corroding your ECU terminals? I've never known one to go bad but water can kill them. On the FPR, supposedly you can test functionality by listening with a stethoscope. In the meantime I'd hotwire your cold start injector to run, better off rich than lean.

This may help you out on the diagnosis:

http://www.ncttora.com/fsm/2000/Repa...n/cip0171p.pdf
http://www.ncttora.com/fsm/2000/index.html

The TPS I went to the point of tracing out the wires back to the ecu to make sure that none of them were bare or finding ground somewhere. The ecu plugs are clean as can be... I am curious... where's this cold start injector located usually? I guess I can poke through the service manual and try to locate it... The more I think about it... it does act like a clog in the fuel feed, here's my logic... I'm getting gummi bear fuel mileage right now as if the fuel isn't "spraying" from the injectors more like dribbling out, so it's not atomizing enough thus I'm burning it up in the cats...
I think I need to pull some plugs this weekend, look at the bottom of the charcoal canister and make sure there's no crack, even though I did the carb clean test... and check the fuel pressure at the rail...

Pull your injectors out and have them professionally cleaned. As far as running lean then rich, I'm thinking thats just the computer trying/fighting to get your a/f ratio right. I think your problem is in the fuel delivery. Since you are pulling injectors, I would replace all the intake manifold gaskets including the lower plenum. I had that code on mine and it was the lower plenum gaskets.

I don't really ever have a running rich condition anymore, the exhaust is always super lean. A new thing that has started, don't know if this clues into something, but when I first start it in the morning it runs like it has a high lift long duration race cam in it for about 30 seconds then straightens out. I can stab it quick lightly and it stops right away. If I push it straight to the floor really quick, it boggs terrible and lean pops through the intake plenum.
Best way I can describe how the engine is running is if you disconnect the battery and let the ECM / ECU re-learn everything... that period of stumbling and coughing it goes through... that's how it seems to act.

I'm leaning towards I'm starving out of fuel somehow... but I'm going to be checking everything this weekend that has been discussed here, evap canister, clogged fuel rail... etc.

I cannot personally come up with a reason why a mechanical error would be affected by disconnecting the TPS. If your regulator was stuck open, rail was clogged, etc pressure would be low all the time, in my mind. Worth a look, but because your said TPS affects it, I'd suspect electrical.

If you listen by your pump when someone turn the key to "on", do you hear it priming? Does the truck run OK when not under heavy load? If "no" and "yes" then suspect the circuit which gives full current to the fuel pump for startup and load, may be running through the resistor 24/7, not ok.

And again, your altitude sensor will lean out a mixture if it senses your at high altitude. Don't know whether that takes precedent over O2 signal etc, but worth a shot.

Before I go crazy chasing wires, I'm going to disconnect and blow out some lines check for flow this weekend, the go from there.
Does anyone know if the fuel line from the front of the fuel filter to the feed side of the injector rail is a aftermarket or dealer part that's obtainable? Or once the stock / factory one is dead .... make your own?

thanks, I'll post up my findings...

I did some testing and noticed before a cold start when it normally will start up then run rough for 15-30 seconds, if I clamp the return line to the tank... the engine never ran rough... has anyone ever seen a FPR get stuck in a Low PSI position and no longer adjust accordingly? Just curious... didn't have the weather to dig into it further unfortunately...

What's the verdict?

the way it sounds it is almost like fuel cut. You may try a new crank sensor. the only reason i say this is that i've seen it twice. once on a 3rd gen runner and once on a taco. both 5vz. the sensor doesn't seem to pick right as the rpms rise and it starts cutting fuel. just a thought.