3.4L Fuel (?) Issue

I have concluded that the fuel filter on my vehicle is connected to a problem that has existed with it since purchase: 3 years, 15k miles, and countless maintenance items trying to make it run like a top, never noticing any improvement to what I always felt was not quite right. This just got worse and worse over time to the point of now - where I can't accelerate unless I mash the pedal for a downshift, while going down hill. No power, rough idle, stressed engine noises under the hood.

So I could no longer write off the crap performance and now 13-14mpg as a result of heavy modifications, big tires, and a general slaying of aerodynamics. Cleaned the MAF and installed an OEM fuel filter 3 weeks ago taking shots in the dark and it made this now heavy ass vehicle run twice as good as it did when I bought it in stock form. Towed 1,500lbs with a smile on my face and stomped the fuel economy of my unloaded figures! I couldn't say for certain at the time which fixed it - I had done the MAF the day before so I didn't give things a fair chance to learn - and I hadn't reset the ECU.

That lasted for a week, 1.75 tanks of gas, <500 miles. All symptoms returned same as before. Figured either MAF was failing or the new fuel filter had clogged, so I ordered a brand new Denso MAF and a new fuel filter. Changed the MAF and reset the ECU, drove 100 miles, still ran like crap. Changed the fuel filter again this evening and BAM, problem solved - again. So now I need to figure out what to do from here to avoid spending another grand and 3 years throwing parts at it. My CEL works, I've tested it many times forgetting to plug stuff back in. It has never thrown a CEL so whatever the problem is, the car doesn't recognize it or thinks it has adequately adjusted

If fuel tank is really so dirty that it clogs filters in a week I must rationalize:

1. That in the 14 years/241k miles prior to me owning, the car went through some serious crap gas or somehow rusted in the tank despite being a rust free vehicle
2. Why a new filter would clog in 500 miles, but the filter I removed had not completely clog (it was on the car when I got it 15k ago, and was likely way older)
3. How the pump didn't burn out if it was sucking up sludge for years

If the fuel pump is failing I must rationalize:

1. Why changing the filter has breathed life back in to the pump, twice now, but only for 500 miles
2. How the pump has continued to work at poor to borderline undrivable for 3 years without fully kicking the bucket
3. Why it has never caused the car to stall, fail to, or even struggle to start

If an injector is failing I must rationalize:

1. Why my idle noise and vibration is rough but consistent - not like missing or stumbling that I would expect from one or several injectors failing
2. ^ - by that token, how all 6 injectors could perform poorly OR perfectly in sync with one another
3. How the hell a fuel filter change suddenly wakes up 6 dying injectors, twice, for a week. Are they clogged and the dry firing of them for 10-20 cranks as fuel lines prime clears them out just enough?

If a sensor or regulator of some kind is failing, wtf now:

1. What kind of sensor or regulator could be 'rebooted' by a fuel filter change or the 10-20 cranks it took to get started - No ECU reset, instant effects, so no learning was involved
2. How did it not completely fail after 3 years
3. You know the propane regulator on a grill? I'm thinking something that performs like that, electrical or mechanical, where it gets tripped - and either the dry cranking or lack of fuel pressure reset it.

If anyone has suggestions - please post up!

 

Excellent idea. Cutting open the filter would be a great idea. Make sure not to do it with an electric saw

 

It doesn't sound like it's your sensors or injectors if a filter replacement helped. It's related to the filter, the tank, or the pump. I have seen filters clog with rust particles that have gone through pumps without clogging them. You may have to drop the tank and look in it. If the tank is rusty you'll see a lot of fine, red particles slushing around in the bottom.

 

Unlikely that this is the root of your issues, but have you cleaned the throttle body and IAC valve? If particulates have been passing through your fuel system it is likely that those need to be thoroughly cleaned regardless.

 

This^. If the filter keeps fixing it, then the filter must be getting clogged. Unless it's picking up particles along the fuel line, then it's coming from the tank. Check the filter first, and if it's warranted check the tank. In my opinion it's easier to remove the bed, than drop the tank.

 

if i only had a garage.....

 

A garage is a nice "tool" to have. Old house didn't have one, new house does. I don't think I'll ever buy a house again that doesn't have a garage. If you do ever get one, try to keep it cleaner than mine haha.

 

impossible to keep it clean... dirt bikes jetskis truck parts thered be no end...

 

Cleaned the tb yesterday to no avail before I ended up doing the fuel filter over again, didn't touch the IAC though.

So an update, it runs like dook again. I had done the filter towards the end of the day yesterday and it was good for a 20 minute test drive. This morning I noticed it didn't sound as healthy under the hood once the high idle stopped, and it drove poorly. After a few stop lights the idle vibration also returned to the party. So the first replacement filter lasted a week and ~500 miles, the second lasted for 20 minutes and 10 miles.

I've ordered a Denso fuel pump kit and tank gasket, might as well go for it. If the filters are actually getting clogged then I'd have to drop the tank anyway, and I wouldn't go through that hassle without spending the $80 bucks for a new pump and filter sock while in there. It also gives me an opportunity to cut my tank vent pipe shorter since I can only fill ~14 gallons after riding the gas light for 50 miles. 99 4Runner drama, clearly no previous owner paid attention to the TSB.

It's weird that I have no noise from the fuel pump... something makes me think this is a pressure related thing due to a valve, I just hope it's actually a component in the tank and not something cheap under the hood. Like FPR?

 

This is the filter that I removed three weeks ago that was put on by the previous owner, no less than 3 years ago and ~15k miles. Doesn't look brand new, but it certainly doesn't look like the tar black filter media I've seen come out of others.

I tested to see whether a vacuum was forming in my tank causing the fuel pump to struggle. I drove without the gas cap on for 30 miles and it felt the same- awful. At the end of that 30 mile drive I pushed the fuel flapper down and there was no whoosh of air at all, so I don't that's causing my problem. Oddly enough, I did not throw a CEL doing this.

New fuel pump should be here at the beginning of next week. If that doesn't fix it, I'll see if I can bribe a Toyota tech from a local offroad group to check it. If he doesn't know, I'll try one round of diagnostics at the dealer. If that doesn't pan out, I'll sell the bitch for scrap.

 

don't need a garage I did mine in the driveway like this need a 17mm socket,breaker bar,wd 40, 2 strong men, unplug all the rear light wiring theres threads how to do it. hardest part is unbolting it, then walk it back rest it on the rear wheels

 

Guess I can't rule out fuel pump voltage quite yet. I was happy to see PO didn't cut a hole in the floor, but the electrical tape on the left definitely seems newer.



Thought I was on to something with the brown staining on this harness. Most of the brown is goop - like dielectric gel. Some of the brown is stained on the harness though



Bleh



Seems like the four wires from the white harness just go to the back of the tank somewhere though, not the ones that drop directly in to the tank. Not sure what they do, but if they aren't the ones supplying power to the pump then I wouldn't assume they're to blame for anything

Doesn't look like PO forgot to disconnect anything here before dropping the tank, if he or another previous owner actually did the pump at one time.

 

Can you check fuel pressure at the rail on the 3.4? then check the spec on it to see where you stand ?

 

Apparently that's a task in itself, no accessible valve to simply connect to under the hood. The service manual references some specialty connection and is still like 30 steps. I really wish I could at this point though, as it'd likely be pretty telling.

 

I just recently picked up a 2001 Tacoma with the 3.4 and 115k on th odometer.

New parts I've tried
Upstream O2 sensor
Plugs and wires
Maf
Fuel filter
TPS
Fan clutch (old one was stuck engaged)
Cat delete
FPR

From day one it just didn't seem to have the power it should. CEL was on when I got it. Turned out to be an upstream O2 sensor. Replaced that thinking that might be the problem. Still seemed to not run as good as I thought it should.

I began having high idle issues which lead me to replace the TPS. That fixed my idle issue. Truck also ran a little better. Still felt sluggish and required downshifting on small hills to maintain 65 on the highway.

I then cleaned the MAF. That didn't help anything but it had also been replaced recently. I then changed plugs out. It had new wires but they didn't replace the plugs. It had some iridium plugs in it that were shot. I replaced them with oem double electrode plugs. Seemed to run a little smoother but still not right.

It felt like something was still holding the truck back. I thought maybe the cat was stopped up. Removed the cat and did the DIY rear O2 simulator. Still didn't help the power on hills.

Replaced the fan clutch since it was stuck engaged. Well worth it just to not heat it roaring and gained a little power.

After all that the trucks runs and idles much better. Runs great on flat ground with plenty of power. It just losses power on the hills still. It just acts like the fuel pump isn't keeping up.

I've ordered a Denso fuel pump kit with new sock filter. That's really all that's left.

 

Following.
Hoping both of you figure out your issues. Sounds like maybe the fuel pump may indeed be your issue looking at your replaced parts list.
Will stay tuned for fuel pump replacement to see if that helps!
Good luck!

 

It's possible that the injectors themselves have been fouled if there are any particulates that have passed through the fuel filter. It's not terribly difficult to remove the injectors and send them off to be cleaned and flow tested so they all match. There are several companies that will do it with 48 hour turn around.

https://www.rceng.com/Fuel-Injector-Cleaning-P43C0.aspx
http://www.witchhunter.com/