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Old 09-17-2016, 05:57 PM #1
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Repeated fuel filter clog, failing fuel pump, or ?

TL; DR Changed fuel filter, instant mind blowing positive change, 1.75 tanks / a week later all symptoms return identically. Ideas greatly appreciated as I want to solve this correctly, not by throwing a new filter on it every week.

Spitballing potential causes
  • A ton of sediment or rust is in the tank and reclogged the filter as I ran the second tank down. This would almost suggest that the fuel filters are technically uncloggable, as the old filter would have been completely plugged otherwise.
  • There are normal levels of sediment in the tank, and neither the old filter nor the new one are significantly clogged, but my fuel pump is failing can't handle back pressure from anything but a pristine fuel filter

I don't think an injector is clogged because any vibration seem uniform, like everything is suffering equally. I also don't see how changing the fuel filter would have instantly cured an injector for 2 weeks. I also don't think it's related to air intake, sensors, plugs, wires, etc. as sensors are clean, filters and plugs+wires range from new to very new. All I can think of is pump or wicked tank sediment.

Blabbing story

The performance of my 99 3.4L auto had steadily decreased since purchasing 3 years / 14,000 miles ago to the point of being an absolute stress filled chore to drive. I attributed this to the evolution of the vehicle: take a heaping dump on aerodynamics via lift and roof rack, hanging hundreds of pounds of steel up front, running oversized knobby tires, etc...

I changed the fuel filter with an OEM Toyota one like two weeks ago and every symptom I had with the vehicle was immediately resolved. This lasted for ~400 miles / 1.75 tanks of gas / about a week. The first 325 miles occurred the day after the filter change, towing 1,500 lbs on the interstate and up high elevation mountain trails. It performed flawlessly doing this and felt better than it EVER had. It also raked in +4.6mpg on the first tank of the trip than I had seen in 2 years, unloaded. Unloaded 100% highway tanks had literally been around 13.

Anyway, the second tank got me home and I continued my week driving the 4runner in absolute bliss in the city and on the highway (75 miles - fuel gauge now at 1/4). Then the other afternoon in stop and go traffic, I come to a stop maybe 5 minutes after the engine reached operating temp, and notice the dreaded idle vibration was back. The rest of the drive home revealed all symptoms were back identical as before.

Symptoms prior to, and 1 week after fuel filter change
  • Cold idle sounds fine for ~45 secs, then tinny and almost sputtery after rpms drop
  • Idle at operating temperature also sounds bad, with consistent vibration. The noise and vibration are much more prominenant after it has been at operating temperature for several minutes and had the engine worked
  • Engine RPM and noise never change when pressing gas at city or highway speeds. You have to keep pushing until the transmission is forced to downshift. The sputtery tinny noise does increase though. Maybe that's better called lugging the engine?
  • Gutless even after you force it to downshift if not rolling downhill
  • Cannot maintain even 55mph going up the mountains as other 3.4L armored Tacomas/4Runners blow by me
  • Transmission heats up ascending because it won't downshift on its own appropriately, and turning OD off basically means 'knock 20mph off current speed instantly and still have no power'
  • <13.5 mpg unloaded on a 100% highway tank at 65-70mph - no mountains

Immediate changes with new filter
  • Cold, warm, hot, and HOT idle sounds healthy and throaty, no sputtering or vibration
  • Every gear has something to give in the city or highway when pushing the gas to accelerate. Engine roars smoothly as engine rpm increases and I gain speed. No tinny sputtering noise, no sound of rocks in a can. Pedal feels perfectly responsive, transmission downshifts if it needs to without me pushing the pedal to force it
  • Can keep up with traffic even while towing
  • Everything ran cooler and smoother, even while towing, because it was able to shift seamlessly when it needed to, not when I forced it to
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Old 09-17-2016, 06:36 PM #2
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Where are you getting your gas??
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Old 09-17-2016, 06:55 PM #3
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Quote:
Originally Posted by frodiesel View Post
Where are you getting your gas??
Typically Shell, and seek out the non-run down gas stations. A habit that I first developed in my days of turbo car ownership. If I have sediment trapped in the tank I don't think I've contributed to it in the 3 years I've owned it by purchasing low quality gas, but that'd also mean that 3 years of quality gas hasn't flushed the tank of gunk. This of course assuming that the problem isn't due to a failing fuel pump..
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Old 09-17-2016, 07:56 PM #4
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If changing the fuel filter corrected your issues I would suspect that either you have a good amount of debris in the tank or your fuel pump is putting out minimal pressure . Drive it until you are low on gas, buy a new pump and drop the tank. If debris is obviously your problem you can return the pump. If debris is not the problem I would replace the pump just to be sure.
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Old 09-17-2016, 08:26 PM #5
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Any way you can check your fuel pressure?
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Old 09-17-2016, 10:22 PM #6
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Do you have a CEL? if so, get it checked (AutoZone/Advance Auto will do it for free) and report back the DTC(s).

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Old 09-17-2016, 11:06 PM #7
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Like @JBurt said, check your pressure. Also pull the vacuum line off the FPR to check for gas or at least the presence of it.

At least it isn't coolant mixing with the oil.
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Old 09-18-2016, 12:40 AM #8
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Did you cut open the old filter to see what's inside? I suspect weak fuel pump or mega crud in tank, if the filters are being clogged.
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Old 09-18-2016, 07:08 AM #9
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Checking the fuel pressure in the engine compartment will not tell if it is a bad fuel pump or debris/clog in the tank. Cutting open the recently put in filter and replacing as suggested will tell you if it is being clogged. I would still go through the effort of dropping the tank and making sure.
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Old 09-18-2016, 07:51 AM #10
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Thanks for input all. I forgot to include in my original post that the vehicle has never thrown a check engine light during any of this, not when sputtering up hills at 20mph tops nor when vibrating wildly at idle afterwards.

I didn't cut open the old fuel filter as I figured whatever approach I took short of a hack saw would have a high potential for sparks. Now that the old filter has sat for two weeks I might give it a whirl. I have a bunch of cheapo generic filters on the way from Rock Auto so I'll also cut open the new one when I replace it... pending that I can get a generic filter on without leaks.

JBurt, I can see if that info is available on my Torque app.. but I think if so, it'll be one of the many sensors in torque that's all over the place, as in no consistent reading. Will check out.

But yea St Runner, I think I'll go through the motions of fuel pump replacement and do some inspecting while I'm in there, and return the pump if need be.
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Old 09-18-2016, 09:26 AM #11
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A lot of times when a fuel pump is failing you can hit the tank and it will get that pump going. Old hammer trick. Works on stuck starters also.
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Old 09-18-2016, 11:29 AM #12
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Don't forget there is an in-tank filter before the pump. This puppy:



If there really is a pantload of gunk in the tank, that will be clogging up and starving your pump. For the record, I just changed mine (along with the pump) at 17+ years and 180k because I had the tank out, and it was pristine as was the tank (inside).
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Old 09-19-2016, 12:56 AM #13
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Quote:
Originally Posted by JayRolla View Post
A lot of times when a fuel pump is failing you can hit the tank and it will get that pump going. Old hammer trick. Works on stuck starters also.
Hah thanks, I'll remember that should it leave me stranded.

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Don't forget there is an in-tank filter before the pump. This puppy:



If there really is a pantload of gunk in the tank, that will be clogging up and starving your pump. For the record, I just changed mine (along with the pump) at 17+ years and 180k because I had the tank out, and it was pristine as was the tank (inside).
Yeah, I've read about those. Also not the only higher-mileage owner to say their tank was clean inside. Leaves me completely baffled, I know the fuel filter had an immediate and enormous benefit but I can't imagine changing something downstream of the fuel tank would have helped if the pump itself was starving over a clogged filter sock. And if the tank isn't starving for fuel and the original filter was clogged, how did it clog again so quickly?

I will say that I've probably run the tank low a lot.. I was under the assumption that inaccurate gas gauge and crappy tank venting caused me to fill up with a few gallons left in the tank after riding the gas light for a ways, always. Further reading just the other week suggested that the tank vent tube is too long and there's likely very little gas left when I'm filling ~14 gallons.

I've never taken my 4runner anywhere to be serviced, short of Discount Tire and Firestone for alignments, but I'd happily pay for a pro to get to the bottom of this. I had a brief taste of what a properly running 4runner feels like and it'd be so worth the bill to have that consistently, but I don't know what kind of troubleshooting a pro would do that I can't, just out of ideas.
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Old 09-19-2016, 01:29 AM #14
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That pre-filter only filters larger stuff. It's not likely to cause your pump to starve for fuel, but protects the pump from big pieces that could damage the pump's impellers. Pieces of smaller sizes, or microns are what clog filters and that sock doesn't catch those little pieces.

The answer lies in dropping the tank and physically inspecting it. All of the "what if's" in the world aren't going to change that.

The check engine light didn't come on because there weren't any symptoms that would throw the fuel and/or emissions systems out of whack. The sensors did their job as calibrated, despite the lack of fuel flow.

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Old 09-19-2016, 02:33 AM #15
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Maybe a small tubing cutter would be a fairly safe way to cut the filter apart. Use gloves and keep a fire extinguisher at hand.
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