I've got an 06 tacoma, 4.0L. For years I've been trying to figure out this issue.

I'm not sure if I'm posting this in the right place.

- The events are sporatic - could be months or even a year in between events, but I never know when its going to leave me stranded.
- Twice it was diagnosed as a faulty fuel pump (I"m pretty sure incorrectly diagnosed) , and the fuel pump was replaced ($$$$) - 6 months apart. (2nd time I replaced it with Toyota pump, first time mechanic insisted on auto zone part based on his experience...) So when it does this glitch, the auto shops do whatever test they do to diagnose faulty fuel pump, and it indicates faulty fuel pump. But I'm pretty sure that's not it. The 2 fuel pump replacement events were early in the game - not long after I acquired the truck, so it may have been doing it with previous owner and he dumped his problem on me. The first fuel pump replacement may have even involved running out of gas - I was running low and was looking for an exit to get gas, but my trip meter suggested I had a few miles left. The gas gauge was inaccurate at the time (it has been repaired now), so I used the trip meter to monitor fuel, and maybe at 90-100 on the highway I was using more fuel than usual.
- I've replaced the evap canister, which for a while seemed like maybe the issue went away after that, but it resurfaced again, so that was not it. (is there any sort of a filter associated with the evap canister?)
- Sometimes when I'm driving down the highway (70-80MPH) the engine just cuts out. I've not clearly identified the conditions yet, but it seems like some sort of extra load happens - like going up a significant hill - asking for more fuel. Last time I noticed I was on cruise control, but don't remember if I've been on cruise for previous events. Sometimes its just a hesitation (enough to make me panic) - a hitch and starts running again. Sometimes I have to take my foot off the accelerator and put it back on and that gets it going again. Once that didn't work and I swerved left, right, left, right... and it started going again. 2 times it didn't start running again and got towed in - fuel pumps. Maybe for those fuel pump replacement episodes, I could have gotten it going again by playing with the accelerator pedal or swerving? The first time may have even involved running out of gas - I was looking for an exit to get gas. When they replaced the fuel pump, the fuel take was clean.
- Twice I drove the truck home - everything working normal, parked and went inside for the night. The next morning it would not start. One of those times I had it towed to mechanic a day or so later and it started when it got there (we assumed something got giggled on the tow truck ride). I think I remember that for that episode, I had just filled up at the gas station before coming home and parking. (That led to the suspicion that it could have been evap canister related from topping off the gas past the first click off at the pump.)
- Two days ago on Saturday morning it did this next day no start (no fuel). I tried again later in day and nothing. On Sunday afternoon I was getting things moved around to get ready for a tow on Monday and tried it again and it started. Nothing got giggled, just 1 1/2 days time and it went away.
- The mechanic can't diagnose it if its not doing it... I'm pretty sure its fuel related.
- I've wondered about a connection issue at the fuel pump (why did previous mechanics diagnose fuel pump - they banged on the fuel pump and it started working again?) I don't think me moving stuff around in the truck would be enough to giggle that connection and have it restart 1 1/2 days later.
- I've wondered about a wiring short, but that would not make sense with it starting itself 1 1/2 days later? (This truck has had the frame replaced, and apparently the centers that do that are doing it really fast and other things get crimped and broken...)
- I've wondered about some sort of a vapor lock, but don't know what to look for if it is. Its one of the few things that make sense - if it goes away on its own with time.
- I've wondered about some sort of particle in the fuel system, and once pressure dissipates, the particle shifts and falls away from whatever orifice its blocking? (is there some way to do a fuel system flush?)
- Fuel filter?

 

Do you know if the entire fuel pump/float assembly was replaced or just the pump itself?
Does the check engine light ever come on? Even if it is not on, scanning for codes could help if there is a pending code in the computer.

If possible, find out how the mechanics diagnosed the fuel pump. If they tested fuel pressure and nothing else, that could be anything in the fuel pump electrical circuit or a clog somewhere. If they tested the electrical resistance of the pump and it failed, that could also be the circuitry in the assembly and not necessarily the pump. If they just guessed then find another mechanic.

Something floating around in the fuel tank is something to consider, but I would think the strainer would be noticeably clogged when they removed the pump. I doubt a fuel filter would cause problems so intermittently, but it could be possible. Wouldn't hurt to replace it anyway especially if it is original.

Intermittent problems are always a pain to diagnose. Installing a fuel pressure gauge in the cab of the truck so you can see what it does when the problem happens might be a good next step. If it has full pressure, then it is not the pump. If pressure is lost then you know for sure it is in the fuel system.

Since you said the frame was replaced, follow all the fuel lines to make sure none are bent, look for loose or smashed wires, or any loose or corroded grounds. Also check for the same thing in the engine compartment.

 

Supernerd:

- The entire fuel pump assembly was replaced 2x - entire assembly is apparently the only way it can be purchased.
- Check engine light never comes on. I've checked for codes and there are none.
- I'm not sure how mechanic number one diagnosed. It was my brother's mechanic in Florida, and the mechanic and I are on bad terms now - charged me $1200+ for a repair that didn't need to be done. He may have actually tested fuel pressure, but I have no idea.
- Mechanic number 2's diagnosis was to bang on the pump and it came back on again.
- I'm on mechanic number 3 now. The truck has never been in his hands and not working, so he can't diagnose anything.
- The lines and wires have been traced by mechanic #3 and no apparent damage found.
- Nobody has ever tested anything electrically. The pump assembly has been replaced 2x, so doubtful its any circuitry in the pump itself. If it is electrical issue, its outside the pump assembly. I have always wondered if it could be electrical interruption to the pump, but that doesn't make sense for the truck running fine when I parked it on Friday night, and then not working on Saturday morning, and then working again on Sunday evening.
- This is what make me ask about vapor lock. I don't know if that is a thing these days. When I was a kid, my father had an auto parts store and a mechanic shop next to it, and I remember them talking about vapor lock. Maybe that was a carburetor thing?
- This last time after it quit working,my body was in and out of the driver's seat a few times, and I was in and out of the bed a few times for tools - including shutting the tailgate and topper door, but I can't picture any of those jostling the truck enough to shake a wiring connection loose (or shift debris in the fuel system). I do live on a gravel road, but no bumps caused it to shut down while driving - it ran fine when I backed it into its parking spot and shut it off. The other time it did this no start after parking and running fine, it got towed to mechanic #3 and it worked when it got there - so we hypothesized that the ride on the flatbed shook something up. Now it appears its just about time (pressure relief). I've thought about trying to open up the fuel line to relieve pressure if it happens again, to see if the relief in pressure shifts something and makes it work again - bypass the 1 1/2 day wait when it shuts down, and not be stranded.
- Mechanic #1 had the tank off and it was clean, and the strainer was not blocked at all. (Supposedly swished it around and dumped it into a jar, and no debris. It was reported that it had very little fuel in it - which makes me wonder if it was just out of gas, but he didn't go there. He said he diagnosed the pump to be the problem.) The problem has happened before the first pump replacement, between pump 1 and pump 2, and after pump 2 - so seriously doubtful any debris in tank is the issue. Pump replacement 1 and pump replacement 2 were 6 months apart.
- This truck apparently does not have a fuel filter. I think Toyota is calling the screen on the pump inside the tank the filter. Hardly replaceable. Other models have an inline canister on the frame rail under the driver's door. This truck does not have it. (There is a heatshield and an exhaust converter nearby, so maybe a bad place for a fuel canister? I can't see any in-line filters in the lines under the hood (loose sight of the lines when the climb the firewall and head toward the intake). When the parts store looks up fuel filter, it only refers to the dealer for the screen on the pump. So I wonder if there is somewhere that a loose particle could clog the whole fuel system pre injectors? If it was an injector, it would only clog one injector at a time and it would run rough, not cut out entirely. Highly unlikely all injectors would clog at once and unclog at once. However, a loose particle that clogs the system and then when pressure dissipates (assumption) 1 1/2 days later is the only logic that makes sense to me at the moment.
- Installing a fuel pressure gauge is an interesting idea. I wonder if I would have time to notice the blip when I'm driving down the highway and it cuts out at 80 mph. This is usually a fast turn around and I'm in traffic, so I don't know if I'll look at the gauge at the right moment.

 

I would also agree that it is probably not the fuel pump assembly. The first mechanic may have put a low quality fuel pump in, or did not install it right, which is why the 2nd mechanic got it working by kicking the tank. Basically the 1st mechanic created a new problem along with the existing problem.

Vapor lock happens the fuel gets hot enough to start boiling in the line causing vapor which cannot be pumped. Typically this would happen with carbureted vehicles with external fuel pumps. Internal fuel pumps mostly solved that problem. It is still possible if the fuel gets hot enough in the fuel line to vaporize, but the fact that your truck would not start after sitting overnight a few times basically rules that out.

I did not realize that 2nd gen Tacomas do not have external fuel filters. I looked it up and you are correct. I also agree that it would be unlikely for all the injectors to clog/unclog at once. If the fuel pressure regulator is fully clogged, then the line pressure would be as high as the pump could handle and I would think the truck would still run, possibly rich, but it could make the system more susceptible to a vapor lock problem and would be very hard on the pump.

A diagnostic pressure test might give some clues, but installing a permanent or semi-permanent fuel pressure gauge on the dash would diagnose all these possible fuel system problems or rule out the fuel system as a cause. Autozone (and probably other parts stores) will loan you diagnostic fuel pressure gauge for a quick test, but I would consider getting a cheap electrical gauge off Amazon and mount it in the cab. If it will not be permanent, zip tie it somewhere on the dash easy to see, wire it to a 12volt plug to use the cigarette lighter for power and run the signal wire anywhere that is easy, possibly through the window. I did this years ago with an air fuel ratio gauge to diagnose a carburetor problem in my truck and it worked well. Most of my experience is in the older trucks, but I believe your truck will have quick disconnect fuel lines and will need an adapter to attach into the fuel line to attach either of the gauges.

If you have another time where the truck will not start at all, spray some carb cleaner/brake cleaner/starting fluid or pour some gas into the throttle body and see if it starts briefly. That will also be a good sign it is definitely fuel related.

Another thing you can check is for anything loose near the fuel pump relay, and the relay itself. It also appears that these trucks have a 2 speed fuel pump system with a second relay and a resistor. Checking all of those for loose or corroded connections is a good idea.

 

Thanks supernerd.

I'll start working on getting a fuel pressure gauge.

And I'll look into locating the relays and resistor.

The mechanic showed me how to disconnect the fuel quick connect and turn the motor over to see if its pumping gas (for when there is a no start situation.) Seems like the pressure gauge would do the same thing.

It may be months before it does something again, but the hitch when I'm going 80 on the hwy seems to happen a little more often.