Possible fuel pump issue
 

Hey guys, having kind of a unique issue and thought I'd try here to see if anyone else has had a similar one. I have a 2011 LE. 120,000 miles, bone stock aside from a 2" lift and some wheels/tires. I've owned this truck for about 8 months now, and have never had an issue. Recently, I was pulling into the local pew-pew range, which has a steep decline leaving the highway into the parking lot. Another car was coming out, so I stopped and pulled to the side so he could pass. Once back on level ground, I noticed an odd stumble/hesitation. On the way home, it turned into a full blown misfire, and got a CEL with multiple misfire codes. I checked all the plugs and coils, which seemed to be fine, but I replaced them anyways (Denso coils and plugs) as at this mileage they were unknown age.

Fast forward a few days, and I pulled off the side of the road for an ambulance. Was off camber for a few seconds, but when I pulled back on the road, another stumble and hesitation. Filled with fuel later that day, and didn't have another issue for about a week. Leaving another store up a somewhat steep incline, it stumbles and hesitates again. The stumbles and hesitations only show up when the tank is under about 5/8 full. I put a clear piece of hose on the hard fuel line in the engine bay, and when running just the fuel pump off 12V it looks good until pumping the fuel down a bit. As the tank gets lower, I see more air bubbles in the fuel line coming from the pump.

My question is, has anyone seen this kind of issue before? I searched and found nothing on all of Google describing a similar problem aside from a single thread on a Tacoma site describing air bubbles in the fuel line. It almost has to be something in the pump/suction assembly, so I've ordered a new Toyota unit. I'll update more once I get the part replaced, but figured I would check and see if anyone else has seen this happen before. I did pull the tank already, and pulled out the pump. I ran the pump out of the tank in a bucket of gas, and saw no leaks in the lines. Obviously I can not replicate the conditions in the tank exactly, but my only theory is that when the tank level drops low enough, either the "fuel bowl" that the pump sits in goes partially dry or a very small hole in one of the hoses causes a venturi and sucks air in (this makes no sense to me, as a pressurized line should leak outward not suck air in but it is possible). The fuel return line dumps into the bowl, so not sure how it would go dry. Maybe the return has a hole and brings air to the bowl, then gets sucked up in the pump? Idk guys, I'm open to any theory y'all can muster.

If I forgot, thanks in advance.

There was a fuel pump recall, but a quick look shows it to be for newer 4Runners like 2014 and on. But it does sound like the pump has problems when the fuel in the tank gets below a certain point. I guess you could prove this by keeping the tank close to full and see if you ever see the problem.

Recall was 14-15 only what I could see. The fuel pump/hat assembly has a new part # so they probably only sell the new version. Such an odd problem, if I hadn't dropped the tank already I'd keep it full to see if that's really the difference but I'm not pulling this tank again, so it's not going back together until the new pump is installed. Looks like the part won't be in until tomorrow at the earliest, so guess we will see.

I do know I have read a few 2010, 2011 years had sending units that would go bad and causing stalling with 1/4-1/2 tank showing. I had this happen, engine would die at 1/4 tank. New OEM pump assembly fixed this. Not completely related but thought I would mention it.

This seems right in line with what I was seeing due to air being introduced in the fuel line. Once Toyota gets the part in stock I'll have a solid yes/no if this fixes it. Mostly I just wanted to document this in case anyone runs into it in the future.

Unlikely, but could the fuel gauge be faulty, showing 1/2 tank when actually near empty?

Unfortunately I'm not that lucky, mileage said it was roughly 1/2 tank. I also was able to pump out about 9 gallons of fuel (1 still in the tank) when I dropped it yesterday so it seems the gauge is accurate. It read between 3/8 and 1/2 on the needle.

Does sound weird, a fully submerged pump pulling air.

Have someone check your fuel line pressure. It's not as simple as some cars with a schrader valve on the fuel rail, you need the special fittings to check it.

I did the fuel pump recall and my replacement pump went out in less than a year. Was a Toyota (allegedly) part. Put a new pump and everything was good again. I did eventually throw some misfire codes.

Well boys, new fuel pump came in finally. Tis seems to have solved the issue for now. I can't find anything visually wrong with the old unit, but I kept it for autopsy. Ill report back if I find anything there, bugs the crap outta me to not know exactly how it failed but knock on wood, problem seems fixed.

The only other thing I can think of - is the vent line. If clogged or pinched, could cause issues - but it would probably be all the time though. My old 2000 Tundra fuel gauge reads wrong when it gets cold. Above freezing it works fine; but below it reads way off. So, I just go by mileage now!

I have seen near imperceptible hairline cracks on the top of the fuel pump that will allow air in the system. Just plastic aging.