Intermittent Fuel Pump Failure

I have a customer with a gen 2 with 214k miles. He was having an issue with poor ICE performance, and the car would stall when driving on the highway with no warning. Had codes P0A0F, P3190, P3191 and C0205. From the information I can gather, it seems this problem usually happens when the car is low on fuel. I don't think it ran out of fuel, I think the fuel pump is intermittently failing.

I hooked up a fuel pressure gauge with a T fitting so I could monitor it while driving the vehicle. When I first connected the gauge, I commanded the fuel pump on with TS (key on ready off) it only read 34psi, but I have an inline filter that I put after the gauge so no gunk gets into the fuel rail, and it was not completely full of fuel yet, it was still half full with air, so I was thinking the reading could be off. Once I started driving the car and the filter was full of fuel I was routinely seeing 44psi, which is in spec (44-50psi) there was a few times it looked like it dropped to 42psi but I also had to be looking at TS to see if the pump was on or off. I have not been able to reproduce this problem, I tried running it as hard as I could to get it to fail but it wont fail when im driving it. The last time I tested it it had one bar of fuel so I put in a few gallons, but now that im thinking about it I need to test it when its low to see if that will make it fail, I will also record how many gallons it takes to fill up the tank, if its taking more than 10 gallons (11.9gal is total capacity i think) then perhaps the guess gauge is off and the car is running out of gas, if it takes 8 gallons or so (my prius takes 8 gallons when I fill it right after the low fuel warning comes on) then the gauge is probably right.

If the gauge is correct than heres what I think is happening: driving on the freeway, fuel pump is under heavy load for extended periods of time, fuel level starts getting low, pump overheats and shuts down, the engine starts loosing power and throws P3190 (poor engine power), and then it stalls and throws P0A0F (engine fails to start), it tries cranking more and it still won't start so it throws P3191 (engine does not start). At this point the customer is trying to pull over off the freeway but is still moving so the HV battery gets drained down pretty quick, red triangle and warning lights are on. Once the car sits for about 30 min it will finally start back up and drive, and thats the part that really makes me think it did not simply run out of fuel or it wouldn't be able to restart until gas was added.

I guess this post is turning into a novel so heres some more information. I'm the 3rd mechanic to try to fix this problem, the last guy put it a MAF sensor, he forgot to put in one of the screws which could allow air to go around the sensor, although theres an o-ring that makes the seal so even if one screw was missing it still shouldn't leak, but i put in a screw of course. The plugs were also recently changed, I pulled one and it didn't look real bad. I put in a new air filter, and did a complete fuel and intake system cleaning with a pressurized cleaning machine I use, here's a video I made

, also cleaned the maf with maf cleaner. I went through all the common stuff, 12v, intake/exhaust leaks, oil level, can't find anything wrong with those. The car drives fine mileage is around 42 mpg and seems to have good power.

This reminds me of an 1988 BMW 325i that I had, it was given to me by a family friend because nobody could figure out what was wrong with it. It would start up and run great for a few minutes and then die, cool down for a few minutes, then it would start back up. Long story short there was a corroded connection on the connector to the fuel pump, high resistance in the connection would cause it to heat up, the hotter it got the more resistance, until it would fail, then once it cooled down it was good again. This Prius runs and drives fine and the fuel pressure is within spec (but on the low side), until it has this problem, I need to get it to fail with the pressure gauge attached that would be the ultimate truth. Tomorrow i'm going to test the resistance on the pump motor, I have to dig up the specs, that could also tell me. I'll share what I find. With this high of mileage its definitely possible the pump is going bad. It's also worth noting a failing fuel pump will cause poor performance (duh i know), poor mpg, surging and even overheating (lean burning?)

 

I will do that tomorrow and share what I find. Yes I explained to customer about not letting it get so low but at this point, with me being the 3rd mechanic trying to fix this issue, he doesn't want any doubt with the car. He got pretty upset that all 3 of us missed the problem but i explained these intermittent problems can be tricky to nail down and I was following the flow charts and what we know on here to be the most common issues; but the car is over 200k I think its unreasonable to get mad at Toyota, but there should be more info in their service information (i have an Identifix subscription which supposedly has all of the OEM service info) there's practically nothing besides to check the fuel pressure which in this case doesn't prove anything. There's a short video of a woman who pulls out that relay "cassette" as she calls it and u can backprobe on the bottom of it to look at voltage signals.

 

Just wanted to give an update, it was able to devise a test to prove if the fuel level sending unit was not calibrated (and the car is just running out of gas) or if the pump is failing due to overheating from a low fuel level. With this test I proved it was the fuel pump. Here's a video I made: