Fuel/pump/tank question - RX300

Jaystar77 · March 26, 2022

Hi folks,

Been a wee while since I've hit any problems but here goes..

2002 RX300 (MCU15) with a reoccurring P0174 fault code (mixture lean) which I can't seem to nail down. Have worked through the list of stuff and fixed a few issues (iffy looking coils and some exhaust leaks) so it was time to remove and inspect the fuel pump in the tank this morning. Removed rear seat and both the main pump on the drivers side and the level sender on the passenger side.

Couldn't see anything visually wrong, fuels clean and I swapped in a fresh filter sock however I did notice the fuel level on one side of the tank was a lot lower than the other - the passenger side was practically empty. It's as if the pump is only lifting from that side and what I'm getting is actually fuel starvation. Does that sound plausible or does the pump only empty one side of the tank first?

I pumped fuel from the driverside across and roadtested to find it's behaving itself again but I just wanted to bounce it off someone with actual knowledge!

Planning to order a pump anyway as it'll do no harm on a 20 year old machine.

Thank you for any light that can be shed!

Spock66 · March 26, 2022

Is there a fuel filter, could that be blocked? or maybe your injectors are partially blocked?

ColinBarber · March 26, 2022

If the fault was related to the fuel pump/tank then I would expect you to also get lean errors for the other bank of the engine (P0171) as well. If it was fuel starvation you would normally feel the issue with the vehicle stuttering on acceleration around corners.

I would expect your issue to be due to a fuel injector or O2 sensor on bank 2 of the engine.

Jaystar77 · March 27, 2022

Yes I'm getting a stuttering/hesitation that reminds me of fuel starvation so the theory sort of fits. I follow your thinking with the fault codes, strange that it's only getting a P0174 (before I fixed the exhaust leaks I was seeing a P0171 as well).

Just trying to get the fuel pump operation straight in my head as what I found seemed really odd - should the pump lift from both 'sides' of the tank equally or does it drain the drivers side first then lift from the passenger side?

Jaystar77 · March 27, 2022

Oh and all injectors are ticking away nicely, doesn't seem like any are misbehaving. Appreciate the assistance!

Spock66 · March 27, 2022

15 minutes ago, Jaystar77 said:

Oh and all injectors are ticking away nicely, doesn't seem like any are misbehaving. Appreciate the assistance!

That means they are working ok electrically, but they can get clogged just like your shower head.

Another thought is that your fuel pressure is too low, electronic fuel injection works on the principle of constant fuel pressure and the ECU works out how long the injectors should be open to control the amount of fuel, so if fuel pressure is low the mixture will be lean.

Jaystar77 · March 27, 2022

I understand but my main query is should the pump lift fuel from both sides of the fuel tank equally?

If so then I might have found my issue.

Jaystar77 · May 15, 2022

Just following up on this. Seems I've been tackling a few multiple issues all in the one go..

Symptoms: Poor performance, starting issues, engine warning lamps, starting issues

Checked the plugs first to find signs of over fueling and noticed there were cracks on the sides of the ignition coils so they got replaced. Performance improved but EML back on.

OBD2 reader gave me a P0171 code. On visual inspection a lot of the exhaust was rotten. Every time I patched one hole another appeared. Finally got most of them patched but this LED to a P0174 code which signals a lean condition. Figured I'd order fuel pump and filter whilst it was away for the exhaust work. Custom stainless system sorted the exhaust leaks, fitted a new universal post cat sensor whilst we were there. On return I replaced the fuel filter and pump because I was overthinking things (see initial post).

Pretty sure it was just the exhaust but everything else was done because I was in the area and wanted to leave it 100% Theory is that the post cat sensor was seeing misleading readings because of the exhaust leaks and the ECU was throwing too much fuel in. An oil and filter change seemed to support this as there were signs of oil dilution in the old oil.

Left me with the starting issue though. And no fault codes. Figured it was the coolant temp sensor as I've seen them go before in the past. Seems that hunch was correct. These going faulty also can cause overfueling so I was happy to swap it out for a new one.

Have playtested it for a week and besides a little modification of the new exhaust all seems sweet again.

Yesterday I noticed that the fuel filler neck (which I'd taken care to check for leaks about a month ago) had decided to start leaking. Honestly don't think it featured in the whole kerfuffle as I had kept inspecting the lines and fuel tank the whole way through thinking they looked a bit suspect.

Sorry for the saga but thought it worth sharing.

Rust is definitely catching up with the old wagon 😣