GenericUse

Been having issues with my '93 LS400 since I replaced the fuel pump around december. It's been killing fuel pumps every few months since then, and I'm at a complete loss as to what's causing it. I've replaced the pump three times since then, the pressure regulator, the EFI relay, the fuel filter, and I've checked the trunk wiring too because I was told the trunk hinge wiring could cause a short. It's a good thing autozone gives you free replacements for pumps under warranty or I'd be broke right now. Getting really tired of replacing the pump, I'd just like to be able to put the back seat in and leave it there for more than a few weeks at a time. If anyone has any idea what could be causing this, please let me know.

Moarpower

HOw is it running after the pump is replaced? Is everything normal? Any other info you can give us ?

VolumeToo

You don't say how the pump is failing. Is it electrically, or mechanically?

And what does the pickup filter look like?

GenericUse

It runs fine for a few days after the pump is replaced, then the car starts losing power over the course of a few weeks. It's run a little different each time when the pump is almost completely dead, but for this one the car knocks and pings occasionally when cold but idles fine otherwise, and generally the noises stop when it warms up. The pings kick it into high idle for a second or two. I have no idea how the pump is failing - it seems like it just slows down, although I haven't been doing fuel pressure tests when it's warm as I'd rather not light the engine on fire. I should probably do a test later today but I'm going to work in about three minutes so I'd have to wait a few hours after I get back for it to cool off. The pickup filters look only slightly darker than when I put them in, and there's no debris in the tank as far as I can see.

Moarpower

You really need to do a pressure test man.

oldskewel

iTrader: (1)

Very weird problem. One thing that may help you eventually find the solution is to get an OhmMeter (multimeter) and measure the resistance across the motor when brand new out of the box. And then again after it has "failed" and you take it out to get a warranty exchange.

It will be helpful if you can narrow down as much as possible what exactly fails. You seem to know that replacing the old pump with a new one fixes the problem, but more details beyond that may help figure out what is causing it to "fail." Is the motor spinning fine, but internal accelerated wear on the gears or impeller means it is not generating the pressure or flow required? Or is the motor just not spinning like it should?

Is the fuel filter pretty new?

Fuel pump resistor checked out OK?

RA40

iTrader: (6)

Some supplemental reading if you have not found this thread:
https://www.clublexus.com/forums/ls-...m-problem.html

My other suggestion is avoid those "lifetime warranty" rebuilds under the house brands. A Nippondenso or Aisan fuel pump as applicable. Every "lifetime warranty" rebuild I have put in any car has died within 2 years. I've paid double-triple labor to have that junk removed-reinstalled. After those lessons, no more of the rebuilt stuff from the auto parts stores.

oldskewel

iTrader: (1)

This post here, by me, also has that circuit diagram and some discussion of trouble shooting steps.
https://www.clublexus.com/forums/ls-...ml#post9777959
But if everything works when you first put the new pump in, I don't know how an issue with the rest of the circuit could be causing it to fail so soon. But I'm not saying such a thing does not exist.

Also on RA40's good comments on rebuilds ... there's no way this is a rebuilt fuel pump, right? I know when I bought mine, a Genuine Lexus/Toyota one would have cost $300, a China eBay nobrand would have been $30, and I went with the Amazon Denso made in Japan one for $100 and the win.

GenericUse

The first two pump kits were from Autozone, although I'm pretty sure they weren't rebuilds. The one that's currently in the car is a Denso I bought off of RockAuto. It's lasted longer than the first two but it's definitely getting weaker. One interesting thing that I forgot about; the first replacement pump was fine until a point, then one day the car just started pinging and knocking like crazy the second I turned the key. Found little bits of plastic in the fuel filter so I assumed something in the pump just exploded due to a defect or something. That's the most recent filter change I've done (2200 miles ago or so, and I never want to do it again because crush gaskets are the absolute worst).

Last time I checked the fuel pressure was right before I replaced the pressure regulator, and it was high so I assumed the regulator had failed. Will check it later today when the engine cools off.

dicer

So how do you know the fuel pump is kaapoot? When its gone out do you check for voltage at the pump? I think the 93 still uses a fuel pump resistor, so how does that check out? After the supposed crapped out pump is out and dry hook it up to a battery does it work? Running them dry is not good for them so don't do that with a good one.
With out knowing the voltage checked at the pump when its crapping out who knows what the problem is.

GenericUse

Where would the resistor be in the car? Like I said, I've changed the relay out but I hadn't heard anything about a resistor until this thread.

oldskewel

iTrader: (1)

Resistor, relay, etc. are on the right inside fender wall of the engine bay, near the air filter and MAF, igniters, etc.

The resistor is maybe 3x the size of the relay, made of cast Aluminum, with cooling fins.

1on1

Sounds like an electrical issue. Look into the ecu capacitor fix since you dont see issues with the wiring on the car. If your car is lowered, check the driver side fender well to see if you have any exposed wires.

dicer

If it is not where oldskewl says then it could be in the right side in the trunk, I think. You need someone with a manual to say for sure, I do think they moved it either in 93 or 94.

oldskewel

iTrader: (1)

The thing I said is true at least for my '91. And "right" side means starboard, passenger side. No guarantees about other model years.