zukikat

Totally "stock" (unmodified) 1994 LS400 base model with sunroof option.

Timing belt, caps/rotors, plugs, etc, etc have maybe 10k miles on 'em so that's not the problem. Coils came with the car, no idea if they've ever been replaced but when it does start it idles fine and runs smooth in town and on the freeway. Alternator was replaced last month but it did this a few times before that too...

So I think my fuel pump is unhappy but Sewell Lexus' parts site shows 2 different pumps for the car, Aisan and Denso, with 2 different part numbers and 2 slightly different prices, both well over $300. and I don't know which one my car has because I haven't taken it out yet, assuming it's never been replaced with some cheap ghetto aftermarket part... I called their parts department, gave 'em my VIN, and they still can't tell me which one my car originally came with...
Also, Napa has 2 different Bosch pumps depending on which factory pump my car got and one costs about 1/2 of what the other does which seems suspicious to me...

Then there's the cheaper aftermarket auto parts stores that only list those usual bargain brands at about 1/2 the price of what the Lexus ones cost...

So are there any to avoid and any that seem to work well besides the >$300. factory Denso and Aisan ones?

I can't find any flow specs on the factory ones or those other replacement ones so I don't know if I can just buy a nice $99 Walboro and retro-fit it into my LS or if I should go with something else.

I'm not 100% certain that it's the problem but the car spun over normally and failed to start on the first try randomly for several days then spun over normal but wouldn't start at all no matter how many times I tried.
There were no diagnostic codes being reported so I tried the fuel pump diagnostic jumper and moments later the pump kicked in and ran briefly until I removed the jumper, thinking it was a spark problem based on that...
Then I turned the key just to test it again and the car fired right up and went to idle speed for a few seconds as usual but then it suddenly started slowly losing rpm's, then surged back to idle for a few moments, then started to lose rpm's again, then jumped back to idle and stayed there.
I opened the trunk and played with the "Fuel Pump Computer" connector (all but unplugged it) and wiggled the wires with the car idling and nothing changed at all. So then I shook and banged on that computer with the car still idling and still nothing changed.
I got in the car and pressed the gas pedal and it seemed to respond normally so I turned the key off, waited about a minute, then tried again and it fired right up again and I'm sure I can drive it the 50 miles to work if I wanted but I haven't tried yet...

The fact that it took moments after inserting the Fuel Pump diagnostic jumper and seeing the little spark from my jumper wire before the fuel pump finally kicked in makes me believe the pump is failing but isn't quite dead yet and at this point I suspect that its' funeral is rapidly approaching...
The odometer on the car is approaching 200,000 miles and I have no idea about the car's maintenance history before I bought it so it wouldn't suprise me if the pump is just tired and wanting to retire asap...

I didn't get to pull a spark plug boot off to check for spark before the car decided to start again but seems odd that there'd be no spark on any cylinder unless the crankshaft position sensor was having problems and I'd expect the main computer to realize a sensor issue like that and report a code if it was unplugged or a wire was broken or the sensor went bad?

Has anyone tried the Denso pump that can be ordered from Advance Auto Parts and is it a close match to the original pump at all?

Thanks in advance for any assistance that's offered!

zukikat

Well friday I got an emergency call from the office and gave the LS a try and it fired right up so my 50 mile trek to work began in the LS. About 1/2 way there it went from cruisin' fine (cruise set at 70mph) to acting like I'd turned the key off for about 2-3 seconds (engine bay got quiet), then it jumped back to life and went back to cruisin' again for the rest of the trip like everything was fine.
Many hours later when I was ready to leave I turned the key and it cranked fine but didn't even hint at actually wanting to fire up, leaving me tired, hungry, and stranded at the office.
I tried the fuel pump diagnostic jumper again but this time heard nothing, and no matter what I tried it wouldn't start so I was stuck at work 50 miles from home.
A few hours later a buddy who lives near my office lent me his (used to be my) IS300 for the night to get home and get some sleep and today I headed back to the office where we tried starting my LS again and still had no success and still got no fuel sound with the Fp jumper inserted...

None of the dealers had a pump in stock and the only pump we could get from any of the auto parts stores was an Airtek brand which did NOT include the screen/sock/filter thing on the bottom of the pump and of course that piece was $20 extra and was "required for the warranty"...
When we finally got the back seat unbolted to access the pump cover plate with the few tools I had in the car, just to test things I turned the key on and inserted the Fp diag jumper one more time and he could faintly hear the pump running really softly but no fuel was making it to the engine bay which made us wonder about the filter too.

So I made the decision to swap out the pump anyway because I didn't have the tools with me to deal with a fuel filter, then with the cheap auto parts store pump installed I turned the key on and inserted the Fp diag jumper and we almost instantly had the engine bay fuel flowing sound again, yay.

At that point I handed him the IS key back and my LS made the trip home with no complaints and we'll see how it behaves in the near future.

Since the old pump was actually running really quietly I do have to wonder if the pump was just dying and/or if the filter might be the real culpret so I'll probably also replace the filter in the near future anyway with almost 200k miles on the car at this point but for now I'm just going to drive it and see how things go...

I wish I could've gotten a Denso pump instead of an Airtek but at least the car started.

zukikat

Side note... Looks like my LS had the factory Aisan pump based on the Toyota EPC diagram on the Sewell website.

During the first couple of road trips to and from work the car made me nervous several times while running along at a steady 70mph pace as it seemed to fall on its' face like it was going to stall and then it'd recover moments later and cruise fine for a long while again for no apparent reason but since I replaced the fuel pump it fires right up every time I turn the key now and after 3 trips to work and 2 trips to a friend's place 35 miles from my house those symptoms seem to have vanished, the throttle response has greatly improved and the car is a little stronger and a LOT more consistent when I get agressive on the gas pedal, and my LS seems to have pretty much settled back down to how it behaving was before the "cranks normal but won't start" problem appeared last month and my car anxiety is pretty much gone.
A 96 Camry I had 2 cars ago that had almost identical symptoms did the exact same thing after I replaced its' pump and I sold the car thinking there was something else wrong that the fuel filter and pump didn't fix but that Camry's been running fine for 40k more miles over the past 2 years so I guess the cheap "auto parts store special" electric fuel pumps need a little break-in run time or something like that...

I still haven't changed the LS' fuel filter yet but it's on the to-do list when I find the time...

There's still something else not quite right and I have no idea what it is but for now my LS is back to how it was behaving since I bought it and replaced the main ECU 6 months and 10k miles ago so when I find some time I'll try swapping out the "fuel pump computer" and coils and igniters with spares I got from the local junkyard last weekend and see if anything changes or not.

I wouldn't really say I'd recommend the Airtek pump, as I'd much prefer the Denso that noone stocks, but so far it's doing what I need it to...