tomtheslac

Hello all. First post, so nice to have a resource like this.

I recently got a hand-me-down 1991 LS 400 from my brother-in-law. 771K and still going (more or less...)

It had a leaking fuel line, so I replaced all 3 lines and the fuel filter. I also changed the air-filter, cleaned the TB, and changed the oil. I now have a rough running isse...

Car won't start on first attempt, but will always start on second try. It runs rough for a while after startup, but is still driveable. It will pull at WOT just fine, and it seems that all problems go away at 2500 rmp. It is as if it has a separate set of cams of something, because it will start to haul right away. It seems that at low rpm, and under heavier load like a hill, it will start to bog down and start to chug, but so long as I go to full throttle, it will overcome it.

I have cleaned the MAF, and checked the plugs (which were fine.)
The car has thrown no codes at all, so any suggestions would be appreciated.

Thanks in advance!

Boyscout

iTrader: (3)

same problem here

tomtheslac

I bypassed the fuel pump resistor and all problems went away. I replaced the resistor with another one out of a friends and the problems returned. Most likely a fuel pump issue. I recently replaced the fuel lines and filters. MY guess is that the fuel pump is on its way out or the sceen on it is plugged since I drained the tank. The resistor should slow the pump down when rpms are under 2500. The paperclip bypass may solve your issue, but may cook your fuel pump a little sooner...I just don't want to mess with it or it may give up....

hobojoe

I am in the process of fixing this right now have a new relay, risistor, and fuel pump coming in and once the risistor comes in tomo, im going to change them one by one till the problem is fixed. But I can tell you right now I already tried the relay and that wasn't it.

There have been a few others with this problem and after lots of looking I can say I is probably the risistor but wont know for sure till I try it.

RA40

iTrader: (6)

Fuel filter and check that the fuel pump screen is also clear of any sediment/debris. I can't speak for the 1 -LS, the fuel filter in the 2-LS is a 60K service interval.

Just curious, how is the tranny fluid and shifting?

tomtheslac

Shifting is good. It has 772K so it is well worn in... Fuel pump screen is what I am hoping is the issue. Otherwise my only problem is that it will not start on the first try when the engine is hot. Always fires up the second time still. Going to check the VSV, apparently that may cause the issue.

hobojoe

^^ Is that on the original Tranny???

python

iTrader: (4)

i say its ur coils

tomtheslac

Just wondering if you mean the hard start problem or the bypassing the resistor issue? Car runs fine otherwise, wet or dry.

SaintNexus

771k miles? 0.0 Props to Lexus for building reliable cars. A bmw wouldn't even come close to half of that, lol.

Boyscout

iTrader: (3)

- cleaned the air filter (K&N)
- replaced the fuel filter
- replaced the upper coil

...still having the hesitation/bogging under 2500 rpm. its like it gets no power (almost felt like it was going to stall last night) under 2500 and then almost as if a switch was turned on, the car gets power.

im going to be replacing the lower coil in the next couple days.

where is this fuel pump resistor located? is it in the fuse/relay box by the coolant container?

tomtheslac

scroll down for pic and description of location

https://www.clublexus.com/forums/ls4...problem-2.html

Boyscout

iTrader: (3)

thanks.

ive ordered a Walbro 255LPH fuel pump as well. maybe that will help

kuziwk

no i think he means KM, 1.6 miles to 1 km. 480 000 miles, wow though, wow...

Boyscout

iTrader: (3)

lol...he is from Ontario, so i would assume it's kilometers. i only have ~130,000 km on mine (~81,250 mi)