moving2

My '94 LS400 w/ 113k has been gone through (hoses, plugs, wires, caps/rotors, fuel filter, pcv, timing belt/water pump, all fluids synth, etc.) No codes and using 91 octane here in LA, I'm still seeing only around 10MPG in city driving with the AC on all the time (recent heat wave for past few months). With 3/4 highway and 1/4 city and A/C on this rises to 16MPG. Is this normal? If not, any suggestions on what to check?

timmy0tool

iTrader: (7)

a very common culprit is the coolant temp sensor! very easy fix, just make sure you replace the right sensor.
https://www.clublexus.com/forums/ls-...read-this.html

DIY!
https://www.clublexus.com/forums/ls-...ange-pics.html

moving2

Forgot to mention I already did the coolant temp sensor (the right one) along with all the other work.

dicer

Both o2 sensors then.

moving2

So you would do an o2 sensor even if there are no codes?

dicer

Was there a code for the ECT?
Go ahead and just watch their voltages and response first then. When were they last replaced?
If they are 21 years old they are due to be replaced.
ECU caps ? Air filter? Cleaning throttle body that sort of stuff.

moving2

No codes, but you would replace them even if no codes? If out of spec, I would see a CEL, no? I have not had the ECU caps looked at, so that's a possibility. Air filter, throttle body cleaning, etc. all done.

dicer

Bad Caps = no codes

LsG86

Check your tire pressure. I just got 420 miles on about 20 gallons of gas, and this was on slightly deflated tires (26 psi) and mosly highway driving.

moving2

I'm going to followup on ECU and tire pressure. The fact I've blocked my EGR may be related, as well. In the meantime, would some of you mind posting your typical city (stop and go driving) fuel economy numbers with AC on full-time? I'm seeing around 10-12MPG under these conditions and wondering if this is normal. Please keep in mind AC is on all the time and I'm doing 100% city stop/go driving in LA.

RA40

iTrader: (6)

That's about right for the crawling LA traffic/parking lots. On my commutes it is 14-16 MPG though on downtown like areas it is 12-14. First gens get a bit less MPG.

dicer

A question how old are the o2 sensors?
No code doesn't mean the sensors are like new condition.

http://www.knowyourparts.com/technic...-replace-them/


No code ?

Another no code.

amason61

I just registered 17.9 mpg using 87 octane gas on my 1995 LS400. Mostly stop and go with about 200 miles of highway trips mixed in. A/C was on all the time as well.

timmy0tool

iTrader: (7)

when i frequent LA city driving my MPG drops to 16-18 instead of the usual 20mpg in the suburbs.

you mentioned a blocked EGR, in which i would say that's a contributing factor to poor fuel economy.

bdazzler

I usually get about 20 mpg but it's combined, maybe 50% highway and we don't have all the stop-start like in La La Land here in Tulsa. I don't put my foot into it much because I changed patterns when gas shot up to $3.50 per gallon. Anyway, inflate your tires to 40 lb (I think my max pressure is 50 on the current tires which are Falken). The LS400s have such a soft ride you're not going to feel it much w/ that much air like you would a Honda Accord.