Mastana

Hey guys, i got a problem with my sc400. I have a 1998 Sc400 114k on the dash , it is giving me some issues. I'm getting 16 mpg and that's me driving calmly. I have a couple friends who are getting 18 mpg same year without an issue and they beat on their cars more than i do. I brought my car to 10 different mechanics and none of them had the answer to the problem. I change my battery, alternator, air filter , fuel filter , spark plugs, and used techron this was all done about 5,000 miles ago. I do my oil changes every 3k miles Mobil 1 fully synthetic 5w-30 and i fill up my car with BP, Exxon, Hess and Sunoco gas super all the time. Its weird i cant get to the bottom of this and find out why. Any comments, ideas , or help would be greatly appreciated .
Thanks for reading

Dougspeed

iTrader: (2)

The only two other things I can suggest is check your brake caliper pins to make sure they're not frozen and check the wheel alignment. But to be honest, 16-18mpg in the city is pretty normal. I'd only worry about it if you were getting this kinda mpg with a lot of freeway driving.

durps

iTrader: (8)

^This. Also buy new o2 sensors. I bought both my OEM densos on ebay for 85$ shipped. Try a new pcv valve, new gas cap seal, check tire psi, etc.

t2d2

iTrader: (8)

What would frozen brake caliper pins have to do with bad gas mileage? Wouldn't dragging brake pads be extremely obvious? I feel like I'm missing something here.

grumpi300

iTrader: (1)

i'm just throwing an opinion out there, not a fact, but couldn't leaky capacitors potentially cause the same problem too?

Dougspeed

iTrader: (2)

Nope, unless both the upper and lower pins are frozen, it won't be "extremely" obvious with just one of the pins being stuck. Brakes might heat up a bit more than usual, but won't be burning hot since the brakes always have a small amount of drag by design, even when the pins are greased up and working properly. I had a frozen pin on one side and didn't notice till it came time to change my pads out.

t2d2

iTrader: (8)

Okay, now I need to go check my caliper pins...

1997Soarer

iTrader: (1)

^ This.

PCV valve, and raise your tires to 32 psi.
If that doesn't change anything, then replace the O2s (only the 2 primary's). They're due to be replaced anyway because of the age, but because they can be a real nightmare to change, I always tell people to replace them last

Also, inspect all your factory ground wires. Follow the - wire from the battery to the chassis and the engine and see its condition.

NYKnick101

If your using a MPG dash counter, Reset it and start over. It could be just an estimated average of you and a bunch of other factors. ALSO switch up gas stations and run with one specific brand of fuel. I used to get from a local Citgo and half tank 93 premium driving around town would last 2 days (no more than 40 miles) but I switched up to Shell and I drove to CT 60 miles each way (120 total) and still have a quarter tank from a half

Maserati

iTrader: (1)

I had a caliper drag it sucks, Jack car up ,and spin the wheel for resistance. I was in the process of doing O2 sensors do i have to do all 4? or just the front?

csalazar87

I had this same exact issue...I was getting 10-12 MPG on my SC400 1992.

I bought it @ 111k and it was super clean but it had terrible gas mileage so I started searching CL.

Here's what I found:

https://www.clublexus.com/forums/ls4...capacitor.html

If you haven't already, change out the caps since they probably need to be replaced.

Good Luck!

p.s. I saw that you're in NJ...if you send me the ECU I can help you with this.

Mastana

Thanks I actually just dropped my car off at my mechanic yesterday and im replacing two o2 sensors, pcv valve, and a coolant temp sensor. If it doesn't do good after that then ill look into this. Also what county are you located in?

csalazar87

I live in bergen county but my buddy has his equipment in Carteret right off the turnpike. So if it doesn't work just shoot me a message.

We were able to replace everything in about 2 hours.

good luck!

csalazar87

Hey just an update...

I did a full tank test and I went up from around 225 miles per tank to around 378 or about 19MPG

WOOT WOOT!

Mastana

NICE! I wish that was me lol But are you going to the meet april 12 in jersey city at liberty state park?