topgun129

Hello All,

I got a 93 LS400 with about 142000 miles on it. I did a tune up probably 15-20K miles ago, but recently I've been noticing the car is burning gas a lot faster than usual.

My MPG is around the low teens! I did change the fuel filter about 20K ago and 8-10K miles ago I put a fuel injector cleaner bottle in with a gas fill up. One idea that is coming to mind is that maybe the fuel injector cleaner left behind some small debris that it cleaned and that might be blocking some injectors.

One thing I've noticed with the car is that the RPM once in a while fluctuates downward at idle which causes the car to vibrate and shake for a few moments. Also when driving I notice some subtle hesitation (it feels like something is holding the car back) when accelerating.

Thanks!

97CE LS400

did u change the wires , caps & rotors during your tune up??
Other than that make sure ur air cleaner is good as well as the tire pressure correct.

topgun129

Hi,

During the tuneup I did the wires(NGK), spark plugs (NGK), rotors , caps, PCV valve, and cleaned out the throttle body. The air filter is clean and the tire pressure is good.

avalon42

iTrader: (1)

One of your ignition coil packs is dead or not putting out enough voltage. Use the resistance test on both coils and you'll find the culprit. My money's on the drivers side coil.

Just wanted to add to check the resistance on your new wires as well. Maybe something happened when they were made. It happened to my friend's MBZ and he couldn't believe new wires did that.

topgun129

Hi,

Somebody also told me the ignition coils could be the culprit.

I was also recommended that the cats and 02 sensors might be failing. I currently don't have any check engine lights on, but is there any way to check if these are the culprits?

Thanks!

avalon42

iTrader: (1)

Resistance test the coils and the wires, you can also resistance test the O2 sensors to see if they are in range. You can try and see if the cats are red, but I don't think they are. They will become red if your car runs rich all the time.

agrawalr

I have a similar issue: 93 LS400, I replaced the spark plugs, wires, caps, air filter, but I'm still getting really low gas mileage (around 250 miles to the tank.....).

One mechanic took a look at the car, saw that the spark plugs and everything were fine, and that I most probably need to clean the fuel intake, and possibly the gasoline filter if cleaning the fuel intake doesn't help much.

When I called up another mechanic that handles cleaning the fuel intake, he said that he's gonna shut off the fuel pump and run the ls400 on a chemical that works in two stages to clean up the injectors. Does this sound about right? My dad was "maintaining" the car before me, and I'm pretty sure he didn't use fuel additives or anything to clean the car.

Is there a DIY involved that I could maybe do? I saw the DIY posted on lexls.com:

Fuel Filter change:
http://www.lexls.com/tutorials/EFI/fuelfilter.html

Throttle Body cleaning:
http://www.lexls.com/tutorials/EFI/throttlebody.html

Are these sufficient?

williamb82

id say its prolly the o2 sensors need replaced. the only time they will give a code is if they short out or open. if they are working, but just giving the wrong voltage reading, then there wont be a code, but the a/f ratio will be off. i finally got a new ecu for my car so im gonna check the milage after this tank. previously i was getting ~18mpg and 85%+ of my driving is highway. from what the manual says i should be getting 24mpg highway at least. im hoping it was just my faulty ecu(had bucking issues and tps code even though tps and wiring where good). car runs awesome now so we shall see. if it doesnt improve enough ill change the o2 sensors. no telling how old they are.

KMinAF

I agree, O2 sensors will have the most dramatic effect on gas mileage. Check out this site for easy testing and a good explaination of how they work
http://mr2.com/TEXT/O2_Sensor.html