AlaskanLS

Check the timing of your car. Poor mpg and sluggishness means that probably the timing is off by a tooth or few, if it was fine before replacing timing belt.

Moarpower

All timing marks lone up. It idles fine and revs smooth.

is it possible the timing is out even if marks are lining up? Maybe lined them up on the wrong rotation or something?

I'll pull codes shortly and report back. Then I'll do a compression test

AlaskanLS

Get a timing light, I am going to upload a pdf that will explain how to check the timing on 91 LS400. Go to the page IG19 on this pdf. Checking timing, it is super easy but you need a timing light.

AlaskanLS

For compression, if it's a bit low on compression use Restore. It is really good stuff and will restore compression. Get the V8 version of this.

AlaskanLS

Before you start throwing parts at your car, I would suggest to take to a professional mechanic and have him check fuel trims. They have those expensive OBD scanners that can monitor fuel trims on OBD1 cars also. They will tell you the cause of poor mpg. Read this:

Moarpower

Do I need to buy the test tachometer also ?

AlaskanLS

You don't need tacho meter. You can get your readings from the one inside in your car's dash. Keep in mind you have to hook the timing light wire to cylinder number 6 and not number 1 as people usually do for checking timing of other cars.

Moarpower

So while i had the car up a couple of feet i noticed the following issues. Unacceptable play in front lower control arms. One of the 5 year old tires is starting to split badly on the inside. Front left shock is done. Leaking fluid badly. Power steering leak that isn't coming from the pump, at least its missing the alternator. And fluid on the trans. I cant tell if this is PS fluid that is spraying back or a trans leak. Split flex disk which would be causing some bad vibration at higher revs.

I guess ill start with the tyres, guibo, then find that leak before I worry about power loss. Going to buy a UV leak dye on Ebay