RobTek88

My 94 LS400 started to run really rough and sluggish. Wouldn't get over 35 and was choking terribly. 2 days after this I changed out the Fuel Filter on the car.

The Car will turn over, but it will Not catch.

Is there a way to prime the fuel lines?
Any other possibilities of the problem?

Any and all information would be greatly appreciated.

PureDrifter

iTrader: (10)

why did you immediately check the fuel system but not the ignition system?

RobTek88

Have not had any troubles with the ignition.

(I am not a mechanic in any way)

Describing the problem to many people that know far more about cars then myself, have all said Fuel Filter.

SC400slide

iTrader: (11)

Sounds like a main something or computer. I'd go with the ECU. Or what fixed LSCowboyLS' problem, leaking ECU capacitors. And yea, sound's too extreme to be anything fuel. I'd go main stuff. GL.

cobalt91

How many miles? Have the maintence intervals been done? Need more info.

LScowboyLS

yes, this sounds like exactly what my 96 LS was like, and it drove me crazy trying to find the problem, until it dawned on me that it was the ECU capacitors

I would bet $100 that this is the problem with your car, I recognize the not going over 35 (try manually shifting each gear and you can go faster) and the choking, poor acceleration, rough running.

and fuel filters tend NOT to be a problem on LS400, it's as if they have a lifetime fuel filter

and even if by some remote chance the ECU capacitors are not the problem, you haven't wasted any work, because this is a known defect in the LS400, they will eventually be a problem on ALL LS400's

very little auto mechanic skills needed (just a bit to get the lower glove box and ECU out), what is needed is soldering skills!

PS: - if you must use the car in the mean time, please start it with starting fluid, the starter in the LS400 will not hold up to long or repeated cranking attempts, and doing that starter replacement job is a nightmare!

RobTek88

Mileage is up around 240,000.

I have been doing the Maintenance as best to my knowledge.

Tires, Breaks, Plugs, Wires, Oil, Making sure there are no leaks in hoses, Coolent etc. (And not with a once over. Actually putting it on a lift, and going through pretty thoroughly at least every 3 months).

By ECU (Engine Control Unit) you also mean PCM (Powertrain Control Module)?

Yamae

Some companies may call it a PCM but Lexus / Toyota calls it an ECU. The LS400's ECU controls not only the engine but also the AT and the AC. Since you have been doing mechanical related maintenance jobs fairly well and I don't think the problem you are facing is not related to those.

I quite agree with those 2 guys SC400slide and LScowboyLS judging from my experience and your thorough jobs. I suggest you to check the ECU located under the passengers side of the dash.

RobTek88

Ok. I will start that now. Thank you all for the help so far. I'll post more as soon I find out about the ECU.

LScowboyLS

to remove the ECU - remove bottom pretty light panel under glove compartment at passenger foot area, then remove lower glove compartment (it can be a bit tricky due to a hidden bolt or two located within secret panels within lower glove compartment.

once lower glove box is out, then disconnect negative battery cable, unplug 4 connectors to ECU - then remove ECU (a book size aluminum box among several others, but the only one with 4 connectors containing a total of 100 wires going to them)

cobalt91

You haven't mentioned if you pulled any codes. Was the check engine light on? I agree the capacitors are gonna need to be done, but IMO basic stuff needs to be checked first. Fuel, spark, and copression.

RobTek88

I checked the ODB and no codes came back, also had a Mechanic friend test a second time to make sure I was doing it right, and it all came back normal.

I did read that the Fuel Pressure Regulator would give me all the symptoms that I have experienced if any of the lines where going bad. On an outside inspection, there was nothing wrong, I have not removed them, but I also figure if I am going to remove them, I may as well have a new one to go in, for troubleshooting. I'm at the point, that I am waiting for the battery to charge up, as doing the ODB test, and the couple times of cranking the motor after different attempts, the engine seems as if it is getting fuel to it again, but didn't make the fuel crank due to the battery being low.

I was also looking for a purge valve on the fuel line, to attempt to let any air out that may have gotten in the line when I changed the filter.

And I started to question about a Inertia Switch that may have been triggered due to the line being open when I changed the filter, and if that happened how would I reset that....

Soon as it charges I'll get back to everyone.

LScowboyLS

do a test, start car with starting fluid, drive in first gear and manually shift car gear by gear and see what kind of top speed you can attain pretending it is a manual shift car

RobTek88

Update -

I got the car running again. But the choppy, choking no power, coughing idle, is still there.

My next course of action is going to the Fuel Pressure Regulators and see if that is the problem. Keeping my fingers crossed.

LScowboyLS

ECU capacitors and possibly Idle Air Control Valve as well