LANcr3w

Ive posted awhile back about 94 Ls400

Ive replaced:
Fuel
Starter
Intake gaskets
Spark plugs
Plug wires
Distributor caps and Rotors
IACV

Ive also checked:
Compression
Fuel pressure
Timing

After replacing everything spark related it would start up but immediately go to 3 or 4 grand and sit there. Hitting the gas would only bog it down and backfire.

Everything checks out good and i have no idea why this thing will not run.
I was told to check the ECU. I actually found that 2 of the capacitors leaked onto the board which I was to believe i just solved the problem to everything.
No... I snagged a 93 Ls400 ECU from the junk yard and opened it up to check if anything was wrong before i purchased it and no leaks or burns practically was brand new.
Got back to plug the ECU and did all the ECU resets

First few start ups it acted like it wanted to run and a few more trys i have got absolutely nothing other than the starter trying to start the motor.

I am completely out of ideas on what it could be. As far as i know this thing should have started by now.

NEED HELP PLEASE

truongrobe

Throtle possition sensor ?

LANcr3w

Glad 1 out of 37 people suggested something. I was actually just now looking at that.
Somewhere it was saying if the TPS sensor was adjusted wrong it could cause too much fuel or not enough to be put in the system.
What i do not get at all is why i have 2 TPS sensors along with the 2 butterfly valves in my throttle body.
Cant find anything on the internet about it and this could be another possiblility id like to eliminate towards having my car running.

YoshiMan

LS400s without traction control only have 1 butterfly valve and 1 TPS.

On yours, the first valve and sensor are operated by the electronic throttle control actuator that will slam it shut and cut engine power when you try and spin the tires on ice. the second one in is the one that gets used every time you hit the gas, so that's where you should look.

From my experience with Toyotas, the TPS innards fail and the sensor fails to close properly and sticks when you let off the throttle, which results in the ECU assuming that you are giving it gas when the throttle is totally shut, resulting in flooding and running very rough/not at all.

Pull it off, test it, and check its condition before just replacing it.

LANcr3w

See i found how to check if it works and what you have to do to set them correctly, it does work i believe but looks like i have a lot of play before it actually starts to open the valve. So this definitely could be a problem that wont allow my car to start or run? Because ive literally run out of things i can even think of.

LANcr3w

I was also suggested that the theft system might prevent the new ecu from working with the car without programming.

LANcr3w

Lets say my TPS is good and adjusted where need be, what could possibly be my problem? There is literally no reason i can think of why it will not start. I have everything you need to at least get this thing to even start up and im not even getting that now.

I see that there are only about 25 Engine codes i could possibly have. I dont believe this is as complicated as i am seeming to make it.

Any imput or suggestions would be greatly appreciated!

Back to the TPS... is it really possible if this were not to work that it cause my engine to not even start up?

YoshiMan

Have you checked the fuel pump/Pressure?

LScowboyLS

how do you know the junkyard ECU has good caps? - they look fine in the early stages of deterioration, so the new ECU may be practically as screwed up as the old one! - but both can be fixed using my step by step procedure!

LANcr3w

Like i said i carefully inspected the new junkyard ECU pulled from a previously running car. I didnt see any damage that was obvious like the one i pulled out of my car. I also scanned around with a magnifying glass and couldnt spot anything so i believe its good.

Yes ive tested fuel pressure and compression. I also have tested the TPS sensor and the Ignition coils. They are both in spec.

YoshiMan

Ignition fuse good? Mass air flow sensor? A break or large crack in the intake system?

Probably not much else we can offer other than naming off random things that could possibly cause a no start issue.

LANcr3w

Thanks for the suggestions really its helps for more ideas to eliminate any other issues. I actually too the exhaust off today and it wanted to fire up Immediately but runs on like one side of the motor.
I believe the cats were clogged so that helped more.

Im stuck to believe now its somewhere in the entire ignition system.
Ignition fuse? I actually havent checked that. Could be a possibility, thanks!

LANcr3w

Actually does anyone have a picture or diagram of where the ignition fuse is? Im sure its labeled or somewhere obvious but id appreciate it so i dont have to waste time looking for it.

LANcr3w

I have gotten it down to the problem that the ground to the Igition coil is grounding out somewhere causing the ignitor plug wire to go off at random when the key is turned on.




So far the is the most helpful video ive had for my car since ive started.
This turned out to be where my problem is, located somewhere in this system.

Yamae

The ignition coil terminals are not grounded. The high voltage terminal is connected to the distributor, pin 1 to the battery and pin 2 to the transistor in the ignitor. The transistor turns on and off in accordance with the drive signal from the ECU. So nothing is grounded. The body is grounded but internal parts are not grounded at all.

The video is somewhat helpful but I must say some people might be confused because his explanation contains a dangerous old method that damages electronics circuits. Mechanics now a days should understand how the drive circuit is organized. Supplying 12V via a bulb is not always safe as it used to be when ECUs were not introduced. Push-pull drive circuits do not withstand the external power which exceeds the current limit. Sometimes it is up to 30mA. Most of bulbs pass more current than this.