Cold Starting Problems

[watts93]

Hello,

I recently bought my LS400 and it seems to have a problem.

Sometimes when I come to start it, it cranks and turns over but does not start at all. It has happened 3 times now. I can come back to it a few hours later and it will start in a second and run no problem. It seems to happen when the temperature outside is < 10C, it has never happened during a hot start. Any help would be much appreciated.

Thanks

[steve2006]

There are many things that can cause the problem and 2 areas fuel related or spark related, first thing to do is get the OBDII codes read to see if there is anything stored which may help you diagnose the cause.

Common temperature related causes are the CPS and CTS but do't just replace these in an atempt to sort the problem diagnose further first.

[watts93]

No error codes, could it be the ecu capacitors? Is it worth taking the ecu out to check? If so is it under the drivers side or the passengers side in a RHD 96 ls400?

[Titch LS]

Toby, only LS400's for the U.S. market are OBDII compliant. Yours has 2 older style diagnostic ports; one in plain sight near the fuse box in the engine bay (smallish oblong plastic box with a flip up lid, filled with vaseline/grease)) and one low down close to the steering column which is round in shape. Using either one of these you can obtain some very basic codes by bridging the connectors with a large paperclip and reading the number of coded flashes on the dash. Sorry, but I can't presently recall which 2 connectors are used but a search on line should yield results. If you decide to go to Lexus they will charge you in the region of £180 for a diagnostic test on their very expensive equipment. I've used the paperclip method before on another car I once had. It does work, but is not as convenient as OBDII obviously.

[Titch LS]

Toby, a small correction--- the port by the steering column is NOT round on a Mk 4 (but might be on yours, a mk3?) and looks for all the world like an OBDII port , but it still WON'T connect to a generic code reader, I promise you. There is some software you can buy which will allow connection, but a hand held generic OBDII reader off eBay will not work, believe me. The paperclip method is the way to go----- and it's free!

[ambermarine]

There is a couple of scenarios that could relate to your problem with starting.

The issue of the temprature sensor for cold starting,as raised its head a few times on the Ls400 engine .There is a sensor located just to the left of the front of the engine below the second bank coil.it should be green in colour and screws into the head to the side of the water pump, this is the cold start temprature sensor .The purpose of this sensor is to guage the temprature of the coolant and on that information sends a signal to the engine ecu instructing it to increase or decrease fuel in the combustion mixture.

It as a double edged affect depending on how it fails and because the other effect is too much fuel even after the engine as warmed up it is difficult to ascertain weather that is the cause of poor starting .

They are not expensive and worth a punt just to eliminate that as a cause of the problem.

The other scenario that occurs is the stop too soon after start and that occurs even on my 25k engine if you stop the engine a few seconds after start up .What happens is the plugs get saturated because the ecu on information from the coolant temprature sensor is instructing the fuel injectors to flood the chambers with extra fuel and when simultaneuos ignition occurs the engine starts normally the problem then occurs because the plugs will be wet and won't dry out if you immediatly turn off the engine when an attempt is then made to restart the more the engine is cranked the more saturated they become .The reason this does not happen when the engine is warm is the fuel evaporates immediatly it enters the chamber either by heat or combustion.That is why it starts after a rest period.That might not be your issue but it is an issue on cold engines and not just Lexus engines.

[watts93]

Hello, thanks for all the help so far.

I drove the car yesterday and it started from cold easily. But then as I was driving a few minutes later it stalled (the temperature gauge had only started to move) and would not restart immediately but started after a few minutes.

I have read the error codes using the flashing engine light and got the following codes: 12, 13, 21, 28.

From what I have read this is rpm signal 1 & 2, main oxygen sensor signal (twice?).

Does this mean the oxygen sensor needs replacing and what does the rpm signal code mean?

Thanks

[Malc]

just a thought ............. does the throttle body need cleaning out ??

Malc

[Malc]

air filter choked up ?

Malc

[ambermarine]

The codes you are getting relate to the problem through the Oxygen sensors

The fuel supply is governed by the engine ecu on information given from the oxygen sensors .

The Ecu will determine how much fuel to supply to the engine depending on the exhaust gas analysis so if the signal is fuel mixture too rich it cuts down the amount of fuel, so you will not get any at all eventually depending on how bad the sensors are.

The rpm signal is related but without the troubleshooting section of the workshop manual it is difficult to determine how.

It sounds like the oxygen sensors have gone down and there are four ,two to each exhaust one pre catylst and one post catylst.

Sourced through Lexus they are expensive but you can get them elsewhere for half the price.

There are threads both on this site and the US lexus owners site that cover this topic extensivly.