cuda6pak

92 Ls400 Hard To Start Only When Warm

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I posted about this problem on clublexus with no help so far, wanted to see what you guys thought.

When the car is cold, it will start right up first crank no problem. But if it has been driven for anything more than 5 minutes, it ALWAYS takes two cranks to start up. And by that I mean the first time I hold the key over to crank it, I can hold it there as long as I want continually cranking and it will never catch or even act like its starting. But as soon as I quit cranking it, wait a second, then start cranking again, it will start right up!

So far the spark plugs, wires, rotor buttons, both ignitioncoils, fuel pump, and timing belt have all been replaced. Not sure what's left?

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coolant temp sensor? Maybe its failed and telling car it is cold when it is warm. ECU is over correcting and sending too much fuel and flooding engine.

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coolant temp sensor? Maybe its failed and telling car it is cold when it is warm. ECU is over correcting and sending too much fuel and flooding engine.

Good tip, hadn't thought of that!

The only thing I can say is that there is no SES light on and that the car tends to smell at idle. It runs completely perfect otherwise with no hesitation anywhere at any throttle position. Also I noticed that if I shut it down when warm and start it right back up in about 15 seconds, it starts up fine, but if I let it sit for more than a few minutes it does what I first posted.

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The light won't always trigger, especially if it's an erratic problem, the ECU has to see the fault twice in a cycle before coming on. The connection on the coolant temp sender can corrode and only make minimal contact at times, when heated it's expanded enough to complete the circuit. Unplug it completely and you'll get a better answer.

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If it is consistent, that is really good news. It gives to you a chance to try various things. I would be curious to know if it had spark when it wont start. That would be my first step in troubleshooting. Isolating the fuel vs. spark issue.

How long has this been happening? Any significant repair just before it started happening?

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coolant temp sensor? Maybe its failed and telling car it is cold when it is warm. ECU is over correcting and sending too much fuel and flooding engine.

Good tip, hadn't thought of that!

The only thing I can say is that there is no SES light on and that the car tends to smell at idle. It runs completely perfect otherwise with no hesitation anywhere at any throttle position. Also I noticed that if I shut it down when warm and start it right back up in about 15 seconds, it starts up fine, but if I let it sit for more than a few minutes it does what I first posted.

A failing coolant sensor could cause a hot start prob. Could be a faulty fuel pressure regulator. Could also be a faulty cold start injector or time switch - or a faulty ecu timer for the injector. Another could be leaky injectors. You could pull a plug to see if it's wet after the first shutoff. The smell could be a poor connection with an injector to the manifold. The hard start could even be an efi relay prob. Your symptoms aren't necessarily connected.

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Just to update the thread I bought a new coolant temp sensor from Autozone and installed it. Still acts exactly the way it did prior to install, hard to start when warm and still smells a bit rich at idle. Haven't driven it enough on this tank to check on fuel mileage but I assume its the same.

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Just to update the thread I bought a new coolant temp sensor from Autozone and installed it. Still acts exactly the way it did prior to install, hard to start when warm and still smells a bit rich at idle. Haven't driven it enough on this tank to check on fuel mileage but I assume its the same.

Spark when it wont start?

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Just to update the thread I bought a new coolant temp sensor from Autozone and installed it. Still acts exactly the way it did prior to install, hard to start when warm and still smells a bit rich at idle. Haven't driven it enough on this tank to check on fuel mileage but I assume its the same.

Spark when it wont start?

It's hard to say that, because you would think that if it was spark related it would do it all the time. There is a window from about 2 minutes after the car is shutdown that lasts for a few hours that it's hard to start. If it's cold, starts right up. If it has just been shut down, it will start right back. Which makes me think what eatingupblacktop suggested is that there are some leaky injectors. Whatever it is, it doesn't sound like a normal LS problem as I can't seem to find anyone else with this same issue.

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Put a fuel pressure gauge on fuel rail. If injectors are leaking then pressure will drop quickly after shutting off engine (leaving puddle of fuel to deal with on next start. If injectors hold well then pressure should stay up for a while after shut down.

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Put a fuel pressure gauge on fuel rail. If injectors are leaking then pressure will drop quickly after shutting off engine (leaving puddle of fuel to deal with on next start. If injectors hold well then pressure should stay up for a while after shut down.

Is there a schrader valve hook up somewhere on the fuel rails to hook a gauge up to? I glanced after work today but didn't see anything.

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Put a fuel pressure gauge on fuel rail. If injectors are leaking then pressure will drop quickly after shutting off engine (leaving puddle of fuel to deal with on next start. If injectors hold well then pressure should stay up for a while after shut down.

Is there a schrader valve hook up somewhere on the fuel rails to hook a gauge up to? I glanced after work today but didn't see anything.

No but usually the fuel pressure gauge kits some with several T's and adapters to splice into all types of fuel rails.

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I posted about this problem on clublexus with no help so far, wanted to see what you guys thought.

When the car is cold, it will start right up first crank no problem. But if it has been driven for anything more than 5 minutes, it ALWAYS takes two cranks to start up. And by that I mean the first time I hold the key over to crank it, I can hold it there as long as I want continually cranking and it will never catch or even act like its starting. But as soon as I quit cranking it, wait a second, then start cranking again, it will start right up!

So far the spark plugs, wires, rotor buttons, both ignitioncoils, fuel pump, and timing belt have all been replaced. Not sure what's left?

my car has EXACTLY the same symptom. Did you fix the problem with confirmed root cause?

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I posted about this problem on clublexus with no help so far, wanted to see what you guys thought.

When the car is cold, it will start right up first crank no problem. But if it has been driven for anything more than 5 minutes, it ALWAYS takes two cranks to start up. And by that I mean the first time I hold the key over to crank it, I can hold it there as long as I want continually cranking and it will never catch or even act like its starting. But as soon as I quit cranking it, wait a second, then start cranking again, it will start right up!

So far the spark plugs, wires, rotor buttons, both ignitioncoils, fuel pump, and timing belt have all been replaced. Not sure what's left?

my car has EXACTLY the same symptom. Did you fix the problem with confirmed root cause?

Update: Swapped out ECU's with a known good one. Still did not fix it. Seems like the only things left are the fuel injectors....on top of my continuing A/C problems, I'm getting closer and closer to selling this thing.

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Hopefully you already tried switching gasoline brands. Might just be a simple case of vapor lock with all this hot weather. You are using Premium fuel aren't you?

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Hopefully you already tried switching gasoline brands. Might just be a simple case of vapor lock with all this hot weather. You are using Premium fuel aren't you?

Yes, always used premium fuel, doesn't matter what station I get it at. Someone on CL had mentioned that it could be my VSV for fuel pressure. Does that sound like the case to anyone?

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Hopefully you already tried switching gasoline brands. Might just be a simple case of vapor lock with all this hot weather. You are using Premium fuel aren't you?

Yes, always used premium fuel, doesn't matter what station I get it at. Someone on CL had mentioned that it could be my VSV for fuel pressure. Does that sound like the case to anyone?

here is some more detail:

www.clublexus.com/forums/ls400/514908-fuel-pressure-vacuum-switching-valve-vsv.html

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I wanted to post up what my problem was for this issue. I have looked all over the Lexus and Toyota forums with no luck for weeks. So I just started testing stuff. When it was warm outside (over 65°f) and the car was driven to the point that it was warmed up the car wouldn't want to start even though it ran perfect before hand until I parked it. I had already rebuilt the ecu last year, replaced the coils, tested the mass air flow sensor as well as the coolant temp sensor, and spark in general. All were good. So while I was stranded 100 miles from home it started to hesitate and the car was bucking. First time in the 70's in a few months. So first issue in a month since it cold all month. We pulled into a gas station and let it sit for awhile while we where there we got a drink out of frustration. We got back to the car an hour later and still no go. I had my buddy get in the driver seat and turn the key to one while I had the fuel cap off with my ear to it. Fuel pump didn't kick on at all. So I took out the cloth/carpet in the trunk to get to the tank. I had him try and start it while I punched the tank next to the pump. It started up just fine. Drove it 50 miles. Died again. Let it sit again. Wouldn't start. Punched the tank again as he started it. Started up again. Definitely the pump. Still really far out though so I called AAA and had it towed. I ordered a aftermarket performance pump (walbro 255) since it was the same price as a oem one. No more issues. Runs fantastic.

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Glad you got it worked out. It can get expensive dealing with car problems so far away from home.

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38 minutes ago, sha4000 said:

Glad you got it worked out. It can get expensive dealing with car problems so far away from home.

I wish I didn't listen to other people about the fuel pump. Everyone said it was rare for fuel pumps to go out. So I avoided it. I got my 97 with 80k miles on it in late 2015. I've put 40k miles on it. My first problem with it was at 110k miles last fall and everything I read matched up to the ECU. I was hesitant to rebuild it because none of the caps were leaking. But when I did the car ran better then it ever has. The coils, caps, rotors, and plugs where done at the same time. Though not because I was throwing parts at it but more because they had 110k miles on the original equipment. The fuel issue was new the first time it got into the 60's this year. I'm in Indiana. Yay global warming... Got it towed home because I had no idea. Felt like the trans was giving out the way it jerked and shifted. But it started up and ran great again. It wasn't above 50 for awhile. First time it got warm again it did it again. I knew it was getting spark because I had starting fluid with me. So that's when I put me ear to the fuel cap. No whine= no fuel pump.

I just want someone to see this post because it's really easy to check for fuel with out pulling spark plugs. The ls400 tank is really close to the fuel cap. So it's very easy to hear it when it's working. Though it's best to have a buddy there turning the key to on (not starting it) since the pump only primes for a few seconds. 

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Having a 92 Lexus LS400 myself I greatly appreciate the follow up on this, if I ever experience anything like this the first thing I will check is the fuel pump... BTW have you also changed out your fuel filter as well, it's always good to change them out in 50K mile intervals.

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6 minutes ago, Spartan0536 said:

Having a 92 Lexus LS400 myself I greatly appreciate the follow up on this, if I ever experience anything like this the first thing I will check is the fuel pump... BTW have you also changed out your fuel filter as well, it's always good to change them out in 50K mile intervals.

In my personal experience of with cars built in the 90's on up as well as friends and family who have worked on cars for a long time. In line fuel filters very rarely needs replaced. I haven't looked into Toyota when it comes to this but with Honda's, Mitsubishi, bmw, and a few others  I've dealt with consider those good for the "life" of the car. About 150k to 200k. Mine hasn't hit 130k yet

My tank was very clean and the in tank pre filter off the pump was very clean. Fuel pressure with the old pump was at oem spec. I'll look into Toyotas recommendations. I know all are built different.

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7 minutes ago, B17what said:

In my personal experience of with cars built in the 90's on up as well as friends and family who have worked on cars for a long time. In line fuel filters very rarely needs replaced. I haven't looked into Toyota when it comes to this but with Honda's, Mitsubishi, bmw, and a few others  I've dealt with consider those good for the "life" of the car. About 150k to 200k. Mine hasn't hit 130k yet

My tank was very clean and the in tank pre filter off the pump was very clean. Fuel pressure with the old pump was at oem spec. I'll look into Toyotas recommendations. I know all are built different.

I have just made it a habit of changing out my filters every 50K-60K miles, its like changing out your air filter every 20K miles, if it does not need it done but you still do it anyway it can only help not hurt....

Speaking of which I need to clean out my IAC and Throttle Body (just got the car 1 month ago), this is all stuff I do when I get a new pre-owned car, its a bit over the top but I am a perfectionist.

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I plan on a few more serious mods down the road and when I get to that point I'll get to that.

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