96 Ls400 Doesn'ts Start/ Starts Then Dies

landar · June 20, 2013

You definitely have a reason to suspect the ECU. You might want to locate the ECU and pull the connectors, clean them and reattach. Sometimes the connectors get corroded over time. Long shot but won't cost anything to try. I am still wondering about the ignition switch.

BobSmith007 · July 18, 2013

Ok An update, because well I'm still not winning at life.

So I suspected the ECU, I pulled it, which is not the easiest job for large people because you must bend in ways that are unnatural. But I succeeded. And then I put it back in. And... Car is still doing what its doing in the video.

So I put on the new alternator I had picked up. And... Car is still doing what its doing in the video.

I thought maybe somehow it is the MAF, so I picked up a new MAF. And... Car is still doing what its doing in the video.

So I decided maybe I should see if I can throw a code, and see if that is function as it should.

So I unplugged the MAF, And the car did what it did in the video, but when I then plugged up my code reader It pulled two codes. That are both related to the MAF, so I replugged them up, and the codes went away, and the car still did what it did in the video.

So the car is not throwing any Codes.

SO I got a rag that had some gas spilled on it... Held it up near the air filter.

The car ran for about 5 seconds. The fuel line does get hard (indicating its pressurized) when turning the key, but it gets less hard almost immediately. I know from other tests the fuel pump is sending fuel out when turning the key, and is doing so at normal pressure.

SO where I am, and what I'm hopeful from the quality humans around here. Suggestions and ideas of what would turn off the fuel pump, or disable the injectors or something in the fuel delivery system. As in it works for a moment, then shuts off. Because it seems like that's whats happening. Its been just shy of 2 months, and I miss my car functioning.

Thoughts, please.

landar · July 18, 2013

'SO I got a rag that had some gas spilled on it... '

Whew, for a minute there, I thought your next step was going to involve a lighter or matches!
Well, you are certainly getting more clues and I applaud you for the tests that you did. Pretty clever. I would have to agree that it does now seems to be starving for fuel...but why? The first thing that I would do is to put a fuel pressure gauge on the fuel line somehow. If that is normal then you can go after the injector system.

Now however, before you go to the trouble of hooking up a pressure gauge, did you monitor the fuel pump relay as I mentioned in post #21 to see if the relay might drop out when the engine first comes to life? It should be fairly easy to check.

BobSmith007 · July 18, 2013

I did look and listen to the fuel pump relay. But I'm not entirely sure why I was looking or listening for. So any tips or suggestions would be handy.

(Car repair is not my normal area of knowledge)

I do know I do not, or do I have access to the required set up to do the fuel pressure test on this car. I have a setup I've used on other cars in the past, but it seems this car has a less than standard setup. But in a stroke of luck (or not) I found the following quote online:

On the mid ‘90s Lexus LS400 V8,
you simply watch a small screw on the pulsation damper to see if it moves when
the key is switched on. If it does, and
the stuff in the rail is gasoline and not water or diesel, you have enough
pressure to get the car started if all else is okay.

Now does that sound legit? Because I feel real good that it is getting plenty of fuel to fire up, but then the fuel goes away, either via the pump not pumping, the injectors not injecting, or maybe the fuel pressure regulator not regulating. Or something else, I am sure there could be a half a gross or more possible reasons that XYZ is happening to the car, but sooner or later I'll eliminate everything, or I'll be picking up that rag and a lighter. Well not really then I'll be tow dollying it to the Toyota place and hoping that the bill isn't insane or anything.

landar · July 18, 2013

Ok, let's review the fuel pump operation for a moment. When you turn the ignition key to the 'Run' position, the fuel pump relay is energized to supply power to the fuel pump. The relay has a set of contacts that get pulled together to supply power to the pump. If that relay is de-energized during the start sequence, the pump will no longer run or supply fuel to the injectors. So, your job is to determine if the relay is staying energized. You cannot necessary "look and listen" to know for sure. It would be best to instrument the relay with a voltmeter on the +12v feed side to the pump and ensure that +12v is being continuously supplied to the pump while starting and running.

BobSmith007 · July 19, 2013

Ok, let's review the fuel pump operation for a moment. When you turn the ignition key to the 'Run' position, the fuel pump relay is energized to supply power to the fuel pump. The relay has a set of contacts that get pulled together to supply power to the pump. If that relay is de-energized during the start sequence, the pump will no longer run or supply fuel to the injectors. So, your job is to determine if the relay is staying energized. You cannot necessary "look and listen" to know for sure. It would be best to instrument the relay with a voltmeter on the +12v feed side to the pump and ensure that +12v is being continuously supplied to the pump while starting and running.

So I pulled out the back seat, because well as best I can tell that is how you replace a fuel pump, which would mean you would have access to the wires going to the fuel pump.

Now here is what I learned.

1) When I put the key to the run position, the fuel pump is just hanging out not doing anything, I called the local toyota place and they said this is normal.

2) When turning the key to the start position, aka cranking the car, the fuel pump gets the same voltage as the battery. As in 12.4v the first attempt, down to oh 12.2ish on the last try. I had all the doors open, so I assume some of the battery while not running was powering the lights, thus a slight power loss.

3) I had a !Removed! of an idea, to test the relays using some wire and a 9v battery. I checked a known good relay, and it actuated. I checked a known bad relay (from another car) and it didn't actuate. So I tried my idea on 4 of the relays from my car, and all actuated as intended. Was this a good check, hell I dunno. Maybe?

4) Taking the backseat out is overly easy compared to messing with the front seats.

Also I looked at that screw that random website on the internet said to look at, and it moves, and the car has gas in it, so does this mean I have good fuel pressure, I do know when I undid the fuel line back by the fuel filter, and I turned the key, it shot gas out like a rocketship lifting off. So I feel like pressure=enough.

So if the fuel pump is getting the juice, (and with the backseat removed I can easily here the fuel pump doing its thing, verses when the seat is in, its pretty hard to hear), and the relays seem to be good? Am I now angling towards a different component of the Fuel Delivery system?

AKA What are the other parts of the Fuel Delivery system? Injectors?

Again Huge props to you Mr. Landar, I am not a mechanic but I sorta kinda pretend to be one on the internet in an effort to fix my sad little car.

landar · July 19, 2013

Well thats good info and you certainly got adventurous removing the rear seat although you did not need to do that to check the relay. I have no doubt that the relay and fuel pump are fine and working. What I want to know is if the ECU is telling the relay to stay energized when you let off the key to the 'run' position. If it is not, then we need to figure out why not. And if the relay is staying energized, then the ECU may not be driving the fuel injectors (cam or crank sensor malfunction?). But first, try to determine if the relay is staying energized in the "run" state.

BobSmith007 · July 20, 2013

Well thats good info and you certainly got adventurous removing the rear seat although you did not need to do that to check the relay. I have no doubt that the relay and fuel pump are fine and working. What I want to know is if the ECU is telling the relay to stay energized when you let off the key to the 'run' position. If it is not, then we need to figure out why not. And if the relay is staying energized, then the ECU may not be driving the fuel injectors (cam or crank sensor malfunction?). But first, try to determine if the relay is staying energized in the "run" state.

Well I plan to recover the rear seats at some point, so it was good practice. Also I wanted to check the voltage at the pump, just to be certain It wasn't losing any along the way.

I do know, I certainly heard the fuel pump for just a moment or two AFTER the car had died.

So the time line would be.

Turn key to crank, Hear fuel pump, car starts, car dies, still can hear fuel pump for just a brief bit of time, then it cuts off.

I assume its because

1) the car has failed to stay running, thus it's smart enough to turn off the fuel pump

2) The fuel pump is smart enough to turn itself off, because its pumping gas that isn't going anywhere.

I don't know a whole lot (admittedly) about how it all works, but for some reason it seems to me like the gas is getting where it needs to go for just that short moment that it starts, before it starves itself. Which would suggest something (ECU via a Sensor/etc?) is telling something else (Injectors) to shut down?

fsuguy · July 20, 2013

Hi,

Couple of points that may be helpful - try to bypass the relay - there should be schematics that show you how, if not, I can dig through volumes of stuff and find one. This can be done with a jumper, but only for a short time and just to eliminate the relay as a source for the problem - if bypassing the relay resolves the issue, you're home free.

Next, the ECU is prone to leaking capacitors according to Yamae, an electronics engineer in Japan who has posted some pretty good pictures showing the ECU PCB with corrosion from the capacitors. It is a well-known fact that some of the electronics on these early models were not designed with longevity in mind - think 15-20 years, as evidenced by issues common to the 1st & 2nd gen. vehicles (LCD failures, rear-view mirrors, fluorescent lamp failures, sundry other cluster related failures, etc.) Don't get me wrong, the mechanical characteristics of the Lexus is world class, and the engineering is superb! However, the electronic components were produced by secondary markets and as a result we see these failures. But back to the point, the ECU may be the culprit, if everything else seems to be fine. If you can get your hands on a known good ECU and test it in your vehicle, it may help resolve this possibility - by the way, Yamae has posted replacement capacitors types and values somewhere on here to effect repair of the ECU!.

However, as several other posters indicate, a good objective test of the fuel system is in order, since several things may be the issue - tired fuel pumps get hot quickly and while have capacity while still cool, become useless when hot, etc.

Good luck & hope you can get resolution soon!

BobSmith007 · July 23, 2013

Well today's update.

I did the cap change in the ecu. Or rather I had someone more skilled do it. Looked like quality work.

Car is doing the same thing it was doing.

I'm at the end of my rope.

landar · July 23, 2013

Justin, you are at the end of your rope only because you are not listening to all of the suggestions. You MUST, some way or the other, get a pressure gauge on the fuel rail. You are a smart guy and you can figure out how to do that.

If you do not want to do that, the next step is to put her on a flatbed and ship it up to me. Sign the title first. Check will be in the mail. ^_^

BobSmith007 · July 30, 2013

It wasn't so much I didn't want to do the fuel pressure test, but the first fuel pressure tester I picked up didn't have the proper banjo bolt adapter, and I finally was able to get what I needed.

Fuel pretty is hitting right at 40 when cranking, then goes to 42 as its dying before it slowly starts to creep down over time.

At 5 minutes afterwards it's still at about 33 lbs.

landar · July 31, 2013

That is a perhaps a little low but should not prevent it from running. Time to check fuel injector signals. I would suspect the ECU is cutting the signal. I wonder if this smacks of anti-theft like operation? Not sure.

BobSmith007 · July 31, 2013

Well if you could point me in the direction of how to do a fuel injector signal testing, because a quick google has got me fairly no where.

landar · July 31, 2013

I would probably use an oscilloscope on one of the fuel injector connectors but you may not have one. So, how about using a 'noid' light? Or you could possibly hook up a voltmeter to see what is happening.

So, you would instrument a fuel injector connector to determine if the pulsing signal is present or not during starting and when it dies. Since your engine will keep running if you artificially inject some fuel (like using starter fluid), you can keep it running while you monitor the injector pulse signal. Now, a little homework and light reading for you:

Here is a video on the noid light ->