Update....

(And I acknowledge that continuing to replace parts until the problem disappears is not a scientific approach, but my reasoning is that if the car can eventually be made to run it will have been a good investment, and if not, then - worst-case - I can always keep said parts for (1) a possible replacement car of this type, or (2) sell them.)

1. I bought a new MAF sensor (ADL Blue Print brand). Better than risking splaying the loom connector poles by inserting probe wires into them. Fitted, no difference. (However the engine did once again stop cranking with a jolt - but was OK once I'd freed it off by turning it over a fraction manually via the crankshaft bolt. If the ring gear is damaged then it's too late now anyway.)

2. I removed the plate on top of the TB and cleaned out the micro bore-holes. (They were quite caked up with soot, actually.) Still no-start, although it did (kind-of) cough once.

Whilst I re-capped the ECU over two years ago, I do wonder if there are any known semiconductor issues that are now starting to show up on these boards. (I have been told that there are!)

Just for info once again, please see table attached, showing specs of original caps when new, as found, and of those fitted as replacements.

Thanks again,

R

 

Okay I'll guess lol, it seems the thread starter is okay with it so my guess is it's related to your ecu somehow, I mean it doesn't take much to mess these things up as good as you are with these things.. there are still events that could happen even very mild static event, that could damage that board when you had it apart that transpired to fail later on down the road but worked for a time. I mean I understand speculation that's what forums are about kind of breaking things down and disseminating. So I bet it is electrical and probably revolving around issues with the ecu somehow. It just makes sense, you had it out and were messing around with it, I used to work on electronics a bit myself and it can happen. So without doing any tests not knowing anything, I will postulate you have an ecu // ecu related issue. Like I say I don't mind speculating as long as the thread starter is good with it. Could maybe have triggered a security event which is disabling your car, who knows, an immobilizer issue perhaps.

 

I would check all of your fuses, all of them. You might have issues there as well, seems simple but it's possible.

 

Side note: there is a 2nd fuse box in the driver footwell that many people gloss over when checking fuses.

 

There are things on the fuse block that pertain the cars ability to run or not run. So before jumping onto the ecu, comb over all the fuses, and also the relays, that pertain to the cars ability to run, or not run. Its entirely possibly the problem is there as well.

 

All valid points - for which I am grateful - although I will say that I was careful in taking ESD precautions with the ECU at the time.

The problem now is weird, in that the difficult starting began when they changed the composition of the fuel in the UK, got much better after a couple of tanks of BP Ultimate, then got worse again on a tank of Esso (supposedly E5). Despite this, went like a rocket on a long high-speed trip. Now barely coughs when attempting to start - if I'm lucky.

(Plus of course it looks like I've trashed the starter with all the cranking. This seems to have killed the battery too, which is now 5 years old and not holding a charge very well.)

R

 

Sounds to me like your ECU may be the issue. If problems are intermittent and hard to diagnose, then its likely failing capacitors, even though rare on the 98-00s they are getting older and problems are starting to present themselves.

 

Usually it shows a rough AT shifting as an initial symptom when ECU capacitors for a 98-00 are failed. A 98-00 is a quite different animal compared with older ones. Measuring the ripple voltage at 5V lines in the ECU will help you to troubleshoot. A 98-00 ECU is completely different from former ones due to the use of newer processors that consume less current as well as newer ceramic capacitors in parallel with QAS capacitors. Those two reduce the stress to QAS capacitors and these seldom fail faster compared with former ones. I'd simply measure the ripple voltage level first in accordance with the method in the FAQ page, If I only have a multi meter. But I have two oscilloscopes (analogue and digital) and I use them for the precise ripple measurement.

For the quicker trouble shootings, electronically controlled cars often need to use an oscilloscope. Without it, you'd wastえ time and money. I recommend DIYers who want to DIY modern cars would add an oscilloscope to their tool box. These days handy type of small ones are available inexpensively. .

 

Yes, it is true that I should invest in a hand-held oscilloscope. (I have a full-size mains-powered one, but that is not the tool for the job here! ) But in any case, what is the cause of ripple in these cars? Where does smoothing of the alternator output take place - if not the battery itself? (And obviously, there will be no ripple without the engine running )

In this case, whilst it could be an ECU issue, I'm now leaning towards fuel-delivery as the problem. However, there was a hiss of air when I removed the fuel cap - suggesting that the fuel pump was working and building up a good pressure in the system. Perhaps I should try and get some starter fluid today...

R

 

I have done a little more investigation today. (Getting serious now!)

From the diagram kindly supplied by Yamae in a previous thread (see below), I have deduced that the Circuit Opening Relay is not operating with the ignition on. (12V is present on pin 5, via the main relay, but there is also 12V on both ends of the coil - suggesting that the open-collector transistor in the ECU is not pulling down pin 1 when it should.)

Clearly, this explains why the fuel pump is not operating. (Can't really see what else it can be, without the whole diagram.)

The only presumption I'm making is that the Circuit Opening Relay should operate simply with the ignition on, and not specifically during cranking and then when the key is released (i.e. when the ECU thinks the engine should be running).



If I were to obtain a second-hand ECU, would it be a straight swap-in replacement, or would there be issues with odometer display, programmable features or anything else?

 

When the ECU detects a certain serious condition which is considered dangerous to keep running the engine, it disables the circuit opening relay to supply +B to the fuel pump. Thus the engine has no idea to keep running. We call it an inhibiting mode.

What are those conditions? There are 4 below. When one or more of these are detected, the ECU stops the fuel supply opening the circuit opening relays contacts.
1, No signal from the MAF for more than 3 seconds.
2, No signal from the crank position sensor for more than 5 seconds.
3, No signal from the cam position sensor for more than 5 seconds.
4, No IGF signal from the igniter for more than 3 seconds although the IGT signal is sent.

Regarding an ECU for a 98-00 LS400, the immobilizer chip is there inside and a straight swap-in replacement is not OK. The starter works but the engine doesn't start because the ignition and the injection are disable by the immobilizer system. There is a way to deal with this. Swapping the immobilizer chip makes it possible to start the engine. The chip's ID is IC900 or IC901. Sorry that I don't remember well. Anyway it's a 8 pins EE-PROM. All you need to do is to remove the chip from your ECU and place it in the replacement ECU. This needs some soldering skills though.

 

Many thanks Yamae,

As an interesting development from what I found yesterday, it does appear that the engine has to be turning over before the ECU will enable the fuel pump. (I know that on the Gen1 it is only necessary to have the ignition on.)

Having cranked the car today (after reseating various connectors - including the camshaft sensor, which incidentally measures 1k), the fuel pump did operate, as there was a hiss of air from pressure in the tank when I opened the fuel filler cap afterwards as a test. (This was not the case after just having the ignition on.)

• At its connector, the fuel pump resistor measures 0.7 Ohms (within spec - outside temperature 15c.)
• With the fuel pump relay removed, the fuel pump itself measures 0.9 Ohms between pin 3 of the relay socket and ground (within spec.)

Kind regards,

R

 

Well, sadly I think it's the end of this car. Having got nowhere with it, I had it towed in. Mechanic did get it to start on a jump pack, but according to him it ran as rough as hell and he could hear something "not right" and "metallic" deep in the back of the engine. Plus, the starter continues to jam, most of the time. And this is even before trying to figure out the original starting issue, which is still a thing. So right now it's sitting in his yard looking as beautiful as ever in its Fjord Mist and sea-green leather. (And now I'm deciding what to do with it next.)

At least it was always there for me when I really needed it. Not so sure 166,000 miles is enough, but it is what it is.....

Thank you to everyone who responded, particularly to Yamae for his wisdom and experience.

So.... (wait for it...) I've just bought a 430 and will be heading over to that section of the Forum soon! I may have paid a little too much for it, but it drives like it's on rails, there are no clonks or suspension noises whatsoever, the engine runs like a sewing machine and there is no vibration at all, even in D at a stop. It was described as having a "fastidious" previous owner, but I guess there are differing interpretations of that. (Mud around the trunk hinges and slightly dirty interior is not evidence of fastidiousness as far as I'm concerned.) The rear tyres aren't great, the PAS fluid desparately needs changing and the telescopic gearing for the steering wheel is broken. (Hopefully that's a simple fix!) I think the front carpets have been taken up (maybe for O2 sensor work, which there is an invoice for). 'Low tire' warning came on when I was on the motorway - not a pleasant experience - I had to exit, find a safe place to park and check them manually - to find they were actually fine.

An LS400 in a restyled bodyshell it ain't! (And have not even scratched the surface of all the new features it has!) First impressions over the 400: Better drive, more toys, but cheaper build.

Cheers guys - and maybe see you on the other side!



R

 

Congrats on the 430! That's to bad about the 400 but as you say, that's the situation it presented.

 

That's a bit sad story but you already have a LS430 now and I find you still love a LS.

If I were very close to you and were able to investigate together with you using electronics tools, there 'd be some other result. 166,000 miles is not enough or should I say too little. But it's your car and you can decide everything.

Anyway thanks for the update and as a moderator, I will be finding you at the LS430 Forum in the future.