1994 LS400 random misfire

[garagestmarien]

Hi all,

Quite a while since I have been on this forum.

I have an odd misfire problem. I have looked through the topics but cant find anything that resembles what I have.

So, I have built a complete Stainless steel manifold back exhaust system, using magnaflow parts.

Done a full service, correct oil and filters.

During this time the Battery died and I ordered and fitted a new one. Varta blue G7.

Then found the alternator was not working, so now have a genuine Denso one on. Now everything fine.

But after the car warmed up it was losing 4 cylinders, so I suspected, plug leads or coils. What I found was everything was original, so 23 years old.

So I have fitted new rotor arms, dist caps, leads, coils and spark plugs.

The car ran perfect for about 3 weeks, then the misfire came back when warm. Checked at work and the opinions was maybe dirty connections. So cleaned all connectors, although they looked fine.

But this did happen when I was low on fuel.

Since then another 3 weeks without any problems until yesterday shortly after leaving work, 4 cylinders again and again I was low on fuel. So filled up and car seems good again.

Now, when I filled up (weather 32degs c) i noticed a huge amount of pressure come out of the tank. More like i was emptying a compressor.

So the 2 times i have had this misfire seems to be when i was low on fuel, but i dont understand how i would lose 4 cylinders with a fuel problem. (It looks like my fuel gauge is not reading the same as it used to, which may or may not be due to the new Battery and alternator, which means I may be running lower than I think I am).

If i stop the car and then restart it runs fine again for a bit, then misses again.

When the misfire happens I get check engine light and trac off display. I have checked, but there are no stored codes.

Its a weird problem and maybe I have not explained it well enough, but this weekend I am on holiday with it and going on a 1000km trip to France. I hope to make this without issue.

So if anyone has any ideas I would really welcome them.

Just to add, the fuel filter was also replaced. Only thing not touched is the ignitors.

 

John

[runsgrateasanut]

not really able to give you any advice on what sounds like a complicated problem but I would ask one Q. and also mention something I had happen.

Q. you say a bank of four cylinders is out.  How sure are you that 4 cylinders are out? I imagine that the car would not be at all driveable.  I once replaced plugs and leads and had a misfire.  Found I'd cut the lead to the nearest cylinder one side when replacing the plastic housing.  Also, are the leads properly following the path they should?  Not sure but crossed over leads may possibly cause a misfire? 

sorry I can't be more helpful.

[garagestmarien]

Yes the leads are new and correctly routed with no damage.

It feels like a bank of 4 out as it is the same sound as when I previously tried with one coil unplugged at a time.

It is drivable but with severely reduced power. But got me home.

This is what confuses me, it seems like one bank of 4 are going out and yet seems to have happened only when I was really low on fuel. Maybe that is a coincidence as I can't see a fuel problem causing the misfire.

 

[Malc]

did you check the air filter too ?

re petrol, you usually have about 100 miles left in the tank when the orange light appears

Malc

[garagestmarien]

Yes, brand new air filter. Throttle valve cleaned out. Throttle position sensors adjusted and also throttle and gearbox cables.

The 2 times I have been low on fuel, the orange light has only just come on after the misfire starts.

On filling it looks like I am almost empty.

But still find it strange that it's fuel related.

The only parts I haven't changed are the ignitors.

 

[ambermarine]

John 

Sounds like a fuel pressure problem there was a member who had all kinds of problems with acceleration and engine revs which after trying every possible avenue over a four year period turned out to be a clamp on the fuel filter inlet that had been left in place after a service .

I suggest you check your fuel filter Its at the rear just in front of the nearside rear wheel or if not there up over the  differential.

If you have never changed it it as never been changed in the last 15 years.

[runsgrateasanut]

Have you used injector cleaner recently?  The other worry could be the ECU.  Have the Capacitors been changed as I've read that this can cause all sorts of problems.  You will be aware that they are known to leak.  Someone will put me right if I'm wrong on this.

[The-Acre]

It could also be the fuel filler cap, although not so likely if you had a rush of air when you unscrewed it.  It the cap isn't seating properly and tightened correctly it can cause running problems.  

[garagestmarien]

Thank you all for the replies.

My comments as follows.

The fuel filter is new. It is a K&N race one which has more flow than standard and uses hose clamps instead of the unions. My old filter was 23 years old and nearly fell apart when i eventually got it off. I will post some pics sometime. In fact everything on the car is original, therefore 23 years old, which is a pretty good advert for the quality of Toyota parts.

When I changed the filter, i let both pipes run out a bit to make sure no muck was in them, so am sure no dirt went through the system.

I haven't used injector cleaner and I do have a set of caps to put in the ECU, just haven't got round to it yet.

My fuel cap is the screw on type that has a ratchet so you can only tighten it the same amount each time you use it and to be clear, when i unscrewed the cap at the petrol station, the air was under pressure in the tank and it took a few seconds before the pressure stopped. For this reason I didn't take the cap straight off, rather waited for the hissing to stop. Now it was a hot day and the tank was pretty much empty, but i do wonder if that much pressure should have built up. Is there a vent somewhere?

I have also been all over the car tonight and cleaned all connectors, mad new earth cable for the Battery and just for the hell of it, changed every fuse.

The ignitors are the only thing I haven't changed, but tonight I cleaned and swapped the plugs over.

Starts fine, idles fine, revs nice. So I will see what happens tomorrow on the way to work.

But I am always open to any suggestions from anyone for other things to look at.

[Malc]

17 minutes ago, garagestmarien said:

but i do wonder if that much pressure should have built up.

yes, it's not that uncommon for me to hear this when I'm refilling her on a hot day, a second or two of a huge gush of  " air " .........  I'm assuming it's a little vapour being pressurised and escaping when the cap is unscrewed...............  not likely to be the issue i fear 

Malc

[steve2006]

You appear to have replaced all ignition related components and given the fact that the problem only seems to occur when the fuel tank level is low would suggest the misfire is fuel and not ignition related.

The whooshing noise heard when the fuel cap is released is actually air being let into the tank not out due to the suction of the fuel pump. The problem could be due to a faulty fuel pump producing insufficient rail pressure as the level in the tank drops and the vacuum increases however actually measuring the pump pressure is not easy given the metal pipe work and lack of a suitable test connection point.

A quick check for adequate fuel pressure can be done by connecting a shorting link between the +B and FP connections at the engine bay diagnostic socket and the engine not running, if you look at the passenger side fuel rail you will see a device which looks like a "top hat" where the fuel pipe banjo joint connects. On top of this is a little pop up pin which should fully extend when the link is fitted indicating full fuel rail pressure is present.

When the misfire happens have you released the fuel cap then retightened it and then checked if the misfire has gone?

Have you also determined which cylinders are suspected of misfiring, are they all on the same bank or 2 on each bank?

[garagestmarien]

What I described as pressure in the fuel tank was definitely positive pressure. You could feel it blowing out.

I haven't tried releasing the fuel cap and replacing when the missfire occurs, because since I filled up, I haven't had the problem.

Obviously I need to completely fill the tank so I can the next time see how much fuel I use compared to the gauge reading, which I suspect has changed what it shows slightly.

As for the missfire, I think it is 2 cylinders from each bank as in disconnecting one coil. The engine is still very smooth which I think would rule out random cylinders.

Which leads me to thinking it is electrical and just coincidence with it happening while low on fuel.

Today it seems to have run fine on the way to work, which while this is a good thing, what I really need to know is what is causing the problem so I can get my confidence back.

Also the 2 times this misfiring happened I had check engine light and trac light on, which I don't think a fuel problem would cause. (1994 OBD1 system). On checking, no codes were stored.

It's a weird one, or maybe my car just doesnt want to go to France

[Cotswold Pete]

4 minutes ago, garagestmarien said:

It's a weird one, or maybe my car just doesnt want to go to France

I did wonder if it was fuel pump, and on low tank there is a pressure issue, but reading your symptoms not so sure it's that simple.  Also not so sure the problem relates to capacitors failing, as in my experience that causes stalling after long runs, when you let revs drop.  Not sure if it is worth you giving the chaps at Japex a call see if they have any ideas.

But it would seem like you can get round France so long as you never let fuel go too low, so knowing guage reading accuracy seems like a good thing.

Best of luck with the trip, and sounds like you have way more spare time for replacing so much gubbins.

[Malc]

petrol gauge on mine when on orange shows the gauge/needle  to be totally empty BUT when refilling ( as i always do to the top ) it's only ever about 70 ltrs and I know the tank holds 85.1 ltrs and therefore probably 100 miles left in it at the time.

I'd have no hesitation driving around France for a few 000 miles tbh but i would always totally refill the tank ..............  and avoid it getting to the orange light too.

These cars are designed for Grand Touring in comfort and security.

Malc

[plexus914]

Got a diagnostic code yet? Check your car's evaporative emission (EVAP) control system.

- visually inspect charcoal canister - look for cracks or damage

- (could be clogged) check for clogged filter and stuck check valve and diaphragm

You will find procedure in the repair manual under Emission Control.

Blockage preventing the tank from properly venting. This could be due to a plugged charcoal canister or canister filter, a stuck closed canister close valve, or any sort of blockage in the evaporative system.

[garagestmarien]

So far, no codes stored. I tried the normal set up and the other one where you get live codes while driving and so far nothing. Car is still running fine since i filled up.

But the charcoal cannister is something i haven't checked yet, which i will do next.

 

[runsgrateasanut]

You might want to check Plexus 914 contribution in the following thread as regards Capacitors etc.

excsee fuel consumption

(not my spelling -  but as is)

 

[garagestmarien]

Just as a matter of interest, can anyone tell me where the charcoal cannister is located.

1994 ufc10 engine with traction control. I have looked around the engine bay and cannot see anything.

[Malc]

hi John, when I had my 1994 M reg Mk2 Ls400 I didn't have traction control on my car, neither do I have it on my N re Mk3 1995  ! ( to my knowledge )

Do you have an ordinary Ls400 of that period ?  or is it a rebadged Celsior and an import maybe ?

And I've never heard of this Charcoal Canister thing either on these cars ........  what does it do and where might it be ?

Thanks

Malc

[plexus914]

A repair manual is such a wonderful thing to have, isn't it? 

EVAP system UCF10:

 

 

 

EVAP carchoal canister location UCF20 (model year '95-'97):

 

[ambermarine]

The charcoal canister was not fitted to UK Models of the LS400 as the requirement for preventitive fuel vapour emissions here is not as stringent as the California statute.

They were only fitted to USA imports .

The workshop manuals are based on USA imports as you can see from the diagrams they are left hand drive  and have double A/C radiator fans which UK models did not have,also the brake servo and fluid reservoir is on the left.

[plexus914]

My car (RHD-UK-model '97) is fitted with it. How about earlier models? Let's find out and confirm. 

PS: I look for and take every LS related repair manual I can find....:o)....

 

[plexus914]

Just another hint. Where to look for part number and location:

UK-model Europe RHD year '94:

http://www.japan-parts.eu/lexus/eu/1994/ls400/ucf10r-aepgkw/4_431210_005_/body/7701_fuel-tank-tube/2

[ambermarine]

Sorry Gents 

I have misled you all, the charcoal canister and associated parts are quoted in models from 94 onwards in the toydiy as" Q " says the Mark 4 as it above the fuel tank but I know on the Mark 1 it was not fitted there as I stripped a Mark 1 to the body shell.

I think it might have been hidden below the front bumper below the offside headlight.

[garagestmarien]

Okay,

I am back.

I left for France and drove 880kms without any problems.

Then the car sat for 2 days. Today 27/6/2017 the plan was to go to some shops 30kms away. After about 10 kms the loss of power and missfire cam back and to not be stuck in the middle of nowhere I turned round and slowly drove back to the house. Had a cup of coffee and then went to check the car. As before, it started and ran perfectly. This time i had more than half a tank of fuel, so i could rule that out and also no pressure built up in the tank. The last 2 times this has happened, the car has run faultless for many kms. So off on the journey to the shops again. This time made about 20kms trouble free, then it started jerking up and down the revs, so i pulled in to park and take a look, as i was parking it cut out completely. So I waited a few minutes and restarted, which it did, but held the idle at 1800rpm, i stopped and restarted 2 more times and the same thing. So i figured these were enough revs to make it back to the house where my tools were so i could take a better look. Long story short i made it back. Another cup of coffee and then back to check. Started and ran fine, so i deceided to take a closer look at the connectors. But first i unplugged one coil and founf the car wouldnt start, so plugged it back in and unplugged the other one. The same, wouldn't start, which makes me realise that before when i thought i had lost 4 cylinders, must be wrong as i would not have been able to start it. So while it was idling normal i looked at the vacuum lines and electrical plugs, When i touched the plug on the tps it cut out straight away. It restarted and then when i moved the plug about the idle would go up and down and the roughness would appear that i had before. So i removed the plug and checked the wire and terminals which all looked fine. but i cleaned them up anyway. Since refitting the car runs fine and no amount of wiggling causes the problem again. To the poimt if i unplug the tps while the engine is running the revs rise and when i plug it back in it goes back to 650rpm (at normal temp). So it looks like that may have been my problem all along.

Tomorrow I try to reach the shops again and see what happens. If all is good, I may just order new tps and traction tps modules to be sure.

I will let you know how it goes, I hope this is the answer and I would really like to end this post with FIXED IT! We will see and on one note, to date, I still haven't found the charcoal cannister.

John