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Diagnosing 1UZFE V8 overfueling in LJ70. Let the games begin...

Rusty Bottoms

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Hi everyone, as some of you might know, I recently picked up a rather nice looking 1988 LJ70 with the Toyota 1UZFE V8 conversion - again some of you may have recognised it as one of the forum member's old LJ builds.

From what little information I have been given, seems West Coast had it for a long time after the V8 install trying to sort some running issues, and from the receipts I have, it seems the now defunct Thor Racing had a go at solving the engine problems after it left WC. The seller didn't offer much information, I didn't ask a ton of questions really, and it had a slight misfire just off idle when I bought it. But hey, it made it home 360 miles!

Well, it drove home ok, a slight misfire in town, but ran fine in the end on the motorway and pulled like a freight train on hills only using half throttle.

I had it booked in for its MOT tomorrow (expired about three weeks ago) but ended up canceling.

Yesterday and today it is fouling all eight spark plugs like nobody's business - completely black and soot covered, and runs very rough - without the MOT I can't legally drive it to clear the plugs and it misfires pretty badly as it's loading up on fuel.

So time to get the multimeter out and start diagnosing. The engine itself is ok, compression and all that, but of course there are a ton of possible faults causing this problem - given a 25 year old complex motor with a ton of electronics plonked into a 28 year old diesel truck with lots of wires running amok...which I shall eventually tidy up in new looms.

Fun, but I figured owning it at first wouldn't be that easy.

After reading forums specifically on the 1UZFE motor, I am starting from scratch and going through the whole lot methodically, so I expect this will take some time since two garages could not fix it.

Again, it blows smoke when cracking the throttle and is running very, very rich - I bet I've only seen plugs that fouled maybe 3 or 4 times in the past 30 years. Covered in black fuzz and soot.

I started unplugging and cleaning connectors, while spraying for vacuum leaks as well. I unplugged the MAF and it stalled immediately. This apparently means it is something else, as it should default into limp-home mode if the MAF goes south, but I'm not trusting the MAF 100% just yet.

I took the ECU out tonight and will inspect the capacitors for leakage and solder new ones in if needed. From there after getting the right diagrams I will check ground connections and make sure the MAF and other sensors are getting the correct voltage. Looks like someone may have replaced the MAF, but there are two different types and the wrong one is, well, wrong!

I bet at the end of the day is it something simple, either no/low voltage to the right part, bad earth connection or something like the coolant temp sensor telling the motor it is -25C outside or a mass of gunk on the crank angle sensor...I don't think it is related to specific ignition components such as HT leads or dizzy caps (two), as all eight plugs are fouled, not four, so something is telling it to pump fuel like mad.

I don't know if anyone on here messes about with 1UZFE conversions, but it would be interesting to chat to them. Otherwise, the swap is common in Australia and New Zealand, and to a lesser extent, the states, so fortunately there is a lot of info out there for me to chew on.

If anyone has any thoughts, they are welcome to throw them out there. I WILL get this sorted as I miss driving it already!
 
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Good luck Rob, I will be following this closely as I'm currently gathering the parts for my conversion. :thumbup:
 
I am no good to you whatsoever with this but my immediate thought was timing is out .

Setting it correctly would i imagine be child's play to the experts you mention and i will guess the previous owner knew how to set it too . So why won't it stay set ?

Inexperienced guesswork from me is all .
 
I am no good to you whatsoever with this but my immediate thought was timing is out .

Setting it correctly would i imagine be child's play to the experts you mention and i will guess the previous owner knew how to set it too . So why won't it stay set ?

Inexperienced guesswork from me is all .
Hey Shayne, Yeah I'm tempted to just start replacing electronic parts, but the pockets are a little empty after buying it! Ha. I think the ignition timing is set by the ECU and timed off the crank angle sensor, not adjustable as far as I know, but will do some research on this. I see it has a new cam belt, just wondering if one of the cam gears on one side is a tooth out?? These are not interference motors from what I've read, so it would run w/o damage to the head. Possibly. Anyway, the plot thickens, I'll have to recall some of my skills from my mechanic days, I worked on German and Japanese motors for about 10-12 years, mostly 80s and 90s motors. Can't believe I'm getting that old already!
 
Stupid things first, blockage in the air intake, does it have a map sensor? Is there any way to get fault codes out of the ECU? Possibly linking contacts. Is the fuel pressure too high?

Just a few thoughts.
 
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Not sure on how these engines are mapped, but it might be worth plugging it into some kind of diagnostics to monitor everything going on. With my VW I use a system called Vag com and I can pretty quickly pick up problems by seeing actual sensor values, cross referencing them with a baseline value.

Also does your 1UZ have Variable valve timing? I believe the later gen engines came with it...
 
Is there an O2 sensor (or plural - there may be an up and downstream one on the 1UZ)? If that's missing that will lead to overfuelling as it won't pick up what's going into the exhaust, and therefore not feed back into the system properly.
 
Just for reference, and reading material, as this post got me curious and I started looking I found this post and thought that the gent who wrote this may be worth contacting.
If you have already seen it then please disregard.
 
Stupid things first, blockage in the air intake, does it have a map sensor? Is there any way to get fault codes out of the ECU? Possibly linking contacts. Is the fuel pressure too high?

Just a few thoughts.

Not sure on how these engines are mapped, but it might be worth plugging it into some kind of diagnostics to monitor everything going on. With my VW I use a system called Vag com and I can pretty quickly pick up problems by seeing actual sensor values, cross referencing them with a baseline value.

Also does your 1UZ have Variable valve timing? I believe the later gen engines came with it...


Is there an O2 sensor (or plural - there may be an up and downstream one on the 1UZ)? If that's missing that will lead to overfuelling as it won't pick up what's going into the exhaust, and therefore not feed back into the system properly.

Just for reference, and reading material, as this post got me curious and I started looking I found this post and thought that the gent who wrote this may be worth contacting.
If you have already seen it then please disregard.

Wow, thanks everyone, some good questions here. Where to start - I'll see if I can pull diagnostics from the port on the motor this morning. I'd also like to check vacuum hose to fuel reg on the rail for any funny business. I might pull the fuse for the fuel pump and let the motor run till it quits to clean the plugs temporarily without having to remove all 8 of them again (backyard engineering, ha!)

The motor is out of a 1995 Lexus LS400 based on the ECU serial and an owners handbook which was with the paperwork when I bought it, so no variable valve timing, that's one thing not to worry about.

This one doesn't have individual coil packs, rather two distributors, one on the front end of each head, the plugs are easier to get to than I first imagined, which is good as I'll probably be removing them several times in the near future...

I spotted one O2 sensor downstream, there must be a second on the other manifold, will verify this today - I'm afraid to see how dirty they are, but if they come out, I'll clean them and run a multimeter check.

Thanks for the Lextreme post - I had seen this but will save the link, a ton of reliable info here from someone who really knows these motors inside out.

As a 'Plan B' in lieu of throwing money on new coils, igniters, etc. etc., I've emailed Phil from ExtraEFI in the UK who sells the Megasquirt engine management system, so if my work is steady this autumn I may just start from scratch and run an aftermarket engine management system, I've heard some good things about the megasquirt. And I could plug my laptop in and get live engine parameters! (May need deep pockets though). If I can't afford the plug n play set-up, I might go for the controller and make some looms as and when, but I'd like to be driving this again before Christmas!

The other extreme option is to just buy another complete running motor and ECU (£450 on up) and start swapping bits left and right till she goes, then maybe sell the motor on! This would actually be cheaper than the megasquirt.

We have a four week old baby girl, so I may not be able to work on it everyday, but hoping for a fix in the near future. Thanks for the input everyone - I will definitely keep you all posted. 9/10 it's something simple, says I... Cheers!
 
I spotted one O2 sensor downstream, there must be a second on the other manifold, will verify this today - I'm afraid to see how dirty they are, but if they come out, I'll clean them and run a multimeter check.

You'll be as good just to through a new O2 sensor in as opposed to cleaning it - they are a probe as much as anything that does clog over time; they really are a wear item that people don't realise.

As a 'Plan B' in lieu of throwing money on new coils, igniters, etc. etc., I've emailed Phil from ExtraEFI in the UK who sells the Megasquirt engine management system, so if my work is steady this autumn I may just start from scratch and run an aftermarket engine management system, I've heard some good things about the megasquirt. And I could plug my laptop in and get live engine parameters! (May need deep pockets though). If I can't afford the plug n play set-up, I might go for the controller and make some looms as and when, but I'd like to be driving this again before Christmas!

The other extreme option is to just buy another complete running motor and ECU (£450 on up) and start swapping bits left and right till she goes, then maybe sell the motor on! This would actually be cheaper than the megasquirt.

A couple of my mates run MS in their cars (replacing Bosh LH2.2 or 2.4) and have done the whole lot themselves from the kit. If you can get hold of a basic tune map then that's a really good starting point, and as long as you all the sensors plugged in correctly it's not too bad to tune on the fly - we re-tuned a car over a 5hr road trip once with the laptop on my lap and pressing re-map every so often!
 
You'll be as good just to through a new O2 sensor in as opposed to cleaning it - they are a probe as much as anything that does clog over time; they really are a wear item that people don't realise.



A couple of my mates run MS in their cars (replacing Bosh LH2.2 or 2.4) and have done the whole lot themselves from the kit. If you can get hold of a basic tune map then that's a really good starting point, and as long as you all the sensors plugged in correctly it's not too bad to tune on the fly - we re-tuned a car over a 5hr road trip once with the laptop on my lap and pressing re-map every so often!

You'll love this Ed - one of the O2 sensors is missing and the plug is just hanging next to the block. The clutch slave cylinder is in the way of the mounting for the O2 on the left side (as you sit in the car) of the motor, so they just ran a blank into the port and called it a day! I don't know if it can even run closed loop on one O2 sensor... this may partially explain the running rich symptoms.

On top of that, the wiring harness ground connector on the right cam cover was loose, the bolt was finger tight. Just for the laughs, I disconnected it while it was running, and it didn't change a thing! It had not fully warmed up yet, but I strongly suspect it only runs in limp-home mode or open circuit at best. I do notice the idle speed drops right down after it warms up a bit. It was running pretty good today, I pulled all eight plug wires in turn, and each cylinder dropped when I did this. So... lots to check still.

Whoever did this installation did a pretty poor job, there are tons of little things I need to sort, some of it is pretty shocking, but it can all be fixed with some re-routing and fixing in place.

Waiting to hear back from megasquirt, this may be my salvation!
 
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You'll love this Ed - one of the O2 sensors is missing and the plug is just hanging next to the block. The clutch slave cylinder is in the way of the mounting for the O2 on the left side (as you sit in the car) of the motor, so they just ran a blank into the port and called it a day! I don't know if it can even run closed loop on one O2 sensor... this may partially explain the running rich symptoms.

On top of that, the wiring harness ground connector on the right cam cover was loose, the bolt was finger tight. Just for the laughs, I disconnected it while it was running, and it didn't change a thing! It had not fully warmed up yet, but I strongly suspect it only runs in limp-home mode or open circuit at best. I do notice the idle speed drops right down after it warms up a bit. It was running pretty good today, I pulled all eight plug wires in turn, and each cylinder dropped when I did this. So... lots to check still.

Whoever did this installation did a pretty poor job, there are tons of little things I need to sort, some of it is pretty shocking, but it can all be fixed with some re-routing and fixing in place.

Waiting to hear back from megasquirt, this may be my salvation!

Simple fix for the O2 sensor that isn't there... get an O2 sensor that fits the plug, and find a nut that is the same thread. Step drill a suitable size hole into a convenient spot and weld the nut on, screw in O2 sensor and the problem is solved. My O2 sensor actually came with a new mounting flange so we did that and welded the flange on - instant improvement of 3L/100km; instead of 14L/100km (20mpg) it now does 11L/100km (25mpg) on a good run!
 
Simple fix for the O2 sensor that isn't there... get an O2 sensor that fits the plug, and find a nut that is the same thread. Step drill a suitable size hole into a convenient spot and weld the nut on, screw in O2 sensor and the problem is solved. My O2 sensor actually came with a new mounting flange so we did that and welded the flange on - instant improvement of 3L/100km; instead of 14L/100km (20mpg) it now does 11L/100km (25mpg) on a good run!

Ah great stuff, will go that route. I just ordered a new o2 bung to weld on from ebay. I found a couple of toyota o2 sensors I think will work (front sensors, plug looks correct). Going to bite the bullet and order two of those today. Got to start somewhere, and this seems as good a point as any.
 
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Good luck with it Rusty. I hope it is 'that simple'.

3 years and counting on my Smart, complete engine rebuild and new ECU from Merc (£700 plus coding) and now has a cursed gearbox fault. I remember feeling elated as it looks like you do, to find faults that I thought were causing problems.
 
Good luck with it Rusty. I hope it is 'that simple'.

3 years and counting on my Smart, complete engine rebuild and new ECU from Merc (£700 plus coding) and now has a cursed gearbox fault. I remember feeling elated as it looks like you do, to find faults that I thought were causing problems.
Me too! Hate seeing it sit. Wished it ran as well as it looks. I have two new lambda sensors and a set of plugs on order to start, and am going to weld a new bung in the down pipe where they left out the nearside lambda due to interference with the clutch slave. I suspect the engine has never run in closed loop. I've been reading an article on wiring up the 1UZFE so I can start the epic task of checking for continunity from the ecu end of the harness to the sensors. There are exactly 50 wires coming off 4 plugs on the ECU that are required for proper running, so I get to chase all those out, but once I know they are good, then I can start eliminating the rest.
Hope you get yours in shape soon!
 
There are exactly 50 wires coming off 4 plugs on the ECU that are required for proper running,

Hope you get yours in shape soon!
Thanks, in truth it has all but beaten me. I cannot spend another penny on the damn thing and now hate it with a purple passion.

Watch out for wires that are joined inside the loom.
 
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Me too! Hate seeing it sit. Wished it ran as well as it looks. I have two new lambda sensors and a set of plugs on order to start, and am going to weld a new bung in the down pipe where they left out the nearside lambda due to interference with the clutch slave. I suspect the engine has never run in closed loop. I've been reading an article on wiring up the 1UZFE so I can start the epic task of checking for continunity from the ecu end of the harness to the sensors. There are exactly 50 wires coming off 4 plugs on the ECU that are required for proper running, so I get to chase all those out, but once I know they are good, then I can start eliminating the rest.
Hope you get yours in shape soon!

Great work so far Rob. :thumbup:

Fancy a holiday down under when you've finished yours? Probably going to need a hand getting mine running. :icon-wink:
 
Thanks, in truth it has all but beaten me. I cannot spend another penny on the damn thing and now hate it with a purple passion.

Watch out for wires that are joined inside the loom.
Sorry to hear that, some motors just don't want to go right! Thanks for the tip on the loom, as many techs had theirs hands on this, it could be something just like that...
 
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