Thanks guys!
I’ve treble checked the inlet manifold for leaks as that was one of my early thoughts and it all seems fine but just as a temporary bodge I also whipped a smear of hylomar around all the ports. I’ve smoke tested it as best I can and run 15psi down each trumpet base runner with valves closed and can’t detect any leaks anywhere.
Vacuum is dead steady at 14hg which from the limited info I can find seems ok?the car ran perfectly fine for ten years with a 3.9 motor using the 4.2 ecu so I’m sure the ecu can cope and I’d rather not put newer tech in it.
Til now I’ve been very happy with the easy to test/ simple nature of the 14cux..

Currently while on non cat map I’ve set the afm to 1v, I have tweaked it down lower but it makes no difference to the miss/ fumes. I had it set to 1.8v on cat map. I’ve tried my working til now afm plus a spare that worked fine from a breaker and bought a new blue box one which seems to test out fine and meters up better than my two used ones. No change with any of them.
The misfire is throwing off my normally good sense of mechanics. All 8 plugs look the same/ too rich but it seems like it’s cyls 3&4 that are least happy and down on temperature and have been suspect right from the beginning of the running problem and persistent through this and the previous build before the block cracked.
I can’t recall the fuel trim figures when it was on cat map but they weren’t wildly off and the new lambdas seemed to be cycling just fine..
I did take some screen shots and the only odd factor seemed to be that once fully hot that the idle valve is nearly fully closed. That also made me think air leak but an un metered air leak on cat map would make it run lean wouldn’t it?
Fuel system has been checked many times, I’ve ended up renewing everything from end to end and it tests up perfectly.
If I unplug the afm it stalls but will restart but run worse without it. Unplugged the cts with no change, throttle pot tests spot on, I’ve renewed the throttle spindle seal and checked throttle disc. Base is is set but screw is very close to fully home, like only one turn left to fully closed yet it does the Rev a bit too high from cold start thing that’s usually a base idle/ idle valve prob.
Dizzy has been pulled apart, all good. Tried two sets of leads/ gen cap but do have an expensive new genuine cap/ rotor on its way in the post just in case but I’m sure that won’t be the problem.

I only tried the un metered air check while on non cat map to see what the engine did, assuming with no lambda feedback that if it was overfuelling that a little extra air that the ecu couldn’t see might help? Didn’t help tho.
Compression figures aren’t as good as would like for a new motor but I think that’s partly down to trying to run it in with it running so off. Figures vary from 165 to 185 cold from memory and all go up around 10psi with a wet test. I’m hoping they might get better if I can get the thing to run right as it’s only done 300 miles else i’ll rip it apart and hone/ re ring it yet again.

if theres an unmetered air leak, the MAF will request less fuel, the O2 sensor will request more fuel to compensate, hence your fuel trims would be way off, if they are OK then you dont have an air leak. At least, its unlikely, if the trims get closer to normal with higher revs, that also points to an air leak
what is the MAF reading at idle?
An air leak would cause revs to increase and thus IAC would close to try and correct

sorry only just read the re-ring comment. the rings bed in <100 miles and need some full load action to fully push the rings out to make a good seal that will last

Thanks Kermit, got that about rings. After the build I did the cam bedding in for 20 mins then took the old girl out for a good ring bedding in with plenty of positive/ neg pressure on them over a few blasts counting a couple of hundred miles. At that point the misfire and errant hc emissions stopped play and I’ve been trying to diagnose it since . I think now it’s done too many short drives or idling with poor running and messed up the ring seal. I can’t give it a good run as the mot is out now and I can’t get it through an emissions test. Legally like..

This is the second time I’ve put this engine together in short succession as first time the block turned out to be cracked in no.4 but i took 500 miles to realise why it blew a hose every time I took it out.. it now has fresh turner top hats and more new rings. the running issues with the misfire and cyls 3&4 temps have been much the same since the first build up although first time round all the plugs looked lean which I don’t get but have put to the back of my mind.. right from the beginning it sounded to me like either an air leak or badly timed cam. I’ll eat my children if there’s still an air leak. I found two ages ago- the throttle spindle seal and a tiny blow from the afm to plenum pipe joint. The cam is definitely timed as per spec, I made sure I was really anal about it til I felt like I’d worn no.1 lobe out testing..
I did the add air via vac stub the other day with the car on a non cat tune so that the 02 sensors wouldn’t get involved just to see what affect it would have on mixture as over fuelling had been suggested and it seemed like a plausible way to alter the mixture for a moment? Currently maf is set to 1volt while on non cat tune and I had it set to 1.8 volts previously when it was on a with cats tune.

I went back through my photos and with the car hot after a drive on a cat map, fuel trims settled it was showing + 20% for one bank and -18% for the other so it seemed to me that the lambdas/ ecu weren’t showing major signs of the misfire?
I don’t know how much the cam and bigger valves would throw off the fuel map/ lambdas from their expected zero point.

Fuel trim min/max is usually 25, so yours seem quite off with too rich and too lean.
Have you tried running without the maf? You might see one of the values go closer to zero.
Just my opinion, but i would expect the ecu to add fuel if you introduced an air leak

OK, sooooo this is a real niggly little one. Mechanically everything seems to be where it needs to be but there is still a misfire and fuel trims not quite right. With Rovergauge, can you see the O2 sensors, what they are feeding back to the ecu? Where you have been running the engine in non-cat tune, it is possible the O2 sensors and/or cats have been adversely affected. I don't have a vast experience of lambda controls but I would be inclined to check the Lambda control. If you have a couple of known good used O2 sensors, try swapping them in and see what happens. A couple of years ago I helped a guy with a Westfield SEight, it was fine cold but as soon as it warmed up and switched to Lambda control it ran super rich and misfired and basically didn't want to work. Checking the system found there was no power to the O2 sensors. After fixing this, it was found that the rich running had stuffed the sensors, I found this out by substituting the sensors with a couple I had. With working O2 sensors, it ran like a top so I would suggest it is worth investigating.

I know the best way to check the O2 sensors is to hook them up to an oscilloscope but a voltmeter should be able to show them switching hence the question about Rovergauge. Also, have you reset the ecu? With the various messing about a reset would probably be a good idea.

Thanks guys, ideas much appreciated.

I have tried running it without the maf and it ran just a touch more off at idle, I didn’t have roverguage plugged in at the time so I don’t know what it would see, will add it to the list of things to try.

It’s only been running a non cat map for a few minutes idling and not driven as I wanted to see what it would run like without lambda feedback altering the basic fuel settings, I’ve been trying not to run it any more than I have to til I’ve sorted it as I’m concerned about carbon build up and fuel down the bores now.

I haven’t checked the lambdas with a dvm but they are brand new ntk ones fitted when the engine went back together this time as one of the old ones was sluggish to respon so they have only done 300 miles but are probably quite carboned up as the exhaust is.. On roverguage with a cat tune selected they show to start cycling in less than a minute from cold start. I’d have to get the car mica and hot again now to allow the trims to settle as the ecu has been disconnected a few times while testing.

Ive tried all the tests with a spare 4.2 ecu and there’s no difference but for the sake of it i’ll also try an older 3.9 ecu i have in the boot for failed wading emergencies which I know the old 3.9 ran on just fine.
I need to try and find a garage that will let me stick it on a machine so I can get a good idea of emissions I think. My trusty old Gunson is saying 1.6% co, I’ve no idea of hc now except it stinks, might help in determining what’s going on.

Hi Rusty, gas analyser would be useful for sure. FWIW there is no difference between a 4.2 ECU and a 3.9 ECU I am aware of.
Since rebuilding and ragging it around a bit, have you checked/re-torqued the head bolts? It is a bit left field I know but you seem to have tried everything else. Other thoughts include checking the alternator output and what's the battery like? I would also say double check ignition wiring (HT and LT) and maybe undo, clean and reassemble the main earth points, pay particular attention to the efi loom and the main engine earth.

After that I am just about out of ideas and would be tempted to pop the top off again to replace the valley gasket and reassemble ensuring the ram housing and plenum are clean and sealed. I think you could probably leave the heads alone but maybe just take off the rocker covers and check the head bolts.
Good luck.

Thanks Kev.
I haven’t given up yet but i am pretty much out of ideas too.
I cleaned up the braided earth strap by the coil last week while pulling apart and checking the lt wiring. By main earth you mean the one to starter bolt?
Ages ago when putting the engine back in the car turned over really badly and i assumed the battery was weak. Turned out I’d left that earth stuffed inside the inner wing.. i put it back on and magically the starter whizzed like it should do!.
I know I cleaned the efi earths on back of head when it all went together but I’m going to go over all the efi wiring so i’ll whip the earths off and double check.
I’ve also bought a little smoke tester that should perform better than my home made one so i’ll give double checking for air leaks a good go when I get time.
I have to do a run up to snowdonia in June and if I can’t do it in the rangie I might just throw my toys out the pram and buy an old jap 4x4...

Glad you haven't quit!
If you're going to Snowdonia you'll be passing quite close by, why not drop in and say Hi.

Thanks Kev.
I’m not sure if I’ll have time on the June trip as it’s just a weekend run up to scatter my uncle atop snowdon with some of my family and it’s looking lile the rangie wont be ready by then. I’ll definitely be up a few more times in the year though so it would be great to pop round.
I’ve done a bit more probing on the car and it’s still not looking good.
I’ve not had much time on it so I’ve taken a few short cuts but as I’ve either tested or replaced everything more than once anyhow I’ve taken the shotgun approach this week..

I bought one of those cheap Chinese smoke testing machines to double check for vacuum leaks. It’s a bit poorly made but it made good smoke and found two small leaks-
A teeny tiny one from the round Lucas stamped end plate on the throttle position sensor, will put a dab of superglue round it i think and a small one I can’t see round the back of the plenum either from the idle valve mounting/ vac stub or possibly a kick in the hylomar between plenum and trumpet base. I don’t think either leak are big enough to be causing the problem though.

I tried swapping cyls 4&6 injector loom plugs over in case it was a wiring issue causing pot 4 to run colder. No difference.after running for one minute I have 6 cyls running at 400 deg c and pots 3&4 at 250 deg. Misfire remains the same. Very noticeable at cold start and quietens as engine warms but remains.

I stuck colourtune plugs in pots 4&6 to see what they look like. Both pots seem to be much the same with mostly blue combustion with similar occasional bright orange flashes.

I ran the engine for only a minute or two before whipping the plugs out to put the colourtune plugs in and plug 4 was partially wet and smelt more of fuel than yhe other plug but on wiping it with my finger it seemed more like clean oil than fuel so i’m thinking it may have just been a stray bit of baby oil from the smoke tester yesterday as it did seem to spit a fair bit of oil into the induction pipe. Shining a bright penlight down both plug holes made me cringe at how much black crap is on the piston crowns. Looks more like a 150k mile engine than a 300 mile one.. I’m starting to think this is something more major mechanical rather then efi or ignition even though I was 110% sure the engine went together spot on.
I also have a new emissions tester in the form of my neighbour who came around to complain after I’d run the car for all of five mins as I was stinking his house out.. sadly he’s not a petrol head but I might complain next time the smell from him smoking weed wafts onto my property.
Maybe I should buy a disco3 and spend my time fixing air suspension and electrical faults instead!.

Hi Rusty! For sure pop round if you're up in N.Wales, I might have something of interest so I'll drop you a PM.

Anyway, I agree, very small air leaks from the TPS and maybe a bit from the plenum wouldn't necessarily be a big issue and it doesn't explain the low cylinder temperature on No.4; potentially you would also have unstable vacuum readings.

There can't be many other possible causes. I think you've discounted sticky valves, again this would show up on a vac test but I wonder if stuck piston rings on No4 could explain it? The problem here is that the only way to find out is to tear down the engine again. It doesn't sound like an efi or ignition problem an din the absence of a suggested electrical fault/problem I thin you are right to consider a mechanical source. Whether or not it would be a major mechanical issue is debatable because the engine does actually fire and run suggesting the basic requirements are there unless it is something crazy like a holed piston on no4 but other tests say not likely. Not sure I can offer any other thoughts.

As for buying a Disco 3... I did! So far no suspension problems and no big electrical issues either. I've done a lot of other things because it is best to know they are done, brakes, fluids and filters etc. but I have to say I really like it.

In other news, I sold my RRC. It has gone to a new home, I was sad to see it leave but knew it was time.

Hey Kev,
I thought you were a dyed in the wool classic man but I do hope you enjoy the disco3!
I think the are the last of the line before they went all too plastic. I bet it’s a lovely drive.

That made me chuckle as the more I get fed up with this engine issue the more I hover over bidding on one myself.. I have a car dealer friend who’s able to hook me up with an array of bargain ones or older l322’s all needing gearbox or suspension work. I haven’t quite given up just yet though..
I’ve decided I need to rip it apart again and see what on earth is going on inside the motor. Gaskets and some elbow grease won’t cost too much..
I’m betting on a valve issue or something. I’ll start logically checking valvetrain/ cam lift etc on my way down to the pistons/ rings. i’m undecided on what to do with the cam, I don’t think it can be at fault in design, even another v8 supplier said they are fine and I know other people have used the same cam and not had issues. off idle the car has so much more power than its ever had but the shotgun is at the ready to just pull it out and fit something that someone can guarantee will work, preferably with a similar power curve as I don’t want a low revving tractor, I like to hear the v8 rev after years of it not pulling past 4.5k with the old original engine.

If I can I’ll clean up a pair of standard heads and just put them on for now to eliminate the fancy big valve work but I’m mid moving my workshop so all my tools are in storage and i only have my kitchen to tinker in.
I’ll let you know what I find once I pull it apart.

Hahahahahaha I liked that. To some extent I am indeed an RRC kinda guy but I couldn't get around the fact I can't stay on my feet too long and I now have restricted mobility and iffy balance because my feet/ankles don't work properly which means keeping a 30 year old RRC on the road is just a bit too much for me. The Disco 3 has, so far, been quite a revelation. It is indeed nice to drive and in most cases would see off the poor old Rangie on and off road. Can't wait to see if it is any good in snow but the electronics can be both a blessing and a curse whereas the old Rangie it was just a case of deciding if you wanted to go death or glory with a screaming V8 and all 4 spinning like mad - have to say I rather enjoyed that, a sideways Classic making all the right noise... fantastic!

Anyway, do let me know what you find, if you want or need to bounce anything around or look for alternative thoughts and theories just drop me a PM.

Thanks Kev. You have been a mine of information and help as always and i’ll Keep you informed of what happens here.
I’ll hopefully start work on the engine at the weekend.
If nothing else then this problem has been an education for my 10yr old daughter who now has an unhealthy knowledge of how v8s work! Or not.. when I told her there just might be another lse needing a resto she asked what work it needed and entirely understood the list then asked if we could find somewhere to work on it and save it..

After your fall I don’t blame you at all for getting a newer landy, I hope it treats you well!

No worries Rusty, you're welcome to pick my brain if you can find it! Nowt wrong with getting the youngsters educated in how things used to be done, even better if she wants to learn and likes to get oil under the fingernails. I think it's great if your daughter understands and appreciates the venerable old RV8, have you taught her to weld yet?

Take care, no doubt we'll touch base again soon.