V8 Engine swap- can't get running right.

I have recently had fitted a 3.9 V8 from a Disco into my ex army 2.5na 110, fitting the new engine, converting the R380 to fit etc has all gone well but getting it running right has not. The efi system from the donor was a mess, it had been previously converted to LPG, various electrical connectors had been soldered and messed around with. For simplicity I decided to go for an edelbrock/weber 500 carb instead and no LPG system, the mechanic who helped fit the engine thought the issue is carb related and suggested taking it to a specialist to be set up, carb specialists are a dying breed and that's not been practical with lock down. I have been trying to resolve the issue myself, I have researched the carb setting up (loads of info on youtube via USA) and they appear relatively straight forward, I am not convinced that us the issue. I am in the unpleasant stage of every day thinking I have found the solution, getting excited and buying parts but when fitted it's no better, it's become the proverbial money pit! plus single figure mpg as I do road test!

The issues are:

• At factory timing settings, ie 4-6BTDC static the car will idle but bady misfire at 2-2.5k rpm, this includes a back fire that is a can be exhaust and intake.
• The engine needs to be significantly advanced c.20 degrees BTDC to rev beyond 2.5k rpm
• The car then has a lighter misfire and reluctance to gain revs beyond 4-4.25k rpm
• Engine pinks under light load due to the excessive base timing
• The timing position influences at what point in the rev range it misfires
• There was evidence of arcing on the inside of the distributor, this was affecting two posts. Black burns.

The areas I have checked are:

The pulley/harmonic balancer tdc markings against having a rod in the spark plug hole indicting tdc is in position
I have treble checked the firing order is correct
I have removed the rocker covers and checked for any broken valve springs or obvious play in valves
The carb is brand new and regulated to spec at 5.5psi
I have tested for vacuum leaks nothing obvious, a vacuum gauge shows 21"hg at idle
I have measured carb float bowls and set to factory spec
I have removed distributor and visually checked springs/weights are present, when the top shaft is turned the weights move out and spring back. I marked the no.1 position before removing.
The vacuum advance is new and is working
The ignition pick up air gap has been checked, it was slightly larger than spec and readjusted.
The cap and rotor are supposedly good quality made by Beru which I have used on other cars without issue. Have replacements on order.
It has new 8mm premium HT leads, cables are not touching
New NGK B6BPES plugs
New bosch coil
New ignition amplifier
The carb is jetted to this engine size

Some thoughts I have had include were changes made by previous owner to the distributor/distributor position somehow as a function of being LPG fuelle? I don't know anything about LPG systems but have read the timing requirements are different. I am toying with buying a distributor as it's the last piece of the ignition to change but a good one is expensive

Any thoughts would be greatly appreciated.

Unless one of the electrical advance gizmos (such as the A&R sold by RPi for example) is fitted the dizzy would just be much further advanced to get the best out of LPG. Without the gizmo & running as dual fuel you'd just advance the dizzy as far as possible to still allow running on petrol. Best set by road test.
Pattern dizzy caps should be avoided - I had issues with one some years ago, very poor inside, lead pickups fully exposed, not just the part that faces the rotor & none of the shielding ridges you find inside a decent one. Misfire at higher revs (60/70 mph) when dry & persistent misfire in damp conditions. On both fuels.
Avoid rotor arms that have the metal strip riveted to the plastic.

Thanks for the reply, I had wondered if someone might adjust the mechanical advance curve in the distributor to suit an LPG engine. I have swapped the cap and rotor/HT leads and have been able to move the misfire up to c.5k rpm with base timing very advance, if I lower timing down to 6 degrees the misfire is at 2-3k rpm. When I hold the strobe light on the pulley and rev, the mech advance adds about 10 degrees, I cant tell as it's off the scale but roughly to that indent in the harmonic balancer, as the only item left that's not new in the ignition system is the distributor I have ordered a new one. I have also bypassed the fuel regulator to make sure it was nt fuel starvation and it ran the same.

Something simple, what voltage coil do you have fitted? Does the setup have a ballast wire or resistor in the circuit and you have a 12V coil, trying to run on 7V? If you have a 12V coil, try running a lead directly from the battery to the coil to see if that helps to solve the problem. If so, then you have a path to tread.

About the only way you will get a misfire from a fuel related issue is if you have a very lean mixture. With the carb you have that would be either low float level (which you don’t have) or too small main jets which you also discount. Have you tried edging on the choke when the misfire starts to see if that makes a difference? Just something else to try. With a 500CFM there shouldn't be an issue with capacity and the engine will not come close to reaching the capacity of the carb.

Thanks for the response. I have bypassed the ignition amp (a new premium one) with one that came with the new distributor and there is now no misfire.

Sounds great! What has happened to "power" & "MPG" now?

I have been able to better test the car this morning after bypassing the amp last night, the misfire has gone and I can rev beyond 4k rpm which I could not before. It still had the ignition timing quite advanced, I have today tried to set the timing to c.6degrees BTDC, whilst the car will idle at the setting it will stall when I accelerate, I can mitigate it wanting to stall by advancing the engine timing, I suspect its needing c.18-20 degrees at idle which is alot less then before swapping the amp. It's suggesting something else is array. I have also adjusted the idle mixture screws to see if it was a fuelling issue and that did not change the issue. Not been able to do a meaningful road test yet.

After having done the engine swap and three months of chasing this issue, it's nice to be able to open the throttle, the secondary jets come on strong and you can feel a surge of power the car. I have not been able to do any MPG tests, has been c.11mpg since fitting the engine, I am hoping to better this but having had a 3.9 RRC I don't expect much more on the short journeys I do. A new issue has presented itself which is a clunking through the transmission when reversing or moving forward at slow speeds, the impact of the clunk is influenced by whether the clutch is engaged or off. I am assuming its the transfer box knackered now.

Sorry if I've missed anything in this thread but i think i read is not electronic ignition, ie has contact breaker/points?
Have you replaced the condenser? Even new ones can be duff

15MAS said:

A new issue has presented itself which is a clunking through the transmission when reversing or moving forward at slow speeds, the impact of the clunk is influenced by whether the clutch is engaged or off. I am assuming its the transfer box knackered now.

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Common problem on many older Land Rovers is the 'A'-frame ball joint.
Makes its presence known by a loud clunk as you reverse or drive away, esp from stationary.
Use a pry bar & lever the A frame away from the axle. There should be no play in the ball joint but when they clunk they're usually well gone - had this on my RRC.
Don't bother trying to get the old one out of its carrier on the vehicle, remove joint & carrier.
May be best to get a friendly garage to press the old one out & the new one in. Well known for being tight.

ETA. Was trying to find this earlier. Seems to be OK despite photobucket's attempts.: https://www.landyzone.co.uk/land-rover/a-frame-balljoint-renewal.110342/

Ratae said:

Common problem on many older Land Rovers is the 'A'-frame ball joint.
Makes its presence known by a loud clunk as you reverse or drive away, esp from stationary.
Use a pry bar & lever the A frame away from the axle. There should be no play in the ball joint but when they clunk they're usually well gone - had this on my RRC.
Don't bother trying to get the old one out of its carrier on the vehicle, remove joint & carrier.
May be best to get a friendly garage to press the old one out & the new one in. Well known for being tight.

ETA. Was trying to find this earlier. Seems to be OK despite photobucket's attempts.: https://www.landyzone.co.uk/land-rover/a-frame-balljoint-renewal.110342/

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Thanks. I will check that out.

kermit_rr said:

Sorry if I've missed anything in this thread but i think i read is not electronic ignition, ie has contact breaker/points?
Have you replaced the condenser? Even new ones can be duff

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It has electronic ignition, the donor car was a 1995 serp belted Discovery engine. I have managed a proper test drive tonight and its' still not right, whilst I have it idling there is a slight hesitation as the engine is revved, not a misfire but more a bogging. A gentle throttle seems better, beyond that initial take up it drives well, noticeably more responsive and requiring less throttle to maintain speeds. If I advance the ignition further it does improve it drives normally, it's also proving tricky to start when warm (which it was ok before swapping the amp and fiddling with timing/carb!).

Did it ever run right? If not then I'd go back to basics check the cam and ignition timing, check the valves are all fully opening and closing, reset the carband take things from there.
What colour are the plugs when it's set up 'right'?

kermit_rr said:

Did it ever run right? If not then I'd go back to basics check the cam and ignition timing, check the valves are all fully opening and closing, reset the carb and take things from there.
What colour are the plugs when it's set up 'right'?

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Yes, I ran the donor car for a while and it was ok. The ignition timing is one of the issues, it needs a lot of advance to run, I have had the rocker covers off while and started the engine, no obvious issues. I need to recheck the plug colours. I am increasingly convinced there is an issue with the ignition system, perhaps the previous (more powerful) amp exaggerated the problem and caused the chronic misfire. I am planning to go back to basics on the ignition wiring, also tempted to buy genuine lucas cap and rotor arm but the reviews are mixed. I noticed that there is an additional wired connected to the coil negative terminal which I don't know what it does and disappears into the loom conduit. I did some more testing last night, varying timing as I drove round. The car is difficult to start and hesitant/round on the initial take up of the throttle but once seemingly ok at higher revs.

it does sound like ignition to me, as though its not advancing as revs/engine load increase, yet you say the vacuum advance is working. how have you confirmed this and have you tested in situ?

kermit_rr said:

it does sound like ignition to me, as though its not advancing as revs/engine load increase, yet you say the vacuum advance is working. how have you confirmed this and have you tested in situ?

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It does mechanically and vacuum advance, it now has a brand new distributor, when I rev it I can see with the timing light that is adding advance.

Have had a breeze through this; sounds like a nightmare.
21" vacuum at idle is pretty strong. My 3.9 only makes 15".
Your ignition timing is very advanced. AFAIK the 3.9 was never made for carbs so ignition timing, advance curve and then valve timing, lift and duration would have been set up for the efi. Clearly a carb conversion is nothing new on a 3.9 so it will be something simple.
Apologies if I have missed it but I would suggest playing about with the jetting. Have you also considered the exhaust? Is it big enough or is there any restriction affecting the way the engine breathes?
BTW the wire off coil neg would probably have been the efi run signal wire so I wouldn't worry too much about it.
HTH, good luck and don't forget to post how it goes.

classic kev said:

Have had a breeze through this; sounds like a nightmare.
21" vacuum at idle is pretty strong. My 3.9 only makes 15".
Your ignition timing is very advanced. AFAIK the 3.9 was never made for carbs so ignition timing, advance curve and then valve timing, lift and duration would have been set up for the efi. Clearly a carb conversion is nothing new on a 3.9 so it will be something simple.
Apologies if I have missed it but I would suggest playing about with the jetting. Have you also considered the exhaust? Is it big enough or is there any restriction affecting the way the engine breathes?
BTW the wire off coil neg would probably have been the efi run signal wire so I wouldn't worry too much about it.
HTH, good luck and don't forget to post how it goes.

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The carb has been jetted to the engine, I used an MOT emissions sniffer and was getting good AFR readings at part open throttle etc. I found the additional wire on the coil was a feed for the fuel pump relay that I had n't noticed, it thought it was wired to the amp, I have since created a new switched live connection so the feed to the coil is clean. I have gone through all the electrical connections in the ignition making sure they are sound, soldering the connectors to the wires etc. The inside of the distributor cap does show some signs of arc on the terminals, I am alternating caps/rotor arms to see if they make any difference. When I run the car with the premium amp the throttle response seems crisper and drives better, more power but misfires at 4k rpm plus, when I bypass to the standard it feels less crisp, less power but no misfire. Yesterday I scaled off the timing markings and marked the pulley/balancer with a paint pen so I can more accurately read the vacuum/mechanical advance movements and different throttle positions. I have to drive away from the house into a field to adjust the timing and rev the engine, the noise annoys the family and neighbours!

Good news- I have discovered my mpg is not as bad as I first thought, the kilometres trip computer on the speedo is c.20% out, having measured against GPS I reckon the fuel consumption around town has been 12-14mpg.

silly question, as you're switching distributor parts, are you keeping the cap and arm matched? Thats a prime reason for arcing/burning in the cap

kermit_rr said:

silly question, as you're switching distributor parts, are you keeping the cap and arm matched? Thats a prime reason for arcing/burning in the cap

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Yes, the replacement distributor (from Powerspark) came with a new cap and arm, have been running with this. As an experiment I swapped back to an one of previous distributor and the issue was the same. It is the only piece in the ignition where I am not sure about the quality versus having genuine lucas parts but I am getting weary now about buying part after part.

Genuine "Lucarse" is utter crap, avoid anything in the green box..

Distributor doctor do great parts for the RRC.

Regarding the running the 3.9 runs at 12-14 static and 34 all in, you will more than likely have issues with the Weber 500 running the vacuum the timed vac port creates too much vac for almost all systems.

You're disconnecting the Vac and plugging it when timing it?

Right?