Engine and Transmission Tech

Hi

I have had a strange fault on my Land Rover V8 that I just can’t seem to fix.

It’s series 3 L.R. But is running a 3.5 V8 from a classic Range Rover from the mid ‘80’s.

It drives well for 45 mins. Then starts to pop from the exhaust and hiss a bit. Then from traffic lights/ stand still, it pulls away with almighty jerks and shakes like the clutch is going. Then when I limp it home and start it again from cold, all is well until the dreaded 45 minute cycle starts again.

I’ve changed the coil, but I do think it ‘s something to do with an ignition component breaking down under heat. Or possibly fuel evaporation once hot in the carbs. Twin SU’s that have been professionally examined and serviced by Burlen Fuel systems (real experts in this field).

2 electric fans running off an electro thermostat sensor. Temperature gauge reads 82 Degrees.

I’m now loosing faith with it and need some tips please.

Thanks Guys

P.

Hello and welcome.

It does sound like vapour lock. Fortunately, something that my Series III Lightweight V8 does not suffer from.

As regards ignition, the coil or ballast might be suspect, but when they play up it just stops, so I would set that aside for now.

Presumably you're running E5, never E10?
And the carbs have the usual heat spacers on the inlet manifold?

I would be looking at the routing of the fuel line. Rubber line is probably going to be OK so long as it's not touching the engine, but any metal line needs to be insulated. Last time I had this issue, two years ago, I used a wrap of asbestos string.

Does it have headers, or the usual cast manifolds? Headers can generate an awful lot of heat.

You may find a larger pool of Land Rover advice at Land Rover UK forums where we love Series Land Rovers.

Edit; a post elsewhere has just reminded me that in the matter of ignition faults, a bad condenser can mimic the symptoms of fuel starvation. If you are running points, you might buy a new condenser from Distributor Doctor where you will get reliably high quality parts.



Edited 1 time(s). Last edit at 06/03/2024 04:50AM by 88v8.

Thanks very much for this.
I have the spacers on the carbs. And it’s got an electronic ignition. Not sure about the inlet manifolds, think they are cast as they look standard. Not sure how you tell?
A Vapor lock sounds very likely. But I do have rubber fuel lines. So if I wrap them maybe? Any other tips for vapour lock?
Have been running E5 but just changed last time to E10 to see if I could notice a change in symptoms. But I’ll change it back again.
I’ve been on Landy Zone and series11 forums but thought as it’s v8 specific I might have more advice here.

Really appreciate your help on this. Any more fuel Vapour lock advice and how you detect/cure it is very much welcomed!

All the best and thanks again

P.

It does sound fuel related.
Is your fuel tank vented properly? The hissing is interesting. Where is that originating?
It may a fuel starvation due to vacuum build up in the tank.
Try it with the cap loose or off to see if that makes a difference.
If it is a genuine vapor lock , adding a fuel return line to the tank will virtually eliminate it.
What floats are you running? Anything with plastic floats will be damaged by the E10, and E5 over time. The hoses will probably start shedding as well.
I would strongly recommend changing to metal fuel lines for a number of reasons. Rubber lines front to back have multiple issues.

Cheers
Fred

Thanks Fred.
I have a return to the tank. Floats are brand new, but lines are rubber.

P.

Another thought just struck me.
Possibly a loose muffler baffle or something similar blocking the exhaust.
That would fit with all of the symptoms.
Now I'll go get a scotchy scotch, that thought was movin when it hit me!

Cheers
Fred

Could be, but would this happen only when driven for longer than 45 minutes?

If the rubber line is old, change it, as ethanol attacks old rubber.
Gates Barricade is ethanol-proof.

What Fred said about vacuum in the tank... although 45 minutes is a long time. When it happens, take the cap off the fuel filler, see if you get a hiss (or suck) and if it will then run OK.

The manifolds... the exhaust manifolds, are they cast or tubular? Tubular manifolds make the engine bay very hot.
Put up a couple of pics of your engine bay. Photobucket and paste the link.

When my cars have had vapour lock, they start to run unevenly, won't pick up, may stall altogether. Had this with my Rambler two years ago, and my Lanchester around 50 years ago so it's not a new thing, it's just that ethanol has made it worse.

See here, that short run of metal line running across the top of the engine, after I had vapour lock on a hot day, I wrapped it in asbestos string and no problem since.






Edited 1 time(s). Last edit at 06/05/2024 04:43AM by 88v8.

Ok. Thanks a lot. I have cast manifolds. I will definitely check the route of the fuel lines and try the filler cap trick.
I’ll get some photos up when I can. I’m also thinking of putting the air box and fresh air tube back in place as that’s been off since the carbs and inlet manifolds came off . And must be raising the temperature of the engine bay.

Thanks for all this by the way. It really helps.

P.

Yes, it doesn't need much heat input to cause vapour lock, just a short length of fuel line.

The air box doesn't look very sexy but it does help.

I help my Landy with a different sort of air feed....



and my previous V8 Landy... hot air out, cool air in.



Sorry about the wide-screen , dunno why it does that.

Hello again! Been busy at work. So had to down tools for a bit. Got out there to check the route of the fuel lines and lo and behold one of the rubber pipes was sitting right on the exhaust pipe underneath! Very dodgy. I’m going to re route that and perhaps do some sort of heat shield wrap all the way to the carbs. Changed the king lead from the coil too and will change the in line filter. I would be interested in hearing about your hot air out cool air in system @88v8

Have a great weekend all

P.

They're cabin vents from a boat.... like this.
Also called mushroom vents.

Thanks a lot Ivor. 👍

Hello! So after re routing the fuel line and adding a big old fresh air tube to the carbs from the front grill. I did a test drive. It went well ish. Juddering started but much more mildly and after a greater amount of time. Almost an hour! It does it initially turning left or right at a t junction and is worse in reverse. Then starts from pulling away in a straight line. So basically under load when engine bay is hot, That said it was definitively an improvement.

So here’s what I think. It is still heat related fuel problem that I’ve improved with what I did above. So I might now wrap the fuel lines in some sort of heat shield tape.

Fit the air box and attach the fresh air tube to it.

I also think that it’s worth changing the rear universal joints on the prop shaft. As I hear somewhere (may be on here) that they can fail under heat.

The left and right thing and reverse thing could be telling for you experts out there?

Plus any tips for what shielding tape to use would be really helpful as I’m not sure you can get asbestos tape anymore @88v8

Have great Sunday

Paul

I know you are thinking this is fuel related, but it could also be a breakdown of the ignition. This is REALLY easy to diagnose however. Simply source a small incandescent bulb (very small - approx 3watt - like from a dash board / gauge illumination), and connect some light-duty cable (like speaker cable) across it, mount it somewhere on the dash that you can easily see, and and connect the other end to each side of the coil.

When its working correctly, it should always be on when the engine is running, and will likely glow brighter between idle and 1500 RPM when its going to be as bright as it'll get. When driving, if it flickers when the issues arise, you know it's an issue with the electronic ignition. If it doesn't ever completely flicker (just gets dimmer as the RPM drops) its definitly not related to the ignition amp (but could still be a coli issue - genuine bosch coils aren't that expensive BTW - I wouldn't bother with a non genuine).

FWIW, The small black modules on the RRs in the 80s thru 90s were really good at breaking down with exposure to prolonged heat, but then operating perfectly when they cool. They are easily replaced, but make sure to use heat-conductive grease between the module and the dizzy to get the heat out of it. Interestingly, the modules were relocated from the side of the dizzy to a heat sink plate behind the headlight in the last years of their use, as this is cooler than the body of the dizzy - but even the ones in this location can - and do - break down over time.



Edited 1 time(s). Last edit at 07/05/2024 10:26AM by turbodave.

Thank you for this. I do have a brand new dizzy and electronic ignition set from a MG R v8. That I was thinking of swapping out. But the light bulb test is a good idea first.
Do you think the MGRv8 dizzzy and amp would be compatible out of interest?

Thanks again

P.

Pretty sure all the RV8 dizzy's are compatible with the engine, but need to be mated to the appropriate amp and coil as appropriate.

Ok cheers Dave

P.

The in reverse thing.... worth checking that the axle U bolts are tight. Back them off and retorque. They can work loose and that causes juddering on take-off.

If the ujs were bad you would have vibration all the time.

Ivor

Thank you Ivor.

I have done that but unfortunately still no difference.

I am now going to replace the electronic ignition module with a brand new mobiletron which comes with a dedicated dizzy that has no brand name? I inherited it but there are no instructions. I suspect that the current module, which I hope is failing under heat. This new one has definitely not been used before.

I’m uploading a couple of photos to see if anyone recognises the brand and whether I can just whip the old dizzy out and pop this one and the same position.

Thanks folks.

P.