3.9 Bad Misfiring
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3.9 Bad Misfiring
Hi, this is my first post on here.
I have fitted a 3.9 V8 EFI from a discovery 1 to my defender, with an auto box. The engine had 70k miles when I installed it, had been sat for the best part of 5 years. An oil and filter change (20W50) and the engine ran really smooth, couple of lifters were a little noisy but not worrying. Now have covered a couple thousand miles , and last weekend travelled to Anglesey. By the time I had arrived, a small misfire had developed, not very noticeable, more noticeable at low revs. After the weekends competition, driving home, the misfire had turned into 2 cylinders, and engine is now down on power. Got it out today and its running very rough, permanent misfire, not intermitent. I have swapped all the plugs, leads, dizzy cap, and coil (these were all new when i swapped the engine) which made no difference. I am assuming that the camshaft has finally worn past its usefulness?
If so, is there anything I should do to help the oil feed to the camshaft before installing a new camshaft? I have average oil pressure (around 20-35psi when driving) , would it be worth renewing the oil pump gears at the same time?
FYI, I did a compression test 2 weeks ago, and got 160psi +/- 10psi on each cylinder.
Thanks
I have fitted a 3.9 V8 EFI from a discovery 1 to my defender, with an auto box. The engine had 70k miles when I installed it, had been sat for the best part of 5 years. An oil and filter change (20W50) and the engine ran really smooth, couple of lifters were a little noisy but not worrying. Now have covered a couple thousand miles , and last weekend travelled to Anglesey. By the time I had arrived, a small misfire had developed, not very noticeable, more noticeable at low revs. After the weekends competition, driving home, the misfire had turned into 2 cylinders, and engine is now down on power. Got it out today and its running very rough, permanent misfire, not intermitent. I have swapped all the plugs, leads, dizzy cap, and coil (these were all new when i swapped the engine) which made no difference. I am assuming that the camshaft has finally worn past its usefulness?
If so, is there anything I should do to help the oil feed to the camshaft before installing a new camshaft? I have average oil pressure (around 20-35psi when driving) , would it be worth renewing the oil pump gears at the same time?
FYI, I did a compression test 2 weeks ago, and got 160psi +/- 10psi on each cylinder.
Thanks
- Ian Anderson
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£20 infra red thermometer from Maplins
Check which cylinders are down on temperature on start up then inspect those ones. May be gummed up injectors or iffy contact in electrics feeding them
Ian
Check which cylinders are down on temperature on start up then inspect those ones. May be gummed up injectors or iffy contact in electrics feeding them
Ian
Owner of an "On the Road" GT40 Replica by DAX powered by 3.9Hotwre Efi, worked over by DJ Motors. EFi Working but still does some kangaroo at low revs (Damn the speed limits) In to paint shop 18/03/08.
I can get an infrared thermometer from work. Will give that a go. I have replaced the wires to the amplifier on the side of the coil. When I was changing the dizzy cap, i accidentally just moved the wires, and the engine wouldnt start. took me forever to realise, but the wires were just badly corroded at the connectors.Ian Anderson wrote:£20 infra red thermometer from Maplins
Check which cylinders are down on temperature on start up then inspect those ones. May be gummed up injectors or iffy contact in electrics feeding them
Ian
I have also been advised that the misfire could be just due to a slack timing chain? Is this a common issue?
Tom
Can't see chain stretch causing a misfire.
Cam wear doesn't happen quickly - unless you had a lubrication problem. The first signs are the engine being down on power at high revs. It would take thousands of miles for it to wear down to the point where it misfired.
I've seen then worn virtually round and you still get a smooth idle and no misfire.
I'd be inclined to try a new ignition amp. They do fail - although usually completely rather cause a miss. But anything's possible.
Cam wear doesn't happen quickly - unless you had a lubrication problem. The first signs are the engine being down on power at high revs. It would take thousands of miles for it to wear down to the point where it misfired.
I've seen then worn virtually round and you still get a smooth idle and no misfire.
I'd be inclined to try a new ignition amp. They do fail - although usually completely rather cause a miss. But anything's possible.
Dave
London SW
Rover SD1 VDP EFI
MegaSquirt2 V3
EDIS8
Tech Edge 2Y
London SW
Rover SD1 VDP EFI
MegaSquirt2 V3
EDIS8
Tech Edge 2Y
There is no coolant being lost, there is a lot of condensation on a cold start, but I am assuming this is normal for petrol engines?
If I remove HT lead number 8, with the engine running, the misfire doesnt change. however it sounds like it is missing more than 1 cylinder.
I am at the point of taking it out to replace it for a bigger lump (4.2 or 4.6). looking at the Land Rover Workshop Manual, the oil pressure for this engine is low, and I cannot source a replacement timing cover/oil pump for the engine, since it is a suffix B with the oil pump driven from the crankshaft.
Tom
If I remove HT lead number 8, with the engine running, the misfire doesnt change. however it sounds like it is missing more than 1 cylinder.
I am at the point of taking it out to replace it for a bigger lump (4.2 or 4.6). looking at the Land Rover Workshop Manual, the oil pressure for this engine is low, and I cannot source a replacement timing cover/oil pump for the engine, since it is a suffix B with the oil pump driven from the crankshaft.
Tom
You do need to measure the oil pressure accurately first - the dash gauge is often wrong. And even then, there seems to be a lot of tolerance with sound engines.
A fairly good indication of bearing wear and really low pressure would be the pressure warning light coming on at any time on a very hot engine.
A fairly good indication of bearing wear and really low pressure would be the pressure warning light coming on at any time on a very hot engine.
Dave
London SW
Rover SD1 VDP EFI
MegaSquirt2 V3
EDIS8
Tech Edge 2Y
London SW
Rover SD1 VDP EFI
MegaSquirt2 V3
EDIS8
Tech Edge 2Y
Oil Pressure
I have hooked up a proper testing gauge for the oil pressure. Actual figures areDaveEFI wrote:You do need to measure the oil pressure accurately first - the dash gauge is often wrong. And even then, there seems to be a lot of tolerance with sound engines.
A fairly good indication of bearing wear and really low pressure would be the pressure warning light coming on at any time on a very hot engine.
Cold @ 2500rpm = 35psi
Hot @ Idle 750rpm = 10psi
Hot @ 2500rpm = 25psi
These figures are not really a cause for concern, but it is lower than what the workshop manual states. I am concerned that since the oil pump for this engine is no longer available new, I could be spending money on a dead engine.
As someone said earlier down my post, the cam wear cant just happen like that. This engine has always been pathetic at high RPM, and I have always suspected that the camshaft would be on its way. However in the space of around 600 miles, it has gone from running perfect, to misfiring, not all of a sudden, it has happened gradually. It must be a mechanical fault , an electrical fault would be permanent or intermittent.
I have kind of made my mind up to get a new engine - there are still some saleable parts from this engine including the EFI system, and the block would make a nice coffee table
A 3.9 in factory condition wouldn't be pathetic at high revs.
If it really has only done 70,000 miles the rest of the engine should be near perfect, condition wise. And fitting a new cam is an easy job with the engine in the vehicle.
If it really has only done 70,000 miles the rest of the engine should be near perfect, condition wise. And fitting a new cam is an easy job with the engine in the vehicle.
Dave
London SW
Rover SD1 VDP EFI
MegaSquirt2 V3
EDIS8
Tech Edge 2Y
London SW
Rover SD1 VDP EFI
MegaSquirt2 V3
EDIS8
Tech Edge 2Y
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- Top Dog
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Re: Oil Pressure
You can get the pump upgrade kit that solves the pressure issue, alternatively, the front cover from a GM 3,9 litre V6 is a bolt on part and you get the uprated pump with it.tomg978 wrote:I am concerned that since the oil pump for this engine is no longer available new,
Cheers,
John
John