3.9 as flat as a pancake

Hello and good evening,

So, got a 3.9 that was on LPG at some point in its life,

Since owning it (and driven a total of 250 miles) since last year its lacked any grunt and "performance"

I can live with the 10mpg, however lack of go is an issue,

Put a LR tech to it to find its running rich, the lambda sensor on the nearside isnt functioning, so getting both done before going back as I have no ideas what to do next,

I've replaced all vacuum pipes, check timing, got a new dizzy, new HT leads and coil, new spark plugs (but could be ****e ones i'll admit since i dont know the preferred brand of choice), changed all the belts, all the filters (only the fuel one to go, but cant get a charcoal one these days), refurbed plenum chamber, new MAF, even put shell optimax stuff in,

The 91 RRc has a 4speed ZF box mated to a B&W transfer box, all with new oil and filter in the gear box,

Car revs fine, just takes an age to get going, to a point where I'd say its on the verge of dangerous,

Tyre sizes are standard defender sizes, tyres are General Grabbers AT2

Any ideas would be great as this is the last issue since I cured the stalling when warm issue with it,

Rover V8s aren't power houses, but should be enough to get you going...

NGK BPR6ES for spark plugs, also I hope you have genuine ignition parts specifically a minimum of rotor arm and distributor cap. HT leads can be any decent set. The castings for non genuine rotor arms and distributor caps are, quite frankly **** - and can cause even more problems than first anticipated. Not loss of power obviously but other issues.

I take it the timing has been set correctly since the new distributor was fitted, you'd be surprised how much more poke you can get advancing the timing to just before it pinks under high load, rather than 4/6/8BTDC or whatever the manuals say. Plus if done with a timing light using the timing marks on the crank, these can sometimes be a bit off.

How many miles has it done? High mileage V8s that haven't been looked after can be rather tired and worn, particularly camshafts.

Have you done a compression test yet? Sometimes if one or two cylinders are particularly lazy they'll still fire but won't be providing grunt and the slack will be taken up by the other 6 or 7 cylinders.

If haven't done a compression test you might find either one or two are down or all of them could be through the floor.

Defender tyres are 235/85/16s, standard RRC tyres are 205/80/16s. I am also running 235/85/16s and there is a noticeable difference caused by the difference in gearing from the larger tyres. Acceleration was slightly better with the original tyres but with an autobox you don't have to change gears as much as with a manual.

So perhaps a combination of all things, tired engine, different gearing because of tyres, etc etc. Fingers crossed you can get down to the bottom of this! Keep us posted!

I agree with Marccleave, especially about getting the compression tested, also, does it use any oil and coolant above what might be expected.

Col

All parts have been either genuine or OEM, the dizzy was from Britpart, but an OEM unit,

dash says car has done 145k, wouldnt suprise me if cam is are worn,

Compression test it is,

By all means, i'm not expecting to do wheel spins or anything, but for it to be faster than my 05 td4 freelander would be nice

Jonnyb1990 said:

All parts have been either genuine or OEM, the dizzy was from Britpart, but an OEM unit,

dash says car has done 145k, wouldnt suprise me if cam is are worn,

Compression test it is,

By all means, i'm not expecting to do wheel spins or anything, but for it to be faster than my 05 td4 freelander would be nice

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You're right, a properly running 3.9 should be able to live with a td4 freelander, I know my RRC can.
As has been said if you're down on power first port of call has to be a compression test assuming ignition and efi are alright.

So, an update after i've had a week off from work,

Striped the exhaust, on both sides, missing all the short head bolts on the offside of the block, new exhaust on and new head bolts and compression is right up,

Blowing oil out the back which is to be expected after who knows how long its been like that,

Now pulls much better though the gears, still not quick by any standard, but explains the poor idle at maneuvering speeds and stalling when warm,

but a low cost fix for what could of been my worst nightmare should there of been no thread in the head....

The missing head bolts are a standard 'mod' believe it or not. It was found that having them tended to tilt the head & exasperate gasket failure. Later heads no not have that row of bolt holes. I take it you've checked out other possible causes for sluggish performance ie binding brakes, seized/partially seized VCU, low transmission oil level - the list goes on. The V8 Classic is not designed for performance, nearly 2 tonnes in kerb weight with permanent 4x4 driving though 2 gearboxes & the aerodynamics of a brick outhouse are not conducive to acceleration or high speed, but the performance should be adequate ie 0 - 60 in around 12 seconds.

Mod or not, its a stupid thing to do,

Brakes are good, both gear boxes are good, handbrake retracts fully,

Not expecting a race car, just dont want to be a liability on the road !

On a 91 you could have removed the cats / sensors and changed the tune resistor

cooltide said:

On a 91 you could have removed the cats / sensors and changed the tune resistor

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That's what I've done, passes emissions test an all

Absolutely! My '91 breezes the emissions test, passed again just last week. You would need a noticeable engine/injection and/or ignition problem not to pass the basic emissions test but no way can you get the emissions to meet catalyst test limits, I tried just for a giggle and was close but hey, as long as it is running go and enjoy!

Deleting the outer row of bolts isn't a stupid mod. On the later engines the heads aren't even drilled for them. As mentioned LR found that the outer row of bolts, torqued to their full value, had a tendency to tip the heads, leading to the head gaskets blowing into the valley. If you feel that you must fit them, then it is best to nip them up to a very low torque setting just so they don't fall out. Has the engine got a really good earth? Especially the injection element of the wiring? There is a company which can help you sort out the injection and power. I had them look at my 3.5 when I fitted it with a 3.9 hotwire injection system. In the space of an, expensive, hour on a rolling road and with the use of a laptop. They had doubled the power output of the engine.