Very poor MPG on V8 - Help needed! :-(

My Landy is still eating Petrol and LPG (8-10mpg at best), I've tried everything but am at a loss (both mentally and pocket) so am asking for help.


It's a 1984 Defender with:

Brand new 4.6, 4.6 heads, new cam, timing chain etc.. the whole works mated to a 4 speed ZF auto box. Just fitted new leads, plugs, cap, rotor arm too and all set up as best as possible. It also has no cats with 4 branch, distributor (new), hotwire system, brakes not binding either.

It runs reasonably fine, but not as powerful as it should be (my opionion), a bit lumpy and not as smooth as a V8's I've had in the past, but by no means awful. It's been to a couple of mechanics the last one deals with LPG and races Rover V8's and seems like he knows what he's talking about, but even he can't quite work it out.

It runs very rich and on petrol will foul the plugs in 3 minutes (very sooty and black), he first thought it was a very worn out cam, but when we removed the inlet it was perfect (inlet then cleaned and put back), he now thinks that perhaps when the engine was put back together the cam may have been put back a tooth out, he says that the ecu would compensate for this so it would run ok'ish but just run very rich. The last car I had that had a cam 1 tooth out (K-series) did run but was very noticeable it was wrong.

Any ideas? Big thanks in advance.

Lead foot?

I wish that was the case, but no I've been driving like an angel, 40-60mph and not much stopping, also go into corners quite wide so I don't have to slow down too much.

fit NOZ,the speed you go at will make your mpg better...

I would look at why its running rich on petrol - the ECU will probably compensate for it on gas too.

Have you run a diagnostics on it, to look for faulty sensors etc? Like Lambda sensors etc?

Air flow meter ok? Or how about have look at the lamda sensor on your exh down pipe.

Not tested air-flow, but when I take leads 2 & 6 off it still runs pretty much the same as with all 8 so not sure if it's that.

Wouldn't mind knowing if anyone has fitted the cam timing chain 1 notch out and if they have had similar results or it would be way off what I'm getting.

thats ur timing then or cocked up plugs mate

It may have a brand new 4.6 but what is the cond, of your injectors.E.G spray patern ok? if they drip they could foul your s.plugs.Do you have the smell of unburned petrol of your tail pipe?

I think it's the timing but from the timing wheel/cam not the ecu, new plugs too.

Don't think it's the injectors as I get poor MPG on LPG and it's just a single-point system so the injectors aren't used.

I'm wondering if anyone knows how it would run if the timing wheel was 1 notch out?

depends.

Itll probably run, just lumpily. And the ecenomy would all be to cock



try it ant see, what the worst that could happen? You waste half a day?

boydy1989 said:

depends.

Itll probably run, just lumpily. And the ecenomy would all be to cock



try it ant see, what the worst that could happen? You waste half a day?

Click to expand...

Well boydy, you may have just answered my question Because it's already running lumpy with bad economy! I may have to put some time into seeing if it really has been incorrectly positioned but I've tried just about everything else, cheers

Right!!!! I reckon it's fixed!!!!!!!!!!!!!!!!

I took the inlet manifold off, then used the DTI guage (had the head on so took 30mins just to secure the DTI down and through the spark plug hole) got ATDC, checked full lift on no.1 inlet - was hoping it was going to be 1 tooth out so (no.1 inlet that should be around 108degrees or close) would get around 90degrees or 126degrees, but was pretty much bang on 108degrees.

Put the inlet back with a new valley gasket and it was ticking over really smoothly, took her round the block and OOOHH MMY GODDD! it genuinely feels 40-50% faster. I don't know what I did? perhaps the gasket was drawing in air or the plenum was? I stumped to what it could have been, I haven't checked the MPG but I'm guessing it should be better as it's running perfectly. Finally hurray!