Thread: Discovery 2 V8 hesitation on downshift

Originally Posted by ozscott

Mate where are you hearing this sound. There is not pressure regulator under the bonnet in a D2 V8. Fuel pressure is dictated by the pump in the tank from memory. If you are hearing ticking it might be an exhaust manifold gasket that's blown out (easy fix) and while that will muck up what the 02 Sensors see downstream of the MAF in my experience that would not account for your horrendously high fuel consumption. Mine is half of yours with 4.6, heavy truck, lifted and 31 inch Duratracs.

Cheers

I know mine is through the roof, I had a discovery 1 v8 on 33s with standard gearing that would use 22 per hundred towing a heavy tradesman trailer. Something definitely has to be wrong just don't want to start throwing parts at it without trying stuff and asking peoples opinions first. I have three mafs here and they all read the same on the Nanocom when connected. It does run a bit rough at idle sometimes but when the aircon is on it definitely runs better at idle. I have had a thorough look and listen around the exhaust and cant find any leaks.

Have you checked the condition of your air cleaner filter?
A blocked or wet air filter will give you horrendous fuel consumption and make the engine run rough.

I might do the coil packs plugs and lead all at the same time then when the manifold is off i will re seal it as the small stumble it has could be vacuum related, It is definitely gutless at the moment too. After that there really isn't to much else it could be it isn't the most complex ECU when it comes to sensors.

I just spoke with the previous owner, he said he has had the manifold of a couple of times to do the coils and leads he re used the gasket so it could be a vacuum leak from the inlet manifold I will start with this (hopefully hasn't burnt any valves). The 02 sensors are fairly new as are the coils. I will replace the leads as they are fairly new but the boots don't really fit properly. The filter is okay but will be replaced anyway. The stumble/hesitation it has makes me think its vacuum related. the previous owner had it for 7 years and averaged around 20l per hundred. It sat for about six months now i have it and it is using 27-33 litres per hundred. It used the least amount of fuel 27l per hundred towing my camper trailer on a 300km round trip the day after i picked it up. I am using Bp 98 fuel

No stutter under gentle acceleration, rough idle, stumble when dropping back a gear and lack of power under hard acceleration has me thinking vac leak is the problem.

Idle and hard accel default to closed loop fuelling, so perhaps a lean condition there.

ECU opens IAC at idle when air con is on, this might give engine enough momentum to push through stumble?

ECU runs closed loop when cruising, so O2s detect extra O2, ECU adds fuel, fuel bill goes up?

Yep I'm not a fan of reusing gaskets. I would say strip it down and attack it like you suggest mate. Should be smooth as silk. Cheers.

Gaskets are ordered so I will keep you updated with what happens

It is on the passenger side of the engine and has a 5-6 mm vacuum hose that runs to it with a plug on it. The vacuum hose then runs out and to the rear of the manifold out of sight. It sits underneath the idle air control pipe. I'm not sure if it is the pressure regulator it just similar like one. Definitely not exhaust leak as when you crimp the vacuum hose the ticking will stop.

AFAIR from fitting a Thor manifold to my RRC 6 or so years ago the pipe that you refer to should be the inlet for the crankcase ventilation. Again AFAIR it has a one way valve about half way along. It should plug into the LH rocker cover at the back. I still have it in the garage assuming it is the same pipe as I didn't use it on my CUX conversion.

Regards Philip A