The V8 Owners Forum -

So, this is one of those faults that suddenly rears up when you've tried to do everything right . . .

I put in a AFR gauge a while ago and found that a pretty much stock 1983 Range Rover with 3.5 V8, dizzy, and CD175s and LT95, (and everything new 20,000 km ago), had all the numbers where I thought they should be, i.e. 12.5 during acceleration, 14.7 at idle, and so on. Then one day on the afternoon school run I was behind a truck at 40 kmh in 4th gear and suddenly the engine didn't have much power and the gauge was reading 16, 17, 18 and randomly off the scale.

It had been perfectly happy before this, and still reads well at idle and during acceleration and cruising at 90 kmh. But cruising around town at 50 kmh it's still doing this, with the vacuum gauge reading about 10 ins/hg. So far I'm managing by pulling out the choke to get a better AFR, which also raises the vacuum reading. Idle is at around 15 ins/hg with the aircon compressor on, a bit higher with it off, and with a steady needle.

I've tried clamping off or removing anything vacuum-related, removing the charcoal canister and put it back after rebuilding it, and checking the rest of the PCV system. There is a lot of suction at the oil filler with the PCV system connected, and none with it disconnected, so while I thought it was an intake manifold leak, it doesn't seem to be. I thought it could also be an exhaust leak somewhere, but that wouldn't explain the lack of power. Then I thought it could be air filter related, but removing them didn't make a difference.

A compression test and fuel system check hasn't happened yet due to an inexplicable outbreak of children but I'm trying to get to that when I have the time. But I tell you what, during decades of car tomfoolery this one has got me stumped.

Are you getting a decent spark from the dizzy - is the high reading just that the O2 is just not getting used - i.e no/poor combustion - you will need a good spark and advance at cruise to light a lean mixture - is the spark weak or has the advance module failed. May also be worth having a look see if you have a split diaphragm in the CD.

Thanks for the lateral thinking, just what I needed. I did check the vacuum advance and it holds vacuum well, and I also checked those CD175 diaphragms, which were of course in perfect shape, so no easy fix there!

I forgot to mention that those carbies have since been replaced with some rebuilt SUs, simply because even though the CD175s were new, they eventually leaked like mad, a hilarious feature of the model. Naturally, the new carburettors made no difference to this weird problem.

Anyway, working on the ignition, I started by swapping all the spark plugs, (they weren't old but it was a good place to start), which was worthwhile because it was obvious that the LH carburettor is running lean - despite needles and jets set up properly. I can only think that something on that bank is leaking but it all checked out so far - I'll have to check again in some other way.

Well, I finally fixed it a few months ago and now finally remembered to update this thread.

I managed to narrow the problem down to the inlet manifold gasket and it seemed okay after tightening the bolts, only to get worse soon after - the car wouldn't even run without lots of choke, and then only roughly.

After more testing everything on the intake side and finding nothing wrong, I took the manifold off and found lots of oil on the gasket sealing surfaces and on some inlet tracts and valves in the heads. So the engine had a bad inlet manifold gasket and was inhaling oily air from the crankcase! I have to admit this hadn't dawned on me, and I've never heard of it before. It was a rubber-coated gasket and it seems that the rubber failed when it reacted to oil and fuel.

With the engine back together, it's been fine ever since, but I wouldn't have figured it out if it wasn't for that AFR gauge.

*Note: before using a new tube of gasket goo, squeeze some out and leave it to make sure it cures. If it's too old, it won't cure and you'll have to take apart whatever you just assembled and clean everything and redo the whole damned job.

Thanks for the update. Good to know!

I have seen the inlet manifolds come loose - I had it on my EFi engine. I put it down to incorrectly fitting it (by me!). I think it's tricky because it has to slide across the gasket as you tighten it, but the tighter it is, the harder it is to slide!

Chris.

Twice I've followed the manual when it said to leave the front and rear gasket clamp bolts loose so it would move as the manifold was tightened up, and both times had trouble. This last time I tightened them up to hold the gasket in place and that seemed to help locate it as the manifold was put in place.