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Car Forum / Land Rover Cars / January 2008Rough running 1990 RR 3.9 EFi
Evening all The saga of the Green RR continues. I have abandoned solving the rumbling/whining noises from the front end in favour of this (new) problem: Idles OK-ish at about 750-800. As the engine speed increases it's apparent that the engine is running less smoothly than usual, a sort of 'roughness about the edges'. As the speed increases the roughness becomes more pronounced and can be felt through various attached items e.g. transfer box selector. It reaches a peak at around 2,000 RPM, when it could almost be described as a vibration, and then gradually decreases. It feels a bit like a gentle - as in quiet - misfire. I wondered if the ignition advance had died but Mr Gunson's Tachostrobe indicates that there is some advance in the ignition timing as I rev the engine. I'm not convinced that the vacuum advance is working cos I can suck on the vacuum tube without effort. I was tempted to remove the transparent cover from under the rotor arm to look at the vacuum advance. Is it worth it? Incidentally what should the timing be set to? Also can I, if necessary, use the vacuum advance from a 1988 3.5 EFi RR? TIA Richard > Evening all > [quoted text clipped - 16 lines] > transparent cover from under the rotor arm to look at the vacuum > advance. Is it worth it? Vacuum capsule is shot. Remove dizzy cap and try turning rotor arm by hand - if it doesn't return ALL THE WAY under its own spring tension, your dizzy needs to be overhauled. Vacuum capsule can be changed in-situ, awkward but possible. Some are torx screws, earlier ones are phillips, knack is locating the capsule over it's drive peg...... > Incidentally what should the timing be set to? 6 degrees before TDC, no vacuum. > Also can I, if necessary, use the vacuum advance from a 1988 3.5 EFi RR? Yes, no issues there. have a play with that one first to see what I mean re. locating the capsule's operating lever over the peg on the baseplate. Change the capsule before setting the timing. Badger > Vacuum capsule is shot. Remove dizzy cap and try turning rotor arm by hand - > if it doesn't return ALL THE WAY under its own spring tension, your dizzy [quoted text clipped - 13 lines] > > Badger Thanks I know that the vacuum capsule on the 3.5 is Torx screws 'cos I Loctited them in last time they came loose ;-) I'll have a tinker over the weekend. As you will see in my reply to EMB I was slightly economical regarding the story. Apologies etc, but I don't think it would influence your thoughts - I hope. Richard > Evening all > [quoted text clipped - 7 lines] > e.g. transfer box selector. It reaches a peak at around 2,000 RPM, when > it could almost be described as a vibration, and then gradually decreases. I would suspect a worn cam lobe or two. A compression test is probably in order. > I would suspect a worn cam lobe or two. A compression test is probably > in order. Mm! What I neglected to mention in my haste to post the question was that these symptoms appeared on the way to work about 2 weeks ago. Having had a hopeful stare under the bonnet I noticed that the hose to the fresh air flap vacuum reservoir had parted company at the reservoir and the roughness did not continue when I left that evening. If it is anything more than a very simple fix, this will hasten it's disposal. Any suggestions for a replacement? Must be capable of passing below a 1.87m height restriction. Richard My RRC did this. Thought it was the loose dizzy, tighten it up and all was fine until i used the windscreen washers. This annoying mis fire/rumble/call it what you want came back. Found the cause in the end....the pipe from washer bottle to Y junction was split and each time i washed the windscreen it also washed the right hand side plugs as well!!!!. Can't you make the height barriers taller Richard??!! Dom > My RRC did this. Thought it was the loose dizzy, tighten it up and all was > fine until i used the windscreen washers. This annoying mis [quoted text clipped - 5 lines] > > Dom Morning Dom, Dizzy tight and now fitted with working vacuum advance ex the blue RRC. Interesting selection of plugs fitted, of which #6 was a balck as sin and having no effect on the engine (possible Hurrah!). Top of pot 6 also black and perhaps oily, possibly fewer hurrahs. All other plugs look fine, swopped #1 and #6 plugs and roughness has gone. Will peer into pot 6 to see if the black has gone. If not, what do you suggest? Redex or ignore it?? TTFN Richard >> My RRC did this. Thought it was the loose dizzy, tighten it up and all >> was fine until i used the windscreen washers. This annoying mis [quoted text clipped - 19 lines] > > Richard Check the lead resistance from inside the dizzy cap to the plug cap, carbon filament HT leads are the devils gonads IMO just another thing to check and discount as being the cause. I did check Peggy's ( EFi in the heady days when I could afford <10mpg ) even a good set can give as much as 15% varience in resistance between the shortest and longest lead I had one that was closer to 30% higher Derek > Check the lead resistance from inside the dizzy cap to the plug cap, > carbon filament HT leads are the devils gonads IMO just another thing > to check and discount as being the cause. I did check Peggy's ( EFi in > the heady days when I could afford <10mpg ) even a good set can give as > much as 15% varience in resistance between the shortest and longest > lead I had one that was closer to 30% higher These 'carbon string' leads have a resistance proportional to the length. IIRC, about 10k ohms per foot. The total resistance including carbon brush and king lead should be of the order of 30-50k.  Signature*Monday is an awful way to spend 1/7th of your life * Dave Plowman dave@davenoise.co.uk London SW To e-mail, change noise into sound. > The saga of the Green RR continues. I have abandoned solving the > rumbling/whining noises from the front end in favour of this (new) > problem: > Idles OK-ish at about 750-800. As the engine speed increases it's > apparent that the engine is running less smoothly than usual, a sort of [quoted text clipped - 3 lines] > it could almost be described as a vibration, and then gradually > decreases. > It feels a bit like a gentle - as in quiet - misfire. First thing I'd check is the plug leads. And also check their routing - they can crossfire. Signature*What do little birdies see when they get knocked unconscious? * Dave Plowman dave@davenoise.co.uk London SW To e-mail, change noise into sound. |
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