kevinr Posted October 21, 2008 Share Posted October 21, 2008 I've just replaced all the sparkplugs, HT Leads and King lead, rotor arm and dizzy cap on my '97 P plate disco. I was a very good boy and only used genuine parts and Champion Sparkplugs, even set the gaps correctly and torqued them up to the correct setting and made sure all my HT leads were layed across the engine neatly avoiding crossing wherever possible. After I started her up to check all was well, my revs now sit at 1000rpm instead of 750. Is this a cause for concern (apart from the extra fuel consumption) or is there something I can adjust to bring it down again? Quote Link to comment Share on other sites More sharing options...
teabag Posted October 21, 2008 Share Posted October 21, 2008 Unlike the 3.5 you can't adjust the tickover on a 3.9, the ECU looks after that, although there is the base idle speed that is set at the factory you should not require to set this adjustment. Have pulled a hose off or have a split hose, you might have an air leak or have put a kink in the throttle cable. I never done it but there are concerns when replacing the rotor arm in that the springs in the dizzy and come loose but if there was a problem then the engine would misfire I think. I would look for an air leak. Quote Link to comment Share on other sites More sharing options...
discodave Posted October 21, 2008 Share Posted October 21, 2008 I've just replaced all the sparkplugs, HT Leads and King lead, rotor arm and dizzy cap on my '97 P plate disco. I was a very good boy and only used genuine parts and Champion Sparkplugs, even set the gaps correctly and torqued them up to the correct setting and made sure all my HT leads were layed across the engine neatly avoiding crossing wherever possible. After I started her up to check all was well, my revs now sit at 1000rpm instead of 750. Is this a cause for concern (apart from the extra fuel consumption) or is there something I can adjust to bring it down again? Hi Kevin, I read in the tech archive about only using NGK plugs in more than one post I think, dunno if it would affect your tickover but take a look here. http://forums.lr4x4.com/index.php?showtopic=16476&hl hope it helps. DD Quote Link to comment Share on other sites More sharing options...
landmannnn Posted October 21, 2008 Share Posted October 21, 2008 The dizzy might not have been tightened up properly, you could have advanced the ignition by turning it a bit. Quote Link to comment Share on other sites More sharing options...
kevinr Posted October 21, 2008 Author Share Posted October 21, 2008 thanks for the replies all I've heard conflicting stories over the spark plug thing, some advocate NGK other champion..I went with champion as that was all Paddocks had in at the time, but i'm not sure these would affect the revs... I'll check for leaks when I get in from work tomorrow...I did move a few pipes out the way to get at the plugs, so i's possible I have losened a join I guess And the dizzy cap..would that make a difference if it was not exact? the retaining clips have a bit of play in them, and the catches on the side of the cap are fairly wide, I'd assume the ECU would account for this, aslong as the fireing order was correct..which I assume it is..I was meticulous about numbering everything up when I put ht enew leads on..and I never really put any force onto the dizzy itself when I put the cap or rotor arm on..infact, everything was stable..but I'll give it a good once over in the light tomorow Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted October 21, 2008 Share Posted October 21, 2008 I've heard conflicting stories over the spark plug thing, some advocate NGK other champion..I went with champion as that was all Paddocks had in at the time, but i'm not sure these would affect the revs... Any changes to the ignition can affect it, idling higher does not mean it's faulty, it could be because this is the healthiest it's been for years that it's suddenly idling higher. I'd assume the ECU would account for this The ECU is nothing to do with ignition whatsoever. Unlike the 3.5 you can't adjust the tickover on a 3.9, the ECU looks after that I believe you can, it's just the adjuster screw is capped off. The ECU controls the idle stepper motor which should maintain the idle at the same speed regardless, the fact it's not doing so for whatever reason could be any number of things. Quote Link to comment Share on other sites More sharing options...
First_Fleet Posted October 22, 2008 Share Posted October 22, 2008 Any changes to the ignition can affect it, idling higher does not mean it's faulty, it could be because this is the healthiest it's been for years that it's suddenly idling higher. That was also my immediate reaction. If you haven't adjusted the throttle cable knurled wheel at the throttle body, I would be looking at a tweak of the base idle as per the W/M instructions. I don't believe it will need much though. Quote Link to comment Share on other sites More sharing options...
ThreeSheds Posted October 22, 2008 Share Posted October 22, 2008 Unlike the 3.5 you can't adjust the tickover on a 3.9, the ECU looks after thatI believe you can, it's just the adjuster screw is capped off. This would be base idle speed? If it's a hot-wire with 14cux, then adjusting the base idle speed (within reason and according to the book) should not affect the actual idle speed. The base idle speed is a sort of base which the ECU controlled stepper motor then works on top of. The stepper controlled valve can increase tickover above 'base idle' (and should) but can't get below it, and if the base idle speed is set too low then the ECU will open the stepper valve more to obtain the correct idle. IIRC the correct base idle speed is 500rpm (just checked - it would appear to be 525 +or- 25). If the base idle is set too low then there will be a tendency towards stalling after releasing the throttle from higher (2500+ from experience) rpm. If you wish to try adjusting the base idle there is info in the tech archive about checking the hotwire system (which I can never find) which probably includes instructions for this. It is not possible to adjust the base idle setting accurately without blanking both ends of the air bypass hose. Ask me why I am such an expert on base idle setting Back to the problem: When I was trying to sort out my rich idle I found that I could increase the actual idle speed by playing with the small vacuum hoses, eventually leading to me find a split in the heater control reservoir hose. I then found that allowing air into this pipe would increase the idle above the 750-950 setting. I think that the reason is that the hose allowed air in downstream of the AFM and with my rich mixture it was acting like opening the throttle. This combined with the fact that somebody - no NOT me - had adjusted the base idle speed too high, meant that even with the stepper controlled valve fully closed, the idle was too high. So - vacuum hoses yes - but also what about temperature sensors perhaps? If the ECU thinks that the engine is cold then I think it will set a higher idle speed (it does on mine). Also - if it thinks that the screen heater or air-con are on (or similar high-load items) it will increase the idle speed. Checking the hot-wire system according to the tech archive would (I think) be well worth the effort. Rog Quote Link to comment Share on other sites More sharing options...
teabag Posted October 22, 2008 Share Posted October 22, 2008 thanks for the replies allI've heard conflicting stories over the spark plug thing, some advocate NGK other champion..I went with champion as that was all Paddocks had in at the time, but i'm not sure these would affect the revs... Hi Kevinr, I have also seen the NGK/Champion spark plugs debate in LR forums but haven't taken any notice. Land Rover supplied my disco with Champion and the service department replaced the plugs with Champion, and now I do my own servicing, I recently replaced my plugs after 20,000 miles of use and fitted Champion. The new plus certantly made the engine more responsive. So I don't have any probs with Champion. Quote Link to comment Share on other sites More sharing options...
kevinr Posted October 22, 2008 Author Share Posted October 22, 2008 Yeah..to me a plug is a plug, aslong as it does the job the vehicle needs, then I'm not to fussy, I only see the argument if your talking performance plugs..which I don't need. Had a little problem this morning..the car started judering under load..I nearly cried..just seems one thing after the other with this car atm...however..after a 2 minute fiddle with the HT leads, I found one wasn't fully seated..now it is, all is well..infact, better then well..all the little niggles have gone from the acceleration aspect, the car feels like it isn't even turned on when stationary, and the revs have sorted themselves out..the needle does bounce very slightly at tickover, but I guess I'm just being too criticle. Now..as long as the car behaves itself, I can start concentrating on modifying the damned thing Quote Link to comment Share on other sites More sharing options...
teabag Posted October 23, 2008 Share Posted October 23, 2008 Funny I had a new lead pop out within a day or so of fitting the leads so had to double check. So u don't know what was the cause of the high tickover then. Quote Link to comment Share on other sites More sharing options...
kevinr Posted October 23, 2008 Author Share Posted October 23, 2008 Funny I had a new lead pop out within a day or so of fitting the leads so had to double check.So u don't know what was the cause of the high tickover then. No idea!, it's completely behaving itself now, and is a much better drive then it has ever been Quote Link to comment Share on other sites More sharing options...
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