iomlt Posted April 20, 2011 Share Posted April 20, 2011 Hello all, I'm forwarding on a message from a friend that we are having trouble with his 1985 110 V8 mind boggling. "Bare with me a bit of a story and I’ll keep it as brief as possible. Original (when I bought her) engine was 3.9 on carbs, ran beautifully for 10 years, 100k on it and i was travelling back from France and she developed a slight miss fire now and again. after a brief check all seemed fine and i carried on. Back up near Cumbria and it got worse. Did the normal V8 thing and bought new plus, leads, arm, cap and coil oh and amp, still no difference. For around 6 months now I’m puzzled with this and as i was losing water i put it down to the usual liner slip or similar. So got another engine and dropped that in using my electrics and exactly the same fault miss fire on load but this engine had low oil pressure but i again tried to see if i could get rid of this miss fire while looking for another engine. When i fitted this engine i noticed one off the heater pipes where it joins the manifolds to have a pin prick of a hole so maybe my 3.9 engine wasn’t loosing water to a liner slip or etc..... but anyways moving on. wife starting to ask question, "your spending alot of time on the landrover how much have you spent" type..... hahaha So i managed to get another, engine number 3 engine 3.5 from a disco getting desperate. through that in (getting fairly quick at doing this now oh and it ran nicely in the disco i checked this time first). Plumed her all together didn’t change a thing, all the bits off the disco apart from the exhaust. Fired her up and exactly the same misfire on load. tick over like the other 3 engines perfect. so again bought in new leads, plugs, cap, arm, fuel filter still no difference. A friend of mine came round with his V8 90, and just to put my mind at reset and we knew his was working perfectly we change, Dizzy, cap leads plugs coil. still exactly the same so that put my mind at rest about the electrical side, we by passed the ignition system to the coil and ran a direct feed from the batter, we check and added earths. So the only thing common to all three engines that i can rack my brain around is exhaust manifolds and the little gauze filter in the tick tick fuel pump. I have done a compression test on this engine and all within tolerance. I thought about posting on here so while i'm checking and sorting out the pump and my exhaust (as to be honest it needs doing and especially after hearing my friends V8 90 with tubular manifolds and a very well sealed system it made me realise how nice a good exhaust system on a V8 sounds) any ideas. i'm on the verge of throwing a nasty diesel in, but part of me wants to see this through to put my mind at rest and for the love of god! haha " P.s i'm the friend with the V8 90 trying to help. Cheers in advance. Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted April 20, 2011 Share Posted April 20, 2011 Have you serviced the carbs? If you've elimnated the electrical side it has to be fuel, surely? Quote Link to comment Share on other sites More sharing options...
iomlt Posted April 20, 2011 Author Share Posted April 20, 2011 Yup full kit and checked for air leaks etc. on the third engine. on the 1st and second engine had different carbs, but all engines have had the same issue. Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted April 20, 2011 Share Posted April 20, 2011 Ignition amp? Don't know which one if at all it will have TBH.... is it the one on the dizzy, or under the coil or....? If the dizzy one I guess you have swapped them, but if its the one under the coil then it could well be that. What plugs are you running? Quote Link to comment Share on other sites More sharing options...
iomlt Posted April 20, 2011 Author Share Posted April 20, 2011 it had the old stylie under the coil. he elimated that when engine changed and it had the later type with it attached to dizzy, then we through all mine off My 90 the whole ignition system and same fault.. we also by passed the vehicle ignition and gave the coil a live feed from battery to test. Pretty sure the plugs are NGK r8's, bought from rpi could be r6's i have just confuesed my self now. but there from RPi and plug cap checked all ok and they run perfectly in my V8 90. i'll contact him and see if he has found anything with gauze filter in pump and exhaust. Al Quote Link to comment Share on other sites More sharing options...
iomlt Posted April 20, 2011 Author Share Posted April 20, 2011 Some info i missed, he also had a gas system attached to the oringal engine and every time he put a new engine in and it wouldnt run right he then plumbed in the gas and it does the same thing on gas, the missfire. so we think this rules out the carbs / jetting fueling, the fuel pump as mentioned above. He is currently attacking the exhaust, manifolds off and through the rest of the system Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted April 20, 2011 Share Posted April 20, 2011 He's not got a crappy ignition advance box installed has he? Quote Link to comment Share on other sites More sharing options...
iomlt Posted April 20, 2011 Author Share Posted April 20, 2011 He's not got a crappy ignition advance box installed has he? he did have but unpluged now and we're trying with just petrol. rechecked timing. still popping under load, Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted April 20, 2011 Share Posted April 20, 2011 Hmm.... Mega... Oh never mind Still thinking... Quote Link to comment Share on other sites More sharing options...
Gromit Posted April 20, 2011 Share Posted April 20, 2011 Seeing as we're all guessing - I'm going to plumb for an earth fault or blocked fuel pickup. Quote Link to comment Share on other sites More sharing options...
iomlt Posted April 20, 2011 Author Share Posted April 20, 2011 this is what we need random suggestions. ticked both of them, added extra earth cables new fuel tank fitted. pump bottom filter cleaned and new filter fitted. we disconnected the carb side and it fills a jug nicely with good flow. Carbs been rebuilt. Third engine same fault different carbs, also does the same fault when running on gas. keep them coming Quote Link to comment Share on other sites More sharing options...
Gromit Posted April 20, 2011 Share Posted April 20, 2011 duff battery that can't keep up for some reason. (someone who is actually familiar with the evils of V8s should really be responding ) Quote Link to comment Share on other sites More sharing options...
stuck Posted April 20, 2011 Share Posted April 20, 2011 Too obvious probably but maybe a vacuum leak? Quote Link to comment Share on other sites More sharing options...
Quagmire Posted April 21, 2011 Share Posted April 21, 2011 So, to recap- you have (and I may have missed things here): A misfire under load- not present at idle. Two 3.9's and one 3.5 all exhibit the same problem. The other engines were fine in the vehicles that they were seen in, but are not happy in yours for some reason. You have changed/tested with known good/different: Engines! Dizzy cap HT leads Plugs Coil Dizzy Carbs Fuel pump filter Fuel tank You have verified that: The fuel pump actually pumps. (have you compared the rate of flow to any online stats for the pump?- if there are any...) The fuel filters are clear. You have the correct plugs (are they gapped correctly?) The same misfire occurs on LPG and Petrol. Have you verified the voltage you are feeding to the coil? Does the misfire occur under load at any RPM? Does it happen only when hot/cold/both? Does the engine idle evenly or does it hunt at all? How did your exhaust checks go- any leaks anywhere? Sorry to ask more questions without giving any further answers myself, but I thought it would be good to summarise at this point... Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted April 21, 2011 Share Posted April 21, 2011 Vacuum advance unit operating properly? Quote Link to comment Share on other sites More sharing options...
Gazzar Posted April 21, 2011 Share Posted April 21, 2011 My guess is an exhaust leak, at the manifold. But moving away from guesses: Make sure the coil matches the dizzy (Electronic coil)- or maybe the eureka wire is causing trouble. Check the resistance between the battery and the pos lead to the coil. If high replace. Also suggest you replace dizzy with electronic job, and matching coil. Also, pull the plugs in turn and see if they look like the pictures of "healthy engine" plugs - white to tan in colour. My educated guess is the spark breaking down under load, due to current supply issues. Or the vacuum tube is leaking. Quote Link to comment Share on other sites More sharing options...
iomlt Posted April 21, 2011 Author Share Posted April 21, 2011 Added answers You have verified that: The fuel pump actually pumps. (have you compared the rate of flow to any online stats for the pump?- if there are any...) works perfectly and compared The fuel filters are clear. News ones fitted and tested flow good You have the correct plugs (are they gapped correctly?) Yes and swoped them out of my running 90 perfectly The same misfire occurs on LPG and Petrol. Both the same Have you verified the voltage you are feeding to the coil? yes, and ran a direct feed from the battery missing out ignition just incase Does the misfire occur under load at any RPM? yes any Does it happen only when hot/cold/both? yes both Does the engine idle evenly or does it hunt at all? runs beautifully at idle How did your exhaust checks go- any leaks anywhere? leaks on the Y piece he is sourcing new parts to make it sealed, should be complete over the weekend Sorry to ask more questions without giving any further answers myself, but I thought it would be good to summarise at this point... exhaust replacement and sealing not complete yet he'll finish off over weekend and i'll report back. thanks for the above and above posts, nice to double check and the likes. thank you. report back over weekend Quote Link to comment Share on other sites More sharing options...
Tanuki Posted April 21, 2011 Share Posted April 21, 2011 Check the spacing of the HT leads: I've come across a couple of instances on old Rover V8s where the HT leads are clipped close together and they inductively cross-couple - so a spark sent to one cylinder 'leaks' across to an adjacent HT lead whose piston is actually on the intake stroke - and half-heartedly fires it! Worst case this can cause a massive backfire through the intake system - and blow all the oil out of the SU dashpot or explode the intake-trunking if you're running a crude 'venturi'-type LPG setup rather than a proper injector-per-cylinder system. Quote Link to comment Share on other sites More sharing options...
Range Rover Blues Posted April 24, 2011 Share Posted April 24, 2011 Worst case is a holed ppiston. He's talkimg about no/s 5 and 7 on the LHS, the "cure" is to run the lead for cylinder 3 between them all the way down. I'm not clear on something, was it running badly before you refitted the LPG system? have you checked for manifold leaks in the LPG system? either air causing a lean mich or LPG leak causing a rich mix. What spr tof LPG system is it. single or multipoint? Now, thinking outside the box, how do you know it's a misfire under load? what EXACLY are the symptoms, when does it occur, can you predict it, have you checked anything else? I ask because I had a middfire on a V8 under laod that was only really noticeable in 5th, the engine was in sympathetic vibration (harmonic) with a slightly out of balance front propshaft. Neither fault on it;s own caused the vibe, only when it was in 5th and the engine speed and prop speed were similar and the engine was under load. New valves and a prop balance sorted it. Now unless you are terribly unlucky it is something that you either carried over to the new engine or it's something else on the car. Quote Link to comment Share on other sites More sharing options...
webbersdad Posted April 24, 2011 Share Posted April 24, 2011 Swap the distributor. webbersdad Quote Link to comment Share on other sites More sharing options...
iomlt Posted April 24, 2011 Author Share Posted April 24, 2011 swopped dizzy with working one from daily car, no change he has today refit exhaust replaced manifolds all clear and system sounds great now but still missfiring under load. happens on gas and fuel, seems to be left bank (drivers side) idols lovely, he thinks it gets worse with heat, which would indicate coil. but as described above changed all that. tomorrow he is going to check / add more earths and try little things that really should make that much of a difference as mentioned above checking and keeps ht leads seperate there currently in their holders but you never know. we have changed them for genuine and known working onces so not hopeful. thins is doing our heads in! Quote Link to comment Share on other sites More sharing options...
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