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| ian series 1 Member Since: 17 Nov 2014 Location: south Posts: 3127   
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 80" 80" 86" 88" 90"
Wanted, Forward Control Anything considered. |
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23rd Nov 2016 9:26pm |
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| Rickydodah Member Since: 14 Jul 2014 Location: East Sussex Posts: 1091 |
I'd start to look at spark plug condition and gaps now, possibly if the mixture is too lean and spark duration is not long enough at higher engine speeds then this would cause misfire. Do you have any way of checking mixture to see if hydrocarbons increase with engine speed?
 I started with nothing and still have most of it left! |
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23rd Nov 2016 11:58pm |
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| charcoal Member Since: 28 Jul 2014 Location: Hampshire Posts: 941 
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Sadly I got no way of measuring hydrocarbons. Is that something which could only happen under high load? The engine can run at high rpm's without a misfire at lower speeds. I got a new set of spark plugs already which I'll have a go at fitting tomorrow anyway! 1999 Land Rover Defender 110 td5 station wagon
1998 Land Rover Defender 110 County Station Wagon ~ Sold 1995 Land Rover Defender 110 V8 Station Wagon ~ Sold 
1985 Land Rover 110 ex mod project Tithonus ~ Sold |
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24th Nov 2016 12:04am |
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| Rickydodah Member Since: 14 Jul 2014 Location: East Sussex Posts: 1091 |
The hydrocarbon element of the emissions are the unburnt fuel, they will always be present and at idle they're normally at their highest, a large increase at higher engine speeds can be indicative of the mixture leaning off and causing a misfire, particularly if the spark duration is too short to cause effective combustion. If the plug gap is too large or the ht leads have too little resistance it can cause the spark to be weak or too fast. With SU carbs engine vacuum effectively enriches the mixture by causing the pistons to rise and depending on the profile of the needle graduates the richening procedure. If the oil in the damper is too thick or the springs too heavy this will also prevent an optimum mixture. Good luck
I started with nothing and still have most of it left! |
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24th Nov 2016 10:55am |
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| K9F Member Since: 12 Nov 2009 Location: Bournemouth Posts: 9610 
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How is the advance/retard ignition timing factored in? If it is the old diaphragm capsule arrangement check the diaphragm and the connecting vacuum pipe for splits, degradation and or leaks. If you go through life with your head in the sand....all people will see is an ar5e!!
Treat every day as if it is your last....one day you will be right!! |
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24th Nov 2016 12:36pm |
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| charcoal Member Since: 28 Jul 2014 Location: Hampshire Posts: 941
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Thanks for the information Ricky, I will need to check the dashpot oil too, what type of oil should be in there and how would I know when it's full? Can't fit these new spark plugs yet as I can't find a socket but I also found another set of ignition leads I'll fit to see if it helps.
K9F, the vacuum advance is working correctly now, on my old distributor it was jammed but this unit definitely works, the pipe was split a little while ago so I cut the split end off and it made no difference, that was when the old distributor with the jammed vac advance was fitted though. 1999 Land Rover Defender 110 td5 station wagon 1998 Land Rover Defender 110 County Station Wagon ~ Sold 1995 Land Rover Defender 110 V8 Station Wagon ~ Sold
1985 Land Rover 110 ex mod project Tithonus ~ Sold |
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24th Nov 2016 4:39pm |
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| rallysteve Member Since: 10 Feb 2014 Location: Cumbria Posts: 2200 
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Is the static timing definitely correct? (measured with the vac advance disconnected IRC). I seem to remember the timing values are different for each engine version.
You can ensure the vac advance is working correctly by removing the pipe from the manifold and sucking on it with the engine at idle. You should hear the engine change pitch. What are the conditions when the misfire appears? e.g. high revs but engine braking, high revs with foot hard down, high revs but cruising etc. Will be worth removing the plugs, cleaning and checking the condition and gaps as the duff coil may well have ruined them. If the issue only occurs when first applying throttle then stabilises as you reach speed or when lifting off, check the dash pot oil. It shouldn't cause any other symptoms if no oil is in them. idle might be a little rougher if the needles are fluttering. It is well worth checking all the simple things again to rule those out, i.e: Check all vacuum hoses for splits Check throttle linkage is working correctly on both carbs. I have had lean running issues caused by one carb throttle butterfly not opening correctly. Check plugs and gaps Check Dizzy clamp is both tight and actually holds the dizzy correctly. Ensure both carb needle/pistons can be easily lifted by light finger force and drop back down to their seats. I personally like to remove the air filter and both inlet elbows and see the relative movement of the two needles and plungers as I rev the engine to ensure both are working correctly. You can do a check that with the engine idling that, if you lift the piston/needle your should hear the revs drop I think, look this up online, I cant remember which symptoms are correct. this is a reasonable aid to at least confirming the idle mixture is roughly right. Another possible source of the issue could be fuel starvation if it only occurs under high load, this could be a fuel pump issue or incorrectly set float. Steve 02' 110 TD5 Double Cab Rebuild Thread 84' 90 3.9 V8 Caged Pickup Build Thread - Now For Sale |
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24th Nov 2016 5:34pm |
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| charcoal Member Since: 28 Jul 2014 Location: Hampshire Posts: 941
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Thanks for all the information Steve. As far as I'm aware the timing is correct, when I had the new dizzy fitted the timing was set up properly with a timing light. I tried sucking on the vac advance and the pitch changed like you said it would. The vac advance pipe is in good condition with no splits.
The exact conditions are as follows: Engine under load around 70-80mph, can start misfire as low as 60mph if driving into the wind. It will start of as a light misfire that recovers instantly if you give it less throttle, if you increase the throttle or keep pressure on the pedal the misfire will start to get more violent to the point where the vehicle is jolting and loosing speed quite rapidly. At this point you cannot recover and have to pull over and let it idle for a few seconds before pulling off again. The cold misfire has since surfaced again so the new coil mustn't have helped that much  This misfire happens under load again but around 20-30 mph and generally happens when I've set off before the temperature gauge reaches operating temperature which is always dead in the middle of the gauge, when this misfire happens it will jolt without light misfiring beforehand, less violent though most likely due to the lower speed. If you give it more throttle at this point it will sound almost like only four cylinders are running. At this point the only option is to pull over and either restart the engine or give it a few revs until it starts firing on all cylinders again.
The gaps should be correct on a new set of spark plugs shouldn't they? I will replace them and inspect the old ones once I've found a new plug remover, melted my one I used to use 
The throttle linkage could be a potential problem as the bolt in the top of the throttle linkage rod (ETC4728L) has sheered, a nut still fits on the end though and appears to hold the two linkage parts together. There is also a bit of play in the throttle, when it's at it's idle position you can push the linkage down a bit more and it will lower the rpm almost to the point of stalling, it can only be pushed down about half a centimetre though and when revved goes back to the correct position though. The dizzy clamp is down tight but I wouldn't know how to tell if the dizzy isn't held in correctly. The carburettor pistons can be moved with little force and when one is lifted the idle speed drops and would probably stall if I lifted it any higher. Fuel starvation was my first thought too so I went to the garage last month to get the fuel pressure checked, it was running at the correct pressure. Don't know what to do if it is an incorrectly set float though, how could you find out if it was for sure? 1999 Land Rover Defender 110 td5 station wagon 1998 Land Rover Defender 110 County Station Wagon ~ Sold 1995 Land Rover Defender 110 V8 Station Wagon ~ Sold
1985 Land Rover 110 ex mod project Tithonus ~ Sold |
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25th Nov 2016 1:27am |
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| ian series 1 Member Since: 17 Nov 2014 Location: south Posts: 3127
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Have you done a compression test?
Electrical stuff aside, could be wear on camshaft, weak valve springs, worn valve seats, worn lifters? To me, with the parts you have replaced I would say it's time to look a bit deeper? 80" 80" 86" 88" 90" Wanted, Forward Control Anything considered. |
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25th Nov 2016 8:24am |
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| charcoal Member Since: 28 Jul 2014 Location: Hampshire Posts: 941
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Definitely time to look deeper. I got a compression test and a booked into my local garage next week. I'm thinking it could be valve seals due to what looks like oil being burnt on startup. Will get back to you with the results on Tuesday Ian. 1999 Land Rover Defender 110 td5 station wagon
1998 Land Rover Defender 110 County Station Wagon ~ Sold 1995 Land Rover Defender 110 V8 Station Wagon ~ Sold
1985 Land Rover 110 ex mod project Tithonus ~ Sold |
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25th Nov 2016 4:39pm |
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| Iggle piggle Member Since: 10 Sep 2014 Location: Wales Posts: 378 
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With you saying when it happens you need to stop and & idle for seconds to clear it, it does sound more like a fuelling issue than ign,
Have you tried pulling the choke out when it happens? I had something similar at low speed and pulling the choke cleared the stutter, With me it was the K&N filters & once removed the issue went away, I have to say though the speeds you mention in a lot of posts (70-80) make me wince a little, for your engine & your wallet!  how many RPM?? that misfire could be simply "valve bounce"? |
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26th Nov 2016 9:20am |
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| ian series 1 Member Since: 17 Nov 2014 Location: south Posts: 3127
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It would be worth checking the primary fuel pick up.
I had a V8 2 door RR, that would idle fine and run at lower revs, as soon as you pulled away fast or come out of a roundabout at speed it would cough and splutter? Returning to idle it would run fine. To test it, I rigged up a separate fuel supply with a fuel can feeding straight into the carbs. Problem solved, no misfire, no lack of power. It turned out the fuel tank was full of crud, and on high fuel demand it would simply suck the dirt up around The already badly blocked fuel filter. Taking the tank out and flushing it and fitting a new pick up filter cured my problem instantly. This was my last port of call after replacing ignition components, stripping the carbs numerous times thinking that was the problem. I'm not sure if yours has a filter in the tank? But well worth a look. 80" 80" 86" 88" 90"
Wanted, Forward Control Anything considered. |
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26th Nov 2016 9:34am |
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| charcoal Member Since: 28 Jul 2014 Location: Hampshire Posts: 941
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A fuelling issue was my first thought too so I took her to get the fuel pressure checked, they were fairly sure it was running fine, that's not to say something in the fuel tank could be getting in the pickup filter but it did have the fuel tank cleaned when the engine was installed to clear out all the diesel. Is there anything else in the fuel system that could cause a problem?
I tried pulling the choke out when it misfired while running under a cold start and it had no affect. I didn't try it when misfiring at cruising speeds though. I don't have K&N filters fitted but I do have a smaller air filter box from a Rover 25 fitted if that could be causing problems in some way? 70mph is perfectly fine for cruising, sometimes you need that extra speed to overtake something though and I don't want to overtake something only to misfire and have to pull over. The RPMs at that speed are around 3-4k, nothing the engine can't take even under load. Replaced the spark plugs this afternoon and they all look the same as the one shown below. The plug gaps were all around .7 - .8 thou which is where they're supposed to be. I fitted the new ones anyway.  Click image to enlarge Can't comment on cold running misfires but the motorway misfires were still present. It may have been just me but they did feel a little more manageable though, when I felt them start around 75mph I gave it a little bit more throttle and the speed picked up a bit more before dropping slowly to around 65mph with no violent jolting this time. After sitting at 65mph for a little bit I could apply the throttle lightly again and bring her up to 70mph. 1999 Land Rover Defender 110 td5 station wagon 1998 Land Rover Defender 110 County Station Wagon ~ Sold 1995 Land Rover Defender 110 V8 Station Wagon ~ Sold
1985 Land Rover 110 ex mod project Tithonus ~ Sold |
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26th Nov 2016 7:36pm |
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| Rickydodah Member Since: 14 Jul 2014 Location: East Sussex Posts: 1091 |
Do you mean .7-.8mm plug gap? As 7-8 Thousands is way too small.
I started with nothing and still have most of it left! |
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26th Nov 2016 8:07pm |
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