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paul connor

Land Rover V8 SU carb 3.5 Snatch engine problems

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Can anyone help?

 

It seems a vehicle can really get you down after a while. You spend 18 months rebuilding a vehicle, registering, taxing and Mot'ing and manage 12 miles and it gives up.

 

I had fitted a low mileage engine, as the original was dead. The new engine ran beautifully, some would say like a Swiss watch! until last week. It went on it's maiden voyage and performed as it should. No over-heating, misfiring or anything to cause alarm. I went 12 miles and even left it ticking over in the workshop before it was parked up.

Next day I turn the key and it struggles to start. When it does it has the worst misfire mid-range and will not idle, WHY!?!

 

I have changed the Spark plugs, Rotor arm, distributor cap, HT leads to no change.

I have compression tested the engine and all give the same reading as they should.

I have removed the carburetors and checked the floats are not perforated or sticking, that everything else is operating correctly.

It has the correct SU oil in the pots.

I have re-timed the engine, which was a struggle as idle is increasingly iffy.

It is losing no coolant, oil or leaking anything.

Nothing is obstructing intakes and all breather are OK>

Distributor has been swapped and no change. Vacuum advance is fine.

Fuel is flowing through the filters fine and seems to be at pressure.

I have spark at all plugs and coil and module seems to be correct.

 

 

What am I missing?

 

Someone has mentioned that the cam shaft could be worn and I have a stuck/damaged valve etc. But would this just happend over night and wouldn't this show up during compression test?

 

Totally stuck and your advice would be greatly appreciated!

 

disheartened

 

Paul

Edited by paul connor

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I have a V8 110. I get an occasional problem with it condensing moisture inside the distributor cap. Usually this occurs after it has been standing for a long while and then I take it for a short run in cold conditions - next time I go to start it, it misbehaves.

 

You say you changed the distributor, but was thinking you might have kept the same cap and swapped it across - it only takes a small amount of moisture.

 

Looks like you have eliminated water in the carbs, as you checked the float levels.

 

Only other thought at the mo' is maybe someone swapped a couple of plug leads to play a trick on you.

 

Steve

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Thanks for the reply, Steve.

 

I have a new dizzy cap, so that's ruled out the moisture issue.

The vehicle is kept in a secure workshop, so nobody has access but me. Also the leads are in the right order...

 

I'm quite stumped.

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Paul, the newness of the cap makes no difference to the formation of condensation, this was a common problem when trialing in winter, don't be tempted to spray WD40 in the cap and then start the motor immediately, that can make those dizzy caps blow clean off.

 

Voice of experiance..:D

 

Check for any leaks or blockages in the flame traps and hoses, they can seriously affect the mixture.

Edited by gritineye

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Didn't drop the dizzy cap did you? The slightets crack can cause no end of grief. Could be worth using a gentle hairdryer to go over cap and distribitor.

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Thanks for the reply guys.

 

I know I can't rule out new parts being at fault, but they seem perfect. There is no moisture in the workshop and the caps haven't been dropped. I shall switch it over again for the 3rd spare I have to be sure.

The fame traps all seem intact and the hoses are great condition.

 

Truly stumped.

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From Carbs, do you mean its dual carb? I know from Range Rovers they are the complete Donkey's A** to get balanced. My 101 did something similar, it took real experts to cure it,

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Can anyone help?

 

It seems a vehicle can really get you down after a while. You spend 18 months rebuilding a vehicle, registering, taxing and Mot'ing and manage 12 miles and it gives up.

 

I had fitted a low mileage engine, as the original was dead. The new engine ran beautifully, some would say like a Swiss watch! until last week. It went on it's maiden voyage and performed as it should. No over-heating, misfiring or anything to cause alarm. I went 12 miles and even left it ticking over in the workshop before it was parked up.

Next day I turn the key and it struggles to start. When it does it has the worst misfire mid-range and will not idle, WHY!?!

 

I have changed the Spark plugs, Rotor arm, distributor cap, HT leads to no change.

I have compression tested the engine and all give the same reading as they should.

I have removed the carburetors and checked the floats are not perforated or sticking, that everything else is operating correctly.

It has the correct SU oil in the pots.

I have re-timed the engine, which was a struggle as idle is increasingly iffy.

It is losing no coolant, oil or leaking anything.

Nothing is obstructing intakes and all breather are OK>

Distributor has been swapped and no change. Vacuum advance is fine.

Fuel is flowing through the filters fine and seems to be at pressure.

I have spark at all plugs and coil and module seems to be correct.

 

 

What am I missing?

 

Someone has mentioned that the cam shaft could be worn and I have a stuck/damaged valve etc. But would this just happend over night and wouldn't this show up during compression test?

 

Totally stuck and your advice would be greatly appreciated!

 

disheartened

 

Paul

 

-------------------------

 

You ask , What I am missing ?

 

Sooner or later you will get to the - hydraulic bucket tappets , some would say the Archilles heel ..

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Its quite hard to diagnose these problems without being on scene, but logical order can help Ive always found it best to pinpoint the problem before parts swapping as you can conceivably introduce new problems even with new parts, and that can really give you a headache, by all means swap a part but if it makes no difference put it back in the box and fit the old one. You can always fit it later when you find the problem.

 

By misfire is it popping and spitting or just one or more cylinders are failing to fire, always or only mid range and idle?

 

If its rough at idle most likey a cylinder is not firing or large- ish vacuum leak so pull one plug lead at a time with insulated pliers making sure as best you can not to ground yourself on metal if they all seem to be sort of firing suspect a vacuum leak, or very rich, smell exhaust to decide which.

 

Pull the plugs and closely look at the colour if differences are noted match intake track cylinder to carb and any pipes attached to manifold.

 

An odd one but it does happen it's caused me problems in the past is the rotor arm is not aligned properly with the cap, the spark jumps forward to next contact when the mechanical advance kicks in but thats a midrange pop bang and backfire.

 

Coils can produce a good yellowish spark and still be duff look for a strong blue spark.

 

With good even compression pretty safe to say you can rule out an engine problem, especially as it happened overnight.

 

I agree with other poster after running an engine thats been sat a while or cleaned condesation in distributor is common., but don't rule out you may have fixed the original problem and introduced a new one with a carb overhaul or similar.

 

Anyway hope this is of some help.

 

Best,

Quentin

Edited by marmon
errors

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Cheers again guys.

 

The parts I have replaced I did replace with the originals again. I have learnt the hard way before by introducing more problems.

 

The Carbs are twin SU's which I know can be a right pain to balance.

 

I have pulled the leads early on and they did all appear to have a good blue spark.

 

Currently it struggles to start unless full choke and will then really struggle to idle. When you try to rev the engine it'll choke up and try and stall, but you can feather the throttle and it'll pull through and rev faster. The faster top end of the revs does seem to be smoother, but it's hard to be sure.

 

I have checked the timing and the rotor position and that seems fine.

 

It's very odd that this would happen overnight from an engine that ran perfectly.

 

I suspect I have a weekend of frustration ahead!

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From Carbs, do you mean its dual carb? I know from Range Rovers they are the complete Donkey's A** to get balanced. My 101 did something similar, it took real experts to cure it,

 

Tony , the carbs on Range Rovers were Strombergs and much more troublesome than the SU's on this vehicle.

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Sudden misbehaviour does sound more electrical to me. As you have been very thorough, just wondering about more obscure options :

 

Is the engine earth strap secure.

Possibly try a different HT coil too.

I have heard of a partially blocked fuel line causing starvation, but if it flows OK into a jar then that will be plenty.

It isn't new enough for cats is it? I have heard of cats collapsing and blocking an exhaust (not on a landy).

 

I have had Rover V8s for 30 years, and sudden misbehaviour after a run is rare. When I have had it, then more than once it was condensation inside the distributor cap due to water condensation inside the engine due to standing, once it was a bad connection in the lead to the coil (that was really embarassing as it broke down at the local tip and the vultures were circling), once it was me putting the HT leads on the wrong way round !

 

They are usually pretty tolerant. I used to have one that when parked on my drive engine upwards had trouble priming the carbs with the mechanical pump (real old ones had timing case mechnical fuel pumps), so I used to pour petrol down the inlet and it would fire up.

 

Failing that the car is rubbish, sell it me for next to nothing :D

 

Steve

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Tony , the carbs on Range Rovers were Strombergs and much more troublesome than the SU's on this vehicle.

 

Thanks for that, now I know why I prefer Disiel.

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Do you have those problematic emission control poppet valves in the butterflies? They can lead to sudden rough running if a spring breaks. If so change to plain butterflies or solder the valves shut.

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Sounds like a fuel or carburettor problem, possibly you have shaken up some rust or muck in the tank, provided the petrol is new T in a pressure gauge to eliminate the pump, filter, tank etc, while your at it fill a milk bottle with petrol and let it settle out, I dont have the exact figure but id expect to see 3 to 8 psi with SU's, if someone has the exact specs please jump in, but it should run well at those sort of figures. Carb balance would effect idle a lot more than revving provided they are both opening also pull the oil dampers and watch if both velocity pistons raise roughly equally when revved.

 

You can also pull the dashpots and check the fuel level in the main jets even, present and not flooding.

 

Agree with the other post about the anti overun valves if you have this type solder them shut but again they only cause problems at idle.

 

If it runs well enough take it for a run plug colour will tell you a lot, also I'm still thinking vacuum leak, I'm not sure what you have connected in this application but its worth actualy pulling the pipes and temporarily plugging off.

 

Good hunting,

Quentin

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Hi guys.

 

I have already had issues with the over run valves and soldered them shut.

I will be at the workshop on Friday, so hopefully I can have a proper look.

I have in-line filters and I have drained them and checked for debris and water, there was very little, albeit slight.

I shall take pictures and some video on the weekend.

 

 

Thanks for the replies.

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Hi guys.

 

I have already had issues with the over run valves and soldered them shut.

I will be at the workshop on Friday, so hopefully I can have a proper look.

I have in-line filters and I have drained them and checked for debris and water, there was very little, albeit slight.

I shall take pictures and some video on the weekend.

 

 

Thanks for the replies.

 

Hi, This may help as I have had similar problems and chased them around only to find a new set of plus has gone down.

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Definately an odd fault. Can probably rule out a mechanical fault with the engine. Does sound like its fuel related though. First thing I would check is the rubber diaphrams in the carb dash-pots, they can split or perish. There should be oil in the damper tube, too much can spill down onto the said diaphrams. Assuming the petrol is new and filtered there shouldn't be dirt in the float chamber but might be worth a look. There are no points and condensors to play up and electronic dizzies and modules I imagine are fairly reliable so that leaves the plugs. Is it possible to pull the leads and try and eliminate the cylinders that aren't miss-firing? These are handy for testing plugs and leads etc. http://www.ebay.co.uk/itm/1x-Draper-Spark-Plug-H-T-testers-/361212078232?pt=LH_DefaultDomain_3&hash=item5419eae898

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First thing I would check is the rubber diaphrams in the carb dash-pots, they can split or perish. There should be oil in the damper tube, too much can spill down onto the said diaphrams.

 

No diaphragms in SU carbs, you are thinking of Strombergs or maybe fuel pumps.

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No diaphragms in SU carbs, you are thinking of Strombergs or maybe fuel pumps.
Thought someone said it had Strombergs? Ah brain fade.

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I don't think my opinion has changed.

 

QUOTE. (initial post)

 

I had fitted a low mileage engine, as the original was dead. The new engine ran beautifully, some would say like a Swiss watch! until last week. It went on it's maiden voyage and performed as it should. No over-heating, misfiring or anything to cause alarm. I went 12 miles and even left it ticking over in the workshop before it was parked up.

Next day I turn the key and it struggles to start. When it does it has the worst misfire mid-range and will not idle, WHY!?!

 

---------------

 

I / you ,would need to know a lot more about this "low mileage engine" , even if it was a minta (they have been around for 45 years) , it was effectively in storage for one year + , oil draining back to sump , no mention made of oil priming at all , Vee bank hydraulic lifters known to be cantankerous until got running right using all known procedures (flooding hyd. tappets / cams as a minimum). You could have two or three valves not closing correct , so you will never idle. Damge could have been done in those 12 miles. There are special protective coating lubricants used at box-up to prevent hyd. lifter/cam problems , these could have been all new and still not bedded in - a minuite or less of dry run would damage.

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I've never known a hydraulic tappet hold a valve open when the valve should be shut, they never pump up and do that. They might rattle until the oil pressure builds up, but that won't cause a miss-fire. Besides the compressions are ok.

 

Its all speculation until there's more info from the OP.

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In these days of engine management , are Krypton machine so rare ? now is probably the time for such diagnostics. The OP did come asking for opinion (possibly little to mull over is more benificial) and lots of opinion that is zilch £ but a few more thingies to eliminate. I don't know the new spares £spend to date (diagnosis by substitution) . Probably getting it into a garage & paying £40 may have given a good clue or two and been cheaper.

 

There is a difference of compression testing at cranking speed and running at idle and above. Myself , yes I would have done a compression test but rigged up a compressor for a full "leak-down" test that would probably prove more.

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Thanks for the replies once again.

 

Just to add to the posts.

 

The engine replacement was a recent Army Recon engine that was stored by a company that builds WMIK's and Snatches.

The oil was primed before the first time the engine was started as I know the damage that this can indeed cause.

 

I understand the idea of taking vehicle to a garage but logistically with an armoured vehicle that weighs around 3 tonnes, this can prove difficult. I also do not feel that many modern "mechanics" could diagnose issues as easy as a person with years of experience with engines such as the V8. But, I see your point. Most local garages in my area are not that great and the only other choice is main dealers. Which isn't going to be much use.

 

I ask on here as it's a wealth of knowledge and people are always very helpful. I have not had time to get to the vehicle as yet, but plan to spend time there this weekend. Hopefully I will be able to tackle the fault with a few more ideas and possibilities.

 

I have been eliminating certain parts by substitution, only as I have spares in the workshop.

 

I shall let you all know how it goes on the weekend, as like me I suspect you're all curious of the outcome now.

 

Thanks for the replies, I do appreciate it.

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May be worth enquiring if such as a Hometune franchise , keep an old school analyser in the van ?

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