Bogging down

[choob]

1978 3.5 zenith carb V8 Range Rover

Opposite to the previous problem I had, the car is now bogging at low revs, better at higher revs but feels like it's misfiring. Backfires on overrun sometimes.

Can't find a vacuum leak. Looked at plugs, two looked good and two were fouled. Same on each bank. Mechanic thinks either HT leads and also wants to check tappet clearance, though I'm not sure how that's related.

The only work I've had done recently is to weld the exhaust on after it fell off the centre resonator. The car is behaving similar to a car with blocked cats, but I doubt they blocked the hole when welding...?

Any tips? 

[Davo]

The valve lifters are hydraulic, so no clearance checks are needed unless something has magically gone wrong. With these engines it's almost always ignition first, then fuel. Have all the basic ignition checks been done? Have the carbies been rebuilt? 

[paintman]

Was the car OK before the problem with the exhaust?

[choob]

It was ok, but it was also ok on the drive home after fixing it.

Regarding ignition, he was saying that two plugs on each bank weren't sparking very well. What other ignition checks can I do?

Carbs not rebuilt afaik.

Does the carb version have an ignition amplifier?

Edited June 9, 2017 by choob

[Snagger]

Just because the drive home was OK doesn't mean the latest added parts are good.  Being so soon after replacing the exhaust, I'd be suspicious of the muffler having an internal blockage.  There a multitude of suspects, but I always start with the item changed most recently to the fault showing.

[choob]

He just welded the existing

 pipe back on to the muffler, no new parts. I'll try have a look to see if the hole got blocked but it seems unlikely 

 

[Snagger]

If the pipe was so rotten that the muffler fell out, then the inside of the muffler may be rotten enough for the bafflles or muffling material to move and block the flow.  It it was torn out off road, then it may have been crushed internally.

[choob]

The hangars were broken and I drive 20km of corrugations every time I leave the house, but it was a bit rotten at the junction of pipe and box. 

Will disconnect the joint before the box and see if there's a change

 

[Bowie69]

In my experience, a blocked exhaust feels much more strangled at higher revs than low, I think the issue lies elsewhere.

As above check the electrics are all ok, then check the float bowls on the cards for presence of fuel...

[choob]

Still misfiring when the muffler is loose.

The IAM multiplug snapped when I pulled it off so I'll change that and HT leads tomorrow.

The ignition light has always been dimly on, only visible at night. Is this normal?

[Snagger]

A dim charge light suggests a bad alternator.

[choob]

I have a brand new alternator for a 3.9 efi model, will it work with this engine? Current alternator has a multiplug with 3 wires

[choob]

Changed HT leads, IAM and dizzy cap and now I have no spark from the coil. Tried a new coil and still no spark.

I have 12V when measuring from both coil terminals, is this normal?

Any ideas on getting spark back?

Edited June 13, 2017 by choob

[Davo]

I'll assume "IAM" is the ignition module? They are the cause of many a frustration, so try changing it again. Also, don't change more than one thing at at time as it makes it much harder to work out which new part is bad. (And yes, I know this because I've done it a few times.) 

[choob]

We've traced the issue to the distributor - all parts work fine when installed in another car except the distributor. Resistance at the pins  where the amplifier plugs in is 2.9, I read somewhere it should be 1.6?

I can't find a new distributor anywhere, I tried a used one which was worse. Can I buy the britpart electronic conversion kit and put the bits in the current distributor?

I already had the cap and figured I may as well change the leads as they were so old they had turned black. Original color was red.

[choob]

Sparky soldered something in the dizzy and we got our spark back!

Now we have another issue - car ran for 1km and then cut out. Won't start again. Have spark.

Neither Sparky nor me know how to set timing properly, we set the static timing based on TDC at cylinder 1 then advanced it a little until car would start and idle smoothly.

Could the new non starting issue be caused by timing?

[Beardy Face]

12 hours ago, choob said:

Could the new non starting issue be caused by timing?

If it's far enough out, or moved since you guesstimated the setting yes. You don't have to twist the dizzy far on a V8 to change the setting pretty massively.

[paintman]

Redo the timing & ensure the dizzy clamp is tight, if it's slipped then it could cause your problem. But you need to eliminate it as a cause.

I once managed to refit my dizzy a couple of teeth out & whilst it popped & farted a bit it wouldn't start.

To be sure you've got No1 TDC remove the nearside rocker cover & spark plug from No1. Put a long thin rod into the plughole onto the piston. Turn the engine with a socket on the crank pulley until both valves on No1 are closed & the piston is at TDC - the purpose of the rod. You'll probably go past TDC a couple of times but just turn the engine backwards until the piston is about halfway back down then try again. Once you've got TDC check that the timing pointer is inline with the TDC mark on the crank pulley. The rotor arm should now be pointing at the position for No1 lead. If it isn't & you have enough movement in the dizzy body realign it. If you haven't then you will need to pull the dizzy & reinstall. Note that the drive gear is angled and the rotor arm will rotate as you remove the dizzy. If you are altering the position of the shaft you will need to alter the position of the oil pump drive that the bottom of the shaft engages with - easy to do, just look down the hole & you'll see it.

Once you've got it running again mark the relative position of the dizzy and timing cover - I use a thin line of white paint across the two so any movement is easy to see.

Dynamic timing can be done either with a timing light or by road test. I found the latter to be the best option. This from another website:

This is from the RPi site.

''Its also worth noting that the best ignition timing in any given engine, is to achieve the most advance it can tolerate without pinking. ( Audible pre-ignition).
This is achieved by setting your V8 timing to about 4 deg. BTDC (assuming you've been through the distributor check list completely). Then tighten the distributor so that you can (with effort) still turn it by hand. ideally put a tip-ex mark or small scratch on the distributor body and engine block to record this spot.
Next road test the car and simulate high load by quickly shifting into a high gear or if Auto allow to change quickly up to 3rd or 4th Ideally you need to find a small hill or incline, now if you apply full throttle the engine should respond without pinking, find a safe place to pull over, open the bonnet and turn the distributor through a couple of degrees only, anticlockwise, this will add slightly more advance timing and if you do the same test, and repeat it until pinking is noticed you will be very close to your absolute best timing criteria
So now all you need to do is turn the distributor clockwise by the same amount by an amount to counteract the last adjust, retest for the absence of pinking and that the job done, you will have just achieved the best maximum timing position for your car''

When you've done it, go home, get the timing light out & record the point on the crank pulley that the pointer aligns with - the white paint again!. I found with mine that 6deg BTDC on petrol was optimum - my LR factory manual gave TDC+/-1deg.

 

The low glow when running indicates a fault in the diode pack in the alternator. It may still be - and in your case I would say is - charging. Diode pack is replaceable & there are a few 'how to's' on the internet.

 

Edited June 16, 2017 by paintman

[paintman]

Bit of an afterthought. Did you remove the rotor arm whilst working on the dizzy?

I know from my own - 3.5EFi with standard electronic dizzy - and from experience of others that if you just pull the arm off it can disengage the advance/retard mechanism in the bottom of the dizzy (under the plate). This allows the rotor arm to flop about & can cause non-running. Check by turning the rotor arm with your fingers. When released it should spring back smartly to its original position. 

On the electronic ones you must press down on the reluctor - star shaped thing under the rotor arm - as you pull the rotor. This is not mentioned in any of the manuals, factory or others.

I'm guessing that you would need to press down on the bit that opens & closes the point on a points type dizzy - I stand to be corrected!

Have a look at this (old thread so some of the links may not work): https://forums.lr4x4.com/topic/18599-too-much-fuel/#comment-189315

 

Edited June 17, 2017 by paintman

[choob]

Thanks paintman, I did follow a similar timing procedure with no luck.

It turns out that the carb pistons were dirty and stuck. We have dust like talcum powder here which would get inside the cabin of even the 04 Vogue I had and it's obviously getting past the air filters.

So within the same week we lost both spark and fuel but all is good now, thanks everyone for your help!

[Davo]

Thanks for the update. That type of carburettor works really well but once they're worn or dirty then nothing short of a rebuild will help. 

I live in a very dusty place as well, but don't have a problem with the carbies. How is the filtration on your engine? 

[Bowie69]

I'm suspicious it may be using K&N filters... 

If not, then for dust to be getting through it sounds like a warped airbox or joints or poorly fitted filter.

[Davo]

Yes, K&Ns would be my bet as well. Stupid things. 

[choob]

The original filter box was dented and had gaps. I'm using Ram Air oiled foam filters. They come with a 'dry' lube which I now cleaned and applied filtrex oil so let's see if that helps. Otherwise is there a decent filter that fits direct to the carb? I was using AEM paper filters on my Vogue with no issues...expensive tho

Edited June 19, 2017 by choob

[Bowie69]

Any sports or free flow filter will be junk for your requirements, it needs to be paper I'm afraid, the original airbox was very good, if you can find one I would go with it.