The V8 Owners Forum -

Not sure if I'm in the right posting section?

I've got a pretty much standard 3.5 apart from a unknown upgraded cam, edelbrock 4-barrel set up, a Mallory duel points dizzy and a RPi LPG system with RPi AMP.

I've got this little lump in my Ex Ambulance LDV Convoy.

Over the last couple of weeks I noticed the occasional miss and within a couple of seconds back to normal.

Two days ago I started her up and she was missing badly, I thought it was the plugs in need of a change and the damp weather as it had been a year since my last change and I had bought them 4 months ago but not fitted them. Changed them on the road side but no change, still missing badly. limped home about 3miles away, very poor power. The following day I changed the coil for a spare one I had, and put a new condensor on and checked the points gap. no change!

Today I put a new set of cheapy HT leads on to eliminate a faulty lead (I have Magncore leads at present, 2yrs old) but nothing. did a compression test (All plugs out pedal to the metal and cranked over 3 compressions with the gas and petrol off) on all 8, ranging between 150 and 160 psi.
Checked the servo hose and capped it to eliminate servo leak, nothing! still missing badly!

Any ideas?

Start it at night /dark garage and see if you get arcing across the ht leads.

Get an infra red thermometer and check each exhaust manifold the ones with a cooler reading are not firing.


Is your LPG evaporator freezing up in the cold weather?
Ian

Spray the whole lot with WD 40 and also remove the cap and give a good spray inside there too, nothing to lose but its very often damp that gets in and causes tracking,

Started it from cold just now in the dark, no arcing on the leads.

Check the header tank just incase and no bubbling.

The evaporator looks fine (in the summer when the fan belt snapped it looked like i'd just taken it out of deep freeze!), and temperatures here are not that cold.

I don't have an infa red temperature sensor to check the manifold readings

For the first second or two once she's started it runs fine and then starts missing sounds like a dragster on idle but nothing else dragster about it!

The engine had a strip down and rebuild about 3-4years ago by a local mechanic I know when it was in a MG (engine originally from a SD1) and i've owned the engine for the last two years. Inside is very very clean but needs an oil change. I wondered about a sticky valve? Is this a possibility?

A point worth mentioning? is that when I put the new plugs in the other evening and drove home I travelled about 3-4 miles. When I took the plugs out today to check the compression I noticed that 7 of the plugs had a slight whitening of the earth electrode and plug from No.7 cylinder had no whitening on it, just fresh out the box look?!

ian.stewart wrote:Spray the whole lot with WD 40 and also remove the cap and give a good spray inside there too, nothing to lose but its very often damp that gets in and causes tracking,

Will try tomorrow and give you an update.

LDV8 wrote:took the plugs out today to check the compression I noticed that 7 of the plugs had a slight whitening of the earth electrode and plug from No.7 cylinder had no whitening on it, just fresh out the box look?!

Seems possible #7 is not firing, so as you have new plugs and leads, and if swapping those at #7 still leaves #7 not firing - then as suggested, damp tracking inside the dizzy cap may be cured by cleaning. Failing that, replace the cap.

Some reading material.

http://www.vintagemodelairplane.com/pag ... ion01.html

http://www.vintagemodelairplane.com/pag ... ion02.html

Take a spare plug and clamp to ground somewhere. Plug No7 lead to it, start engine and observe the spark at idle. Do the same with a different cylinder. You could open up the plug gap on this spare plug a little as it will spark more easily in free air than under compression. At idle you can see each spark happen individually. If there's a difference, check the plug leads with a DVM set to measure resistance. Standard leads are so many ohms per foot, and you can work out what that is from a known good one. But a faulty one will be miles out. Check the king lead in the same way.

IMHO, Mallory dizzys give even more problems with cap and rotor arm than Lucas ones - but any burning there is more obvious.

Can you temporarily remove the RPI amplifier?

Chris.

ChrisJC wrote:Can you temporarily remove the RPI amplifier?

Chris.

I second that! RPI seem to flog their box of tricks as a cure for EVERYTHING although I guess for LPG it has the useful function of advancing or retarding the ignition (I can't remember which way LPG needs the system adjusting)

I can't say that I'm a fan of 'points' ignition systems either...and the more cylinders you have the worse a points system gets even with a dual points setup.

I don't know whether your Mallory can be converted to electronics but if it can I know a bod that has a brand new Mallory system doing nothing at the moment, he bought because he thought that he had an ignition system problem. Turned out to be something else but Real steel don't accept the unit back. I think that its a Unilite PCB that goes inside the dizzy but I'm not sure about Mallory stuff as I use MSD myself.

Thanks to all for your help so far.

This morning I removed the dizzy cap, cleaned it and sprayed it with a little WD40 and started her up, no change. I ran the engine for about 30 seconds to warm the manifold slightly and checked the manifolds by hand for heat difference. I could feel that No.7 was cooler (each exit point on the manifold I could only hold my fingers there for about three seconds and my fingers then got a very heated but on No.7 I could leave my fingers there with no problem, warm but not scorching, not recommended I know but I didn't have a infared thermometer!)

So not convinced that the fault was electrical I checked the compression again on No.7, I got ZERO compression. I checked it again afer ten minutes (not started the engine inbetween time) and this time I got 150 PSi!!!

So I started it again and run it for 30 seconds then checked the compression again (No.7 is extremely difficult to get to and impossible to connect my compression tester without touching the manifold, hence short running time!) this time the compression test came up ZERO again!

Your thoughts please, Head gasket/Cracked head?

I can bypass the AMP but not done that yet after finding out the above.

Why at Christmas I ask myself?! Heck why anytime!

LDV8 wrote: I checked the compression again on No.7, I got ZERO compression. I checked it again afer ten minutes (not started the engine inbetween time) and this time I got 150 PSi!!!

So I started it again and run it for 30 seconds then checked the compression again (No.7 is extremely difficult to get to and impossible to connect my compression tester without touching the manifold, hence short running time!) this time the compression test came up ZERO again!

From those results one would say that you have either a sticking valve or, less likely, perhaps a sticking lifter.

It also seems to be affected by temperature -ie, no compression when hot, but compression when cooled down after 10 minutes. Then zero compression when run again for a short while.

As to the root cause, perhaps a blocked oil-way.

Not sure if a huge dose of upper cylinder lubricant or an active oil cleaning additive would bring relief, before having to strip things down.

Someone might know?

I guess it can not be a spark thing then!

You could run the engine with the rocker cover off to see what's going on with the valve gear when there is no compression.

Thanks guys, I will check out both the sticky valve with the rocker off and run some cleaner through the system I've got some wynns in the shed and a new can of oil.

Please, what oil do you recommend for the RV8, its in a working van and I don't thrash it. I first used 10w40 but I was advised to use 20w50, so I'm presently using 20w50. Good, Bad or plain Ugly?!

She has always had a very slight tap, minor but noticable.

Fingers crossed

Merry Crimbo all and thanks again for your help.

sidecar wrote:I guess it can not be a spark thing then!

You could run the engine with the rocker cover off to see what's going on with the valve gear when there is no compression.

Yes - something very odd with those compression readings. For there sometimes to be compression and not at others I'd suspect a sticking valve and lots of noise. But if a valve started sticking with the cylinder firing I'd also expect some backfiring, etc. It's not something I've come across on an RV8.

DaveEFI wrote:

sidecar wrote:I guess it can not be a spark thing then!

You could run the engine with the rocker cover off to see what's going on with the valve gear when there is no compression.

Yes - something very odd with those compression readings. For there sometimes to be compression and not at others I'd suspect a sticking valve and lots of noise. But if a valve started sticking with the cylinder firing I'd also expect some backfiring, etc. It's not something I've come across on an RV8.

Maybe the valves are staying closed due to the lifters not retaining oil or something like that. If that is the case then maybe cylinders in question won't backfire as they won't take in any fresh charge. Like you say its all a bit odd!