v8 still misfiring

ramon alban · Post by **ramon alban** » Sat May 14, 2011 2:29 pm

shawser wrote:Well i cleaned coil, no arcing. Took ht lead off dizzy from coil and cranked engine, sparking no problem,

It does seem like its the timing and its way out, but i just cant undersdstand why, when dizzy was never touched.

As you gradually eliminate the faults, so eventually you'll solve the problem. No Arcing is good!

Progress, but I did suggest there was more than one issue.

Were you able to correct the LT wiring to prevent strain on the coil?

As previously advised try setting the timing to 4 deg BTDC and also check that the plug leads have not been put on to the dizzy in the right order but starting in the wrong place - - No 1 lead would normally be the first one anticlockwise from the front retaining clip.

sidecar · Post by **sidecar** » Sat May 14, 2011 2:54 pm

If you set the lump up with 4 degrees at idle you will end up with around 20 all in. (Well that would have been the case on the Opus that I looked at)...How much BHP can you afford to lose?

For a 3.5 lump you need to be running 36 all in.

ramon alban · Post by **ramon alban** » Sat May 14, 2011 3:47 pm

sidecar wrote:How much BHP can you afford to lose?

Right now I reckon it would be nice to have some BHP to lose. ':(' But with approximately none and the engine showing symptoms of a timing problem and worse, because of the lack of proper description of the parts being used, its by no means certain what system is being used.

Requested dizzy part number but without success so far.

No harm can come by trying 4 degrees to see if the timing issue can be resolved or eliminated.

sidecar · Post by **sidecar** » Sat May 14, 2011 4:06 pm

ramon alban wrote:
No harm can come by trying 4 degrees to see if the timing issue can be resolved or eliminated.

......Very true!

Really I think that the opus system whilst being better than points really is not up to much.

Any of the later systems are more reliable and usually provide a better timing curve. (Or can be modded to get a good curve)

Slightly blowing my own trumpet here but I've spent 3 years fine tuning the ignition system on my 4.6 and on a couple of 3.5 lumps. The amount of power lost both low down and further up the RPM range when using the standard settings is quite shocking!

I now run a programmable MSD with a locked up Lucas-MSD hybrid dizzy, I actually have a 'sorted' Lucas 35DML8 and amp kicking about in my garage but not too sure whether to offer it for sale or not. (I have the coil too).

Muscle Manta's 4.6 now runs the same MSD setup as mine, his face was a picture on the test drive after fitting it! (I was in the passenger seat, my face was not a picture!)

Anyway back to the plot, I'm sure that the motor can be made to run the the opus assuming that its not actually knackered in any way, it's got to be a problem that can be found using some logic!

shawser · Post by **shawser** » Sat May 14, 2011 4:28 pm

checked the leads, no1 is to the right of clip at front of engine, all the rest are in correct firing order. cant see a part no for dizzy, coil is a lucas ballasted 12v. dizzy is the type with the small condenser type thing on side of dizzy body.If the alternator was wired wrong, could that cause any ignition problems? really scraping the bottom of barrel now.

sidecar · Post by **sidecar** » Sat May 14, 2011 4:57 pm

shawser wrote:checked the leads, no1 is to the right of clip at front of engine, all the rest are in correct firing order. cant see a part no for dizzy, coil is a lucas ballasted 12v. dizzy is the type with the small condenser type thing on side of dizzy body.If the alternator was wired wrong, could that cause any ignition problems? really scraping the bottom of barrel now.

If the dizzy has a condenser on the side and does not have points then it must be an Opus (hopeless) jobbie. I can't see how the alternator could mess things up. You can check the alternator by measuring the voltage across the battery without the engine running then with it running, it should go up around 1.5 volts with the motor running.

Have you tried turning the engine over by hand (using a spanner on the crank or via a back wheel with the car in top gear. Get the engine to around 5-10 degrees before TDC. Then take the dizzy cap off and check where the rotor is pointing to. It should either be pointing to number 1 HT post or 180 degrees way from it. (In which case turn the engine one full turn). If the rotor is pointing anywhere else your timing is up the spout!

shawser · Post by **shawser** » Sat May 14, 2011 6:05 pm

checked timing again, seems fine to me. certainly close enough to fire engine up. coil arcing again. Anyone got a secondhand electronic ignition i could buy?

sidecar · Post by **sidecar** » Sat May 14, 2011 6:37 pm

shawser wrote:checked timing again, seems fine to me. certainly close enough to fire engine up. coil arcing again. Anyone got a secondhand electronic ignition i could buy?

I have one, not too sure I want to sell it though!

....but everything has a price, its a 35DML8 with the amp on the side, its had the vac advance locked up and the canister removed. The bob weight springs are setup to give an all in figure at 2700 RPM. It may need tweaking to suit a 3.5 lump so that you get 36 degrees. (Made up sleeves to adjust this, I reckon that if I remove the sleeve it will be bloody close if not spot on)

The Lucas rotor arm has had the location peg dremelled out and a new one fitted to get rid of rotor arm mis-alignment which a lot of dizzies can suffer from. It has a wobble drive on the bottom with a 'slot', not a 'peg'

I know that these dizzies go for a fair bit on fleabay so make me an offer!

I'll bung in the coil for nowt!

ramon alban · Post by **ramon alban** » Sat May 14, 2011 9:25 pm

You mention a 12 volt ballasted coil and its arcing again.

Something here is at odds with normal convention,

The ballast resistor systems were basically designed to use a 9 volt coil as mentioned - early doors - so your 12 volt coil might explains why the wiring was changed to bypass the ballast resistors.

I personally have not come across a system that was ballasted and uses a 12 volt coil.

Moving on however, the whole point of HT coil and dizzy turrets, insulations, rubber boots and plug leads is to contain the high voltage, not to let it out where it can be seen - under any circumstances.

If your ignition system is arcing then four possible (logical?) reasons come to mind.

1 there is still dirt/grime/damp around those places mentioned

OR

2 someone has fitted a high energy coil and it is simply battering the system with A voltage too high for the stock insulation components.

OR

3 some or all spark plug gaps are set too wide and the sparks are preferring to find their route to earth via any other means.

OR

4 One or more spark plug leads are broken and the sparks for those cylinders are arcing across to their neighbours and causing the misfire.

NB, for No 4 to happen implies that there is too much HT voltage.

Regarding a replacement Distributor etc.

If you go for either 35DM8 or 35DLM8 - seen here

http://www.v8engines.com/electrics-1.htm

Then your circuit diagram will need to be something like this:

However because its a stock 3.5 ignition system diagram, that also implies using an unmodified Dizzy with conventional vacuum advance and conventional Timing in the range 4 - 8 deg BTDC.

If you use something modified, be prepared for some empirical sessions.

sidecar · Post by **sidecar** » Sat May 14, 2011 10:19 pm

The engine has a Eddy 500 fitted so it is already non-standard, the vac system (ported or non-ported) of this carb does not work well with any of the Lucas vac advance systems which is why I modified the 35DML8 to suit this type of carb.

It is possible to use the vac system if you run a really low static advance and stiff bob weight springs but the performance will suffer. Running more idle/static advance and allowing it to be all in quite early more than compensates for the lack of vac advance. If you run half decent timing figures AND the vac system the engine will kick back when the throttle is just cracked open at 3000+ RPM

DaveEFI · Post by **DaveEFI** » Sun May 15, 2011 7:50 am

sidecar wrote:
ramon alban wrote:
No harm can come by trying 4 degrees to see if the timing issue can be resolved or eliminated.
......Very true!

Really I think that the opus system whilst being better than points really is not up to much.

Any of the later systems are more reliable and usually provide a better timing curve. (Or can be modded to get a good curve)

Slightly blowing my own trumpet here but I've spent 3 years fine tuning the ignition system on my 4.6 and on a couple of 3.5 lumps. The amount of power lost both low down and further up the RPM range when using the standard settings is quite shocking!

I now run a programmable MSD with a locked up Lucas-MSD hybrid dizzy, I actually have a 'sorted' Lucas 35DML8 and amp kicking about in my garage but not too sure whether to offer it for sale or not. (I have the coil too).

Muscle Manta's 4.6 now runs the same MSD setup as mine, his face was a picture on the test drive after fitting it! (I was in the passenger seat, my face was not a picture!)

Don't want to hijack the thread - but any chance of seeing the advance curve or table you've used? I'm running an MS with EDIS, and I've seen a million different ignition tables for the RV8.

The MS does of course use a vacuum reference.

sidecar · Post by **sidecar** » Sun May 15, 2011 8:25 am

DaveEFI wrote:
Don't want to hijack the thread - but any chance of seeing the advance curve or table you've used? I'm running an MS with EDIS, and I've seen a million different ignition tables for the RV8. The MS does of course use a vacuum reference.

Hi Dave,

The 35DML8 does not have a table as you know because it just uses springs, when I ran this dizzy I ran 12 static 32 all in. (I now think that this was 95% OK but not spot on). My MSD has allowed my to experiment very easily and the results are quite good. (I've finally been convinced after chatting to V8Dev that the 4.6 only needs 28 degrees all in) Some of my finding could be used on the old dizzy.

Muscle Manta's MSD uses a MAP sensor so in fact it does have a vac advance system, for reasons that I won't bore you with I can not use one even though I run the same MSD system so I'll tell you what we did on his car.

I've never managed to get any pictures or graphs up on this forum so I'll just explain what settings we went for. (The MSD software does use a graphical system)

0 to 700 RPM= 7 degrees advance (Makes it easy to turn the engine over).
700 to 1000 RPM= 16 degrees advance (a flat line between the two RPM's). After reading a few books on ignition and messing about with both our 4.6 lumps I can say that both 'like' the 16 degrees figure even if it is way off what Rover specify! The tickover is smooth, the exhaust pulses out of the tail pipes are at a minimum and the vac that the carbs pull is at its highest.
1000 to 2700 RPM = advance climbing to 28 degrees advance.

Paul's (Mr.Muscle) car pulls 15 inHg at tickover and 21 inHg when cruising.
At 17 inHg we started to add vac advance, as the vac climbs to 21 inHg the total vac advance is 14 degrees.

So when cruising at 21 inHg with over 2700 RPM showing the total advance is 42 degrees, as soon as the vac drops below 17 inhg the total timing is 28. In between the two vac figures the timing is a 'mixture' of mechanical advance and vac advance. The MSD MAP sensor is connected to the non timed port of the Eddy 500 carb. (There is no need to use the timed port with this system). The timed port on this carb also has issues anyway, when the throttle is just cracked open cruising about the port does not 'see' the full manifold vacuum, as the throttle is opened slightly more is see's more vacuum. Once the throttle is opened even more the vacuum then drops off again. Sorting out the system to deal with that mess was not worth the bother which is why we used the non-timed port.

shawser · Post by **shawser** » Sun May 15, 2011 10:55 am

Think i will take out old wiring on opus system and rewire, take out all plugs, clean and regap them. Then try again, process of elimination now.

crappycresta · Post by **crappycresta** » Sun May 15, 2011 1:01 pm

hi my car is doing the exact same thing ,i have done nothing to the car and it is getting worse,back firing through carb,very undriveble,thought it was timed wrong,ended up richening carb runs much better,now going to change main jets ,may change rods to.
cheers Al

crappycresta · Post by **crappycresta** » Mon Jun 13, 2011 6:56 pm

just put 83 in secondries,86 in primaries,67-55 metering rods,silver springs.in carb ,turned fuel regulator up to 5 ,sorted running great now ,no back firing.
cheers Al

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