Ignition Issue

[michael sundler]

I wonder if anybody can help me, please. I have a CAV GT40 with a 348 Ford Boss engine with MSD ignition running on 48IDA Weber carbs and seem to have an intermittent problem which I beleive is in the ignition system. Sometimes the car will run fine (last time indicated 430 bhp on the dyno) but after putting it in the garage it will only run on about 4 cylinders! I have take a couple of the plugs out and tried to test the spark but it seems very weak and I think that throttle pumping on starting is causing some of the plugs to foul up with the weak spark unable to burn the fuel on some of the plugs
Any help or guidance much appreciated!

 

[Randy V]

From my own experience, it is pretty darned hard to fuel fowl a spark plug when you have a properly operating MSD ignition system.

I would verify spark at each plug with a spark tester that is grounded.
There have been some occurences lately of failed or failing MSD boxes and you may be having that trouble. Make sure that the BIG RED wire from the MSD is goingright to the positive post of the battery or at least to a high amperage capable bus bar that is connected to the battery drectly. That wire should NOT be running through the ignition switch.


Make sure your fuel pressure is no more than 3.5 PSI at the carbs. Remember when pumping the throttle with Webers, you are dumping the fuel right into each cylinder unlike with a shared plenum intake with a single carb - therefore, it is far easier to flood a car with Webers..

 

[Chuck]

Try opening up the mixture screw a bit on the offending cylinders. That may at least tell you if it is fuel or ignition

 

[michael sundler]

Thank you Randy. I too think that the MSD box may be the problem, do you know of any way to determine if the problem is in the amplifer box or in the coil itself? The problem seems also to be intermittent which makes me think that the MSD box may be at fault (rather than the coil) - do they fail in this manner do you know?

 

[Randy V]

Hi Michael,

Ignition coils are pretty solid performers although they can weaken with age and/or heat. If the ignition is fine when cold, then acts up only when hot, the coil may also be considered as a possible source. From the sound of it though, your MSD box may be to blame. It takes special test equipment to test them out. Depending on the type of distributor you have, you may be able to bypass the MSD box altogether. But if your distributor is simply a trigger and has no built in amplifier, you will need both pieces to make it work.

 

[Rick]

Michael:
Much blame is put on MSD boxes that is unwarranted. They do have two enemies: Vibration & Excessive Heat. They do not generally pick and chose random cylinders to misfire. In your situation be sure the MSD box is electrically grounded AND mounted on rubber isolators to minimize transmitted vibration. Check ALL electrical connections, including the switched 12 volt source for the small red wire. Put in fresh plugs or make sure they are dry and not carbon fouled. Get it running to your satisfaction. THEN when you park it, make certain (look into the carb throats with a flashlight) fuel is not dripping out of the auxilliary venturis and pooling on the throttle plates and into the cylinders. This may be your problem as it will take out both cylinders fed from a single carb. It can be caused by high float levels, bad needle/seat (fuel valve) or excessive fuel pressure too. IF this is happening the plugs in the offending cylinders will become wet and will not fire. I experienced this myself.

 

[michael sundler]

Thank you Rick, I'll certainly look into this fuelling aspect also!

 

[Mike Pass]

Buy a cheap spark tester so you can see if there is good voltage at all the plugs. Lots on Ebay at about £5.00.
eg: SILVERLINE AUTO IGNITION SPARK TESTER | eBay

If no sparks at all plugs then there is an issue with the MSD or coil. Very quick test fro sparks or fuel.

Cheers
Mike

 

[David in Durango]

MSD installation instruction will give you a method for checking spark. (although I have one that won't run but checks HOTHOT spark, sigh).

I am no fan of MSD, but they should put out a spark from hell . . . .

Good luck.

By the way, I just pulled a set of plugs on a 302 w/ a miss (all black and sooty) and two were wet. Check the plugs and find your exact miss! I'm going a step hotter and a little bigger on the air jets.

Again, pull the plugs and find your exact cylinder misfire - someone must have said that already, right?

 

[Mike Hayes]

I had the same problem with the MSD Ignition system on my CAV it was the centre pin inside distributor cap had worn away, changed the cap and rotor arm, no problems since.

Mike

 

[michael sundler]

Thanks Mike I will check this also - stupid question but how does the cap come off the MSD distributor? I have little access and cannot really see; is it just a push down fit or does it have some (concealed) clip or retaining feature?

 

[DaveM]

Michael,
There are 2 Phillips head screws that hold the cap on. Center electrode burning out is a common problem. Make sure the rotor tab contacting it is bent upward enough for good contact or new cap will suffer the same fate.

 

[michael sundler]

Thanks everybody for your input - put problem persists! I have replaced MSD distributor cap and rotor (as recommended) and there is certainly a good spark (now!) and on completion it fired up and ran fine!. Next day, early Sunday, ready for a nice drive - pushed the car from the garage not to wake the neighbours and then - it would not start! I will now try to fit a pressure regulator and gauge on the fuel line to see if there is a problem on the fueling side. Any suggestions on what product to go for bearing in mind fuel pumps are supply 48IDA Webers - or better still what the real cause of the problem is? Thanks for any input.

 

[Neville]

Hi Mike, I had a strange experience with my CAV, similar set up_ 302 ford on 4x48 ida webers, mild cam svo alloy heads, 180 degree exhaust, msd ignition, fuel pressure set @ 3.5 pounds. Took my wife out in it to blow the cobwebs out and noticed the tachometer jumping around a little, car still ran o.k. . if I would lean back in the seat driving the tach would work well, if I moved forward the tach acted up, couple of days later I decided to try to figure out the problem, I guess I got lucky? after pulling the seats and center console out, I found the main front to rear harness had just nicked the sender wire for the tach on a sharp edge on the handbrake support. No problem, insulate the wire and relocate the harness, car ran and drove fine for a couple of months. Take another drive on a nice day in the winter with my wife, after 2hour drive car dies on side of empty road, long story short, the msd 6al box with external rev limiter box packed up- no spark!!! sent pieces to msd they said the tach wire short may have led to the failure . Bought a new msd 6a with no rev limiter for about $170, car has been flawless, I may buy new 6al with their dial type rev limiter in the future if I track the car. Anyhow , it sounds like a spark problem and not fuel, let us know what you find, all the best for now, Neville Nesbitt.

 

[michael sundler]

Thanks Neville - very interesting, I can certainly confirm that on (attempting to ) start the tachometer needle is jumping all over the dial; something that I dont remember seeing previously. I'll try to check out the wiring as you suggest.

 

[Rick]

Generally the tach needle jumping is an indication of the PRIMARY SIDE side of the ignitiion being faulty. This would include the primary side of the coil, its connections, the field coil pickup inside the distributor, the air gap between the reluctor and field coil inside the distributor and the the reluctor OR the wires running from the pickup to the MSD box could be picking up Electromagnetic noise in the engine compartment or its mounting area.