thanks all-- lots of great info here!

Specifically - check your condensor in your distributor. Simple fix (and cheap) and easy to replace.

I went through virtually the exact same thing the summer before last. I changed the pickup coil, the coil, and the MSD box. It still would stop without warning then start right up after cooling down for a while and run just great until it would eventually stop again. Since I had changed all of the parts that could cause this, I decided to check all of my wiring. I found a bad connection in the wire from the key (ignition) to the MSD box. Fixed that connection and never had a problem since.

Check all grounds, wiring connections, etc. It is possible to bi-pass the wiring harness by running a wire from the positive post on the battery to the "switched positive" wire on the MSD box. This may tell you if you have a problem in your wiring but it will not tell you if you have a bad ground somewhere.

Wayne

For those using an MSD box, for longevity of the box itself, you are better mounting it under your dash and away from the heat of the engine. Got this one from an EX MSD engineer............

Bill S.
edit for spelling only

I cleaned all the connections and grounds tonight. I am concerned about the ignition switch too -- it feels a little loose. I bought a new one tonight and will wire it in when it arrives.

We just had a similar problem with our Cobra after trailering it all the way from the Seattle area to Arizona. Dale was about to dive deep into the ignition/fuel mix possibilities when he happened upon a check list that mentioned the fuel filter as a possible cause. Yes, we had black soot, too. That was it! Replaced the filter and it's been running great!

I agree with MR Mustang, mount the box inside out of the heat and it will work better. I had a similar problem with an old truck i had and it was the MSD box.

Question:
You said you were running it hard, or something to that effect. If it is a MSD 6AL what chip do you have in it. The MSD box could be shutting down and then relighting. You may want to just take the chip out all together.

Also, as mentioned above the condenser will also cause similar problems. As mentioned they are cheap and easy to replace. I have seen a condenser act like this in the past when the headers were changed.

What work if any have you recently performed on the car? This may give us some more clues.

Going to clean the fuel filter too. Holley VoluMAX Fuel Filter -- does it just unscrew at the bottom?
Its a manual choke.
About the MSD -- does it have a chip? the only thing I see is a jumper that says 7000-- so that must be the safety over rev.-- is this what I should pull or something else?
The condenser is something I need to check too.

Unless you are absolutely sure you have found the problem, I would suggest a test drive after fixing or changing something rather than tearing everthing apart at one shot. If you change many things at the same time (without finding clear evidence of the problem), there is no way of knowing what the problem was so you don't know what to look for if it ever happens again later on.

It would appear that you have a 7000 RPM rev limiter chip in your box. An MSD 6AL box comes with several chips including a 7000. The MSD boxes generate some heat on their own and do not like to be over-heated so they should be located in a cool area, preferably not under the hood and certainly not right beside the headers.

Wayne

Bolmida,
Yes that is a 7000 RPM chip.

So that tells us you have a MESD 6AL box. This is the same ignition box I had and I had very similar problems that were heat realted. If the box is in the engine compartment, move it to inside the car. I know it is a pain in the butt but it has to be done.

When you stated you "in it hard" Was this just before the pop? If so you may have peeked the chip and the MSD box shut down the power to the distributer. This most definantly will cause the problems you are describing.

The MSD is trying to do what you have ask it to do. By putting the 7000 RPM chip in the box you are asking the box to limit the revs the engine is allowed. Thus the 7000 chip. You have a few choices you should choose careully. You can either change the chip to a higher number 7500, 8000 or remove it all together. The box cam with several other chips. If you do not have the other contact MSD for replacements or take it out all together.

The MSD will work with no chip in it. It simply works like the MSD 6 box, the difference is the "AL" which indicates the automatic limiter.

If you re not sure the red line point on the car you should be VERY carefull remoeving the chip all together. I ran mine without one at all but I knew the limits of the engine, I never raced it.

Try that and let us know. Also as Wayne said do one thing at a time.

I don't think it's the rev limiter chip. When the rev limiter kicks in, it does not shut down the ignition entirely. Instead, it intermittently interrupts the signal to the coil alternating off and on which prevents the engine from rapidly shooting up in rpms. When the rev limiter kicks in, you'll know it because the car will have a bad miss. If the rev limiter chip (it's actually a rev limiter resistor) goes bad, the rev limiter will either kick in at the wrong rpm or you won't have a rev limiter at all. The chip itself should not cause the ignition to shut down.

Have you tried a different coil? Coils can cause the symptoms you've described.

Chris

The group has already given some great hints and common theme is coming out as an electrical/electronic fault and I also agree. An easy ignition test to help nail down fault would be checking the ignition at the plug. Remove a plug wire and crank engine looking at spark at the plug (this should be a neon blue color) a yellow or orange spark is a weak low voltage result showing need to replace coil, condenser or last the box. Check when cold so you can compare if it fails when hot.
Also watch your volt meter because MSD units hate low voltage and will faultier at low supply voltages (low is anything below 12.0 VDC) Ignition system could be fine but drop out after battery V drops from fans and running on the battery if charge system is funky but easy to check the gage. An engine running should show about 13.5 to 14.5VDC at 2K rpm. Hope you find it soon so you do not have to worry anymore. Jeff C

What an ugly coincidence this is! I read this post yesterday and the next ride I take the Cobra suddenly dies for several seconds, and then backfires like a 12 guage shotgun, (scaring the sh** out of the lady in the front yard), and then continues on as though nothing is wrong! I did a quick U-turn back to the garage so as not to be stranded.

I re-read this post and checking the battery on the charger, found it very low. It is being trickle charged now and hopefully this won't happen again.

There may be a slight draw on the battery when the car is off which, over the months takes it's toll. I'll turn off the power switch in the trunk for long periods of hybernbation but possibly this old 1 wire alternator is not charging sufficiently either. Battery is a new Ultima Yellow Top.

Oh Joy!

You said you had spark and fuel, was that right after when the engine backfired?Also when you checked for spark was it at the coil tower or the spark plug boot?
Mike.

Im the guy who started this posting. I did a full ignition test today and it all checked out. Im starting to think its the fuel pump. I have a Holley electric pump and I understand they are prone to failure. Tonight it cut out a couple times but was able to get it restarted again. Whats my pump pressure suppposed to be? when i pulled it in the garage tonight it was only 3 psi-- it should be around 5-8 i think...

Its the fuel pump -- ordering a new one tonight! Thanks everyone for you help with this-- Bolmida

Good going.

How does the fuel pump make it backfire though?

Bolmida,

I run two MSD boxes and two electric fuel pumps exactly because of problems like yours. Push a switch and you're on the backup. I highly recomended it!

Paul

I'm now completely convinced to ditch my Holley pump (and regulator).
Just got through ordering an Aeromotive pump #11203 and their regulator.