Ignition problem (I think)

[Wayne Maybury]

OK, here we go. I will try to explain the problem to see if anyone has any ideas that may help. This car has been on the road for 5 years and never given me any problems at all.

I have a 351W with a 750 dp Holley, mechanical fuel pump, solid lifter Comp cam and all the other regular goodies. Ignition is via an MSD distributor, MSD Blaster 2 coil, and an MSD 6AL box.

Here is the problem and what I have tried so far. Once the engine has been running for about 5 to 10 minutes from a cold start and has just heated up to the normal operating temp, it begins to mis-fire, buck, back fire, you name it. I can just barely keep it running. The car will move in first gear if I don't press too hard on the gas. Going up a gear or pressing too much on the gas results in worse operation. When it did this the first time, a friend thought that a float needle maybe sticking. I took the Holley off, pulled the bowls, pulled the float needles, everything was clean. The power valve was also checked and was fine. The fuel filter had a couple of little specks in it but no big deal. Fuel levels were checked. Put the carb back on, same problem. Fuel pressure is 5 to 7 lbs so the fuel pump is not the problem.

Now for the really strange part, if I shut it off for just a couple of minutes, it will start right up and run normally but in a minute or two it will begin to miss, buck, etc all over again. It really appears that this problem is heat related. If I shut it off for an hour, it will run normally for 5 minutes then start to act up.

I thought that maybe it was the coil. Changed the coil, same problem. Checked all wire connections, grounds, etc. Everything appears to be normal. Called MSD, they suggested a couple of tests including removing the wire from the center of the distributor, tunring on the key, jumping the 2 wires that feed to the box from the distributor to see if the coil will arc from the wire which is placed a 1/2" from a ground. Lots of spark. MSD tech says that this test proves that both the coil and the 6AL box are working normally.

With virtually no where else to turn, I ordered a new pickup coil which I should get in 2 or 3 days. The parts supplier said that he has not sold an MSD pickup coil in years but I was the fourth person to order one in the past 2 weeks. Strange coincidence but no help to me.

Anyone have any ideas? Don't tell me to check the gear on the distributor or the timing as the engine will run normally if it is allowed to cool down, even for just a few minutes. I cannot go far from home to test it as I am now affraid that it may crap out completely. Each time it acts up seems to be worse than the time before.

Regards,
Wayne

[Ron61]

Wayne,

That is a weird thing and you have already looked at most of the logial suspects. Does the car still miss and act up if you are at a stop once it starts to do it? Do you have a neutral safety switch on the car?
How hard would it be for you to switch to a regular ignition system for a while and eliminate all of the MSD stuff?

Ron

[HighPlainsDrifter]

Wayne,
It sounds like your ignition is just fine.
I would check for a vacuum leak in the intake manifold gasket area. Put a vacuum gauge on the carb,see what your vacuum is at startup, then when it runs ruff. Also spray soapy water / wd40 around intake gasket area and bolts and carb base gasket., if the engine runs better then you need to replace the gasket.You may have a warped intake manifold.
Good Luck,
Perry.

[flipper35]

I agree, sounds like you are sucking air. When it's cold you are running rich enough, but after it warms up your choke is off and you get too lean. Good luck.

[ERA Chas]

I think you're on the right track with the pickup coil. Four orders in two weeks with virtually none before is no coincidence.
It's a bad BATCH from MSD that might be the same age as yours, IMHO.
Did you start the car recently with a Battery Tender attached? That's what kills Unilite modules.
Ask me how I know.
Good luck,

[HI Cobra]

Wayne,

I have a 351W also and went through something similar to your problems
a year ago - after 4 years of running well. You may not have this in
your ignition system but since I do and it was the problem I thought I'd throw
in my solution. On my firewall I had a NAPA Mustang computer chip thingy
in an aluminum case that was about 3" x 5" x 1" that went bad. If I sat
anywhere long enough for heat build up in the engine compartment the
car would just quit. Wait 10 minutes and was fine. We checked everythig
to no avail. It died at a friend's house and we tried a trick he had heard
which was to put a wet rag on it and cool it down - worked fine. I left it
on there and made it home - got the new box and haven't had a problem since.
If you have this type controller it could be your problem. $70 to replace.

[Wayne Maybury]

Thanks for the replies,

I have ordered the pickup coil and should have it tomorrow. If it still does the same thing, I will begin to look for other possibilities.

I never considered a vacuum leak but I somehow doubt that this is the problem since it is almost like a switch being flipped. It instantly goes from running perfectly to really bad. I can just barely keep it running and sometimes it will quit all together. If I let it sit for just a couple of minutes, it starts and runs just fine for a minute or two then starts to buck, back fire, etc.

HI No computer chips in that car, only the MSD box.

Wayne

[Rick Parker]

Do you have a point type distributor or for that matter another distributor (maybe a friends?) that you can use temporarily? You may justify your decision or find it is the MSD box itself. BTW points are triggered by the white wire. I chased a similar problem and ultimately realized the distributor was out of phase (trigger wires reversed). The motor would not run past about 3800 RPM without missing and generally running very poorly. I changed coils, overhauled the carb, plugs all to no avail. Not until I stuck a point type distributor in did I realize my error.

Rick

[bkozlow]

Wayne,

My guess is it is the coil or the MSD box. Many times electronics fail because of heat. The condition you describe is similiar to a common problem with mid-60's 289 HP engines in Shelby GT-350's. In this case it was bad condensers that broke down as the engine compartment heated up. I belive it is your MSD box. It may have checked out OK when it was cold but did you check it when the engine wouldn't run?

bill k

[xlr8or]

If you are sure it's a heat soak problem get the car warm so it starts acting up and put an ice pack on the coil and msd box to see if resolves it. If it does you know where the problem is.
You might also want to check your fuel line. Make sure it's not too close to the exhaust and causing a vapor lock. The fact that it runs but stumbles may be the fuel isn't getting to the carb when hot and letting it sit get the fuel bowls full again.

[Wayne Maybury]

I am relatively sure that it is a heat problem, well as sure as I can be considering that I still don't know what the problem really is yet. I feel that there are 3 possibilities as some of you have identified already. The distributor (pickup coil), the coil, or the MSD box. I tried another coil which didn't help and my MSD box is in the trunk away from any heat so that leaves the pickup coil.

I'll let you know what happens when I change the pickup coil. Right now the distributor is in pieces waiting for the new pickup coil.

Wayne

[bkozlow]

Wayne,

Just because the MSD is in the trunk does not mean it is not a heat related problem. It could be the solid state circuits are heating up and breaking down. This can happen regardless of where the unit is located. I hope your pickup coil is the problem and replacing it cures your trouble, if not it only leaves the MSD box.

Bill K

[CobraEd]

Check out the ballast resistor!!!!! They go bad exactly in the way you are experiencing.

[Yetiman]

With the MSD setup he doesn't need a balast resistor... but if he indeed has a balast resistor it could be a likely culprit. Could try bypassing it if there is one.

I had an MSD 6AL go bad on me two weeks ago. I had an intermittant misfire as the car warmed up that got worse and worse. The box itself started making noise like ignition noise on a radio (even though i don't have a radio), and finally made a loud pop; and the engine died.

I was running a points distributor, so i was able to bypass the 6al and get home. Mine was not even a month old, and was 'infant death syndrom'.

New box and i'm rockin'... but i installed a terminal block for the wiring so it will be easier to bypass roadside when it flips out again.

[RallySnake]

Wayne,

Did you mount the coil vertically or horizontally? If it's mounted horizontally, the oil doesn't cover all the internal coil wires and they overheat. It should be mounted with the big distributor wire at the top.

Paul

[Wayne Maybury]

The pickup coil still isn't in so the Cobra is quietly sitting in the garage but this has at least given me lots of time to get my 66 Mustang finished.

As far as I know, I do not have any resistor. I did not install one and the only possibility would be if there was one somewhere in the wiring harness which I really doubt.

I am hoping that it is the pickup coil as the 6AL box is the only other possibility and it is much more expensive.

Paul, my MSD Blaster 2 coil is mounted vertically. I tried another coil (Ordinanary Ford coil) and the problem was the same, maybe even a bit worse. I think that I have narrowed the problem down to the pickup coil or the 6AL box.

Wayne

[wtm442]

May sound dumb, but make sure the metal tang on the rotor is making solid contact with the center post on the inside of the cap. I had a car acting similar to what you mentioned about 20 years ago. Took me about 2 days and $100 to fix. Stupid

[Wayne Maybury]

OK it looks I have finally found the problem.

After changing the pickup coil, the MSD box, and fianlly the MSD coil, I had run out of "components" to change. The engine still did the same thing which was to cut out after running for some time. Let it sit for a couple of minutes and it would start right up and run normally, then stop again after a few more minutes.

I pulled the dash and took a look at the wiring. Checked all the connections on the ignition switch, grounds, etc. All was OK. I then noticed that a 10 wire connector didn't look right. The two parts were not perfectly in line with each other. I checked the wiring and sure enough the wire second from the end that was not properly inserted was the switched "+" feed to the MSD box. I took the connector apart and cleaned all of the metal tabs, put it back together and wrapped it with black tape to prevent it from coming apart again since it is necessary to push it into a tight place before re-installing the dash.

I have to assume that once the engine was running for a while, the connection would get hot and somehow enough resistance would build up to upset the current to the MSD box. Turning it off for a couple of minutes would allow the connection to cool down and re-establish the proper connection. I took it out last night and it ran fine. Time will tell if I really have the problem solved.

Wayne

[Tongue Pirate]

Almost sounds like a fuel delivery problem. Any rubber lines under the hood that might be collapsing when warm? Or could there be anything between the tank & the carb or the carb inlet clogging things up? If there was a clog in the line it could be like your toilet where the water will eventually pass but not fast enough to keep the carb fed?

[SCOBRAC]

Dirty Carb or bad gas... run some chem tool through a half a tank. if that does't work you'll need to install a carb kit, cleaning the air passages and fuel passeges carefully.