Ignition/Fuel Problems??? - I'm Stumped!
 

I’ve got an ignition issue – or possibly a fuel issue- that I can’t figure out. It’s gotten progressively worse over a period of almost two years, and now it’s approaching fatal. I’m hoping that better diagnostic minds than mine can help pinpoint the problem.

About two years ago, I noticed that the car would start up just fine, but after I’d been on the road for 4 or 5 minutes, it would stumble badly. Occasionally it would simply lose fire completely and stop. It would crank, but wouldn’t catch at all. After waiting a couple of minutes, it would start up and run fine. The problem didn’t occur every time I drove the car, but was more likely when the car sat for a week..

Over time, it’s gotten progressive worse. Now, every time I use the car, it will stumble and then die – no fire at all. I have to wait 3 or 4 minutes, then it will start, run rough for a few moments, then clear and run fine, but only for a couple of minutes. Then it’ll die again. After about three of these start and stop episodes, it’ll start and run rough for a while, then clear and run perfectly. Start it up the next day, and it’ll run fine. Let is sit for a week, and all the problems reoccur.

I was fairly certain it was a fuel issue, until I recently noticed that the tach (electric) would bounce all over whenever the stumble occurred – leading me to believe the issue is electrical, not fuel-related.

I’ve got an MSD Pro Billet distributor, no ignition box and no ballast resistor. I’ve replaced the coil and tightened all connections in the ignition circuit, but that hasn’t remedied the situation.

Could this be the distributor pickup gone bad? If it weren’t for the tach going crazy when the engine stumbles, I’d think this was a fuel issue (I have checked the fuel filter, and it’s clean) – but is there any way a bad fuel pump or debris in the carb jets could cause this? Other than that, I’m stumped – and would really appreciate any ideas you might have.

Thanks.

Hey Gary, Even though you do not have an external ballast resistor, very often the actual "run" wire to the coil is a resistor wire that does the job of a stand alone ballast resistor. These often go bad. In the start mode (when turning the key), you run off a different wire for full voltage. Once the key springs back to run mode, you go thru the resistor wire.

regards
Ed

May I suggest a couple of diagnostic items?

Electrical:

1. Until you isolate the problem, strip the unknowns. Remove the MSD box, the strange or funny ignition items and anything else that may inhibit the firign of the spark plug.

2. Make the ignition system as basic as possible. Then run the car and see if it does anything like what it was doing.

Fuel:

1. Remove any questionable situations from the fuel delivery system. If you are drawinf fuel over a hump, up hill or over a long distance, fix those to gravity feed until you find the problem.

2. Strip all of the unusual things from the fuel system. If you have three filters and one is so small it might be stopping fuel flow, bypass it.

3. Install an inline fuel pressure gage and monitor the fuel pressure at the carb. Run the car and see if it does what is did before.

I messed with this same type of problem for a year and was so frustrated, I wanted to hire someone else to fix the problem. Finally, I did a system by system check and found an assortment of things that made the car die.

Once the car is running and you can take it out without incident, add ONE and I mean ONE item at a time until you determine what is the cause of the problem.

I ended up with a new location for a fuel pump and a new pump itself. two new fuel filters and I tossed the ignition assist box ( an old CD ignition system ). I also ended up with new wires and plugs.

Just my $0.02

This is in the primary side of the ignition. The electric tachometer reads the pulses created by the trigger mechanism in the primary (low voltage) side of the ignition system. It sounds like you have done well by acknowledging the "irradic" behavior of your tachometer as being an indicator. If the tachometer did not move, that would indicate another type of problem. To eliminate the tachometer itself as a potential problem, disconnect IT from the MSD (?) box or coil and see if the problem still exists. Secondly, replace the field coil in the distributor. Heat can indead cause an open circuit that will park you next to the road until it cools down. Let us know how this comes out. We all benifit from each others "Trials and Experiences". I am asuming you have checked all the grounds including the one for the ignition box itself (?)

Agree with Parker;
Check grounds!!!
Keep it simple; mechanical/electrical parts seldom fail randomly then recover.
Most likely an electrical ground. change one varible at a time until you isolate it

gn

the magnetic pickup could certainly cause your problem, I would also look at the ignition module in the distributor also, the pickup and the module could be one and the same, I have never messed with an MSD distributor, I had a Ford Ranger that did basically the same and it turned out to be the pickup

Gary,
I would also like to hear when you solve your problem. I am in the middle of the same thing right now. My car has died on me three times now. It has been after hard acceleration. It starts to stumble, then it dies. Since my carb has flustrated me for a while now, I sent it off to be reworked. I have it back now, but have tried it yet. I have already checked all grounds, replaced the battery, and checked all the other connections. When I get mine figured out, I will also post.
One other thing that happened to me in the past was, I had something get stuck in the needle for the carb float. The car would start, run a bit then die.
Scott

What kind of carbs do you guys have?

Jerry

You need to isolate the problem as being either fuel, or ignition. Take some diagnostic tools with you on the road. When the car craps out, check for spark. If spark is present, check for fuel. You'll drive yourself nuts if you can't at least narrow it down to one or the other.

Holley 1000cfm 4150.

The next time it won't run, take off the air cleaner, look down the carburetor and open the throttle fully one time. If fuel squirts down into the engine and it still won't start, it must be electrical.

Gary, It could be one of the 47 wires you have attached to your coil that is dragging down the ignition circuit !!! Sorry, . . I had to say it! :rolleyes:

Ed

Yup! All identified except for the one mystery white wire - without which the heap won't run. :confused:

Thanks everyone for the good diagnostic suggestions. I really appreciate 'em. I'm going to begin work on this tomorrow, and I'll post whatever I come up with.

Thanks again.

I have had a similar problem in the past and it was a bad crimp in a crimp lug.
The lug was bolted down tight but the wire was not held firmly by the crimp.
Just something else to check.
Cheers,
Bryan

Silk,
If the electrical aspect has been eliminated:
When the car "dies out" if it happens to be at low rpm or idling the problem could be fuel flooding caused by high fuel pressure. This would effect the idle circuit of the carburetor. Pushing fuel past the needle and seats. After the car stalls, even more fuel pours into the carb, which may explain the hard to start issue. If you do not have a fuel regulator (that works) on your system this type of problem may occur.

Silk-i had a similiar problem.A piece of? got underneath the magnets in the MSD pick-up and cracked a magnet.As long as the two pieces of the lower magnet weren't too far apart,it'd start & run.Then it would just die.But would immediately start back up when i hit the key.Then one night it wouldn't start(at a car show of course).That's when i found the cracked magnet.

Starting issues sound familiar
 

Bret Ewing:
Your diagnosis sounds like my problem. Car is has always been "tricky to start and now will not start unless the carb is "dry" and I spray a little starting fluid in there. Then it starts, but if I let the rpm's too low, it will die, and will not start again (which is a problem I have not had before) until dried out and with a new squirt of starter fluid. The the whole cycle repeats itself.
It is an ERA 427 with a 351 and a 750 four barrell Holley.
OMathisen:confused:

Gary,
It sounds like the pick-up coil in the distributor. That would be a good place to start.

Well, the problem appears to be resolved. Pulled the dizzy, replaced the mag pickup, cleaned things up (amazing how much corrosion/crap can get inside one of these things) and reinstalled. The problem appears to be resolved, so I'm pretty sure it was a bad pickup. The real test will be firing it up after sitting for a week, but I'm guardedly optimistic.

Thanks for all the good advice/suggestions. I really appreciate it!

Sounds like you are lean. Close idle screws (clockwise on a non-smog carb) and back out 2 turns. If this does not work, your butterfly's may be dialed too far open. Also may be a vacuum issue, check for leaks.