Ignition Coil, Distributor or Other?

All,

Your expertise needed.  I've gotta relatively strange intermittant engine stalling-generally only found to occur when the vehicle reaches operating temperature AND lower rpms (never happended on the highway, just in-town driving).  Symptoms appear as though my electronic fuel pump is going out when its stalling (no backfiring), but this was recently replaced and still exhibits the same issue.  I was told that either the ignition coil was to blame or perhaps the distributor.  I "thought" if a coil goes bad, it plain fails, never a gradual decline in function.  Is this true or can the temperature cause this symptom?  Likewise, can higher temperatures point to the distributor as the culprit?  Is there any way to tell if its one or the other before I go shelling out money, better yet keep forkin over jingle for tow rides home.  Perhaps, its something totally different.

Here is my set-up
(converted Jeep CJ-7 86)
Chevy 400ci
MSD High Vibration Coil P/N 8202
MSD Ready-To-Go Distributor P/N 8360
Holley Truck Avenger carb


Checked timing (ok), Checked the filter (that's ok), all fuel lines ok, dropped the tank (no obstructions).  

got a timing light????   can you hook it onto the coil wire...   tape the trigger on..  drive around with the timing light taped to the windshield..    so you can see if the ignition drops out when the problem happens...


do you have a filter before the fuel pump????    i have had other fuel pump internal bypass valves hold open and dump all the fuel pressure and volume.. this was do to dirt in the fuel system..

just curious./ what kind of exhaust on it..      headers or stock SBC exhaust manifolds with a heat riser valve on the right side...   if the heat riser valve is stuck closed..  the actuator is bad.. the vacuum hoses are bad.. it may close and redirect most of the right hand exhaust stream across the intake manifold and out the other side.. this really overheats the intake and carb...

there is a small possibility that there is a heat soak problem with the ignition system at slow speeds when there is not a lot of air flow through the engine compartment..    i could not find if the module on the msd  needs to be mounted with white thermal paste... or dielectric tune up grease..  so the heat build up can be transfered to the housing and then dissipated to the airflow..

there is a small chance that the coil is causing the problem..   but with the timing light on the windshield to diagnose drop outs..   you will be able to narrow it down to ignition or fuel system..  

When it stalled out did you ever check to see if carb was squirting fuel?  

I bought and installed a new MSD coil and darnit it happened again, but didn't completely stall or quit running (just acted like it was going to go out).  Could the points on the distributer be bad...just thinking here.

Thanks, I'll try the timeing light trick and see if I can duplicate it.

BTW: I do not have a filter before the fuel pump, but recall that a screen (if this justifies as a filter) is included within the inlet port of the elecric fuel pump.  My exhaust is  not stock and have headers.  

You're "heat soak" theory is interesting, because I do have a aluminum radiator with a puller fan and generally speaking my engine compartment gets pretty darn hot, but in a Jeep CJ there is plenty of open spaces for heat to dissipate (on the other hand unless I'm moving down the road there is not alot of air movement).

Maybe the module is bad and heat is causing the problem.  When do you know when your module is faulty?

Many thanks for advice!!  

Nope, but I wished I had.  I was in the worst possible place when it happened and more focused on trying to move the vehicle than be under the hood.  I'm no carb expert by any means, but here's perhaps a hint that it could be carb or fuel related too.  When it stalls or acts like it wants to,  I'm between 1-2k rpm, step on the pedal and then it stalls or it becomes fuel starved.  At idle or at higher rmp (highway driving), it has never stalled yet, but always when stepping on the accelerator. Should I look into troubleshooting the carb - its 2-3months old?
Thanks  

Hi there,
 What fuel pump are you using and what pressure is hitting the carby?
   Modulaters and condensers generally do NOT give warning of once only
 failure.
 I have a ZZ4 under the bonnet of my D/Jag where the heat on a hot day
 is cruel and with 2 different systems have had NO ignition problems in
 9 years.I went back to the stock standard G.M. big boy H.E.I.and no sweat.
  P.S. I gave up on using a points type Dizzy 25 years ago but that's me.
  Hope all goes well from Skyeking....  

Are your fuel lines anywere near a heat source. Sounds like vapor lock to me. The fuel is boiling in the fuel lines. Sometimes you can put your fingers over the vent tubes on the carb and it will push fuel out the boosters because the pump is pushing vapor into the bowl. When it does it let it sit and cool down and see if it starts. Usually about ten minutes.  

I would take fuel lines loose and blow air thru them. You could also take the elec fuel pump off and check to see if its pumping the correct GPH. That would help elimanate some components  

Thank you for all your responses, its greatly appreciated.  I just wanted to provide an update.  So, I've narrowed it down to it NOT related to ignition (coil, distributor)issues and seems like it is "heat soak" or vapor lock.  This leads to more questions and exaclty "how" to fix or prevent this from happening.  Question #1) Would wrapping all lines with Cool Tape (i found this in Summit)cool the lines down enough?  Does anyone have experience and success with this?  Question #2) Could my gas tank be contributing here (vented vs. non-vented).  The vacuum canister was removed long, long ago and tried to find another one (even junkyards couldn't provide the same configuration) so I was told by a friend to ensure to "vent" the tank by running a line much higher up positionally than the tank.  So is this line supposed to be open, plugged or would a two-way valve be sufficient? I installed a two-way valve because fuel was spitting out expecially when I was refilling with gas.  Question #3) Perhaps a higher rating gph fuel pump would work too?  Any thoughts?  Question #4) Part of the fuel line is wrapped in ss-braded lines and think this stuff retains heat vs. help dissipate it.  Question #5) Should I chuck the electric radiator puller fan and go with a conventional set-up?  

Many, many thanks!!!!!  

First thing to do is see if any of the fuel line is touching a rad.hose or heater hose. I had one vapor locking with me because the fuel line was touching bottom rad hose.  

Yeppers....that was it.  Fuel line was in direct contact with BOTH rad.hose and heater hose.  I re-routed the line, drove the vehicle and haven't had it happen again.

I hope this thread comes in handy for others for such a simple fix.  It saved me from a full re-direction of my fuel-line from any heat sources, wrapping and moving my pump near my tank.

Many, many thanks!!!  

Hi There,
    Nothing succeeds like success. Good to hear that all is O.K.

    Sometimes the most obvious is the least noticed..Skyeking...  

When you learn things the hard you will always remember them. My vapor locking problem happened about 20 yrs ago. Glad you got it fixed  

Holy (insert profanity)...it just stalled AGAIN.  Been driving several days without incident and behold it happens.  Immediately thereafter I checked fuel line temperature (definately not as hot), let it cool down then it started up.  Do electric fuel pumps go bad intermitantly?  

i had a holley red pump that would go out intermitently...
took it out of the system and went back to mechanical pump

years later, pulled the pump out of the cabinet and got curious...pulled it apart and cleaned it all up...gave it 12 volts and she spun like new...there was some gunk build-up in various parts...most likely caused from mounting the thing on the frame rail...it was on a full-sized truck...probably caught alot of splash from the tire