Spark at coil not at plugs

[cliffhaas]

Hello all. I appreciate the opportunity to pick your collective brain.
I am a new owner of a 1986 CA 5.0L EFI Bronco. The truck came to me a couple of weeks ago and I was told ran well except when first started. I drove the truck through a tank of gas and the more I drove it the more I felt the engine have trouble at idle and sometimes felt as though it were dropping cylinders.
I checked TSB's and as a result replaced the IAC motor and added the adjustable IAC spacer. This didn't seem to correct the issues and as I drove it more was convinced it was an ignition system failing. I replaced the pickup and the distributor mounted module. That still didn't alleviate the issue of rough running and stalling so I went and installed a rebuilt distributor (maybe my replacement parts were faulty?) and a new coil as I have had experience with these going bad on an old e series Ford. The truck started but ran rough and then stalled and wouldn't start again. I had a pulse at the injector but no spark. I installed a new ECM. It started and ran for 15 minutes at idle and shut itself off. current status is that I get fuel pump running with key on for a brief time as I should. I get good ground on 20, 40 and 60.I get hot on 1 and with key on I get hot on two other pins (37 and 57 I believe). The coil gets 11.7VDC on the + with key on and I get a pulse on the -side. I get 3.8VAC checking the #6 term at the module. I get spark out of the coil wire at the cap (new cap and rotor as well) but no spark at the end of the plug wires. I am baffled. The only codes I have been able to pull are 14 and 18. I have checked for grounds and dont see anything dirty or missing but clearly I am missing something. Any insight would be a great help.

[Gary Lewis]

Welcome!  Glad you found us.  

Have you looked and the No Start procedure in Electrical/EEC-IV diagnostics?  As you'll see, the first thing they have you check is the voltage at the throttle position sensor.  But, then they have you check for spark at a plug and, failing that, spark at the coil.  If you have spark there they suggest checking the cap, rotor, and wires - although I don't have that section shown.

So, if you have spark on the coil wire and not at the plug I'd concentrate on the distributor.  Have you checked to see that the rotor spins when you crank the engine?  I'd think that with spark and the coil and the rotor turning you'd have to get spark at the plugs unless there's a serious short on the high voltage side within the distributor.

[PetesPonies]

If you have spark coming out of the coil, you have done everything that needs done, except travel down the line to ground. The line is the plug wire and ground is at the electrode as the plug is screwed into the head. The head should be grounded because the engine is grounded. Check your engine ground.

[cliffhaas]

Gary Lewis wrote

Welcome!  Glad you found us.  

Have you looked and the No Start procedure in Electrical/EEC-IV diagnostics?  As you'll see, the first thing they have you check is the voltage at the throttle position sensor.  But, then they have you check for spark at a plug and, failing that, spark at the coil.  If you have spark there they suggest checking the cap, rotor, and wires - although I don't have that section shown.

So, if you have spark on the coil wire and not at the plug I'd concentrate on the distributor.  Have you checked to see that the rotor spins when you crank the engine?  I'd think that with spark and the coil and the rotor turning you'd have to get spark at the plugs unless there's a serious short on the high voltage side within the distributor.

Thanks very much Gary. I did check the voltage at the TPS and the reference voltage was just below 5 with an idle output voltage of about .9 moving up to 4.75 at WOT. The rest is still baffling me.

[cliffhaas]

PetesPonies wrote

If you have spark coming out of the coil, you have done everything that needs done, except travel down the line to ground. The line is the plug wire and ground is at the electrode as the plug is screwed into the head. The head should be grounded because the engine is grounded. Check your engine ground.

@PetesPonies, I have been grounding my meter and test light as well as the spark tester at the block and have even added a couple of new grounds as a test using jumper cables from the battery (-) to the AC bracket and the radiator support. Your comment does make me think I should test to be sure the heads themselves are actually well grounded. It seems far fetched to me that they wouldnt be given that the block is but at this point if I had all the answers I wouldn't be pestering you guys. Thanks!

[Gary Lewis]

As said, I would concentrate on getting spark to the plugs.  If you have spark at the coil but not to any plug (you need to check all of them) then I would say there's one of two things going on.

First, verify that the distributor's rotor is turning when the engine cranks.  Perhaps the gear stripped or the roll pin sheared or the timing chain is slipping by a worn-out sprocket.

Second, make sure the rotor is good.  If the rotor has a hole in it then it is possible for the spark to come in on the spring in the center and right through the rotor to the distributor's shaft, which is ground.  So swap out the rotor to see if something changes.  And then try a different cap.

[cliffhaas]

Guys, Thanks for all of the input. I checked the rotor turning and looked into the other items you noted. Finally I decided that I would try to buy my way out of the problem if I coudn't get it fixed and replace the system with an MSD ignition box and distributor (8456K from Jegs). My last try was to before that was to buy a distributor cap adapter. That lower portion of the plastic below the actual cap was the only thing in the distributor that I brought from one distributor to another. As unlikely as it seems, I grounded my tester to the exhaust manifold and got spark out of the coil as well as out of the plug wire.
Thanks again for all of the assistance.

[Gsmblue]

Oops! Deleted as inhad not read thenlast post properly!

[Gary Lewis]

Cliff - You now have spark to the plugs?  But does the engine run?