Cranks but won't start

[MY 4 BY]

I did a search and found a lot of good info, and tried those suggestions, but it still won't start. I recently installed a 4Wheeljunky wiring harness, and have not been able to start the truck since. The engine will crank over, but no fire coning from the ignition coil, going to the dist. (secondary high voltage side) With the key on the coil (+) posistive terminal has battery voltage.(primary low voltage side) I've tried 3 different known-good coils and 3 different known-good coil wires (coil to dist.) I've run a jumper wire from battery (+) pos. to coil (+) and still no help.I have a MSD Pro Billet dist. with MSD Blaster coil, that all worked fine before the wiring harness install. All suggestions will be appreciated.

 

[1975SPORT]

i dont have any superhero stuff, but from my experience i would check to make sure the distributor cap was tight and they points were good (if you have points). Then recheck all of my spark plug wires, and if i removed any of them for any reason make sure that they are in the proper order. Im sure you have tried this stuff but i have been broken down a couple of times and figured out it was the cap. Also, this may be a stupid question, but if you have two tanks (or just one) are you getting fuel, is one empty or both, is it a bad filter, or a bad fuel pump.

 

[Madgyver]

Air, fuel and spark.... Troubleshoot in that order...

Sounds like you don't have spark, Check wiring to MSD box...

 

[70_Steve]

Disconnect the distributor from the + and - side of the coil. Turn the key ON (you have voltage at the coil, right?) Take a jumper from the coil - side to ground, then lift the jumper from ground. You should get a spark if the coil is good.

Your distributor is wired like this, right?

 

[Ohio Bronco 21]

Sounds like your coil might not be getting spark.

 

[MY 4 BY]

Mad, the MSD box is not hooked up right now, so can't be that.

70 Steve. Yes I have battery voltage at the coil and my distributor is wired as in your diagram. With the dist. (+) & (-) wires disconnected at the coil, and a jumper wire hooked to the coil (-) and key on, I do get spark on the other end of the jumper when touched to battery neg.

 

[70_Steve]

I do get spark on the other end of the jumper when touched to battery neg.

Sorry, should have been more clear. You should get a spark on the high voltage side of the coil.

The coil creates the high voltage when the magnetic field inside the coil collapses. When you ground the jumper wire, current flows through the coil, creating a magnetic field. When you remove the jumper, the magnetic field collapses, creating the high voltage necessary to cause the spark to jump the spark plug gap.

I would suggest trying grounding the jumper wherever you have the distributor wire grounded, as in the wiring diagram, as well as to the battery -.

 

[MY 4 BY]

70 Steve, I must be doing something wrong. I have performed that coil test on three, what I thought were, known-good coils with what I thought were three known-good, high voltage, coil wires. Does the metal case of the coil have to be grouned?

 

[70_Steve]

Does the metal case of the coil have to be grouned?

No, I don't believe it does. From what I remember, the high voltage connection is actually a center tap on the primary coil.

I'm kinda wondering if it isn't a grounding issue. You may want to do that coil test a couple times, getting the voltage and ground in several different places.

 

[MY 4 BY]

Steve, I tried it again, using the same grounding location as where the dist. is grounded. Still no spark on the high voltage side of the coil. In my first post you may have read, that I installed a 4Wheeljunky wire harness. When I did that I also installed a 1 in. wide 12in. long braided ground strap from the fender mounted starter relay mounting bolt to the frame where, the dist. is grouned. So I think that the electrical system is well grouned.Any other ideas?

 

[70_Steve]

Steve, I tried it again, using the same grounding location as where the dist. is grounded. Still no spark on the high voltage side of the coil. In my first post you may have read, that I installed a 4Wheeljunky wire harness. When I did that I also installed a 1 in. wide 12in. long braided ground strap from the fender mounted starter relay mounting bolt to the frame where, the dist. is grouned. So I think that the electrical system is well grouned.Any other ideas?

Review your grounding scheme. Negative battery cable should be bolted to the engine block. This is because the biggest current draw is the starter, which is grounded internally to the engine block. This ground also provides the ground for the ignition system (spark plugs, etc). Then there should be a ground (strap?) from the engine block to the body. The body ground is extremely important, cause everything else electrical grounds to the body (lights, radio, etc). The frame ground is kinda important, but very few things ground to the frame. The only thing stock I can think of is the fuel level sending unit.

Try the coil test again, just getting 12 volts and the ground directly from the battery.

 

[MY 4 BY]

Review your grounding scheme. Negative battery cable should be bolted to the engine block. This is because the biggest current draw is the starter, which is grounded internally to the engine block. This ground also provides the ground for the ignition system (spark plugs, etc). Then there should be a ground (strap?) from the engine block to the body. The body ground is extremely important, cause everything else electrical grounds to the body (lights, radio, etc). The frame ground is kinda important, but very few things ground to the frame. The only thing stock I can think of is the fuel level sending unit.

Try the coil test again, just getting 12 volts and the ground directly from the battery.

Yes neg. battery cable is bolted to the engine block, with another cable running from the block to the frame, and the braided strap mentioned earlier, from that connection on the frame to one of the bolts that secures the starter relay to the inner fender.