Help! Cranks but won't start

[Lated]

I took my truck out for a drive and didn't make it far before I ended up on the side of the road waiting for a tow truck. Truck had been running fine but while going for the 1-2 shift, I heard a pop from under the hood and the engine died. I tried cranking the engine but nothing happened, the lights wouldn't come one, nothing. After popping the hood I noticed my 50 amp main fuse was blown (installed when I rewired the truck a few years ago with a Painless harness). I wired around the fuse just trying to get the truck home and now it cranks but won't actually start.

Where should I start looking for problems, and any ideas what could have pulled enough juice to blow the fuse in the first place? Truck has a small-block 400 with unknown internals and an HEI dizzy.

[cdowns]

i'd start by checking if the thing has sparks when it turns over by removing a plug holding it to the block and lookin

if no i'd check for 12v supply goin to dizzy// if yes then change module if no i'd b tracin the wire to see why not

[geezer#99]

Maybe your voltage regulator got stuck and your altenator went full charge and the link burned out to protect the battery. THere could be more than one link in your system blown or even some fuses blown too.

[Lated]

Thanks for the leads. If it ever stops raining I'll go out and see if I can trace it down.

[Lated]

Made a little headway this morning. I don't think the voltage regulator is at fault because it is downstream from the blown fuse. If it was the culprit it would have fried the battery before the over power got to the fuse (it's in the positive side between the batter and alt). I'm fairly certain that I have a big short somewhere that is allowed to much current draw which blew the fuse. I haven't checked for good spark yet because I'm not convinced the short has stopped.

Without a battery installed, I checked for continuity between the positive and ground wires with the ignition on (and nothing else) and found that there is indeed continuity. If I'm thinking correctly, the only thing hot when the key is on is the hot wire for the coil. Is this right? I have an HEI and can easily pull the coil and check for a short.

[luvbowties]

Originally Posted by Lated

Made a little headway this morning. I don't think the voltage regulator is at fault because it is downstream from the blown fuse. If it was the culprit it would have fried the battery before the over power got to the fuse (it's in the positive side between the batter and alt). I'm fairly certain that I have a big short somewhere that is allowed to much current draw which blew the fuse. I haven't checked for good spark yet because I'm not convinced the short has stopped.*(GOOD, LOGICAL, AND SAFE THINKING, LATED!!!)

Without a battery installed, I checked for continuity between the positive and ground wires with the ignition on (and nothing else) and found that there is indeed continuity. If I'm thinking correctly, the only thing hot when the key is on is the hot wire for the coil. Is this right? I have an HEI and can easily pull the coil and check for a short.

*QUOTE: I haven't checked for good spark yet because I'm not convinced the short has stopped.*(GOOD, LOGICAL, AND SAFE THINKING, LATED!!!)

Blowing a 50-amp fuse sounds like a BIG short. Therefore, I'd check for something BIG, like the pos. battery cable shorting against a hot exhaust. Personally, I can't imagine the hot wire to the dizzy blowing such a heavy fuse--tho' I've definitely been wrong before!

Since the 'pop' happened as you went for the 1-2 shift, it sounds like it also happened as the engine torqued upwards on the driver side and downward on the pass. side. [Normally, mounts allow much more movement up on driv. side than down on pass. side, indicating problem might be on driver side.] Another high-amp circuit--associated with the shifter column--may be in the horn circuit, so inspect this circuit including the horn relay.

Also look for shorted wires going to/from ammeter--if you have aftermarket gauges installed. If you find one of these wires shorted, I'd say it is a good time to remove the ammeter circuit and replace with a voltmeter circuit--it pulls sooooo much less amperage, gives just as good an indicator of the charging circuit, and requires much smaller wires to install. IMO, ammeter wires give many inches of vulnerable, large-gauge wire, carrying high amps available that can cause extensive electrical damage if breached--so why risk it? [[Another personal idea of my own is that the negative-going half of an ammeter is wasted when installed on an alternator system, as alternators charge/output power, even while at idle. With modern alternators we use on our trucks, they always keep the ammeter's indicator-needle pointing to break-even(middle of gauge)or up, depending on amount of power being outputted--never in the negative half of the gauge.]]
HTH,
Sam

[Lated]

Got it running. replaced everything from the coil down to the ignition module and it fired right up.