Need Help: 720 hit pothole, died, won't start, pops when trying

[gone2long]

I have a 1979, gas powered, Datsun pickup. Just had it completely rewired, and the carburetor jets, etc were cleaned about 6 months ago. Fuel filter is not clogged and elec fuel pump works. The timing chain, chain tensioner, rings and valves were replaced 3 years ago, with only 2,000 miles driven since. The distributor cap looks OK and the coil is only a few weeks old. The points are a bit pitted, and the spark from the coil looks yellow, not blue in daylight.

 

However, the truck ran fine, until I hit a 2' deep pothole in the road at about 15mph, and it simply died.  Will not start, and it backfires during the starting procedure. What could be causing this problem? I thought that the distributor or points might have shaken loose and moved, but all screws seemed tight. Chain tensioner loosened and chain tooth slipped? Possible, but no wierd sounds from the timing chain. I have heard that a "vacuum leak" could be the problem, makes sense given the shock of the impact, but where to look? Could a hole in the exhaust pipe cause such a problem? Please help.

[datzenmike]

Chain cannot slip a tooth.

Hole in exhaust won't do this.

Spark should be able to jump 1/2"

 

 

What engine? L series?

 

Backfire through the carburetor?

Is the choke working? Could be a lean backfire on start up.

Are the plug wires on in the correct order? 1,3,4,2

Try starting at night in the dark... look for any blue flashes on the wires or distributor cap and coil.

 

Backfire out the exhaust...

Loose wire to the coil or from coil to points.

 

 

[gone2long]

Thanks, engine is Z19. order and choke ok.  will tell what I find out after another look.

[gone2long]

yes, back fire through carb = lean  mix or the opposite? vacuum leak? wires ok.

[bottomwatcher]

1. 99% hit bump no worky = electrical issue! 2. 90% electrical issue is bad ground somewhere. Hot humid climate refer back to 1&2. Clean all connections from battery to coil and report back.

[racerx]

Check coil connection or ballast resistor

[gone2long]

23 hours ago, bottomwatcher said:

1. 99% hit bump no worky = electrical issue! 2. 90% electrical issue is bad ground somewhere. Hot humid climate refer back to 1&2. Clean all connections from battery to coil and report back.

As earlier noted, entire electrical system was professionally replaced just week's ago, and coil is new.  Coil connecting wires are all tight as are the others I looked at.  No dirt or grease present. Bad ground is still possible I guess.  .  Gonna be hard to find, so where exactly to look first?  Ground from battery to engine block is heavy cable and seemed solid as a rock, last time I checked it. - a few weeks ago.  Will double check, however. 

 

Ground connection at the battery terminal could have loosened enough to cause a problem, so thanks for the reminder.  It looked OK, but I didn't bother to wiggle it.  Probably should have done that as my first check.  Will make sure it is good and tight. 

 

Still thinking it is a lean mixture, as electrical would not cause the pop, right? 

 

Thanks again,

 

G2L

[gone2long]

23 hours ago, gone2long said:

yes, back fire through carb = lean  mix or the opposite? vacuum leak? wires ok.

I understand now.  Would be lean, as air would be sucked into the mix from an intake manifold, hose or other leak, right?

[gone2long]

3 hours ago, racerx said:

Check coil connection or ballast resistor

See above.  

[gone2long]

Here is a thought.  If I have a vacuum leak and cannot find it, will adjusting the mixture at the carb to make it richer solve the immediate problem and get the truck running again? 

 

It is stuck out on a country road, and I am afraid it will get vandalized if I leave it where it is for long.  Need to get it closer and get somebody who really knows his or her stuff to look at it, if I can't solve the problem myself.

[datzenmike]

You can only adjust the idle mixture and that may not be enough if the leak is large enough. Try closing the choke and force a rich condition. It will likely rev up pretty high.

 

Is the distributor loose? May be out of time.

[bottomwatcher]

Stuck on country road get it to locals house/ farm to prevent vandalism. Only electrical drops you after a pothole. Unless mechanical suspension issues. Otherwise hit pothole engine stops= electrical.

[Stoffregen Motorsports]

Start checking all the electrical connections. Luckily, on a car of this vintage, there are only about two dozen, so it shouldn't be difficult.

 

Could be the ignition switch too. They get loose from years of in-out, in-out.

[gone2long]

Thanks folks, for your help.

 

Trying to make a bit more sense than an episode from the Twilight Zone, let me report the following:

 

As mentioned earlier, the only item that I could find amiss were my points, which were somewhat pitted.  Though I was sure that this could not be the root of the problem, I decided to replace them anyway.  Did not bother to reset them as when the engine died, they were completely closed, so I simply put them back in exactly, or very darn close, to their original position.

 

Before reinstalling the points, however, I noticed that the PARKING LIGHTS were on.  That was very strange, because I had left the truck overnight with all lights off, the ignition key completely turned off, and the key pulled completely out of the ignition switch.  Not knowing how the parking lights could possibly be on the next morning, with the key out, and suspecting some kind of short, I pulled the fuse which governed the parking lights, and, as expected, they went off.

 

After a few minutes, I put the fuse back in, just to see what might happen, and, inexplicably, the parking lights STAYED OFF.  I had (and have) no idea how this could be possible, but not wanting to risk any type of electrical complication, I pulled the parking light fuse once again.  

After that,  I cleaned up the dizzy cap and rotor, both of which were a bit greasy and worn, then installed my new points in the same position that the old ones were in.  I cranked the ignition switch, and "viola" the truck started.

 

I drove it home and today, reinstalled the fuse, installed a new brake light and started her up.  No problem whatsoever, all lights working, and the truck starting with no problem as long as all of the lights were turned off.  It did refuse to start immediately when turning on the high beams, however, so there still maybe some kind of electrical issue going on.  Again, however, both the battery and coil are only a few weeks old.

 

Important to note is that, I only gave a cursory glance to my spark plug wires when originally trouble shooting the problem because I assumed that when I had the truck "completely rewired" a few weeks ago, that the electrician had changed the spark plug wires as well. Today, however, I found that this was not the case and that the number one plug cover was cracked and brittle.  Perhaps hitting the bump caused it to lose enough conductivity to let the spark escape and stall the truck, and that was the original cause of the stall?  Still doesn't explain the parking lights being on with the key off, however.

 

In any case, I taped up the cracked wire and the truck is running well again.  Will replace the wires, dizzy cap and rotor as soon as I can find the parts.

 

Does anyone have a rational explanation for any of the above?

 

At least she is running again now, so thanks to all of you, for your input.

 

Best,

G2L

[gone2long]

Maybe, as one poster noted above, the ignition switch is faulty and makes some sort of connection when it is supposed to be off???  

[Stoffregen Motorsports]

3 hours ago, gone2long said:

Thanks folks, for your help.

 

Trying to make a bit more sense than an episode from the Twilight Zone, let me report the following:

 

As mentioned earlier, the only item that I could find amiss were my points, which were somewhat pitted.  Though I was sure that this could not be the root of the problem, I decided to replace them anyway.  Did not bother to reset them as when the engine died, they were completely closed, so I simply put them back in exactly, or very darn close, to their original position.

 

Before reinstalling the points, however, I noticed that the PARKING LIGHTS were on.  That was very strange, because I had left the truck overnight with all lights off, the ignition key completely turned off, and the key pulled completely out of the ignition switch.  Not knowing how the parking lights could possibly be on the next morning, with the key out, and suspecting some kind of short, I pulled the fuse which governed the parking lights, and, as expected, they went off.

 

After a few minutes, I put the fuse back in, just to see what might happen, and, inexplicably, the parking lights STAYED OFF.  I had (and have) no idea how this could be possible, but not wanting to risk any type of electrical complication, I pulled the parking light fuse once again.  

After that,  I cleaned up the dizzy cap and rotor, both of which were a bit greasy and worn, then installed my new points in the same position that the old ones were in.  I cranked the ignition switch, and "viola" the truck started.

 

I drove it home and today, reinstalled the fuse, installed a new brake light and started her up.  No problem whatsoever, all lights working, and the truck starting with no problem as long as all of the lights were turned off.  It did refuse to start immediately when turning on the high beams, however, so there still maybe some kind of electrical issue going on.  Again, however, both the battery and coil are only a few weeks old.

 

Important to note is that, I only gave a cursory glance to my spark plug wires when originally trouble shooting the problem because I assumed that when I had the truck "completely rewired" a few weeks ago, that the electrician had changed the spark plug wires as well. Today, however, I found that this was not the case and that the number one plug cover was cracked and brittle.  Perhaps hitting the bump caused it to lose enough conductivity to let the spark escape and stall the truck, and that was the original cause of the stall?  Still doesn't explain the parking lights being on with the key off, however.

 

In any case, I taped up the cracked wire and the truck is running well again.  Will replace the wires, dizzy cap and rotor as soon as I can find the parts.

 

Does anyone have a rational explanation for any of the above?

 

At least she is running again now, so thanks to all of you, for your input.

 

Best,

G2L

The parking lights can be used without the key in the ignition switch.

 

Sounds like an incomplete circuit somewhere, and the circuit is "seeking ground" through your parking lights. Yes, very twilight indeed, but totally explainable with science.

 

Did you just say that you had your truck completely re-wired? As in electrical? Have you contacted the guy who did the wiring? He could have gotten something wrong.

 

If that's not what you meant, then another question - does your wiring have any non factory connections, ie- hack fixes? Twisted wires, blue crimp connectors, wire taps, etc?

 

When posed with wiring gremlins, the most likely and usual suspect is bad grounds. There are a handful throughout the car that should be checked. One ground that is commonly missed is the one that goes from the engine to the chassis. They get taken off during engine work, and sometimes not reinstalled. Also, the battery negative should have a ground to the body as well.

[gone2long]

Hi again, thanks.  Yes, had an auto electrician re-wire the vehicle.  Where would the engine to chassis ground be on a 720 pickup?

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[datzenmike]

The negative battery cable is bolted to the intake if you have a Z series engine and the head behind the fuel pump if you have an L series, but in all cases it's bolted to the engine block. You can make your own ground to the body yourself.

[gone2long]

Quote - "Sounds like an incomplete circuit somewhere, and the circuit is "seeking ground" through your parking lights. Yes, very twilight indeed, but totally explainable with science.

Did you just say that you had your truck completely re-wired? As in electrical? Have you contacted the guy who did the wiring? He could have gotten something wrong.

If that's not what you meant, then another question - does your wiring have any non factory connections, ie- hack fixes? Twisted wires, blue crimp connectors, wire taps, etc?

When posed with wiring gremlins, the most likely and usual suspect is bad grounds. There are a handful throughout the car that should be checked. One ground that is commonly missed is the one that goes from the engine to the chassis. They get taken off during engine work, and sometimes not reinstalled. Also, the battery negative should have a ground to the body as well." - Quote

 

I don't quite understand how an open circuit for one utility, let's say the ignition circuit, could "leak" electricity into a separate circuit, but, then again, there is an awful lot that I don't understand about 12v wiring.  Wanted to mention that the parking light circuit  was marked "tail lights" so apparently, they are on the same circuit as the parking lights.  Does that sound right?  One of the tail lights was burnt and was stuck in its seat.  Had to use WD40, and pry it out with a pliers.  Could such corrosion cause the wierd brake light activity, like juice from the tail light going where it should not?  I would not think so, as the seat seems well insulated from any contact with the chasis and from other wires. 

 

Also, if there is an "open circuit seeking ground through my parking lights", does such a condition present any real danger to the electrical wiring as a whole?  Could it cause a fire, or malfunction of a critical system, like the ignition circuit?  Woudl adding an extra ground myself, from the block to the chassis (as suggested by Mike) help remedy the problem?  On a related note, I found the battery - to - block ground, but the only ground from the block to the chasis seems to be the suspension system.  That is, given that the engine mounts  do not "insulate" the engine from the chasis.  Would appreciate your insight relative to the above.

 

Thanks again,

 

G2L  

  

 

[datzenmike]

A corroded bulb socket may affect operation when on, but it can't turn on without the light switch in the first or second position.

 

The front parking light, rear running lights, L&R front and rear market lights, license light and the dash lights all turn on with the headlamp switch in the first and second pull out position. They are not connected to the headlights at all and have their own fuse. 

 

With so many bulbs I doubt is being used as a ground because there would not be enough power to light all the bulbs. More likely there is a +12 volt supply that is touching the parking lights wires.

[gone2long]

Thanks Mike, appreciate your insights.  Now, gotta find that 12v supply. That will be fun : 0

 

Best,

 

G2L

[gone2long]

Wondering if a faulty switch, which appeared to  be off, could have actually been sending current to the parking lights when it should not have.  I will keep an eye on the situation while driving and see if the problem reoccurs.  Thanks again, G2L

[gone2long]

Latest Update:

 

Put in a new coil and ballast resistor.  Replaced the spark wires.  Put in new plugs, new points, had the carburetor cleaned a second time and had the engine tuned and timed by a very experienced mechanic.  Badda bing, the pop went away, and she is running very well.

 

However, other problems have surfaced, as per my related post regarding a rattling sound at high speed and the electrical problem below:

 

As noted in an old post, I had the truck recently completely rewired.  The truck has run well for a couple of months, but one day I noticed that, when turning the key to the on position, my headlights turned on.  Also, the fuel gauge simply stopped working, and so did the temperature gauge, which is really worisome.

 

What could have caused these problems, and what to do about them.

 

Will post this in a new thread if that is more appropriate.

 

Thanks to all,

 

G2L