76er

Hello folks,new to this forum. Great to know there is a site like this,need some help with my old Dodge truck(76 D100).Only get fire when I first turn the key to try to start it(no fire while engine is spinning over) and then when I let off the key getting a spark. Suspect ballast resistor,how do you test it? All the electrical boxes on the firewall are new, key switch is new. Has been running just fine,no warning signs of a problem before this.
thanks,
76er

440roadrunner

Easiest way to deal with the ballast is "buy a spare" and keep in the glove box if you don't need it now. Check the old/ new ballast with either an ohmeter or test lamp. It IS possible, but (play the odds) doubtful that the resistor is intermittent.

There is no real way to check the ECU other than to check "everything else" and then replace it.

Checking power is easy, just put a voltmeter on the switch side of the ballast and turn on the key. Should be "same as battery" or darn close.

Voltage at the plus side of coil will be much lower, because of drop through the ballast, might only be a few volts with key on.

I suspect either a bad pickup coil in the dist, or chewed up reluctor wheel, visually check it. Take your voltmeter and plug into the two prong dist. pickup connector. Crank the engine and you should have nearly 1 volt AC out of the dist. pickup. There is a gap setting, for which you need a "nonmetallic" (brass) .008 feeler gauge.

Make sure you do not get the gap too tight and chew up the reluctor

Some folks on another board who claim to be tune-up guys claim that these pickups fail fairly regularly. I suspect that quality control ain't what it used to be.

If the above checks don't get you anywhere, try another ECU

76er

Hey 440 Roadrunner, that makes sense, i'll try that.
Thanks,
76er

PLYMOUTH BOB

i had this same exact problem with my pontiac and it took me 3 years to figure out the problem, i truly felt stupid. the car would start warm up then if it stalled or was shut of it would just spin over until it cooled then it would fire..the problem, the distributor i have in there is a magnetic trigger and as it got warm the pickup would move away from the magnet and not trigger the spark, upon moving it closer, IE closing the gap some the problem was solved. so depending on your ignition system i hope this helped