86 No spark while cranking
 

Short end of the story:

Motor will crank but I have no spark until I let go of the key, then I will get three or four sparks. If I am charging the battery I can crank the motor over fast enough to have enough momentum and there is enough residual fuel that the car will sometimes start.

I had a similar issue before and it turned out to be the ground behind the fuel filter.

Using sand paper and brakekleen I have cleaned all of the grounds; the one mentioned above, the one on the number one intake runner and both ends of the grounding strap on the transmission.

Other facts: The resistance measured with my Fluke and 10 gauge jumper cable between the number 1 intake runner and the batter ground is (I think this has something to do with charging the battery while performing the test) -5 ohms. When cranking the resistance increases to ~14,000 ohms.

The DME relay is working as intended. While I have not put the oscilloscope to the sensors I am assuming that the crank speed and position sensors are ok as they looked perfect on the oscilloscope last week and, more importantly, the car runs great once started.

Thoughts? Suggestions?

Thanks!!!

Andrew

check ohms on speed and referenece sensor

Finally dragged out the old oscilloscope. Both sensors look great! ohm tested all three right there and everyone came back right in the middle of the range.

I was able to get the car to catch and run for a few but it ran like crap and despite my best wiggling I couldn't get it to clean up.

Any other thoughts? Suggestions?

Have you done anything with the Distributor Cap/Rotor? Check OHMs on those too.

I had a similar problem with my 84 3.2, if i put a hair dryer on the coil it would start. It turned out the coil wire was shorting out to ground. The symptoms were no spark until i released the key then it would try to start. Take the cover off the coil and look for arcing. Also the crank sensor went bad shortly after this problem developed I don't think they were related.

Got it! Turns out the crank speed sensor plug wasn't tight. Grrrrr!