96 Yukon Won't Start. Fuel pump is priming, Spark plugs are sparking. HELP

[Jimbeamrye]

Hello.....Well here's the story, I moved my 96 Yukon 5.7L this morning to cut the grass. It ran fine with no problems. I got done cutting grass and went to crank it up....but all it would do was turn over and over, never cranking up. I re-tried and listened for the fuel pump priming up and it is working as usual. Tank is full of gas. I pulled out every fuse and checked them, all good. I went back to the tail pipe and could smell a strong odor of gas. I went to the engine and pulled off a spark plug wire and put in a spare plug and checked for spark and it was sparking for every rotation of the engine. It did seem a little weak though. The strangest thing the motor has done, is that went I hold the ignition key trying to crank it up for over 10 seconds and let go of the key(as if it had cranked) the motor will sometimes start to run backwards but only barely with what sounds like 1 clylinder firing.This only lasts about 2-3 seconds.

So to sum it up it ran fine 1 hour before and now it won't crank...I'm sure it's a electrical problem or sensor. Just what should I check next? Please advise! Thanks, John

[Eggert]

HI,
there are some recent threads about this either in the Yukon or Suburban forum.
Here is one:
http://www.automotiveforums.com/vbul...d.php?t=375604
here is two:
http://www.automotiveforums.com/vbul...d.php?t=336264
Here is three:
http://www.automotiveforums.com/vbul...d.php?t=381950
They all talk about the ignition module and some more things.
Take care, Eggert

[Jimbeamrye]

Thanks for the links. Would you happen to know if the ECM did malfunction, would I be getting any spark?

[SpitAndDirt]

Ok, first of all, yours is a 96' which means that you no longer have an ignition module. You still have a pick up, but no module should be located under the cap. If you have weak spark on your truck, look at your mileage. Check your cap and rotor first, they always just go out without a whole lot of warning. Usually the cap center electrode is burnt to a crisp. I bet that is the source of your no start condition, because that is exactly what happened to me:weak spark, no start, plenty of fuel pressure = cap and rotor burnt electrodes. Hope this helps -Chris

[Jimbeamrye]

Well I never thought in a million years that a cap and rotor would be the culprit, but as far as I can tell it was!
There was no idication of any problems up to the moment it wouldn't crank up. The first thing I did was pull the cap and rotor out and inspect them and they looked like new...just the usual white corrosion on the aluminum pins on the cap. I cleaned them and the rotor button and reinstalled.....still wouldn't crank. Then I moved on to bigger and more expensive items. I was getting spark at the plugs, but it seemed as if it was firing at the wrong time, so I made my best guess that it had to be a cam or crank position sensor. So the less pricy item, the cam sensor ($40.00), I replaced first...did not help. So after all day, I finally made a important discovery while checking the coil, it was that the coil was popping out 2 inch long 30,000 volt arcs to the nearest ground, but at the spark plug it looked like the spark of a briggs and stratton 3 HP motor...very weak. So I replaced the cap and rotor with the the mind set I was wasting more good money I would need to spend down at the repair shop, AND SHE CRANKED RIGHT UP LIKE NOTHING WAS EVER WRONG!!! HALALULLA Thank GOD. I know the rules of a D.I.Yourselfer, but I broke the dam rule...Always start by replacing the cheapest stuff first(cap, rotor and wires.
By the way it does have a Ignition module, it is mounted with the coil, not under the cap. The cam position sensor is under the rotor button.
Thanks for the help everyone.

John in Pensacola, Florida