Jeep: Start issues., jeep cherokee country, voltage drop test

Question
OK, so here goes.
I have a 96 jeep cherokee country, 4.0 straight six.
it sat for a year at my moms house - long story. but anyway, i replaced the battery and know i have a weak positive end but the power gage is still at full capacity.

It recently (like two days ago) wouldnt start, just randomly, but i didnt have any problems prior. The fuel pump engages and all power is good. I assumed it was the starter. got a new one, put it in, and it started fine, 5 times.
3 hours later, same problem. power good, fuel pump engages, but no start.
not even a click.

the only thing i can think of is an electrical connection somewhere is not connecting properly.
im going to try to get a new relay and see if it helps any...

any help would be appreciated.
thanks.  

Answer
Amy,

First things first: is the issue A)cranks normally but doesn't start B)no crank, no start or C)slow crank, sometimes starts? An engine needs 3 basic things to run: air, fuel, and ignition. We can rule out mechanical issues like lack of compression (which is the fourth thing).

If it's a no crank, pull the trans into neutral and try and start it, even going so far as to wiggle the shifter while the key is in the RUN position. The Achilles Heel (if there is any) of the AW4 transmission is the neutral safety switch (actually, a PRNDL switch). If it starts, then you can either replace it or overhaul it (actually, just disassemble in-car, clean it out and re-lubricate it)

If it's a slow crank, or you have battery connection issues, don't overlook battery cables. With the engine running, you can perform a voltage drop test down both cables (one at a time). There should be very little-to-no voltage lost, since the cable is so thick, and relatively short. Don't try to ohm test the cables -- unless they're completely open, even one strand of copper can read fine on a 99% corroded cable.

If it cranks but doesn't start, you need to narrow down what system is causing it -- check for spark with an ST-125 (any HEI spark tester will do), check for fuel pulse with an injector noid light, and check fuel pressure with a service gauge. Remove the intake snorkle, in case something clogged the air filter or tube. From here, you can narrow your diagnosis to one system, and it becomes easier then. Good Luck!