98 Monte Carlo Z34 won't start

3.8L V6.. Car has had an "under load" miss for a while. (i.e. going up a hill).. Last night my daughter was driving it and it started missing very bad, she pulled off the road and shut it off. That was the last time it ran..

Had it towed home and started the back yard diagnostics. Only codes showing are P0306 (Cylinder 6 missfire)... Fuel pressure is 42-44 psi key on motor off. Hold that pressure for over 10 minutes. With return line capped, it holds 85 psi. Have had Ignition Control Module checked at "da Zone" and it checks OK. Replaced all three coils and am attempting to replace the Crank Sensor behind the balancer. My puller won't work and was wondering if anyone knows what size the three bolts need to be to pull it? I have been told 6mm as well as 1/4" fine thread SAE..

I just feel like I would have had a code if the crank sensor was bad, but no. I have spark although it appears to be a yellow spark and I'd expect to see a strong blue spark.

Any ideas would be appreciated.. We are both unemployed due to this damn economy and I have a finite budget to allow to this (I've already spent $250 and am about out of money..)

Thanks for any help anyone can offer...

When the coils and ICM were off the engine, did you thoroughly clean the ICM, apply heat sink compound, nd clean the mounting base for a good ground? Have you checked the cam position sensor? What is battery voltage at the ICM connector?

You said you had spark at the missfiring spark plug wire boot right? I think you should've swapped the 6 coil for an adjacent one before you went replacing it but that's water under a bridge now. I think if you had an ICM or ignition problem it'd show up on the companion cyliner too. I would next check the resistance and condition of the 6 plug wire. Pull the 6 plug just to have a look at it.

I would check the no 6 injector. The injectors on the 3.8 are easy to get to. See if you are get a pulse at the injector and measure the resistance at the injector.

PS: My bad. Noticed you're saying it wont start and not just a misfire. Like BlueBowtie said you need to trace back over what you did with the DIS. Are you getting sparkon at east two cylinders now?

You said you had spark at the missfiring spark plug wire boot right? I think you should've swapped the 6 coil for an adjacent one before you went replacing it but that's water under a bridge now. I think if you had an ICM or ignition problem it'd show up on the companion cyliner too. I would next check the resistance and condition of the 6 plug wire. Pull the 6 plug just to have a look at it.

I would check the no 6 injector. The injectors on the 3.8 are easy to get to. See if you are get a pulse at the injector and measure the resistance at the injector.

PS: My bad. Noticed you're saying it wont start and not just a misfire. Like BlueBowtie said you need to trace back over what you did with the DIS. Are you getting sparkon at east two cylinders now?

After many hours of head scratching and a few hundred bucks of throwing parts at it, the problem was the upper intake manifold leaking water from the EGR passage into the plenum. I removed the upper and the lower was full of water.. Researched a little and found a pic of where to look on the upper manifold and sure enough, a hole.
Replacement manifold has a new piece for the EGR that no longer touches the upper intake to melt and/or weaken the plastic..
Case Solved... Just wish it would have been the FIRST thing tried.. :-(