96 S-10 4.3 v-6 csefi code 0305

Just the facts:
First problem: missing = split plug boot on #5 cyl, visible bright blue spark jump from wire to exhaust manifold = replaced plugs, cap, rotor and wires

second problem: fuel pouring out of exhaust, #1 and #3 cyl missing, visible clean areas under plenum when looking thru throttle butterfly = split fuel lines to poppit valves under plenum = replaced all 3 driver side injectors and poppits = no leaks

third problem: Starts, but now #5 cyl misses and spark on tester is weak and thready that seems like its firing with all other cyls as there is no hesitation between sparks and seems like fuel in #5 cyl won't burn, since plug is wet and fuel pours out of plug hole when plug is removed. all plugs on #1, #2, #3, #4 and #6 cyl seem to be firing fine = pulled plenum again and pulled all poppits and charged fuel system still no leaks.

Checked fuel pressure initial jumps to 60 PSI and immediately I can hear a wheezing sound from the injector body and fuel PSI drops to 50. After 5 min. drops to 35 PSI.

Next check will be swapping #3 and #5 plug wires to check #5 plug wire, although that still doesn't account for the almost constant spark at #5

P0300 series DTC's are almost always caused by secondary ignition problems, low fuel pressure can also cause them.

What brand and part number are the plugs?
Should use AC Delco 41-993

Random spark sounds like a problem with the distributor cap. What brand and part # did you use?

Cylinders 1 and 3 missing might be caused by reversed wires on the distributor cap. Double check it just to be sure.

http://i561.photobucket.com/albums/ss58/cwhook/97newer43Lfiringorder-Copy.jpg

Fuel pressure is a problem. Key on, engine off, fuel pump running: fuel pressure must be 60psi to 66psi and must remain above 55psi for 3 to 5 minutes after the pump shuts off.

This morning I pulled fuel filter and tested fuel PSI at 71 and constant for over 5 min. after 1/2 an hour dropped to 64 PSI. Can I rule out the fuel pump as the malfunction ?

Can't rule the pump out. The check valve in the pump is working fine but, pump maximum output spec is 78psi to 108psi, your reading of 71psi is too low.

From your earlier test, leakdown was excessive. The check valve in the pump is working which means you have a leak in the plenum, along with a weak fuel pump. You mentioned #5 plug is wet, quite possible the injector is stuck open. The poppet valve shuts off around 35psi or 40psi and that could explain why pressure stops dropping at 35 or 40psi.

Okay!
pulled plenum
hooked up fuel pressure guage
pulled all poppits
hooked up harness to injectors
turned on key
#5 poppit squirts a jet of fuel for 8 seconds
spark jumps out of coil (ran wire under rubber mat by battery)
fuel PSI jumps to 60 and immediately falls to 40 (obviously)
is this a poppit malfunction or electrical ? #5 poppit doesn't do this without the harness hooked up and the #2 and $3 poppits only squirt a drop of fuel for a nano second
The same sequence of events occurs each time I turn the key (assistant)

You have found the problem! The poppet valve has a spring inside and it requires around 40psi of fuel pressure from the injector before it will squirt fuel. Now we need to determine if the injector circuit is shorted, or the injector is stuck open.

Leave the injector connector plugged in, ignition in RUN position, engine off: Using a DVOM, (digital volt ohm meter) measure voltage from the pink wire to the black white stripe wire. All injectors are supplied battery voltage when the ignition is on so there are several pink wires in the connector. The black white stripe wire comes from the ECM and supplies ground to open the injector. Post your results.

Okay,
Battery voltage 12.10
#5 imjector voltage 11.60

During these tests, you might want to remove the fuel pump relay so the poppet doesn't squirt fuel each time you turn the ignition on.

Next step.... Disconnect the injector connector, key on, engine off: measure resistance from battery negative to the black white stripe wire pin in the harness connector. What this test will show is if the black white stripe wire is shorted to ground.

Okay,

with key ON engine off measured about 800 ohms
with key OFF engine off measured about 12K ohms
both from black wire to Neg bat. terminal

The injector is stuck open. Here is a link from the "How-To" section that tells how to replace injectors individually. http://www.automotiveforums.com/vbulletin/showthread.php?t=559014 Autozone and Advance auto parts should both have the injector in stock. It runs around $62. Make sure it comes with the O rings, if not, get a set and do all of them. Nice work!

Chuck you ARE the MASTER ! Thanks for all the assistance

Thanks, been around the block a few times ;) Post back and let us know how it goes. And don't forget, fuel pump max output is low, and you might still have driveability issues after the injector is replaced.