phunnymanguy

I recently bought a 1997 GMC K1500 with the Vortec 5700 L31 in it. 125,000 miles, no known engine work. Shortly after purchase the truck started throwing the PO304 code (Cylinder 4 misfire). Seemed to run smooth regardless except three or four times on cold starts in wet weather when everything would be running fine and then it would miss hard for a minute or less.

So I changed out the seemingly stock wires (Packard brand with cylinder numbers stamped on) and weathered Bosch platinums for Napa Belden wires and Autolite 605 copper core plugs. Code went away on first start but returned shortly after and misfire events continued.

So I replaced the distributer cap and rotor with Napa Echlin 256 and 207. Old cap posts and rotor tip had a fair amount of corrosion. Again the code disappeared upon start-up, even sounded a little stronger at the exhaust. Upon a road test it was immediately clear something was wrong and it felt at least two cylinders were missing every time. SES light began blinking angrily during very brief road test.

Checked TDC with a piston stop tool at Cylinder #1 (front of engine drivers side). Rotor turning CW positive stop at about 11 o' clock, rotor CCW positive stop at about 5 o' clock. Number #1 cylinder cap post is at about 4 o' clock. Completely confused at this point as to what the problem is??? You cant turn the rotor or rotor platform without turning over the engine and you can't mount the rotor 180 degrees out as screws won't allow it (original self blaming thoughts). rotor shaft does have a couple millimeters of play left and right as well as a tiny bit up, but not much.

After reassembling for the fourth time with rotor in the seemingly completely wrong position truck fires right up and immediately starts hunting for idle... and continues to hunt. No codes. periodic small black puffs out of the tailpipe and smells like gas. Giving it pedal motor stumbles variably from idle to about 1500 rpm and then smooths out perfect from 1500-2000 up. Drove for less than a mile and seemed to exhibit the same characteristics under load.

Always starts, but far worse than before the tune-up. Definitely not drivable. Please help me motor gurus!!! Need to confidently travel 1000 plus miles round-trip near the end of the month.

shamrock246

there's a #8 on a small pointer on the distributer line that up with the rotor with the engine at TDC on the compression stroke and that should be it,your puffs of black smoke could be sticking poppets in the fuel injection or a leaking pressure regulator are any of the plugs wet?


Sean

97 4x4 burb