Engine misfire at 2400 rpm

New to this form, but this one's kickin' my butt but good:
95 GMC Sonoma 4.3Vortec, 316K mi...
Engine starts, runs fine, except when at or going thru approx 2400 rpm - wher it misfires, sometimes to the point of killing the motor. No MIL set, no stored codes. Fuel pressure at schrader valve (4.3 V6 w/CMFI)correct during all phases of tests (KOEO, idle, accel, etc). Gas mileage consistent.
I changed the crank position sensor, no joy (GMC's book even calls out this sensor for misfires above 2400rpm).
I'm stumped. Thought tps maybe, but the fact that engine runs fine with no load throughout idle to 3500rpm, kinda nixed that. Same with injector/press reg/spider. To me, if one of these were faulty or failed, engine would run like crap allatime.

What is the camshaft retard setting?

What is the camshaft retard setting?



Copy on the cheap aftermarket parts. But I DO use stuff like WIX/K&N filters, Optima batts, Magnecor wires; AC Delco otherwise.

Still, the crank sens I put in is a Sorenson, as the dealership parts dept was closed yesterday. Problem is - I changed the sensor out and the gripe is exactly the same.

I'm looking for vacuum leaks now...thanks for your reply!

Camshaft retard is the dist setting.
On a 4.3 code W with the VCM computer flat top dist cap with the wires out the side.
It sets the dist rotor to fire dead on with spark plug terminal.
You need a good engine capable scanner to get the camshaft retard reading.
It need set as close to 0 degrees as you can get it.
Also what is the fuel pressure readings?

Camshaft retard is the dist setting.
On a 4.3 code W with the VCM computer flat top dist cap with the wires out the side.
It sets the dist rotor to fire dead on with spark plug terminal.
You need a good engine capable scanner to get the camshaft retard reading.
It need set as close to 0 degrees as you can get it.
Also what is the fuel pressure readings?



All fuel pressure readings are in range/specs (KOEO, idle, rapid acce, accel), also, fuel pump changed last spring, and I change fuel filters every third oil change (@ 3K mi religiously).

I commute 75mi each way to work every day - this morning I drove all the way at 62mph/2100 rpm with no trouble. At the end of the run, I ran the engine to about 3K rpm through all the gears (5-speed man) just to see what would happen...and wouldn't ya know it - not ONE hiccup! I dunno.

I have a scan tool (ACTRON CP9145), on a break I'll check-out codes and such (though the MIL has never came on), but I don't know if it is capable of camshaft retard readings.

I would also tape a fuel pressure gauge to outside mirror or outside windshield and watch fuel pressure on the road and when it is acting up.
MT