My 1994 S10 Blazer with the 4.3L Vin W developed a missfire in the last two days. Here's the details about the truck:

221,300 miles
60,000 miles SNEW Fuel pump and relay
50,000 miles SNEW Spider Injector
100,000 Since transmission service 4L60-E
<10,000 since Coolant Temp Sensor

I'd have to look in the maintenance book, but there has been cap, plugs, rotor, wires, removed cleaned and reinstalled EGR in the last 50,000.

The problem has been that at low manifold pressure, light acceleration less than 2,000 RPM there has been a severe hesitation in the engine. Especially when accelerating from a full stop (stop sign or traffic light). During cruise, 55mph - 75mph between 1500rpm and 2000rpm when I let off the pedal to coast then add gas it hesitates too. Engine temps cold or warm haven't changed it. Moderate to heavy acceleration is normal.

In the last two days I have removed and inspected the spark plugs, timing, distributor drive gear, EGR valve, new cap and rotor, new throttle position sensor, no check engine light so no stored trouble codes...


Suggestions

 

Fuel filter? Cheap and usually easy. Has the ability to cause your symptoms.

Fuel pump? Low fuel pressure can cause your symptoms.

Water in fuel.

Vacuum leak.

EGR valve malfunction. Should set off MIL and give codes, but stranger things have happened. Though if it is the problem, it is likely to have an idle issue along with your other symptoms.

 

The fuel filter wasn't clogged, installed new and didn't change the problem.

Any other ideas?

 

The priming pressure was 65 and the idle pressure was around 60, so the fuel pump is operating smoothly.

We also hooked up his Snap On scanner, and all the parameters were within range.

It seems as if a serious fuel system cleaner is the next step.