O/T: Pesky GM 4.3 V-6 Vortec

I have a GM Vortec V-6 (4.3-liter) on a '93 Blazer that does not like to start after setting for more than a day or two. The engine (a GM "Goodwrench" rebuilt) has about 25K miles on it, and if it is used every day, starts and runs absolutely fine -- not a hint of trouble.

But, if I don't use it for a couple of days, the trouble begins.

When I turn the key to the "on" position, I hear the fuel pump pressurize the fuel system and then shut off, like it's supposed to (about 3-4 seconds, usually). When I crank the engine over, though, it doesn't even offer to start. It'll crank and crank, usually not even hitting on any cylinders at first, and then I can hear the fuel pump running for at least 20 seconds or so. When I turn the key back to the "on" position, the fuel pump will run for 3-4 seconds and then shut off, and I try to start the engine. Same thing happens, and fuel pump runs its 20+ seconds and then shuts off. Strange.

Oddly enough, though, there have been times when I've said to heck with it and left it alone until the next day. When I go out to try it again (at least 12-18 hours), it'll sometimes start right up on the first try.

This first started happening in the winter -- I thought it was cold-related. Tried Dri-Gas (and other fuel water-removal additives). I'd take the heat gun out and warm the top of the plenum, and usually could coax it into starting. But temps here today are in the mid-40s, and I've been hassling with this thing for the past couple hours again.

Fuel pump is nearly new, central-port injector is nearly new, distributor was replaced last summer, fuel filter is only a couple months old... I can't really think of a part that could be faulty.

I'm out of ideas here, guys. What am I overlooking?

-- Maine Fordson

It sounds like it might be moisture related, since it causes trouble when it's cold. I assume all the ignition wires were replaced with the engine.

If it does start better with the battery charged up, you need to determine if the battery is weak, or is being excessively drained by an electrical "leak" somewhere, during the time it sits without being started.

Have the battery checked with a load tester, if possible.

The injectors in that fuel system will not squirt unless the full fuel pressure is available. If the battery is low, or the pump is weak, there will be no fuel injected during cranking, while there is the load of the starter on the battery.

I can't remember the exact fuel pressure spec, you need to find out the spec, and put a gauge on it to be sure the pressure is maintained during cranking. Even a couple of pounds low, and the injectors will not inject.

Also, check all battery cables, connections and grounds... body to frame and engine, etc.

Almost certainly, the answer is low fuel pressure, likely caused by a weak or drained battery, or a poor connection somewhere.

Battery is new, but I had considered the electrical system. I bought a tool that plugs into the cigarette lighter and gives an L.C.D. readout of the system's voltage, both while running/charging, and when the engine's off, as well -- i.e., 14.3v while running, and 12.8v with the key off. Those readings would appear to be in the normal range, I think.

I don't suspect fuel delivery as the cause, because I can always smell fuel after cranking. (In fact, once last winter there was enough fuel in the exhaust system to cause it to ignite and backfire, with that explosion puffing a nearly-new muffler out in the process. And, as I mentioned in the original post, fuel pump, filter and CPI all are new (replaced within the past few months).

The puzzle continues. Thanks for your input.

-- Maine Fordson

Having a spark tester plugged into one of the plug wires would be a good idea, too, to verify whether or not there's spark as soon as you begin cranking it, after sitting a couple of days, to cover all possible angles.