Chevy & GMC Vans

94 safari 4.3 TBI approx 250,000 km

original problem was when accelerating the van would hesitate / bog on light throttle opening, hard acceleration was ok.
when it warmed up after that the hesitation / bog got slightly better and hard acceleration was still ok..
fixed that by putting in plugs, rotor and cap, hesitation / bog virtually dissappeard and hard acceleration was much better.

now when starting from cold (overnite) hesitation / bog is non existant.
go a couple of blocks / approx 5 min running time and the engine temp is approx 40 c, the light throttle opening bog is there,
mid range acceleration seems ok and hard acceleration is still good.

If I drive it for about 1/2 hr and the engine temp is about 60 c the bog almost dissappears and is all but gone.

Any ideas?

TIA

Vacuum Leak?

Jim

check both of the injector spray patterns when the engine is cold... remove the air cleaner assy and run the truck observing the spray pattern while you work the throttle lever with your hand.

I have replaced quite a few of those injectors across different platforms before, if you see anything other than a strong conical pattern like drips or a weak spray or a variation between the two injector spray patterns replace em.

PS: you can always Ohm out those injectors too, but their problem is usually visible... the heat from the engine might be expanding the injector case just that little extra that is needed for it to flow better after the engine is warmed a bit.

when starting, does it fire instantly or does the engine turn over a few times before catching?

If its the latter, i would think you have a slowly failing fuel pump.