1988 Chevy Truck Poor low RPM perfromance

DRPHILGOOD01

MEMBER
1988 CHEVROLET TRUCK

Engine Performance problem
1988 Chevy Truck 6 cyl Two Wheel Drive Automatic 235K miles

1988 Chevy 1500, 4.3L, 375 Transmission (3 speed auto), 235K miles

Father, brother and I are all decent mechanics/parts changers, but this truck has us stumped.

It hesitates during acceleration whenever engine is under any stress. Less noticeable after closed loop. Significant lack of power below 2000 RPM. At take-off, while still in open loop, hesitation is huge, but disappears when I flutter the gas. This also usually results in what I would consider normal power for motor and truck size. Take-off on slight downhill also seems to be more like normal, and more than caused simply by the slight downhill.

Have had this truck 10 years. Installed ACDelco long block at 165K miles, rebuilt tran at 220K, have replaced every sensor, valve, controller, etc. At least once, replaced distributor, rebuilt throttle body. Had it in shop at one time, they claim to have replaced computer. Installed Schrader valve, fuel pressure at rear of TBI held consistently at 11 PSI while driving, even uphill. TPS and MAP sensor voltages read appropriately, even while driving. Some of these changes have improved overall performance, but none has affected this particular issue. Any suggestions?

1 Reply

MIKE H R

MECHANIC
3,094 POSTS

I don't know if this will help but try resetting the computer. Disconnect the positive side of the battery. Ground the positive teminal connection to the negative. I don't mean the battery. This will clear all the computer. With it being a 88 the computer should pick up after driven a couple of miles compared to newer cars that have to be driven over 50 miles. Check for cvacuum leaks around throttle body. If lines look ok still check them. I ahve seen what looked like a new line have a hairline crack in it.