I just had a remanufactured engine installed in my 91 s-10 2.5L 5-spd. Include were new plugs, inition wires, Distributor cap & rotor, Distributor pick-up coil, catalytic converter exhaust manaifold and map sensor. It runs great in the garage under no load. The engine installer tuned it and a friend of mine varified it on his garage engine analyzer. Driving under no load, such as gradual acceleration on level ground in great. But when accelerating to pass or starting a hill climb it starts to break down and lose power forcing me to downshift to reduce the engine loading. The high frquency chatter that comes with the breakdown makes me believe it is electrical. Is this a logical conclusion, could one of the new parts be faulty; if so how do I trace it. Or could this be a fuel pump problem or one of the various sensors not functioning. I'm convinced it must be an easy fix just not an obvious one. Please help.

with basicly all new parts it should run great. Check the compression. It doesn't happen often but the motor it's self might just be a dud. Plus check the spark plug gap while your at it.

I'm sorry that I can't explain the chatter unless I hear it.

Good luck.

I just had a remanufactured engine installed in my 91 s-10 2.5L 5-spd. Include were new plugs, inition wires, Distributor cap & rotor, Distributor pick-up coil, catalytic converter exhaust manaifold and map sensor. It runs great in the garage under no load. The engine installer tuned it and a friend of mine varified it on his garage engine analyzer. Driving under no load, such as gradual acceleration on level ground in great. But when accelerating to pass or starting a hill climb it starts to break down and lose power forcing me to downshift to reduce the engine loading. The high frquency chatter that comes with the breakdown makes me believe it is electrical. Is this a logical conclusion, could one of the new parts be faulty; if so how do I trace it. Or could this be a fuel pump problem or one of the various sensors not functioning. I'm convinced it must be an easy fix just not an obvious one. Please help.
Check for a kinked fuel line.I had a the same problem after the shop put a new fuel pump in my s-10.The fuel inlet line was kinked.It ran fine until under load.The kink let enough fuel thru to run fine at no load but the engine could not get enough fuel thru the kink under load and would starve itself.

do a fuel pressure test when under load to see if that is the problem. it sure does sound like a fuel starvation problem.

i agree with busa

Sounds like the timing is overly advanced.

Did they remove the timing wire from the PCM when they timed the vehicle?

The clatter is detonation.

Thanks for the recommendations. I had a sluggis fuel filter, but when removing each plug to inspect for fouling, I found one wire was not snapping down on the plug. Inspecting I fould the connector was almost a half inch higher in the boot. I trimmed a half inch off the rubber, the boot then snapped on the plug properly and it is running like new