I have a 1996 4door s10 blazer 4x4. I love this truck but i've been an idiot and started throwing parts at it and have not been sucessful. I only seem to see the issue in closed loop (full operating temp) under a load like goin g up a hill. It is prevelant in D and overdrive so I know its not the torque converter. I can visibly see the rpm gauge bounce up and down 500 rpms. When I put it down to full thorttle, the problem goes away until U get back to a hill and light acceleration like 1800-2k rpms. Oh yeah, No check engine light either as well as soft codes. So far I have changed out :

Spark Plugs
Wires
Ignition Coil
Distributor Cap
Button
Coolant Temperature Sensor
Idle Air control Valve
Throttle Positioning Sensor
Mass Air Flow Meter
Fuel Pump / Sending unit
Fuel Filter
Cleaned O2 Sensors
spider injection system

I checked the spark plugs and all seem to be in generally good shape . good compression. Please help I am lost. I think I am just gonna get a MAP sensor and put it in to say I have done EVERYTHING shy of replacing to computer. Thanks again for taking a look.

 

Is the truck shaking and chattering like it doesn't want to go with the rpm increasing?

 

I realize you've replaced a ton of stuff with no success, including the fuel pump. Now it's time to do some diagnostics to find out what the problem really IS. One thing to keep in mind is just because a part is new, doesn't necessarily mean it's good. You may have already replaced the right part, but without diagnostics you'd never know.

Have you checked fuel pressure and leakdown? Key ON, engine OFF, fuel pump running: Pressure must be 60psi to 66psi and must remain above 55psi for 10 minutes after the pump shuts off. Fuel pressure is not monitored by the OBD system and because it's not monitored, it can not set a DTC and turn on the SES light. If there's a problem with a sensor, or its circuits, it will set a DTC.

What brand of parts did you use? Some aftermarket stuff, putting it gently, is junk right out of the box.

 

fuel pressure is perfect. timing is perfect.

 

Define "perfect"

 

fuel pressure pressured and held @ 64. fuels seems perfect to the rail. it only surges when its warm.

 

vacuum is at 17 psi constant @ idle

 

Have you checked camshaft retard? If so, what was the reading?
Do you have a scan tool capable of viewing streaming data?

 

My 1995 Chevrolet S10 Blazer LT 4 doors do the same things. I will try to take a video of it tomorrow if I can get somebody to come with to video tape it for me while I am driving.

 

1995 uses a different computer control system, (CMFI with OBDI or OBD1.5) but it's worth a try