91 350 starts but has no power

[grn91vette]

Good morning, I have a 91 vette that starts and will accelerate and then has no power. I changed fuel filter and removed fuel pump and tested. Fuel pump was fine, blow out fuel lines and still has no power.

 

[Rob]

Welcome to the Corvette Action Center!

Moving your thread to the C4 Tech forum for greater exposure.

 

[Hot Rod Roy]

Is this a new problem? Was there any work done on the engine recently? Have you checked your ignition timing? Are your brakes dragging?

 

[grn91vette]

Is this a new problem? Was there any work done on the engine recently? Have you checked your ignition timing? Are your brakes dragging?

Hi, no their was no recent engine work, timing is on and brakes are fine. Removed exhaust to check if cat was out but had same problem. Car starts fine , rev up motor and is responsive, let idle and rev motor and is starving for fuel.

 

[grn91vette]

Hi, no their was no recent engine work, timing is on and brakes are fine. Removed exhaust to check if cat was out but had same problem. Car starts fine , rev up motor and is responsive, let idle and rev motor and is starving for fuel.

I ran diagnostics and got 1-h74LED display dimming output circuit open or short, 4-h22 tps voltage low and4-h34 map sensor voltage low. Can anyone please explain how I can fix this problem?

 

[ecss]

I ran diagnostics and got 1-h74LED display dimming output circuit open or short, 4-h22 tps voltage low and4-h34 map sensor voltage low. Can anyone please explain how I can fix this problem?

The MAP sensor is bolted on the passenger side rear of the plenum.
Unplug the three pin map sensor electrical connector.

On a 90 the color of the wires are as below. *******Not sure a 91 has the same wire colors.*******

Pin A Black/Pink and is Sensor Ground
Pin B Light Green Map Sensor output signal
Pin C Gray 5 volt reference.

Also Unplug the Three pin throttle Body Position Sensor.
The TPS is bolted to the passenger side of the throttle body.

Pin A Black wire and is Sensor Ground
Pin B Dark Bliue and is the Sensor output signal
Pin C Gray wire 5 volt reference.

Use a digital volt meter.
Set meter to read DC volts.

Connect Black meter probe to Pin A Black/Pink wire of MAP sensor.
Red meter probe to Pin C Gray wire.

Turn ignition ON.
You should read 5 volts DC.

Move Black meter probe to Pin A Black wire of TPS plug.
Move Red meter lead probe to Pin B Dark Blue wire of TPS plug.
Should read 5 volts DC.

If you don't read 5 volts DC most likely the ECM is bad
You could clean the ECM ground which is bolted to the engine block near the top of the oil filter.

If you do measure 5 volts, post back.