Surging at 40MPH

[travis2822]

1999 Blazer 4.3 Vin W

I recently changed my fuel pump and since I changed it my motor surges at 38 - 40mph. I am not sure what is causing it. It surges from about 1,200 rpm to 1,500 rpm. It does it 2 or 3 times then all is good. I have no other performance issues. Any ideas?

[MT-2500]

Originally Posted by travis2822

1999 Blazer 4.3 Vin W

I recently changed my fuel pump and since I changed it my motor surges at 38 - 40mph. I am not sure what is causing it. It surges from about 1,200 rpm to 1,500 rpm. It does it 2 or 3 times then all is good. I have no other performance issues. Any ideas?

Any check engine lights on?
Why was the fuel pump changed?
Was it doing it before or after or both?
How is the Fuel filter and basic tune up?
What is the mileage on tune up?
Any add on performance stuff?
Start with a complete fuel pump pressure check.

Like this.
Check cold start fuel pressure.
Check engine running fuel pressure.
Check engine running on the road fuel pressure.
Then shut it off and watch for fast leak down.
Pinch off at rubber part or block off return line and check full pressure.
Later V6 and V8 gm engines should have 60-66 fuel pressure.
Cold start should be 64-65 lbs of pressure.
If you do not have full fuel pressure on a cold start the injectors will not squirt fuel.
Do not leave home without it.
Engine running should be 60-66 lbs pressure depending on engine load.
Full pressure with return pinched off should be 75-85 or more.
And if it has a fast leak down after shut off you have a leak.
Post back fuel pressure readings.
MT

[travis2822]

I'll post the pressure number once I am able to do it. I can answer the other questions now.

No check engine light.
The surging didn't happen until new pump was installed.
I replaced the fuel filter with the pump.
Tuned it up last summer. Plugs, wires, rotor
I don't have any performance add ons.

It runs fine just once in awhile it will surge a couple of times at about 40 mph once I accelerate it is gone.