Todd Hogan
1999 Blazer
LT trim, 4 door, 2 wheel drive, bone stock

Issue:
When accelerating the engine hesitates. There is one or two "sweet spots" in the throttle that make it accelerate normal, around 1/4 throttle.

Items replaced:
MAF sensor
Catalytic converter
EGR valve substituted with a known good one, made no difference
Fuel filter

Troubleshooting accomplished using the factory technical manual:
EGR valve good
MAP sensor good
TPS good
Fuel pressure is 54 psi at idle. it jumps to about 58 when you snap throttle open. The fuel pressure is not fluctuating while driving or when the hesitation happens.
Unplugging the MAF sensor makes no difference

DTC codes experienced:
P1404 EGR valve closed pintle position
P0300 Engine misfire detected

I have read the other threads on this problem, but didn't find any definitive answers. HELP!! Do you guys think that 54 psi fuel pressure could be causing this? The manual says anything less than 55 psi at idle is no good. The pump was replaced three years ago with a cheapie. I'm not shotgunning a $400 AC Delco fuel pump at this issue!

 

Have you had your plugs, wires, dist cap rotor change lately? Could be a fowled plug? Just a thought.

 

I changed wires, plugs, cap and rotor last year. I'm going to remove the cap today and look for carbon tracking. I'm also going to pull on plug and inspect.

I'll post my findings later.

 

Test your fuel pressure using these steps:
96+ Fuel System Diagnosis

 

I appreciate the help. I have the factory service manuals, but you gave me some good info I needed. After reading your test descriptions I'm thinking my fuel pump check valve is shot.

My fuel pressure drops to zero within a minute or so after the pump quits. How does that affect driveability when the pump runs continously while the engine is running? I don't get that part!

The Blazer starts right up. It's sluggish and is getting 14 mpg average. Where is the fuel going if this is a lean condition?

 

Update:
I pored a can of Seafoam in with only about a quarter tank of gas, and presto, two days later it's running great! It must have had a clogged injector.

 

I had a problem with hesitation when accelerating from a stop. Couple weeks ago I started using Lucas injector cleaner in the tank and cleaned the MAF sensor with the appropriate CRC spray. One or both solved the problem. No increase in mileage but no more hesitation.