Question on This issue as i am experiencing the same or near same issue?
How does Gas get into the exhaust if it has no leaks under the plenum ( Spider lines/nutkit/Fuel pressure regulator?)

Is there any way a CPI or any part therof could leak while its holding a steady 60 pounds of pressure both running and idlling and at Key on position ?

 

Sounds a bit like the problem I had on my '92 were the catalysator was blocked. Check the exhaust pipe outlet if it flows normally.

Jan

 

I have had or am having Nearly every known issue possible with My truck
93 blazer 4x4 ( Vin w 4.3L engine)

The Following tests will Identify and Narrow and usually pinpoint your issue.

1. Fuel pressure test
2. Scan Tool ran on Engine
3. Vacuum test
4. Cylinder Compression Test

Fuel: ( 55-60 constant pressure not leaking down at all hardly)
Scan Tool: identifies Voltage issues with sensors as detected by computer
Vacuum: the vacuum controls the Fuel Pressure regulator and more
Compression: Valve stuck, Piston Rings Blown ect.

Visual Screening:

Check Oil for grey sludge, bubbles, thin and smelling of gas ect.
Start engine run 1 minute, turn engine off pull Plenum look for wet area
Check exhaust for gas , Oil or water leaking / dripping from it.
Watch for Bubbles going into water overflow when turning engine over or running right away ( head leaking, sucking air into the eater chambers)

Maintance that may restore Power:
Clean The EGR Valve and put a screened gasket on it. ( This needs done anyways )
Change PCV Valve, Air Filter, Fuel Filter