Been reading for hours, and kind find my answer. Probably here somewhere, not finding it.

Recently put a rebuilt 4.3L in 99 Blazer, 4x4. Engine ran fine before, accept for a rod bearing. Had plenty of power.

Starts like a dream, idle fantastic. Have a strange "hissing" or "light rubbing sound" after I start up. Seems to continue for about 2 seconds when engine is off. Can't tell where this is coming from. You hear it more in the cab with windows up.

Not sure if this is related, but I thought I should mention this.

When I accelerate I have no power after I would say after 1/4 throttle. If I put my foot completely to the floor, it will surge and you will have some power. Anywhere in between it just is really weak.

Trouble codes:

P0131, 0134, 0143, and 0151.

Replaced sensor 1, bank one. Only code coming up is P0131.

Checked Fuel pressure:

KOEO: Hits 60psi, drops to around 50-45psi, depending how many times you test. Hold.

RUNNING: 54-55psi, needle bounds between the wildly.

RUNNING/THROTLE: Jumps up to 62psi.

Engine off: 52psi

Engine off " 10 min Bleed down": pressure BUILDS to 60psi Pump not running. Slowly build pressure. Have taken gas cap off and hear nothing, still build pressure at Schrader valve.

According to the Chiltons book, I cannot unplug the vac line on the pressure regulator

I"m confused as to why I'm slowly building pressure when engine if off? . why is that gauge bouncing between 54-55, when I feel it should be holding a constant psi?

I have a 98 with same set up, readings are normal on that one. No high psi with key on then drop off. It' just goes to 54 and hold.

Any ideas? I think I need to fix this issue, then get onto the O2 problem next.

 

I had the same type of probs with my 99 4.3 blazer after putting all kinds of parts on it found out what the problem rly was it may not be the same as you have but its worth a shot and fist thing wont cost you much if anything. The fist thing I would check is the 02 wiring on the right side it is close the the exhaust manifold and my you may have a burnt wire. On mine I put a new 02 sensor in it (bank 2 sensor 1) is what the code was giving on mine and cleared the code but a few days later it would come back. So I thought maybe I got a bad sensor so replaced it one more and the same thing happened. So did a lil more digging and found the burnt wire fixed it and ran so much better and much better gas mileage. Here is a pic of it......
as for the fuel issue it sounds like the fuel pump mine did the same type of thing replaced it and no more probs but with the cost of them you may want to do a lil more checking into it........ Hope this helps good luck to you.

 

Hi Forist 72.

I'm sure I have a bad wire. Drove around town for about an hour, out on the highway. Finally came back on, only code is the 0134.

I cleaned MAF sensor. It runs a little better. Matter of fact, it improved the full throttle pretty darn good.

Still hesitates and sluggish.

I'm wondering if not a pressure reg. at this point. The building pressure with the keys out of ignition is beyond me.

My o2 sensor has four wires. 2 brown, not sure on the other two right off The 2 brown are for the heater. 12v using DVOM on these two.

What about the other two? Are they low output/high output?

Could one backprobe these wires with a DVOM to check? Or is that a no-no?

If you can, what would one be looking for one these two wires for voltage?

This has been a battle. Spun rod bearing second day of owning it.

Was stuck in 4x4 low when I put engine in, bad transfer case motor. Fixed.

Wouldn't cranked. Replaced purple wire from NSS to fuse block under hood. Starts like a dream

Just his darn sound, and the sluggishness has me along with fuel pressure building when I shut engine off.

I should mention, it was like 90 plus degrees, but don't see how this could possible make me build pressure.

ALSO, gas mileage seems fine. Have not figured it out, but seems like gage is moving as it should. No major decrease of which I can see. Exhaust smell fine. No gas odor in cab.

I'm all over this thing like a spider monkey, and I'm running out of gas myself lol. No scanner, live in the middle of nowhere, where there are no shops.

If someone can help me on this fuel pressure, I think I can go from there.

I do have a 98, and could rip off that fuel injections and bold it on this if needed. But I can't believe this isn't something simple.

When I unplug MAF, engine is effected, when I unplug Air Temp sender, it goes into a fit.

Vacuum is 16-17 psi at idle. 98 is running same vacuum. Think we can rule that out.

Some Chevy genius step up man, I'm bout to grab 4 low and run this thing up Chevy's engineering departments hind end. Scared I may stall half way in.

 

Hey scooter checking the 02 sensor wires is easy just follow the bank 2 wiring (right side) forward to the ECM check for burnt or cracked wires, then just solder them up with some shrink tube over it and I taped mine as well just to be safe. Them rerouted it up a lil higher away from the manifold.
As for the fuel issue I have read many peoples problems and fixes with fuel pumps, and have found that they can cause a lot of weird things to happen. Mine would act different on warm days V's cold days would get different readings as well.
If you have access to a 98 for parts for a trial I would try swapping the fuel tank presser sensor the lil gasket is fragile so be careful with it, or just swap the hole tank. its a lil work but it don't take to long to do just be careful with the fuel line connectors they brake easy. I may be wrong but if you are trying to save some cash on replacing a bunch of parts (like I did) it might be worth a shot.

 

Is there a vent or return than could be plugged? Doesn't fuel drain back into tank when you turn off engine?

 

I have similar on my 99 Blazer 4.3L. Checked my fuel pressure:

KOEO: Hits 62 psi, drops to around 55 psi. Hold.

RUNNING: 55 psi, holds.

RUNNING/THROTLE: Jumps up to 60-62 psi.

Engine off: 55psi

Engine off, 10 min Bleed down: pressure BUILDS to 62psi Pump not running. Slowly build pressure, THEN SLOWLY BLEEDS OFF OVER TIME. Have taken gas cap off and hear nothing.

 

Mickey- My power loss seems to be an O2 sensor issue. Not sure yet, had to head back to work lastnight.

I bought some scanning software and will go from there.

I'm wondering, if the "Evap. Cannister" is the issue with these? I see no other way to build pressure with pump off.

I'll let you know what I come up with, hope you will do the same.