I'm new to the forum. I'm a member of a few other GM sites and one Ford site but it looks like you guys really know your stuff about the s-blazers.
Here it goes:

Just picked up this '95 blazer. it would not run below 1500 rpm. Had code P1406. Looked around here and found it's most likely the EGR valve stuck open. Sure enough it was. Ran great, drove it around the yard a little tryin to see what it'll do. I was shocked at how quick the 4.3l is. very nice. 4wd didn't work. Looked around this forum again and see it's probably the vacuum control for the front axle. Sure enough. take it out again, it's working great, 4wd works, and it dies on me. the battery is pretty shot, so I couldn't restart it. drag it back to the garage and put the charger on it. try to start it later, and it wont unless you have your foot on the gas, and wont idle on it's own. figured the EGR is stuck again. It's not. the Idle air control is clean and tests good. MAP sensor tests good, so does the TPS. The really odd thing to me, is that I unhooked the pcv valve to make a vacuum leak to see what it would do, and now it runs great. idles at about 800 rpm. the other thing is that is seems to be using alot of fuel, considering i've only put 2-3 miles on it. I put 5 gallons in when i got it because it was damn near empty, and not it shows almost empty on the gauge again....

I'm pretty stumped at this one. I like it alot... It's a fast little truck and is 4wd which we need out here... But I've been at this 2 weeks now and am just about out of ideas...

Any help is much appreciated.

 

1995 4.3's used 2 different fuel delivery systems. If yours is an early production and looks similar to this:



More than likely either the fuel pressure regulator or the lines to and from the injector assembly, (nut kit) are leaking causing an extremely rich mixture. This makes your fuel mileage go right down the toilet and disconnecting the PCV valve allows more air to lean it out and cause it to run better. The upper intake, (Plenum) must be removed to diagnose and service the lines and regulator.

EDIT:
When the plenum is removed, here's what it looks like:

 

That looks like mine. IIRC it was build 02/95 or something...
Please explain this as I'm not quite familiar with this engine/fuel delivery system yet.

 

This engine has CMFI (Central Multiport Fuel Injection) fuel delivery system. One injector with six lines that run to the intake ports with poppets in the end of each nozzle. In the image you can see the lines, they become brittle and sprout leaks. The fuel pressure regulator is on the passenger side, and the diaphragm likes to spring leaks too. When either part leaks, raw fuel drains into cylinders 3 & 4, (center cyl on each bank) and causes a rich mixture. It can also drain into the crankcase diluting the oil. Checking fuel pressure and leakdown will confirm or deny a leak somewhere, but will not pinpoint the leak if there is one. Very common for leaks in the plenum and not difficult to remove the plenum to verify it.

Most auto parts stores stock the "nut kit", usually runs under $60

Dorman Products - 55163

 

Thanks alot. Sounds like this is my problem.

 

So I took the upper intke off today... no obvious leaks when you run the pump... Although it loses pressure almost instantly when the pump goes off...

Does this point to the regulator then, or ???

Thanks

 

The surface of the lower intake manifold should be black with carbon deposits. In the image in post #2, the carbon deposits are "washed" causing the golden color. If the lines leak, the driver side will appear washed. If the regulator leaks, the passenger side will appear washed. In that image, both are leaking. If this problem just started, it may not have had enough time to wash off the carbon. If fuel pressure drops, it indicates there is a leak somewhere. There are several places fuel can leak, but from your description of how it runs, and what you did to improve it, I would strongly suspect something in the plenum is leaking. If you force the pump to run by applying battery voltage to the red "pump prime" wire, you'll probably see it leaking. It is possible that the injector is stuck open, it's not nearly as common of a problem. However, that would also give the same symptom that you're experiencing. Look close for leaks, if you can't detect any, there is a test for the injector.

 

OK. The inside of it is mainly golden as in your picture, so I imagine something is leaking. Will study it closer and post results.

Thanks

 

Heres the intake on my blazer:



So i looks like a leak on the pass. side? Probably regulator maybe?

Also, how exactly do you jump the pump on one of these to force it to run?

Thanks.

 

No image posted, but if it's washed on the passenger side, it's the regulator. Unless the lines on the driver side have been replaced very recently, it would be worth it to do them as long as you're in there

The fuel pump prime connector is located under the hood. It will be a red wire with a black or brown plastic connector on the end. You can manually power the pump with a fused jumper wire over to the battery positive post.

An assistant would be very helpful if you can't find the prime wire. The fuel pump will come on for 2-3 seconds when you turn the ignition to the RUN position