Not to HighJack the thread but i am having the same issues, mine started a month ago out of the blue. was getting 24-25 (yes that is accurate) and with in the last month i went from that to 14-15mpg wither im hard on it or easy on it. I put the platinum Delcos back in it, new cap and rotor and with in that month the Cat started to rattle and i wasnt having much exhaust pressure at all. So i put a new bolt on cat and the mileage is still horrible.
I have no vaccum leaks (i used 2 cans of brake clean all over engine and around any hoses). I have no codes or cel on. I dont feel like im having any loss in power. I asked one of the mechanics i work with before i replaced cat he said it didnt have alot of pressure and that the exhaust that was coming out was super hot which it was. after replacing the cat i can actually hear the exhaust now and to me it smells like its running rich. but he said lean according to my plugs. My plugs where the porceline is had a redish tint to it, but i thought that might have been from the Fuel additives from gas station. Im not sure, but im going to check my fuel pressure this weekend. do you guys have any thoughts as to why it would be an all of a sudden thing, not gradual at all. Ive also tried injector cleaner and fuel treatment and got no difference in mileage betwee 87, 89, or 93.

 

Probably a leaking fuel pressure reg or injectors. Look down the throttle body for any signs of washing or any clean spots. It should look black. If you see gold spots you have a leak. You may need a flashlight.
You should also do a fuel pressure and leakdown test even if you don't see any signs of a leak. Have you cleaned the MAF sensor?

 

No on cleaning maf.... is brake clean OK on cleaning that and do I really need to take it apart or can I just pull it off and spray. I haven't looked in tb yet but I do not have any soot on my tailpipe like most cars. Is that a sign of anything thing?

 

looked down TB and it does look at lttle wet and i can definetly smell fuel, does that mean spiders are leaking or reg pushing out to much? not sure how these setups work. i may go ahead and clean my maf anyways. But does that leak down test work for spiders or regulator?

 

The fuel pressure and leakdown tests will determine if the fuel delivery system is working properly, (fuel pump, injectors, regulator, etc). The results tell you if the pressure is OK and if there's a leak. It will not tell you what the problem is, only if a problem exists or not. If it indicates a problem, further diagnosis is necessary.

 

Is the 4.3 MFI upgrade a GM product only or is this something that was standard on the 02-03 and newer blazers?

 

1996 and newer "W" VIN code uses 6 injectors in a centrally located housing. There is a nylon line that runs from each injector to its respective intake port. In the end of each line, there is a spring loaded, (closed) poppet valve and a nozzle. Fuel pressure from the injector is what opens the poppet valve. The poppets require ~43psi of fuel pressure to open and squirt fuel.

VIN code "X" has an injector located at each intake port, and no poppet valves. 1996 and newer "W" VIN code can be upgraded, (plug & play) to the "X" style injection system.

Several companies make the upgrade kit, AC Delco, Delphi, BWD, etc.

The 8th character of the VIN is the engine code.

 

Not to be cheap but can I have a friend at a junkyard would it be stupid to find a x-vin blazer and use that one? 300$ is a lot of money.

 

Doesn't necessarily need to be a Blazer: Astro, Safari, C & K series pick ups and G vans will work, as long as it's an "X" engine. Using parts from a boneyard is always a gamble, especially electrical parts. The lines and nozzles become very brittle, care must be taken when removing & reinstalling them. You'll need a gasket set, don't use the old ones, they are a "use it once and throw it away" part.

 

I understand gaskets, ill check my cost on new one. Why did some use it some didn't?