I purchased my first truck about a month ago..
The 94 S10 Blazer (Tahoe LT) with the 4.3 L35 CPI engine..

I am getting on average 9 MPG and it's killing me!

I've done a fair amount of diagnostics already:
I tested the fuel pressure for leak down and it performs great
I pulled the plenum and there was some washing down of the regulator side, but not tooo much to speak of.
I replaced the spark plugs with some delcos (they were auto-lites originally)

The truck smells like it's running rich, and cold starts (after sitting overnight or for a few days) are a bit rough. I feel as though she is missing until she warms up.

Either way I get less than 10 MPG..

I have a new ignition coil, cap, rotor, and wires to put in.. but I HIGHLY doubt that'd cause a 50% drop in fuel efficiency.

ANY INPUT IS GREATLY APPRECIATED

 

Wow.. I got bad mileage before but nowhere near 10 mpg




Clean EGR valve, PVC, or replace and run Seafoam in the fuel to clean the injectors.
Replace Map sensor and OS sensor



that should do it
good luck
let's hear back from ya

 

When you say you did a fuel pressure test and leak down test, what were the results? you should have 59-62psi when you have the key on engine off, and it should not leak down below 55psi after 10 minutes (key on engine off)

if it does not meet those, there is something there.


You also said that there was some washing on the regulator side.. that should NOT be there, under any circumstances, that indicates a fuel leak on that side, weather it be the fuel regulator, or the injector poppets on that side. I would guess the regulator.

We really need to know the fuel pressure readings to know what the problem could be.


Also, is there any CEL (check engine light) codes stored? has your CEL been on at all?

 

It REAAALLY sucks filling up my tank every week. I usually get 130 to 140 out of a tank if I'm doing strictly city driving.

I haven't cleaned my EGR yet; which wouldn't hurt. I'll pick up a can of berrymans and get the good ol' pick kit out. My PVC valve hasn't been replaced either.. I replaced my O2 Sensor which made maybe a 1 MPG difference. The old one was getting lazy according to my bench test; and at almost 150,000 it didn't hurt to toss a new one in. I picked up a MAP at the pick n pull ; off of a 93 with over 200K on it; do you know of a test procedure? I am pretty familiar with usage of a DVOM

 

I took care of the fuel pressure test in my shop class. He said my readings were normal (my teacher did a swap of the same engine into his wheeling rig and has 30+ years experience as a technician).
We are in agreement; there should not be any washing down in there.. I reaally just want to rule out any options before I drop $300 on a new injector plus $60 for the line kit.