Hey guys, first off, I'm new to this forum, so I apologize in advance for any stupid questions and comments that I'll likely make.

So I just got a 94 GMC Jimmy SLE with a the "W" vin CPI vortec motor. The truck is as clean as a whistle, a real pavement princess, never been off the road, the interior and paint are, for the most part, in excellent shape. The body has 120xxx miles on it, the engine has ~70,000.

I bought it about a week ago, and it ran pretty good, the only thing it seemed to really need was a tuneup (one of the spark plug wires sounded like it was arcing inside. One of the cylinders was missing, but the ECM compensated for it and it ran smoothly, despite a slight shutter occasionally).

Before the tuneup, it averaged 14 miles per gallon. That's mostly freeway. I took the plugs out, the electrodes were worn and the gap was at .050" (stock is .035 I believe?)

Long story short, I did a full tuneup, engine purrs like a kitten and has plenty of power, but it still returns unacceptable gas mileage. The first tank after the tuneup, I got 13mpg. Even throttle response, plenty of pep, no misfiring. I drive it with an eggshell under the accelerator.

So I'm wondering, does anyone have an ideas what it could be? I haven't plugged into the OBD yet, and the check engine light isn't on. I hear these trucks all have EGR problems, etc. But the exhaust is totally fine, not black, blue, white, or smelling like fuel.

Any pointers would be extremely appreciated. And I understand that people have this problem a lot on this forum, but none of the other posts have helped me at all.

Thanks guys!

-Ted

 

Wow I like have a 1993 GMC Jimmy with like 200xxxx etc... and I get great mpg when I did my tune up I replaced wires cap rotor and plugs I used bosh platinum Once in a while I will add fuel injector cleaner for high mileage cars and then it is road trip time. Good luck with yours !!! Later

 

I would recommend a fuel pressure and leak down test. The CPI engine are notorious for having fuel leaks inside the plenum.

 

swartlkk:

how do you do a leak test?

 

Sounds like my 92, my mpg is right at 14. Several things are leading me to replace my spider injector. Besides the poor mpg, when i went in for an emissions test the CO was about 1.5 times higher than the limit. Did a few tweeks to get it to pass (barely). I spose there is a chance the regulator is leaking but at a price of 40 bucks for the regulator, buying a reman spider unit for $177 (comes with the regulator) seems the way to go. :::fingers crossed:::