In the first week of November I was getting 18pmg with my '94 Blazer (w). The mileage went down to about 13 by the first of December. That caused me to start looking for a cause. I did a full tune-up with AC Delco parts including replacing the fuel filter. The old cap and rotor were very warn and the plugs were worn out. The mileage was still in the 13 range so I kept looking. I discovered leaking injectors. I replaced the spider and nut kit the first week of January. Now I've been running it back and forth to Seattle (about 100 miles round trip) on the freeway and the best mileage I've seen since the new injectors is 15. I'd like to get the Blazer back up to its previously high mileage. What should I check out next?

 

I would look at your PCV valve.. Mine went out on me and caused my mileage to drop a lot. And i would also listen for a vacuum leak, those are just a couple things that could be causing problems.

Also, is your engine getting up to running temp? If not your temp gauge might be bad or your thermostat might be bad, and if it never gets to running temp it will stay in fuel enrichment mode which means burning more gas.

Im kinda chasing the same gas demon now.. I just got a PCM tune and my mileage went up a lot then it all of a sudden dropped, but i did also switch to a different gas station (FredMeyer) on the fill up before it dropped. But i just filled up with Shell so we shall see.

^^ That could also be part of your problem

 

The other thing is did you buy a cheap spider assembly? When I had my 94 s-10 blazer, I put a new set in and it was on the cheaper side, and I actually got worse gas mileage out of them then with factory. (Just a wondering observation)

 

Thanks for the really good feedback. I just got home from a trip to Idaho with my wife driving her '93 Jimmy and we got 18-19mpg on the freeway including plenty of slow, 4WD driving over the Blue Mountains. The Blazer has to be able to get back to that kind of mileage! I'll respond to the items on an individual basis:

1. I hadn't suspected the PCV. Last time I checked it the PCV valve rattled normally. I'll check it again.

2. The engine is definitely getting up to running temperature, assuming the gauge is to be trusted, which I believe it is. I put in a new temp switch in August 2010. I actually think it may be time to replace the thermostat because, according to the gauge, it gets up to about 220°F before the thermostat opens and the temperature drops. I should verify that operating temp with my scanner and IR thermometer but I'm quite sure it's coming up to temperature.

3. The injectors I put in the Blazer were rebuilt by Dr. Injector in Tacoma. I took my old spider assembly to him for testing and found that the springs in the nozzles were weak and the nozzles were staying open too long and spraying too much fuel. He tested the rebuilt injectors to ensure they were dispensing the proper amount of fuel. I took it for an emissions test shortly after I installed the new injectors and it passed with very low emissions.

I'll check the PCV system this week and see what's going on with that.

 

I did some more checking on the Blazer this morning. The PCV valve seemed to be functioning as normally. It rattled when I shook it. I replaced it with a PCV valve from another '94 Vortec. I check for vacuum leaks by spraying carb cleaner around every area where the engine could suck in air. The idle speed never changed. The truck idles perfectly at 650 rpm and runs very smoothly. We'll see what the mileage is on this tank. I'm going back and forth to Seattle a couple times this week so I'll have plenty of time to test it out.

 

Just so you know... if you have a small leak and the idle is smooth/normal you wont find it that way without disconnecting the IAC connector. Because the PCM will just compensate.

That's what it does, right?

 

I had forgotten about the IAC compensating for the change in vacuum. Thanks for the tip!

However, the current project to get the mileage up on my Blazer is most likely on hold. I was parked in Seattle today and some drunk driver clipped the left rear corner. Now the bumper is pushed in, the tail light broken and the rear corner is all crumpled. I've got to sort all that out first. Apparently he also hit several other cars in the area and then crashed his car on a barricade along the on ramp to I-5.

Today was not the day to be in the city.