99 S-10 Blazer getting bad fuel milage

[candywrapper]

Hello;
I have a 99 S-10 4 door Blazer, Its getting bad fuel milage . 13 city and 15 Highway.
Here,s my story ;About 2 months my truck shut off for no reason, it did this 3 times in a row in 20 minutes time. the next day , it did it again, shut off 3 times again, all in town driving. I was noticing a high pitch sound like a fan running, coming from the fuel tank (like the fans running in your computer). My mechanic put it on the hoist with it running and we comfirmed it was coming from the tank. He says maybe fuel pump was going out,told him to replace the fuel pump,He put in a aftermarket fuel pump in (Carquest). He checked the fuel pressure on the old pump before taking it out. He sead it was a little low on pressure.The milage went down hill before he replaced the pump ,He also replaced the fuel filter too. After i got the truck back, I drove it for 2 weeks ,but still got bad milage. So he puts it on a full diagnostics Machine, No codes came up or sencers found bad. Nor any lights has come on in the dash like(check engine light) Now before this all happened , I was getting 16-17 city and 22-24 Highway.The truck has only 54,000 miles on it. I had ask my mech, What about spark plugs ,could they gone bad with only 54,000 on it,Not likely he told me.
I went and called the Chevy dealer today to see what could be done. I told him what was all done to it , so, the first thing the service man asked was, Did you use a AC-DELCO fuel pump or a aftermarket pump in
I told him, we used a aftermarket pump. His comment was( Well thats your problem,you go and put in a AC-DELCO pump and your problem will be solved.) He didnt want to talk to me anymore and hung up on me.
I cant believe that thier is that much difference in fuel pumps.My mech assured me it was set to GM specs.
Im going crazy and dont know what to do next,the mech told me he was going to make some calls ,but nothing back yet
Sugestions , Sugestions Anyone ??
You can email me if you want at
[email protected]

Don

[GMMerlin]

Loss of fuel mileage can be caused by many things...driving habits, warm-ups for cold weather driving, engine performance problem, dirty air filter.
I owned a 96 S truck and was getting about 19-20 average which looks like what you are getting.
You may have sticking injector poppets, which would give you a slight loss in power causing you to press down a little further on the gas pedal...more throttle = more fuel.
just some thoughts.

[candywrapper]

GM Merlin;
Thanks for replying to my post. I did put in a new stock air filter on sat. I had a K&N high air flow filter in it, I had heard rumors that with these computer controlled vehickles, that these filters can change the fuel milage for worse on certian vehicles, something to do with the air ratio flow in to the motor, but im gonna try anything to get my milage back to normal. I had put it in just a week before my fuel pump went out. i will let you know if the filter change helped on friday . as for injector poppets , i;ll ask my mechanic about it. I didnt notice any sluggish performance on acselleration though. Its really confusing, the truck runs so smooth,even on cold mornings and when its running down the road.It shifts normally too when going down the road, somebody told me to see if it shifted in overdrive, it went in overdrive like normal. Man, 13 MPG really sucks. I used a product called Sea Foam,from Advance Auto ,An injector cleaner, 3 cans 3 tankfulls ,that didnt help either.Im running out of things to try.
Any more suggestions????
Don

[blazer01]

I am running into the same problem I was having trouble with 01' blazer with 21k miles starting and after the run around with the dealership I think they finally have the problem fixed. I only have owned the blazer about 2 months ( half the time it has been in the shop trying to get the problem fixed. thank god for warranties. anyways I have the same problem . I am getting about 16 mpg highway driving. and I am wondering if there is anything that can be done. is it really the fuel pump or is there something else. just as a side note. I have noticed that the blazers seem to have a major problem with the fuel pumps if you take a look at peoples posts.

[Glenn Peters]

Ihave a 98 Blazer I'm gettin between13/14 city and 18/19 highway and have been told that that is pretty much normal by other blazer owners.

[GMMerlin]

On the sticking injector poppets subject, allow me to explain.
I had no real feel of loss of power on my 96..understand that I drive a 90-100 mile round trip to work everyday..mostly on the interstate.. when it came time for my 100,000 mile tune-up, I decided to perform the injector poppet unstick procedure outlined in a GM Tech bulletin...I was surprised to find that all 6 of my poppets were stuck closed..matter of fact, it took about 10 attempts to get a couple unstuck..that night driving home, I could feel the difference in power and could definately tell the difference in fuel mileage the first week.....
Point of the story...sometimes we don't notice a gradual loss of power (or of our hair).
If you come out and your car won't start..you will notice that immediately....
If you came to me and have seen a steady loss of fuel mileage with out any indication of a problem, I would look towards the poppets as being a source of the problem based on my knowledge of the product and history of previous repairs to the same type vehicle that resulted in positive results...
Not to say that this is the only cause, but one that is often overlooked.

[Glenn Peters]

What exactly is the procedure to unstick poppets, I'm a tech and would like to give it a try.