Hello,

My Blazer LT 1999 have someproblem with the gasmileage.[:'(]

Highway 18 in 65 Mph. (revs around 1900 rpm in 65)
City 11

I know for sure that I could get 22-24 MPG on highway before. I have changed tires from 27" to 29", some difference is because ofthe tiresize changebut notthat much.

Last time I notices that when I stop and put in the Park the idle is high, around 1200-1300 for some sec and then it goes down to 1000.

I thinkidle used to be around 800rpm.

Does anyone have the same problem or maybe some hints!

On tehe next trip I will hook upmy laptop andlog somedata from PCM, maybe someone can help me read outthe data??

I have noSES lighton the truck!
Regards,
/Sverker

 

The first simple thing you can do is run some Seafoam through the engine in the oil and gas. After that, I would definetly clean the Throttle Body in and out with Carb/TB cleaner. Also check your PCV valve too. Once you run a whole tank of gas through the car I would put a bottle of injector cleaner in the the next tank of gas preferrably and GM backed 'Chevron with Techron'. These small things are good a start with a vehicle that has a lot of miles on it and doesnt cost more than $20 + gas of course. Most of the time, if you have no SES codes, cleaning the throttle body takes care of most high or rough idles. Also when was the last time you changed your oil, plugs, wires, cap, etc. and air filter? Axel fluids too!Hope this helps.

 

OK!

I have changed oil and airfilter for 2 month ago, but not the cap, rotor, sparkplugs and ignition wires! and the truck has 89K on her! So It probobly can make some differens!

I drove the truck today without the rising idle, but today it was warmer weather around 35F ??

Will try!

Havent had the time to log with my OBDII system just yet! Willhappend this week!!
/Sverker

 

HI,
I might have found the problem.....At least I hope so!

Today I hooked up the OBD II and saw that the engine coolant temp Was only around160F and the gauge is showing around 170F
But no Code from PCM??

I will change T-Stat later this week

/S

 

My thermostat was stuck open and it did hurt mpg's some, mine would never warm up on the gauge or via the OBD2 sensor. I dont think this ever sends a code unless it gets too hot.

 

That can definitely have an impact on the mileage. If the engine reaches over something like 165*F it'll at least go into closed loop operation, but it will not operate efficiently.

 

Hi,

My fight against the MPG.... gas is so expensive here in Sweden (1 gallon for $7,5)
Yesterday I replaced my T-stat and now I have 210F on the gauge......Good!!

I have also changed airfilter, because I had one of those K&N filters......and I have probably over oiled it!! so my MAS sensor was dirty.I cleaned it with electronic cleaner and q-tip, and after that the truck had more power,
Next step will be cleaning EGR valve and change PVC valve.
I also checked the cat by give it a good hit with my hand...... and I think it rattles some! NOT GOOD??? [&:]

 

yeah if thats rattling the honeycomb looking cermaic is coming loose into pieces.... I would replace the entire converter if that stuff blows out and ends up turned the wrong way on the way out it could clogg up the exaughst flow and really make things run bad.

 

i had a similar problem i changed my cap rotor wires plugs fuel filter.... but it turned out to be a faulty ignition module...