ok so start off p0452 code and possible loop issue so go that code replaced the gas cap it didnt go away and no woosh sound when i open the gas cap replaced rad cap and thermo twice heater core bled the system temp never reads above 190 ever and wicked hard on gas like way worse then my last blazer btw 98 chevy blazer 4 room ls and can smell gas when i fill up any iinput would be awesome threw money already want a direction

 

Call me old fashioned, but please try again using sentences and punctuation. Then we will be happy to help.

 

since my last thread was quickly closed , to to lack of punctuation. i will try again.
So start off p0452 code and possible loop issue, Got that code replaced the gas cap it didnt go away, and no woosh sound when i open the gas cap. Replaced rad cap and thermo twice, heater core bled, due to no heat issue. The system temp never reads above 190 ever and wicked hard on gas, Way worse then my last blazer. It happens to be a 98 chevy blazer 4 door ls. I can smell gas when i fill up, and ive had two o2 sensor codes pending, and now it started jumping rpm while im at cruise speed on the highway. Any input would be awesome threw money already want a direction now. thank you very much

 

P0452 is an abnormally low voltage from the pressure sensor. It's not going to cause a performance problem, but it will turn on the SES light. You can read about it here https://blazerforum.com/forum/diagno...plained-35142/ Whoosh sound is not necessarily normal when you open the gas cap. With key off, pressure should be vented through the charcoal cannister anyways. Not sure what you mean by loop issue, other than maybe closed/open loop issue? Please advise.

Let's look at the heating issue. 190 sounds just a little low but not so bad. What temp thermostat is in it? By no heat I assume no heat inside the vehicle. Are both the inlet and outlet hoses of the heater core hot to the touch? If so, your blend door is not working.

On the highway, in overdrive, and during steady cruise the TCC hooks up. When you begin to accelerate or if you drop below 45 mph (or tap the brake pedal) it disconnects and the rpms jump up until the TCC hooks up again. Is this what you are experiencing? Slightly degraded engine performance will make this happen a lot more.

What are the O2 sensor codes? Could it be that you have a vacuum hose off of the vacuum reserve tank and this is causing a lean condition, as well as not providing vacuum to operate the HVAC blend door?

Fuel mileage on a 4WD Blazer tends to be between 13-17mpg. Are you there somewhere?

Please give me some feedback regarding these questions/comments and I will try to help further.

 

i replaced my thermo each time with a 195f, the heat inside was rectified by a new core but not engine heat. the jumping rpms on highway was criuseing speed, itll just like 200 rpm repeatedly and then back down. the o2 codes were p0135 and p0155 they only come on once in a while. Im also gonna try annd spray carb cleaner to check for vacuum , as i have no heat on floor. and yea the milage is suoper bad like i will burn a quarter tank in around 21-25 miles

 

I really don't think the coolant temperature thing is an issue - 190 vs 195. I really think the jumping you describe is normal TCC operation for engine with reduced power.

Please report (posting plots would be even better) of your fuel trims (both long term and short term) at extended idle and at 2000 rpm steady. This will tell us if the PCM is trying to compensate for a lean condition and directing the engine to run richer.

As for the P0135 and p0155 - these are both the same condition (O2 sensor heater) but for different O2 sensors. Attached is the factory info and diagnostics for the P0155. Could be the O2 sensors end up giving bad info to the PCM and it compensates with too much fuel (just a possibility). Let's see what the fuel trims are doing.