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Ditto to what mckrishes said. Make sure you are up on maintenance. Also, leave more info. Mileage, make/model (the 3800 was in everything from small cars to mini vans), any other problems like a loss of power…
To add to the list above, you should have a Mass AirFlow sensor on your throttle body. It might be in the boot though, I can’t recall in Series 2. It makes a fair difference. Check your tire pressure.
ok,
mileage is 174000 in a 1999 pontiac grand prix
PCV valve is new
MAF was just cleaned with MAF cleaner (not sure how to tell if the reading on my scan tool is accurate though)
The oil is new and has always been maintained with synthetic oil
Air filter is ok (could maybe go for a change but only cause its like 2 years old it still looks pretty clean)
Spark plugs are less than a year and wires are brand new
I would check your mass airflow sensor and you oxygen sensors for proper operation using a meter. I know the scan tool is good, but I double check the sensors manually just in case.
Was the drop in mileage sudden or slow? Anything you can think of that happened before it? Do you still have good power and a normal engine idle?
Do i check the sensors manually with a voltmeter? please explain this process.
Also the milage drop was fairly sudden. The intake manifold gaskets were recently replaced upper and lower. I have checked for vacuum leaks using choke cleaner and it appears everything is sealed up.
I also removed my heat shield from the resonater due to vibration (long middle muffler after cat).
[quote=”Buggsy” post=32428]If you do find out, let us know. I didn’t know there was a voltmeter test for O2 sensors.[/quote]
DVOM’s do not update quick enough for checking pre-cat o2 sensors. You are best using a graphing scanner or a scope.
You could ohm out a o2 sensor heater circuit, as well as checking your power and grounds but that’s about it.
[quote=”troy5190″ post=32243]hey all,
IM getting about 20 percent worse gas milage than I used to. here is what im dealing with.
3800 GM series 2 engine
LTFT 16.4 at idle about 11 on the highway[/quote]What’s the STFT? If it’s 0 +- then LTFT is doing it’s job.
Honestly I don’t think you need a DVOM to read the O2 sensor, all I usually do with an OBDII car is read the live data on a scanner (it is what the computer sees after all), if an O2 sensor fails it’s usually pretty obvious. I think the issue is not the sensor however. I’d be looking for vacuum leaks first thing since it seems to be adding fuel. The above video should help you with those.
Ok, ive done a pretty good vaccum leak check and cant seam to find anything, I was thinking of hooking up my brake bleeder and seeing if the vaccum system can maintain the negative pressure ( this is the only tool i have that mayt work)
do you think this would be a valid test for a vaccum leak or would it just suck in air from the outside?
Also lets just say that There are no vaccum leaks, why would there be fuel added to my system. My thoughs are that the MAF is giving a falsely high reading???
What steps should I take if there is indeed no vaccum leaks?
Also I know that the car is old but this was for the most part a sudden change, that actaully set a check engine code. If I remember correctly the LTFT used to run at about 5-7.
Your thoughts????
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