poor gas mileage after intake gasket replacement

[funiwant]

Hello. I just replaced the upper and lower intake gaskets on my 97 lesabre and instantly lost 5 miles to the gallon. since then i have replaced the O2 sensor, cleaned the MAF sensor and installed a new fuel filter. has this happened to anyone else, it there anything i need to check? the gasket replacement went well, not sure how anything could have gotten messed up. any help will be greatly appreciated.

[maxwedge]

No check engine lite? reinstalled the vac. hose on fuel press. regulator, from here without looking over your shoulder during the repair even guess work would be tough.

[funiwant]

yes, no check engine light, as far a i can tell all vac lines are connected correctly. the engine doesn't run rough or really give any tells that something is not right. I hate to admit this but i was an ASE certified mechanic for over 10 years and it has me baffled, was checking if anyone else has run across this problem. I don't do mechanic work anymore so i don't really have access to diagnostic equipment all i have it an app called Torque on my android phone, which works great but even watching fuel trims and other info nothing seems out of place. i am puzzled by this.

[jbman987]

that's a shame. i did the same work to my 97 PA and was rewarded with +5 mpg. here is a list of some of the things that went right (and wrong):

1. squeaky cleaned the intake manifold and throttle body
2. properly torque sequenced all bolts going back in
3. replaced all o-rings on fuel injectors
4. completely refreshed all radiator fluid

now on the flipside.......

5. cracked two injector tips upon trying to slip new o-rings back on
6. did not change motor oil right away after getting things back together
7. split a vacuum line going to the fuel regulator

with that said, i drove the car home right after the whole ordeal (even with the two cracked tips on the fuel injectors!!) it seemed okay and running better than normal even. however, the next day, i went to start it and got some very frightful ticking noises. i changed the two cracked fuel injectors and the ticking went away. then i changed all the spark plugs, changed the oil, added motorkote, changed the air filter and tada!!! i am now getting the best gas mileage ever!! (my personal best was 554 miles on one tank of gas during this past summer)

look over my little list and see if anything was similar to your experience and if maybe something may have been overlooked when you put things back together. changing the LIM and the UIM was the best thing ever for my engine.

[maxwedge]

You need to do a full scan here and look at sensor inputs and fuel trims. Check fuel pressure also.

[rnelson]

The mechanic who did my 98 buick left the pvc valve out which i drove for a week before noticing it // might wont to check that //

[happydog500]

5 mpg lower is no problem, it's 5mpg consistently low that would be a problem.

Did you check your mileage once or a few times? Without doing anything my mileage changes more then I can figure out why. I check my mileage every time I get gas for years and it is different some of the time. Sometimes when its pretty far off I figure I miscalculated somehow.
As sure as you calculated it right, make sure you do it at least a few times to make sure it's CONSISTENTLY low.

So many things that could cause it that has nothing to do with your cars performance. I lose 5mpg easy by running the air. In the winter, on 'defrost' your pump comes on and off. Not that this has anything to do with it, just that there is all kinds of things that can cause this without being anything 'wrong'.

Chris.

[funiwant]

thanks Happydog, i check mileage every time i fill up, i did come across some soft/cracked vacuum lines and changed them, also put some injector cleaner in the tank. On my last trip I was gettting 20 mpg so it is going in the right direction. need to do a little more digging i suppose. BTW my car is the same color as yours, lol

[Tech II]

Yeah, 20mpg is too low for that engine.....

[imidazol97]

Originally Posted by funiwant

yes, no check engine light, as far a i can tell all vac lines are connected correctly. the engine doesn't run rough or really give any tells that something is not right. I hate to admit this but i was an ASE certified mechanic for over 10 years and it has me baffled, was checking if anyone else has run across this problem.

Give the FPR a long check as done in this video to see if it's leaking...

Does your Adroid give any of the data stream symptoms this guy uses?

\\http://www.youtube.com/watch?v=AKtR_...layer_embedded