bad gas mileage

[kessler1492]

Hello,

I have a 97 lesabre, just replaced upper intake and gasket as well as the lower gasket, i'm not leaking coolant into the engine anymore, but now my last four tanks of gas, have an average of 21 mpg. Before the I replaced the intakes I got 24 mpg. Two weeks before that I had to install a new feul pump, fuel filter, strainer. about two months before that I put in new plugs and wires. I rechecked all the engine connectors, I believe everything is connected right. The only thing I've run across is maybe to use some GM tec cleaner in an aresol can clean out any carbon deposits that may be disurpting the engine performance ( maybe loosened some deposits when I did the engine work) Any ideas?

Aaron

[Bassasasin]

O2 sensor is the most often culprit.
Air intake filter. Of course theres the usual things like missing and the like.
There are things that some do to help like facing the plugs.

However not from your issues of one day to the next or after a repair job. I hope you havent got a new vacuum leak.

21 Mpg in the city is great.. actually 27 highway only is whats been experienced.

I have heard of lower mileages when running Ethanol too since it has a lower energy available when it burns.

Good Luck

[wrightz28]

Given the work just done and the problem starting just after, I wonder if there is not a small vacuum leak somewhere?

Did you replace it yourself? Follow correct torque sequence on the manifold?

[kessler1492]

Yes I have a manual and followed the right touque settings in inch pounds the one thing that does have me wondering is just how exact does it have to be I bought a craftsman torque wrench to compare it with mine (got it used). it was within a pound of the torque wrench I have. But this was my first time doing anything this major. How do you check for vacuum leaks? My coolant isnt going down at all. And most important if I have a vacuum leak how do I fix it?
Aaron

[wrightz28]

You can buy one of the old fashio vacuum/mechanical fuel pump gauges for dirt cheap. They include asample sinareos to dteremine what hte gaugae reads.

Ruel of thumb is to always amek sure the torgue wrench is zeroed at every use. One pound can turn into many as th ejob rolls on.

[kessler1492]

And if I find a vacuum leak how do I fix it.

Aaron

[wrightz28]

Hopefully it's just something silly like a misrouted hose, not hooked up hose, cracked hose, etc.

IF it's a manifold leak, be it intake or throttle body, you could try to retorque it, but.. chnaces are you might have to do it over.

[BNaylor]

Is this torque wrench foot lbs or inch lbs? You should use a inch-lb torque wrench for UIM and LIM bolts and follow GM's specs. More precise.

Also, one typical forgotten item when doing a UIM/LIM job is replacing the fuel injector upper and lower o-rings.

[Hapynzap]

Vacume leaks - Like was said check for cracked hoses. Hoses loose at the fittings. Replace or even use a hose clamp to secure.

Could winter fuel blend also be affecting milage? Got any trouble codes?

[Bassasasin]

I did a gas mileage experiment with my car this weekend.
Flat road. No winds. 40 degrees ambient temp.

50 MPH = 30 mpg
55 MPH = 30 mpg
60 Mph = 28 mpg
65 Mph = 26 mpg
70 Mph = 23 mpg

Following a large vehicle at a safe distance gained 2 mpg.


Keep em' wheelin'

[HotZ28]

Originally Posted by Bassasasin

I did a gas mileage experiment with my car this weekend.
Flat road. No winds. 40 degrees ambient temp.

50 MPH = 30 mpg
55 MPH = 30 mpg
60 Mph = 28 mpg
65 Mph = 26 mpg
70 Mph = 23 mpg

Following a large vehicle at a safe distance gained 2 mpg.


Keep em' wheelin'

Which car? No wonder most people drive Buick's slow!

[Bassasasin]

Good question...

My Y2K' PAU, now 60Kmiles, just rolled over.
It has it's indicated instanteanous readout. I figure it's close and calculating against injector performance, fuel pulse duration and VSS.

I had been worried about it.
Now I'm more at ease.. Don't know what MPH they do the test and post the results on that sticker they put on the windows.

I am wondering if that cool rag top vinyl roof creates much drag.
I know it rattles and slaps a bit in the car wash under the dry blowers.

I did learn that it tops out at 99 mpg.. down a steep hill in idle.
Just a little weekend fun while counting cars stalled and stranded from the snow storm.

OH yah. while I was driving normally, a Bronco tried to pass me on the right and instantly blew his engine or somthing. I stayed out of his smoke and oil spray and saw it blasting oil of some kind on his right front wheel. Consequenty he just pulled over, got out, set his beer can on the hood and faded behind me into history.

[kessler1492]

Good news! I got a vacuum testor and hooked it up to the vacuum line, it showed a normal engine reading. The seasoned (at least he seemed to know what he was talking about) attendent said if its not a vacuum leak its probably the Oxogen sensor, said sometimes sensor just sets off a soft code Engine light comes on then goes off, it has done this two or three times ( I do admit I did spray a lot of carbcleaner when cleaning out the lower intake engine surfaces quite a bit was sprayed inside the engine maybe it killed the sensor). I have a good multitestor took it (sensor) out tonight and directions said to test it using a torch. Don't have a torch but I do have a gas stove!!! I took the top off the orfice and used this as a torch. My readings were lower than the what were required. But I'm wondering if the stove flame gets as hot as a propane torch. Maybe thats why the readings were within .15 to .35 rather than .40 to .60 as the specs said should be. I'm not sure both the flames are blue. Any ideas?

[Hapynzap]

I'm just curious but if you swipe your finger in the exhaust tail pipe do you get black soot?

[wrightz28]

The torch is more intense thatn a conventional cooktop and could account for the low reading.

MAP torches are avail easily for $20 or so.