Idle vacuum 19-20", good or bad?

[ChemMan]

On my 1995 Buick Lesabre, that is. I've been trying to find the source of my poor fuel economy, and I'm still suspecting a vacuum leak somewhere. I think that 19-20" is low, but I could be mistaken. The last car I had that I actually checked the idle vacuum had a carburetor.

Thanks

[maxwedge]

That reading is fine, as long as the needle is steady.

[Jrs3800]

How bad is poor mileage?

And this can be attributed by the tune of the car... Plugs wires air filter and the like..

As well it may be time to clean the MAF sensor, And you are about due for an 02 replacement... With a bad O2 in these cars fuel mileage can nosedive to as low as 13-14 in town and 23 on the road when they should see 19-20 City and 29-30 Hwy..

Make sure the car is in good tune.. Check the reading from the O2 sensor via a scan tool..

No matter what you do, steer clear of Bosch plugs and O2 sensors... Also we seem to be seeing issues with the Standard O2 as well..

So far the best ones we have seen are AC Delco and Denso

[ChemMan]

The poor mileage started shortly after I returned from deployment. Prior to I was able to get 31 mpg with the cruise set at 55. Now I get at most 23 mpg, and have also noticed a drop in power. The car sat for about 8 months and was only run once in a while, with the exception of one 150 mile trip. Plugs have been removed, inspected, and re-gapped. Wires are brand new Delco and air filter is a new WIX. I replaced the O2 sensor with a Denso unit about 10k ago purely due to age. Could it possibly have been fouled? I have a scan tool and just need a little guidance as to what I should be seeing from a properly functioning O2 senor. I'll also clean the MAF sensor while I'm at it. I did clean it once before maybe 4 years ago, but it isn't hard to clean again.

Thanks

[HotZ28]

Originally Posted by ChemMan

I have a scan tool and just need a little guidance as to what I should be seeing from a properly functioning O2 senor.

When the 02 sensor drops to around 300mv, the PCM commands the fuel system to “go rich”. When the 02 output reaches 600mv, the PCM commands the fuel system to “go lean”. If you observed this function on a scanner, you should see a rapid flash back & forth, between rich and lean. O2 "counts" is how many jumps back and forth it makes. Have you considered the possibility of a clogged cat?

[ChemMan]

I haven't noticed any difference in the car's exhaust note, but I'll look into it a little more closely.

[HotZ28]

A clogged cat will not make a noticeable change in the exhaust note; in fact, the exhaust will gradually get quieter, so you would never notice anything, unless the cat is damaged, or broken. The loss of power & throttle response is also a very gradual process! Stop by a muffler shop and ask if they can do a back-pressure test on your system, some shops will do the test at a very reasonable charge.

[jbjslambert]

i have similar probs right now with 97 lesabre, O2 sensor bad with no codes?? also stopped by exhaust shop today and they didnt want to check cat cause i told them if it was bad that i didnt want replaced right away, what jerks they are, lol, never go back there again

btw anyone know if universal cat could work with this car, bolt on cat too expensive

[maxwedge]

All the parts stores sell both universal and direct fit.