Cascade Crew

BluFbdy · Posted: Sun Jun 10, 2012 9:43 pm Post subject: Sudden crappy gas mileage...

So I just got back from Rochester, filled my tank up before I left, took the back roads and drove nice and I got home with 1/4 tank. Something is causing my gas mileage to suck balls I haven't noticed til now because I only go back and forth to bremerton today wad the eye opener. I found 2 vac leaks the other day and I fixed them but that didn't really help. I ran a scan tool on my CTS and it seemed right, O2 reading was normal, I did my plugs a few weeks ago and I'm getting a normal 02 so I know the plugs are firing right... I'm stumped. I tried finding more vac leaks with a can of carbon cleaner but I didn't even catch the two I found with that method

Anybody got any tips? I've been driving really nice lately so i know my foot isn't to blame!! Odd thing about the CTS is when Luke pulled a datalog on my car the cts showed -40* which indicates a dead sensor or its unplugged, but that scan tool showed normal so idk what to think

aaron_sK · Posted: Sun Jun 10, 2012 9:50 pm Post subject:

Was the O2 switching? I have seen them continue to read but only on one end of the scale. This will not throw a code but the mileage will crap out.

BluFbdy · Posted: Sun Jun 10, 2012 10:00 pm Post subject:

What do you mean switching?? I gotta admit I was out of my element because the scan tool I was usig was a very old snap on one lol it read 435ish mv consistently so judging by your question its not supposed to be a static number lol my old tool I used in az used to highlight problem values on the table in red kind of an idiot proof feature Laughing

aaron_sK · Posted: Sun Jun 10, 2012 10:29 pm Post subject:

Basically the idea is that the O2 will read from 0 to 1000mv with 450mv being the switching point and anything above and below being rich and lean respectively.

You want it to be switching between lean and rich all the time. If it hangs on one side or the other either the sensor is boned (most likely, considering it's a single-wire sensor in a header) or there is a significant mechanical problem that it cannot compensate for (i.e. injector stuck open, ect.).

BluFbdy · Posted: Sun Jun 10, 2012 10:35 pm Post subject:

I checked injectors first for an odd spray or leaky pod and found nothing, the sensor must be toast because ive noticed a strong(er) gas smell, and if under 500 is lean then the ecm must be trying to compensate and dump in fuel. Come to think of it my o2 bung is pretty high up there...it wouldn't suprise me to be honest

Sound reasoning yes?

aaron_sK · Posted: Sun Jun 10, 2012 10:43 pm Post subject:

BTW, does your scanner show cross counts?

BluFbdy · Posted: Sun Jun 10, 2012 11:13 pm Post subject:

What's that?

aaron_sK · Posted: Sun Jun 10, 2012 11:58 pm Post subject:

ECM keeps track of how many times the O2 crosses stoich. That should come up on any scan or datalog as cross counts or O2 counts.

BluFbdy · Posted: Mon Jun 11, 2012 6:09 am Post subject:

I never checked that, ill have to get a tool locally to check but with the way its been acting a 20$ gamble might not be a bad idea

91RSVert · Posted: Mon Jun 11, 2012 9:23 am Post subject:

Doesnt have to be the motor thats causing problems.

Tire pressure
tire alignment
extra weight in the car
draging brake pad
any sort of friction from a fubared bearing

BluFbdy · Posted: Mon Jun 11, 2012 9:39 am Post subject:

This is true but I've noticed a strong gas smell formed Im pretty ocd about all the other stuff too so that's why I'm lookin under the hood first, plus the sensor isn't behaving properly I just need to confirm it.

Twilightoptics · Posted: Mon Jun 11, 2012 12:57 pm Post subject:

Sounds like O2 to me. All fueling is based off the o2's report to the ECM when in closed loop. If the o2 lies, the computer doesn't know unless it's way out of range and puts up a fault code, it just adjusts fueling based on what information it got.

I'd also be suspect of the CTS as you've had possible failures or erroneous readings.

aaron_sK · Posted: Mon Jun 11, 2012 1:41 pm Post subject:

Two more things now that it's not 1am: Razz

Don't buy a Bosch O2 sensor. They are crappy crap. Buy NTK or Delco or something.

If you are having trouble with inconsistent CTS readings then check the wires. I have seen the wire get kinked right where it comes out of the plug.

BluFbdy · Posted: Mon Jun 11, 2012 3:40 pm Post subject:

Well I ran the scan tool on the cts and it behaved normally under the tests, disconnecting I got -40 like it should but when I jumpered the two it was supposed to be in a range of like 180 to 220 or somethig and it landed way below that so the wires failed the test I checked the pins and they're a bit grimy so I'm gonna clean them. I also backed up the cts being good by doing a resistance check as it cooled down all are in range with gm specs

And I did buy a Bosch lol now it makes sense ill snag a delco today and hope it works