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1991 deville
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Discussion Starter #1
After car get warm it gets a rough idle. A chugging sound from exhaust and smells like rotten eggs. Runs great going down highway no engine miss and great gas mileage. Should I lean toward o2 sensor or cat? no cat noise or rattle plenty of power. would an o2 by itself do that?
 

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1985 Sedan DeVille
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how many miles on the odometer, where are you located (general geographic), and do you use any additives
 

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Master of the Dark Art of Diagnostics
2003 DHS - two-2002 DHS, 2003 SLS, 1995 Sedan DeVille, 1989 Coupe DeVille
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19,265 Posts
After car get warm it gets a rough idle. A chugging sound from exhaust and smells like rotten eggs. Runs great going down highway no engine miss and great gas mileage. Should I lean toward o2 sensor or cat? no cat noise or rattle plenty of power. would an o2 by itself do that?
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like always -
the FIRST step in diagnosing a problem is
check for Diagnostic Trouble Codes -
if you don't know how - go here and read the ENTIRE post -

http://www.cadillacforums.com/forums/cadillac-deville-1985-2005-including-1985/138257-how-pull-codes-dtcs.html

if you have any codes - post them here -
ALONG WITH THEIR DEFINITIONS -
 

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Super Moderator
White Diamond '03 DHS (with DTS floor shift)
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86,781 Posts
Sounds like you are running rich. Check for a leaky FPR.
 

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1991 Cadillac Sedan deVille
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591 Posts
The only code is E12. How can I check for a leaky FPR? Thanks ray
To check for a leaky FPR pull the vacuum line from the FPR and see if any fuel is coming out of there.

E12 is no distributor signal. Check the wiring to the distributor (the large 6 terminal, 5 wire connector), and check the pickup coil. Does your engine stall also? Usually interrupted distributor signal will cause a stall.

To check the o2 sensor activity go to parameter P.1.4 and look for rapid swings from about 0.2V to 0.8V. To navigate to the parameter enter diagnostics and wait for 7.0 to display, then press Lo once and after that navigate with Hi to P.1.4.
 

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1991 deville
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8 Posts
Discussion Starter #7
ok no fuel at all in vacuum line to regulator. Went into watch o2 sensor it sits pretty much .74-.80 all the time. if I stab the throttle it goes to.30 and right back to .75-.80 all the time. Is that good or bad?
 

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1991 Cadillac Sedan deVille
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591 Posts
I'm copying my PM response to you:

mc_marto said:
ray364 said:
I went into diag like you said to P.1.4 o2 stays .75-.80 the whole time. If I stab throttle it goes .30 then right back to .70-.80
It should rapidly move up and down. Try another thing - using the same procedure go to the next parameter - P.1.6 and look for cross-counts. The cross-counts are the number of times the o2 sensor swings from lean (below 0.45V) to rich (above 0.45V) in a second. This parameter is used in determining o2 sensor activity. It should rarely go to 0, and under acceleration it should be between 10-20 or so. That's what a healthy o2 sensor will normally output. I suspect yours might be biting the dust, but make sure you also test the FPR. Also, keep in mind that leaky injectors could make it run rich as well.

If you do end up replacing the o2 sensor I definitely recommend the AC Delco brand from experience. I long time ago (soon after I bought my Deville) I was chasing other problems and decided the o2 sensor might be getting old and lazy. So, I replaced it with a Bosch Premium sensor and called it a day. Well, a few months ago I was chasing other drivability issues and started looking closely at the cross-counts. I discovered the Bosch part was frequently going to 0, and the most activity I saw under acceleration was 9. I then put my old AC Delco sensor (which had been replaced some years ago from the previous owners) and I saw the numbers I talked about earlier - rarely 0 and 10s to high twenties under acceleration.
 

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1991 deville
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Discussion Starter #10
No I figured car was only off 10min or so there would be a sign of fuel in the vacuum line. I will ck that though. while its running.
 

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1992 DeVille
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Start the car, let it run for a bit. Pull the vac line off the FPR, then touch a piece of tissue to the nipple and see if it comes away with gas. The tissue really makes seeing the gas easy
 

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1991 deville
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Discussion Starter #12
Ok I will do that this afternoon. I love this car it is like brand new inside and out. I hope I can get this fixed. I figure its o2 , FPR or CAT. It is for sure rich at idle. smells like rotten eggs bad and misses. Off idle it purrs like a kitten.
 

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dchavezo said:
Start the car, let it run for a bit. Pull the vac line off the FPR, then touch a piece of tissue to the nipple and see if it comes away with gas. The tissue really makes seeing the gas easy
Shut the car off before checking with the tissue.

Forgot to mention that
 

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Super Moderator
White Diamond '03 DHS (with DTS floor shift)
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No need to shut down. Just pull the vacuum line at idle and touch your finger to the nipple. If there is gas on it, replace the FPR. If not, move on to the next thing.
 

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1992 DeVille
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mc_marto said:
I'm copying my PM response to you:
Yo mcmarto-

My p.1.6 at idle is a constant 0. When I'm accelerating it becomes 7-12

P.1.4 is fluctuates between .74 and .99 but leans more towards the .9 area at idle.

Not sure if this is a result of this but when I fill up my fuel used is a gallon or two off. Meaning my car says I used 4 gallons but when topping off 5 goes in before automatic shut off.

Bad O2 sensor?
 

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1991 Cadillac Sedan deVille
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Something is suspicious about your o2 sensor. It should rarely go to 0 even at idle. And, yours tends to stay close to 0.9V, which is the top of the range (rich).

You can remove the o2 sensor and see if there are any deposits on it. You can burn the deposits with a propane torch (do not use a cleaning solvent of any kind), and while you do that you'd have an excellent opportunity to test it off the car. Connect your DVOM to it, set it to the 2000mV scale, and warm up the sensor for a bit (while burning off any deposits) until the numbers start to change. Then you want to test how fast and well it reacts to the torch vs air (less oxygen like when a car is running rich vs more oxygen). Basically, you want it to respond very quickly and be able to generate volta below 0.3V (300mV) to above 0.8V (800mV). I'm sure you can find some videos on YouTube if you need to see it in action.
 

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mc_marto said:
Something is suspicious about your o2 sensor. It should rarely go to 0 even at idle. And, yours tends to stay close to 0.9V, which is the top of the range (rich). You can remove the o2 sensor and see if there are any deposits on it. You can burn the deposits with a propane torch (do not use a cleaning solvent of any kind), and while you do that you'd have an excellent opportunity to test it off the car. Connect your DVOM to it, set it to the 2000mV scale, and warm up the sensor for a bit (while burning off any deposits) until the numbers start to change. Then you want to test how fast and well it reacts to the torch vs air (less oxygen like when a car is running rich vs more oxygen). Basically, you want it to respond very quickly and be able to generate volta below 0.3V (300mV) to above 0.8V (800mV). I'm sure you can find some videos on YouTube if you need to see it in action.
Thanks for getting back to me, I appreciate you're response man =)

I though of preemptively replacing it months ago but then decided against it. I'll order a new Ac delving one and while it's on it's way I'll test the current one.

I thought it was weird like you said staying at 0 and reading rich almost all the time
 

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1992 DeVille
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mc_marto said:
Something is suspicious about your o2 sensor. It should rarely go to 0 even at idle. And, yours tends to stay close to 0.9V, which is the top of the range (rich). You can remove the o2 sensor and see if there are any deposits on it. You can burn the deposits with a propane torch (do not use a cleaning solvent of any kind), and while you do that you'd have an excellent opportunity to test it off the car. Connect your DVOM to it, set it to the 2000mV scale, and warm up the sensor for a bit (while burning off any deposits) until the numbers start to change. Then you want to test how fast and well it reacts to the torch vs air (less oxygen like when a car is running rich vs more oxygen). Basically, you want it to respond very quickly and be able to generate volta below 0.3V (300mV) to above 0.8V (800mV). I'm sure you can find some videos on YouTube if you need to see it in action.
So I found a post on here about O2 sensors thanks to ranger. And it said if you unplug your sensor whole in P.1.4 (O2 sensor voltage) it should immediately jump to .45. Which mine does.

The post then says to jumper pins a and b of the 02 connector harness (not the O2 sensor - duh) and the voltage should jump to 0.00-0.05. Mine does not. Mine stays at .45. Which is what happened to the guy in the thread. I found.

The fix was to run a ground wire from pin B to a good known ground (e.g. The alternator or the battery)

Also I haven't found in my FSM how to determine which pin is A and B. The jumpering didn't make that an issue but I'll need to know when I run the ground. Does anyone know which is which or how to tell? (I believe the cable colors are blue and white.)

How would I do this? I'm not huge into electrical engineering so spell it out as if I were a ritard. How would I go about splicing in to pin B. Is it as simple as stripping some insulation off, solder a ground wire and run it to the new ground location and secure it to the ground? Then tape it all up nice and tight?

Be easy on me I'm just trying to learn and fix this issue. Thanks everyone =) I appreciate any tips and tricks or input =D
 

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So I found a post on here about O2 sensors thanks to ranger. And it said if you unplug your sensor whole in P.1.4 (O2 sensor voltage) it should immediately jump to .45. Which mine does.

The post then says to jumper pins a and b of the 02 connector harness (not the O2 sensor - duh) and the voltage should jump to 0.00-0.05. Mine does not. Mine stays at .45. Which is what happened to the guy in the thread. I found.

The fix was to run a ground wire from pin B to a good known ground (e.g. The alternator or the battery)

Also I haven't found in my FSM how to determine which pin is A and B. The jumpering didn't make that an issue but I'll need to know when I run the ground. Does anyone know which is which or how to tell? (I believe the cable colors are blue and white.)

How would I do this? I'm not huge into electrical engineering so spell it out as if I were a ritard. How would I go about splicing in to pin B. Is it as simple as stripping some insulation off, solder a ground wire and run it to the new ground location and secure it to the ground? Then tape it all up nice and tight?

Be easy on me I'm just trying to learn and fix this issue. Thanks everyone =) I appreciate any tips and tricks or input =D
Can you post a link to that thread?

If you look closely at the plastic connector you'll see the letters. They should be both on the sensor side of the connector and on the other one. And, pin A is actually the ground for the o2 sensor, so if you run an extra ground you'd want to run it to pin A, not B.

You are correct about splicing in, soldering, and then connecting the wire to a good known ground. However, you need to make sure you splice into the correct wire. Like I mentioned, pin B is the signal wire to the PCM, and pin A is ground. It's usually tan color by the way. To make sure you see the proper one, follow the wire coming from the outer side of the o2 sensor to the connector, then see what the corresponding pin letter it is on the connector, and what color wire is on the other side.
 

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mc_marto said:
Can you post a link to that thread? If you look closely at the plastic connector you'll see the letters. They should be both on the sensor side of the connector and on the other one. And, pin A is actually the ground for the o2 sensor, so if you run an extra ground you'd want to run it to pin A, not B. You are correct about splicing in, soldering, and then connecting the wire to a good known ground. However, you need to make sure you splice into the correct wire. Like I mentioned, pin B is the signal wire to the PCM, and pin A is ground. It's usually tan color by the way. To make sure you see the proper one, follow the wire coming from the outer side of the o2 sensor to the connector, then see what the corresponding pin letter it is on the connector, and what color wire is on the other side.
Cool cool. I replaced my O2 sensor last night. Original one had a blue and white cable. Replacement acdelco one had brown and white cables. Old O2 was the honeycombish style while the new one was a solid piece. Thought it'd be easier to get to than it was ;)

Here's a pic of the old one. Looks whitish which might suggest a lean condition? Which goes against the car almost always reading that it's running rich.

With the new O2 I've noticed a way better idle and overall power. It's as if the a/f mixture mapping is finally spot on so the car doesn't hesitate when decelerating anymore.

At first with the new sensor the idle jumped around about but I went to top off the tank and while I did I unplugged the battery to reset the comp. did and idle learn after and since then all is well.

I have noticed my O2 cross counts still go to 0 every once in a while. So I'm not sure what's up with that. With the old sensor as soon as I get off the throttle it'd go to and stay at 0. This new one will do that sometimes. Other times it'll stay around 5-10 on decel.

I think replacing the sensor definitely helped but I'm concerned that the crosscounts still go to 0 occasionally and also that my integrator and block learn values (p.1.8 and p.2.0 respectively) are occasionally lower than 128 (sometimes as low as 100ish.)
Again with the new sensor, this is happening less dramatically than the old one. I could get the old one to read 80 at idle or decel easily.

Could my MAP affect this?? Should I try to manually ground the O2 sensor just as a preventative test/step to rule that out??

(I'm okay with throwing parts at it within reason. I'll probably put a new MAP on just because. My goal is to really find out what's causing this) i know it could be injectors and I still need to get gear to ohm them out...they all click steadily.

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Article link:

http://www.cadillacforums.com/forums/cadillac-forum/t-35837.html

Old 02 sensor:

 
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