Very rich burn......?
 

On the '98 SSEi.... I'm getting all of the signs of a rich burn. Two month old tune-up parts like the O2 sensor and front plugs have carbon on them. I think the exhaust smells rich and there is carbon on the exhaust tips.. Combined mpgs are around 20... 50%/50% highway/local. that seems a bit low.

I have an Actron scantool which isn't best for OBD II. But, maybe readings will supply some direction.

Front O2 sensor is at .1v to .9v., never in the negative. The Actron manual says .4v is even burn. (I need to confirm that). So it looks like the burn is in range, but the short term trim is continually pulling back the fuel supply. Neither of the other cars works so much to keep the fuel down. My boost gauge jiggles at idle, because of the up and down.

The long term fuel trim is up at +10,+15% all of the time. Ignition advance is +20, +35. I have no standard numbers to evaluate those.

I need some problem solving steps and will answer any questions if more info is needed.

Thanks.

Ok. 20 does not sound very low at all for 50% city. Heck, I usually get about 18-20 for about 70% highway. But of course I don't know how you drive.

Anyways. Those numbers, were those recorded after the car was fully warmed, in closed loop and after being driven? I imagine that would make quite a difference in o2 reading.

Yes.. the O2 sensor has to be well heated, and it was closed loop. After a half hour of local driving, I hooked it up and tried to get a good look at the values, without driving into a tree.

Putting mpgs aside, there is way too much carbon on the plugs and O2 sensor for such a short time in. Just a few weeks ago I was trying to help a friend with his LeSabre L36. He was getting terrible mpgs. Did the BC tune-up for him. Finally figured out his cat was gunked. He had this much of a burn present.

Have you cleaned the mass air flow sensor lately?

Better give him instructions on how to do that without damaging it.

Hmm...and what about YOUR cat? You are OBD2, right? Is there a way to look at the rear 02 data to see if it is mirroring the front 02? If it is, the cat is either gone or going.

Good idea. If you haven't done that lately - check out this techinfo article. May as well clean up the throttle body while you're at it.

http://www.bonnevilleclub.com/forum/...e=article&k=64

A couple of months ago when I got the car, I steadily went about doing what I consider the BC Best Practices Tune-up.

1-New Beldens, NGK-TR55s, PCV(delco), front bank O2 (delco), fuel filter(delco), oil/filter
2-Cleaned battery cables, TB, MAF, IAC, (BTW, it is difficult to find around here, but Gunk's Intake Cleaner for FI Engines cleans out the TB twice as fast as any other I have used).
3) Gutted the airbox, and dropped in a K&N. This is when I got the only unexpected result. My boost gauge started to read -9 instead of -10 at idle. Went over all the vacuums and replaced many. Enough people reported the same issue, that it is on hold for now. If anything this would mean some unmetered air, and a lean condition.
4) TBD... the 180* stat and swap out the Dexcool.

Only other i thing i did was put in a new steering pump.

The rear bank O2 sensor was giving me a relatively steady .7v reading. I have no idea what that should be. That has no impact on fuel/air mix, though. That's why I'm putting mpgs aside. i'm more concerned on the general mix coming in. My gut tells me the long term fuel trim is positive high for some reason, and the short term trim has to continually pull it back down. I may be way off base, that's why I wanted some informed opinions and directions to chase this down.

BTW, I have been trying to keep in grandpa mode while I'm getting a baseline for gas mileage.

Now I know why you guys have always said it's hard to not lean on the throttle. :D

Did you disconnect the battery to reset the pcm after you installed the new O2?

The "base" voltage for the O2 sensor is 450mv or .45 volts. From that voltage, it can swing down to 0, or up to 1 volt, and should do so fairly quickly. A higher voltage indicates a rich mixture, and a low one, a lean mixture. If the voltage seems to hang longer in the above .45 voltage area, that would confirm your feeling that you are running a bit rich. Was this the same car that had the intake problem? If so, was the O2 sensor replaced prior to that repair?

The O2 sensor works by comparing the oxygen content of the exhaust with a "clean air reference." While investigating this, I found that it uses the wiring for the O2 sensor to sense the clean air around it. So, chafed, burned, pinched or damaged wiring can cause it to malfunction. That would also explain on why it's important to keep the spark plug wires (#6 being the usual culprit) away from the wiring.

Other things that can cause a problem with the sensor is a leaky or restrictive exhaust system, or an evaporative system problem.

Yes. This is the 3rd Bonne I have brought back to performance levels. For me, it's best to let the PCM clear and relearn at many steps. It's kind of fun to watch the numbers tighten-up and feel the car get lighter and quicker. That's why I'm so touchy about this rich burn. I knew it was on the rich side when I bought it, but there was some Bob's O2 sensor in it. I thought putting a new O2 in it was a no brainer to improve it.

The trick to this is finding out how the PCM thinks and where it gets its info. For instance, and this may not be an indicator, if the short term trim has to continually bring down the flow, why wouldn't the consistently positive long term trim be backed down?

I'm going to pull the back plugs. One of the six may show a different burn than the others. There is only one FPR. so the flow through the rail must be balanced in a normal state. Maybe one needs more fuel, so the rest are "flooded". I also got a fuel pressure gauge which says i can measure the FPR and the fuel pump with it. Maybe one of them is sick, and just not dead yet.

The only thing left i can think of would be the coils. I had the battery and alternator tested and they are perfect.

I'll proceed, but I'm hopeful for others ideas or problemsolving routes.

Thanks.

OK, good stuff. The front bank O2 operates in that range and does move quickly. Hard to say if it operates more above the .45v. Does the same median apply to the second bank O2, that one is operating in a narrow range at about .7v..

So wouldn't that mean that the O2 sensor on the cat is seeing a rich exhaust at .7v, which is above the .45v ideal operation? Still within operating limits, but not very good.

That's interesting about the wires doing the sensing.

FWIW, I was able to check the 2 front O2 sensors against each other. They operated in the same range, except the Delco was much, much quicker than the Bob's O2 sensor.

The same median does apply for the rear sensor, but the voltage swings may be a bit less dramatic...maybe roughly between .3 and .7 volts.

Then the sensor is consistent with what I'm seeing. I'm operating at, and above, the high end of the normal range.

The front oxygen sensor will give you a good idea of how well it can help the PCM adjust the air/fuel mixture. The rear oxygen sensor is for telling how well the catalytic converter is doing its job. You may have a bad cat., or perhaps the sensor itself is going bad.