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Discussion Starter #1
Seems to be an aweful lot of Black Carbon buildup in the tailpipe of my 91 Voyager with the 3.3 liter EFI six. Been tracking down another problem in another post so many of the codes have been cleared since it seemed some of the codes were related to a no start condition, but the tailpipe has been black for a long time. This makes me think that there is another issue that needs to be adressed especially when the tailpipe spews and spatters black carbon sometimes at startup when reving the engine a little.
 

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Discussion Starter #3
It definately uses some oil. Using Mobil 1 high milage. Only has 66,000 miles. Wondering how it might be affecting O2 sensor and cat.
 

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If a 3.3 is using oil, first thing to do is check the PCV system. Sure it could be a ring problem, even on a low mileage motor that old, but the PCV is a cheap thing that can cause oil use.

Odds are the oil is not the reason for the black, because the oil is burnt and turned to smoke as it goes through the engine. I'd suspect it's more likely from the normal engine exhaust. Once it's running well, check the gas mileage. However, some cars simply do this from the moisture present in the exhaust system that has condensed as the system cools after use.
 

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It could also be running rich and related to your hard-start/poor fuel economy problem. What color are your plug tips? Carbon fouling would be from an over-rich mixture condition.
Are you running the recommended RN14PMP5 spark plugs gapped at 0.050"?
Have you watched the engine try to start in the dark for any coil/wire/plug arcing?
 

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Probably a stupid question, but when's the last time you changed the air filter. As IC mentioned, a rich condition can cause that to happen. A clean air filter and pcv system is critical for that.
 

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As long as all the sensors are working correctly, a dirty air filter will not affect the air/fuel mixture; the computer will compensate based on what all the sensors are saying. However, if an important sensor such as the O2 is not working right, that could cause an over-rich condition, and black deposits in the exhaust pipe. The O2 could be bad due to other conditions such as a bad PCV overloading oil in the intake and eventually coating the O2 with soot, as mentioned above which might also cause excessive oil consumption.
 

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Discussion Starter #8
New PCV valve, new plugs, new valve cover gaskets oil change to Mobil 1 high milage with new OEM filter about a month and a half ago. Somewhere between 500 and 1000 miles on ododmeter since that service. Oil is quite dirty already. Was thinking that maybe it was running too rich since oil is dirty and tailpipeis so nasty, but it could be the result of what looked to be the original plugs looking really really tired. I don't remember the plug model but I do know that they were the newer recommended Champions since they gave me a different number than the ones recommended in the owners manual. Was told the original plugs had been superceeded by the newer spec'd plug. Air filter looks good. No new wires cause the ones on there look outstanding, but Bob Lincoln says replace them anyway. That's comming soon, but I want to flush the cooling system and replace the themostat, and radiator cap first. Also got a couple leaks in the drivetrain that are gonna need some attention pretty soon so I've been chipping away at these issues a little at a time.
 

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I will second the comment about oxygen sensor(s). Been there, done that, on a '90 GC/3.3. Abysmal gas mileage transformed back to normal immediately. A relatively simple job to replace from underneath as long as you can get the car up in the air a bit, ramps are fine. Do it with the engine cold to avoid burns from hot exhaust system.
 

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You know one of my codes that I had was 51 which I think indicated a lean condition. Don't know if it was accurate but if it was I don't see how that could be the case if the tailpipe is coated black with soot that cakes up on my finger when I swipe it across the inside edge. Maybe the o2 sensor needs a closer look. If they are heavily coated with soot but still functional can they be cleaned?
 

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Fandini: I don't know enough myself to say if cleaning is the solution. In my case, I presumed, without really knowing, that mine simply had failed electronically, though it's plausible I suppose that the reactive surface was contaminated, I really can't say. Perhaps someone else reading this thread can answer your question. As I recall the diagnosis in my case was made by a good friend with an assortment of engine analyzers (he collects, repairs, and resells them), and he used a deductive process to isolate some electronic problem which I don't remember which pointed toward the O2 sensor. So I just replaced it. It was about $40, and I'd already wasted that much in fuel costs in the time since I realized I had a problem.

Regarding cleaning and reusing the sensor vs replacement....When I've got a part in hand, meaning removed from the vehicle, if it's something which could likely fail at some point and if its expected lifespan is approaching, I just replace with new as a preventative. Belts and hoses are good examples. Sensors likewise. If I had a manual transmission removed, I'd replace the clutch even if it had been working fine, just because I'm there, rather than push it another 10k and then have to pull the transmission again.

I certainly can't promise that the O2 sensor is your problem. You seem to have an assortment of issues, so you may have layers of problems working in combination, rather than just one problem. I suggest you find someone who can accurately diagnose your engine, even if you have to pay for it. Then you can set about repairing or replacing what is needed. With such low mileage, unless some serious problem such as overheating or oil sludging has occurred, this car ought to be well worth whatever repair is necessary. The 3.3L engine is an excellent one. The one in my 1990 has just shy of 300,000 miles, and still runs smooth though power is finally beginning to fall off. My 1996 runs well too, and with half the mileage, it is powerful and squeaky clean on California emissions tests.

I'd be curious to know what you finally find out, so please report back when you solve this one.
 

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You know one of my codes that I had was 51 which I think indicated a lean condition. Don't know if it was accurate but if it was I don't see how that could be the case if the tailpipe is coated black with soot that cakes up on my finger when I swipe it across the inside edge. Maybe the o2 sensor needs a closer look. If they are heavily coated with soot but still functional can they be cleaned?
If the sensor reads "lean" when the engine really isn't the computer will add more fuel to the mix. That is how a too lean reading can happen when the engine is really running rich.
 

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you could use a multimeter and check for resistance in the downstream sensor first since it's the easiest to access that oxygen sensor. This diagram is for a 2000 Grand Caravan, but with the same engine as yours :)
 

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There won't be a downstream sensor in a 1991, only an upstream since it's OBDI.

Generally the downstream sensor (when present on a OBDII vehicle) doesn't affect mixture much at all. It's really there to verify 9compared to the upstream sensor) that the exhaust after the catalytic converter is "cleaner" than before the converter.
 

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From the day I bought my Daytona, 27 years ago on the 18th of December, the tail pipe has been black. The fuel economy is great as in more than what the sticker said and performance is also good. I've owned two mini vans and both had black tail pipe tips. One of the vans was a '91. Now, I'm not suggesting that you don't have a problem but if the economy is good and there's no black smoke exiting from the tail pipe then perhaps you don't and it's normal.
 

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Discussion Starter #19
OK, got no start condition fixed and put some wires on. Just pulled the codes.

12
51
15
42
55

Milage is now really bad. Down to about 11 around town on the overhead display where is used to show about 16 mpg around town.
 

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