'91 Black Smoke

1991 RRC V8 3.9L
Approximately 120k Miles
Automatic left hand drive
Cats and silencer are cut out

So. Truck was running perfect and I took it on a 5 day camping and trail riding adventure into the Pisgah National Forest (North Carolina). I drove there from northern Florida (Approximately 340 miles). While we were there, we clocked about 200 miles of off-roading. It was a great time. I wanted to throw some pictures in this but I'm not sure how.

Anyway, during the last day I hit a decent sized bump going faster than I should have. The muffler mounts failed, the exhaust system dropped, and the right (passenger) side exhaust down pipe clean broke just below the flange where it connects to the manifold. It also came close to breaking my brake line.

So before the story goes on, keep in mind I'm over 400 miles from home and probably 50 miles from anywhere that could help me or sell me something.

Naturally, we slammed every wrap, gel, and paste we had in our tool boxes to try and reconnect the down pipe to the manifold. Didn't work. But the RRC kept rolling. However, there were occasional backfires and it sounded like machine gunfire inside of the muffler at times.

What was most concerning, was a black smoke and liquid blowing out of the exhaust when applying gas at lower speeds. It was clearly running very rich.

I called around to exhaust shops but no one could take me for at least a week in the area. So the long journey home began.

So I was pretty much forced to drive almost 400 miles back home with 1 O2 sensor reading and the passenger side exhaust disconnected at the manifold.

So my current situation. I replaced the spark plugs, got the down pipe rewelded, and replaced the broken side's O2 sensor. The O2 sensor was completely coated in soot. I have ordered a replacement O2 sensor for the driver side as well but it hasn't arrived yet.

With these listed fixes, the black smoke/liquid issue still persists and it's running rich. There is also a rattle in the muffler at idle. Will replacing the other O2 sensor be the fix? Is there something I'm not thinking of?

I checked the fuel injectors with a screw driver and they are all clicking. I haven't investigated my fuel rail any further.

Lesson learned. If you have an older truck and you trail ride, check the rubber mounts on your muffler. If they are dry rotted replace them!

Thanks for any help.

Assuming you're losing no coolant the liquid is going to be the considerable amount of water produced as a by-product of burning petrol or diesel.
Usually to be seen dripping out of the tailpipe as some of it condenses inside the exhaust system.
In colder climates it's seen as the white 'smoke' from the exhaust which is actually steam condensing in the cold air.

The black smoke does indicate a rich mixture.
I wonder if the running with a failed sensor has also killed the other sensor?
Rattle in the muffler suggests there's something loose inside it.

How’s your chest?

Ratae said:

Assuming you're losing no coolant the liquid is going to be the considerable amount of water produced as a by-product of burning petrol or diesel.
Usually to be seen dripping out of the tailpipe as some of it condenses inside the exhaust system.
In colder climates it's seen as the white 'smoke' from the exhaust which is actually steam condensing in the cold air.

The black smoke does indicate a rich mixture.
I wonder if the running with a failed sensor has also killed the other sensor?
Rattle in the muffler suggests there's something loose inside it.

Click to expand...

Thanks for confirming some of my thoughts. I'll update once I replace the other sensor. For the moment I'm not running the truck so I don't foul up the new sensor.

I may replace the muffler or just cut it open, gut it, and then weld it back together. Not sure if that's a realistic option though.

Either way, thanks for the input!

RangeRoller dt said:

How’s your chest?

Click to expand...

I'm not familiar with that term. What are you calling a chest?

You need 2 working o2 sensors before going any further, you may need to reset fuel trims as well. So long as you don't have any leaks at intake or exhaust then see how it runs

kermit_rr said:

You need 2 working o2 sensors before going any further, you may need to reset fuel trims as well. So long as you don't have any leaks at intake or exhaust then see how it runs

Click to expand...

Thanks for the input. Good to know I'm at least on the right track. After I got the exhaust rewelded I crawled under and ran it for just a bit and the exhaust appeared to be completely sealed now.

Given the series of events, what would be other areas to investigate while waiting for the new O2 sensor to arrive?

Can you check error codes and live data? If there are no intake leaks then check the maf output. If that's ok and your o2 data is good, you should be on to a winner

Never heard of pisgah forest and i lived around there for a while! Knew folks in pickens and travelers rest

kermit_rr said:

Can you check error codes and live data? If there are no intake leaks then check the maf output. If that's ok and your o2 data is good, you should be on to a winner

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Cool thanks. Oddly it's not throwing any codes. During my drive back I had a check engine, but no number showed on the onboard code reader (the code reader has always worked). Currently I cannot get the thing to throw a code, but I have also tried not to run it a lot after putting the new sensor in. I'll check the MAF. I replaced it not too long ago so I will be pretty upset if that is an issue. Crossing my fingers that the O2 sensor is the fix, but I'm trying to use my time and prepare for the worst.

kermit_rr said:

Never heard of pisgah forest and i lived around there for a while! Knew folks in pickens and travelers rest

Click to expand...

We actually camped in Martha Sundquist, by Hartford. It's near a cluster of national forests. I believe Cherokee National Forest is the most popular/well known in the area. I'm not familiar with the area myself, just there on the trip. It was amazing mountain driving, waterfalls, cool rock streams and all. Being from Florida, which is very flat, it was a really cool adventure. My off roading experience has always been swamps, sugar sand, and creek beds up to the hood haha. So rocky mountain sides were unique, and at times scary. Learning how to drive in the mountains took me a bit.

RoverFL said:

I'm not familiar with that term. What are you calling a chest?

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driving 400 miles in the Florida heat with no exhaust chucking out smoke I’d be coughing up conkers for a week

RangeRoller dt said:

driving 400 miles in the Florida heat with no exhaust chucking out smoke I’d be coughing up conkers for a week

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Haha! yea it was rough. Had the windows down. Luckily my buddies and I have a redundant system of Comms. I have some headsets that work with our base radios (Also great for spotters to comm with the driver). Due to the noise I had to rock those for the return leg. To your point though, it was a miserable 10 hours. My dog was not happy by the end of it.

It was actually cold (for me). I drove with gloves, thick jacket, and beanie the whole way.

kermit_rr said:

You need 2 working o2 sensors before going any further, you may need to reset fuel trims as well. So long as you don't have any leaks at intake or exhaust then see how it runs

Click to expand...

I forgot to ask. What is the procedure for resetting fuel trim? I'm a novice when it comes to mechanicing and I learn as I go. Also, why would I potentially need to do that? What's the science behind it? Loaded question but I appreciate the advice a lot.

Fuel trims....
OK, lambda sensors read the emissions and the fuel trims are adjusted to reduce emissions and help performance.
Resetting the trims allows the cars ecu to reassess the fuel and emissions.
The fuel trims are also in charge of allowing a certain amount of oxygen into the cats to help them burn the crap off. Thats why a lambda sensor pattern has a simple wave form to it. It portrays more oxygène and less oxygène passing through the engine.
There is a way more technical explanation but it's 7.00 in the morning

No point in resetting fuel trims until you have both O2 sensors working. Generally this needs LR specific diagnostics, but high end generic like Snapon, etc might do it.

Not sure if a 1991 classic would have post-cat sensors in the US, but it it did before the de-cat this could also affect fuel trims ? Also fuel pressure will affect it, because the ECU assumes the pressure is within a certain range, and opens the injectors accordingly. If it's too high then you can get too much fuel going in !!

All good advice, thanks guys! I'll keep all this in mind but wait until I change the sensor before I dive too deep.

It only has the two O2 sensors before the cats.

Are they two wire or four wire lambda sensors?