Fuel smell and bad mileage

[SinisterJK]

Injector can but biased lean o2 usually doesn’t. It sees its lean and computer makes up for it by dumping fuel. Check to exterior leaks first. Then internal leaks. Injectors. Then look at o2. If you have a scanner data can confirm a biased o2 fairly quickly.
Josh

your absolutely right. ECM doesn't detect enough O2 in the stream and in return the ECM just dumps fuel into the system that remains unburned and flows down stream making a royal stink, horrible mileage and poor performance overall.

 

[Downs]

If it's dumping that fuel though the injectors you'll kill your catalytic converter in short order as well. A stuck injector dumping tons of fuel can wash the cylinder walls down and remove the oil (and contaminate the engine oil) and cause cylinder wall scoring as well. Pull your dipstick and smell for a strong fuel smell in the oil.

I would not drive it or as stated earlier carrier extinguishers with you. If it's leaking somewhere at or near the fuel rail and injectors those are right above the exhaust header which can reach close to or just over 1000 degrees in certain situations which will easily ignite vaporized fuel. You may not be able to see something dripping on the ground because of how volatile gasoline is it can sometimes evaporate long before it reaches the ground.

A stuck injector or other serious problem may not throw a code it usually takes a full failure of a part to do that or cause a pending code which will not trip the light on. Would still be a good idea to hook it up to a scanner and pull any codes which may be there. If you have a smart phone you can get a code reader on Amazon for pretty cheap that will give you real time data from the OBD port as well as let you pull and clear codes.

Start it and starting at your tank and working forward trace the fuel line forward. You won't have a return line on your year model XJ so you'll only have one line. There are rubber lines at various points along the route. Mainly at the tank and then at the front near the intake manifold when it goes from a stainless line to a hard rubber/plastic line.

Get a fuel pressure gauge. They are dirt cheap on amazon or you can rent one from a local parts store. Hook it up start the jeep then shut down. See what the pressure does. If it drops off immediately or quickly you have a problem somewhere. Get a helper and start the Jeep. Get a pair of vice grips in position to clamp off the fuel line (on the rubber part not the hard part haha) and have the helper shut the Jeep off. As soon as you hear it start to stop clamp the line and go look at your gauge. If it still drops off sharply you probably have a leaky/stuck injector.

 

[Jeepmedic46]

Looks like the Jeep is running rich. Fuel smell out of the tailpipe. Going to change the plugs and filter and get it running right. Couldn’t find any leaks anywhere.

 

[Anak]

Not that plugs and filter aren't worth doing, but I would regard O2 sensors as a higher priority.

If the vehicle is running rich and you aren't getting any codes for it then at the very least something is wrong with the downstream O2 sensor(s), and I would expect the upstream to be bad as well.

I would also be looking to see if the CEL is showing when you first turn the on the ignition. If the CEL is not illuminating (that would then beg some other questions, but I can't imagine you made it past inspection without a functional CEL) I would get a scanner on this thing and find out what codes may be hiding in there. If there are any codes to be found that will give you a good head start on the problem. OBDII is very easy to work with. I don't think it costs much at all to get it to communicate with a smart phone. I like a dedicated scanner, but I know lots of folks are opting to just get a dongle (or some such thing) and link it to their phone.

 

[M Rose]

Here is a cheap OBD II Bluetooth scan tool. Personally if I had a overland vehicle over 1996 I would use this one or similar. It not only reads codes, but gives you real time stats of what your vehicle is doing. Such as gives a full fuel system spectrum analysis. If your injectors are staying open, fuel pressure regulator is sticking, IAC is out of tolerance, all can be seen on the smart phone.

GEMWON OBD2 Scanner Bluetooth OBDII Code Reader 4.0 Car Diagnostic Scan Tool for Check Engine Light & Vehicle System Info (Works with iPhone and Android)

 

[Downs]

Not that plugs and filter aren't worth doing, but I would regard O2 sensors as a higher priority.

If the vehicle is running rich and you aren't getting any codes for it then at the very least something is wrong with the downstream O2 sensor(s), and I would expect the upstream to be bad as well.

I would also be looking to see if the CEL is showing when you first turn the on the ignition. If the CEL is not illuminating (that would then beg some other questions, but I can't imagine you made it past inspection without a functional CEL) I would get a scanner on this thing and find out what codes may be hiding in there. If there are any codes to be found that will give you a good head start on the problem. OBDII is very easy to work with. I don't think it costs much at all to get it to communicate with a smart phone. I like a dedicated scanner, but I know lots of folks are opting to just get a dongle (or some such thing) and link it to their phone.

On the XJ the only thing the downstream sensor does is tell the computer about catalyst health. Doesnt do anything for fueling.

 

[Jeepmedic46]

Will have to see how the Jeep does today. Yesterday didn’t get any smell after the plugs and air filter.

 

[Downs]

What did the plugs look like?

 

[Jeepmedic46]

3 of the plugs looked like they were smashed , Air filter was melted into the air filter housing. No more fuel smell. Jeep is running better. Gas mileage is still bad but I think that’s because of the bigger tires. Will regear when I can afford new axles.

 

[Downs]

You may benefit from a computer reset. Disconnect the battery and touch the cables together for 30 seconds.

 

[Jeepmedic46]

You may benefit from a computer reset. Disconnect the battery and touch the cables together for 30 seconds.

I will try that. Thank you

 

[Rorschach]

I am a bit late to this but check your coolant sensors. Some vehicles have two sensors. I don't know what year this is, probably missed it. One for the gauge and one for the computer. Either way, if the sensor goes bad most of the time the failure tells the computer it is much colder than it is. This will cause a rich condition, fuel smell, and bad MPG.

From there the most likely culprit, as has already been mentioned is an O2 sensor.

 

[Downs]

I am a bit late to this but check your coolant sensors. Some vehicles have two sensors. I don't know what year this is, probably missed it. One for the gauge and one for the computer. Either way, if the sensor goes bad most of the time the failure tells the computer it is much colder than it is. This will cause a rich condition, fuel smell, and bad MPG.

From there the most likely culprit, as has already been mentioned is an O2 sensor.

His year model will just have the thermostat housing mounted sensor which feeds data to the computer and gauge. 96 and down had a head mounted sensor that fed the dash gauge and the thermostat housing sensor was used for fueling.

There's a chart with OHM readings based on temperature of the coolant and intake temp sensors. They use the same ohm readings for a given temperature. Quick and easy to check verify temp with an IR temp reader to determine if it needs to be replaced or not.