Hey all, I have an '88 Ram 4x4 with the 318 and TBI. Recently I have had a lot of problems regarding rough idle, stalling out, etc. After changing some sensors, new plugs and what not, solved my problem with new ignition wires, it seemed I had some current leakage. Over the duration of this diagnostics process my computer has been telling me I had a rich fuel mixture, and I have noticed a drop in my fuel economy. There have been no other codes appearing. I figured that since it was running so well after the tuneup that it would solve this code, but after a 15 minute drive it is throwing the code again.

Its a little bit odd because according to the manual, when the rich O2 sensor code is thrown, the idiot light should stay on, but mine isn't coming on at all, just one of those background codes. I now have no idea what could be causing the rich mixture, and I have to pass emissions testing in a month, so I would like to figure this out. For the record, I have replaced my O2 sensor (2 years ago), my EGR valve is blanked off, all emissions based vacuum lines are disconnected (and blanked), I have true dual, free flow exhaust with 2 cats, also free flow, and the truck seems to be running better than the day it rolled out of the factory. Any ideas on this one would be great, because there is no way I am going to pass etest when it's running rich. Thanks to all!

 

I would also like to add, perhaps there is a possibility that the O2 sensor got ruined during the time that the engine was running poorly. In the winter, my thermostat got stuck open, and my fuel economy cut in half for about 6 months before I solved it, and then it corrected a lot.... but during this time, the truck was obviously running rich and could have carbon fouled the sensor???

Just a thought.

 

Have you checked the injectors spray patterns?

 

Yes, the pattern looked good and even, regardless, I had a second set of control modules that I swapped out just to be sure. Also, I have a vacuum gauge mounted on the dash, and everything looks good with that to, stable and good reading.

 

If you unplug the 02 sensor, it will stop running so rich. I believe it defaults to a "safe" value, that is still probably a little on the rich side, but not overly so.

But, if the computer is telling you its rich, that means it should be trying to lean it. Whenever mine is plugged in, it gives me a lean mixture code, but dumps insane amounts of fuel in the intake.

 

Unplugging the O2 sensor should put it into open loop mode where it will continue to run a rich mixture regardless of engine performance, thus ensuring the engine is still operating if the O2 sensor is to completely fail, but it doesn't explain why the sensor is sensing a rich mixture under seemingly good operating conditions.

 

Control modules? What do you include in control modules? I would consider the O2 sensor one of the control modules. You have said the O2 sensor may be carbon fouled. I would eliminate the possibility first. If the injectors are OK and the control modules are OK then there is no problem other than design.

Where do you live that they will pass a vehicle for emissions with the EGR system disconnected?

 

Sorry, I meant that I have changed the electronic component of the fuel injectors, ie the wires and 2 plug-in chips that sit on top. I was really hoping not to have to do the O2 sensor right away because I have seen a lot of good ones get swapped out as first attempt at a cure, and I'm on the student budget, so I would rather not have to sink 80 bucks on another trial and error parts.

Oh, and I live in Ontario Canada, they are pretty lenient to the old trucks, they will often try and help you out a bit. My egr however is blanked, but it still LOOKS operational, so it can pass visual if need be.

 

I agree on one thing, "I hate parts replacement as a troubleshooting strategy." There are voltage and resistance checks that can be done on the rest of the computer input modules. (MAP, TPS, temp sensor, O2 sensor, and Hall Effect switch) These things and others all have an impact on the problem you are having and need to be checked.

 

The emissions lines you disconnected may be the problem. Did it change after you plugged them off ? Just remeber these things are a system that depend on all parts working. And the EGR mite be it too. I would never disconnect anything on a commputer controled engine. UNLESS you have a chip in the ECU that lets you do this.