2.3L ('83-'97) Bucking, misfire on 1996 2.3... Possible bad o2 sensor?

[cstarbard]

Hi guys,

Dealing with a misfire on my 1996 2.3 and could use some help.

Symptoms: truck idles fine, drives fine for the most part, but under load/acceleration it will sometimes buck and miss. No fault codes or pending codes.

Reading the live data, a few things stuck out. My short term fuel trims are high. They start in the +20s at idle (the highest they get), lower to around +15-17 at 1500 ish rpms, and lower to around or just under +10 at 2500. My upstream oxygen sensor seems to read ok... shifts within range of .1 to .9 repeatedly, but the downstream 02 sensor is always 0.0, no matter when I read it. Both are readings from my scanner tool. My gas mileage has been poor compared to how it normally is.

If I understand correctly, positive fuel trims mean the computer is trying to add fuel because it suspects/reads a lean condition. Do I have that right?

Also, what does the constant 0.0 reading of the downstream 02 sensor suggest to you all? Bad sensor? Does this explain the high short term fuel trim and the misfire? Should I suspect a wiring problem to the oxygen sensor?

Some things I have done:

I did a crude vacuum test by unplugging the IACV while running. RPMS dropped to around 500 and truck wanted to stall. I replaced a bunch of vacuum lines when I got the truck a few years ago as well.

I read that you can test MAF sensor by driving with it plugged in and driving without it plugged in. I saw no change in symptoms. MAF if nice and clean, but I cleaned it anyway. MAF reads 0.01 lb/s at idle.

New coil pack recently, plastic was cracking badly on previous one and it was actually sparking through the plastic, which is why I changed it. Surprisingly it runs no different with the new one.

The last time I did a full tuneup was a few years ago (maybe 30k miles). Double platinum plugs (or whatever the manual recommended, I think they were double plats), wires, fuel filter, air filter, pcv, etc. I plan on replacing pcv and fuel filter soon as I realize they are probably overdue, if anything

I don't have a fuel pressure tester, but would like to own one anyway, so if you think its wise that I check the fuel pressure I'll get one

Thanks guys, any insight is appreciated.

 

[Eddo Rogue]

I have never had luck changing 02 sensors, it never made a difference. And noticed they are usually thrown in with other codes when check engine light comes on. I think this is because its job is to analyze what the engine did after doing its job. It reads the exhaust to let the engine know if it needs to adjust a rich or lean condition. But if the engine cannot adjust, then something is keeping it from doing that, forcing it to run rich or lean past its tolerances of adjustments.

I say start with that full tuneup, then drive a bit and see if the ECU adjusts itself. Also maybe take a peek in the throttle body, mine was caked in crud. But be careful cleaning it! I went overboard on mine and ended up with a high idle. There's a coating on the throttle plate not to be messed with. use throttle body cleaner and no physical contact on the throttle plate itself.

Rangers are picky with spark plugs, at least my 4.0 is, she didn't like NGK's or Bosch, but loves the autolite and motorcraft.
Double plats are because the coil packs have a waste spark system, which wears the plugs down faster.

Also on my previous ranger, I did have a condition very similar to yours, and swapping in a new MAF fixed it (even though the old one still looked shiny). I didn't test it, just got lucky picking the right bad part, I was a dumb (but lucky) kid back then. This was on a 4.0 ohv. Might be worth a shot if you're gonna throw parts at it.

Thats about all I got lol hope it helps, or at least doesn't cause more harm

 

[BAN-ONE]

I recently had a similar issue and my fix was ect sensor(corroded itself in half).

 

[scotts90ranger]

coolant temperature would likely cause the opposite problem, low coolant temperature adds fuel and the closed loop system would take it out. Unless it somehow shorted out which I guess could be possible, that would cause high coolant temperature which would take fuel out... if you put an OBD II scanner on and look at coolant temperature while running that would tell you.

If you are seeing high fuel trims the most likely cause would be a vacuum leak. On mass air systems it is expecting the main air source to come from the air filter through the mass airflow sensor. It uses the MAF to look at a volumetric efficiency table to tell how much fuel to inject based on the MAF reading and engine speed. If there is an unmetered air leak (AKA vacuum leak) it will rely on the pre catalyst (one in the case of a 4 cylinder, sometimes 2 if a V engine) oxygen sensor to pick up the slack. This will be exaggerated at idle because the intake manifold pressure is lower at idle than cruise so it is sucking harder... this could cause some issues in transitions between acceleration and deceleration with the fuel adapt table from the oxygen sensor...

With that said, I've only had my '97 for a few months and I haven't done much troubleshooting on it, it has some odd misfires and I'm pretty sure it is low on power on the highway for whatever reason but it just got 23.8 miles per gallon on the last tank of fuel so it can't be too bad... I prefer speed density fuel systems (using intake manifold pressure instead of mass airflow) for simplicity, they only symptom you have from a vacuum leak on a speed density fuel injected engine is a high idle...

 

[BAN-ONE]

I’m still trying to learn myself that’s why I finally signed up to TRF. My thinking here was it the ect quits the computer read the coolant temp at -40 and goes rich to compensate for the temp. I admit I’m a complete novice

 

[scotts90ranger]

There's all sorts of failure modes, I'm always learning too . They can fail either way, normally it's open circuit but if the housing corrodes away it could short to ground which would cause high temperature (the coolant temp sensors are a "thermistor" that change resistance with temperature, one wire is a ground the other is the signal wire that is used to test the resistance to ground), open circuit or really high resistance is normally -40 degrees (C or F, they're the same there) and low resistance is higher temperature.