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1998 Ram 4x4 P0132, P0135, P0138, P0172 Codes - Running Rich, Stalls at Idle, Backfires at Low RPM

Model: 98 ram 4x4 Fault Code: P0132 Posted: 2008-02-15 11:13

I own a 1998 Ram 1500 Sport 4x4 with a 5.9L V8 and automatic transmission. The truck has accumulated 106,500 miles and recently developed four diagnostic trouble codes: P0132, P0135, P0138, and P0172. The vehicle is running extremely rich, causing it to idle between 100–200 RPM and sometimes stall completely. When approaching a red light and the light turns green, the engine bogs down and backfires—only resolving when I floor the throttle to around 2,100 RPM. I've already replaced both oxygen sensors, confirmed the catalytic converter is not clogged (and was previously gutted due to plugging up on Christmas Eve), and have cleared the codes multiple times—only for them to return immediately. Both O2 sensor readings remain consistently at 1.0 volts with no fluctuation, which suggests a potential issue with the engine control module (ECM) or an underlying fuel delivery problem. During driving between 0–2000 RPM, the engine exhibits erratic surging—only stabilizing around 60 mph. I'm at a loss as to what's causing this behavior and would appreciate any insights into possible root causes related to these specific codes on a 1998 Ram 4x4. Possible contributing factors include fuel pressure issues, vacuum leaks (especially from the intake plenum), misfires, or faulty sensor signals. I'm seeking advice on how to diagnose and resolve this issue effectively without relying on illegal modifications like O2 sensor simulators.

Related fault codes
P0132
Comments (12)
Anonymous 2008-02-15 13:05

Check fuel pressure—could be too high. Also verify the throttle position sensor (TPS) voltage at idle. Ensure distributor timing is correct. Is there a vacuum leak in the intake system? What’s the coolant temperature sensor reading? Does the engine misfire? How did you confirm the catalytic converter isn’t clogged?

Anonymous 2008-02-15 16:36

The catalytic converter was previously removed due to plugging up on Christmas Eve, which left me stranded.

Anonymous 2008-02-15 18:16

Does removing or disabling the catalytic converter cause the O2 sensor readings to become faulty? Could that be the root of the P0132 and P0138 issues?

Anonymous 2008-02-16 01:04

I’m not certain about all these factors, but I’ve been told that if the oxygen sensors show no fluctuation (stuck at 1.0V), it could indicate a failing ECM or wiring issue.

Anonymous 2008-02-16 09:43

On all three sensors? No. If an O2 sensor is stuck at one extreme, it’s usually indicating engine conditions—like rich mixtures—which is exactly what it should do. A flat reading suggests a deeper problem like fuel delivery or ECM malfunction.

Anonymous 2008-02-16 12:33

Since the catalytic converter was removed, would installing O2 sensor simulators fix both the codes and the running-rich condition?

Anonymous 2008-02-16 13:20

Unlikely. You must first diagnose why the engine is running rich before replacing or modifying emissions components. The rich mixture likely caused the initial converter failure—common in these trucks due to internal vacuum leaks from a blown plenum pan. Symptoms include stalling, backfiring, and oil consumption. This issue is well-documented on forums. O2 simulators and removed converters are illegal and waste money. If you're investing in fixes, hire a qualified technician for proper diagnosis—avoid 'shiny go fast' scams.

Anonymous 2008-02-16 14:29

I’ll investigate this further—while it may not be illegal under West Virginia emissions laws currently, that doesn’t mean it’s safe or compliant long-term.

Anonymous 2008-02-16 21:00

So modifying or removing a factory-installed emissions component isn't illegal? Are you sure? I think you're assuming legality because there's no testing. I’d recommend reviewing national emissions regulations—especially for vehicles over 10 years old. Regardless, proper diagnosis and repair are essential.

Anonymous 2008-04-01 22:54

I’m bringing this topic back to life after discovering the real issue: a blown fuse. After finding it and replacing it, the truck has been running smoothly for two weeks. If you're experiencing P0132 and P0138 simultaneously, check the engine control (ECM) fuse first—it's labeled 'Oxygen Sensor' on my wiring diagram. Others may call it 'Engine Control.' Always check this fuse before spending money on parts or simulators—it saves time, fuel, and troubleshooting effort.

Anonymous 2008-04-02 16:21

Obviously—this is a common oversight that many overlook when diagnosing O2 sensor issues.

Anonymous 2012-01-12 12:57

I recently replaced the engine block ground wire, and it resolved the issue immediately. A poor ground connection can cause erratic sensor readings and ECM misbehavior.