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99 Chevrolet Silverado 5.3L Engine P0171/P0174/P0137/P0157 Diagnosis: Lean Condition, Fuel Pressure Issues, and EGR Leak Fix

Model: 5.3 silverado Fault Code: P0137 Posted: 2015-09-20 09:47

I recently purchased a 1999 Chevrolet Silverado with a 5.3L V8 engine that had been stored for an extended period. Within days of ownership, the truck began throwing multiple OBD-II diagnostic codes: P0171 (Bank 1 lean), P0174 (Bank 2 lean), P0137 (Downstream O2 sensor failure on Bank 2), and P0157 (Downstream O2 sensor failure on Bank 1). I've already replaced the mass airflow sensor (MAF), fuel filter, air filter, spark plugs, plug wires, and intake manifold gasket. Additionally, I discovered mouse nests in the air filter housing and behind the intake manifold during maintenance. After resetting the codes, P0171 and P0174 persist—indicating a lean condition on both engine banks—and now P0137 and P0157 are also present. At low RPMs, especially when backing out of parking spots, I experience sudden power loss and the engine appears to stall. The truck lacks proper acceleration and performance under load. I suspect the root cause is related to fuel delivery or air intake leaks. I've addressed a known issue: the EGR hose bracket on the intake manifold was warped and leaking significantly. While I initially considered sealing it with silicone, I now understand that removing or modifying emission components may be illegal. I currently do not have a dedicated code reader but am using local shops for free diagnostics. I’ve tested fuel rail pressure and found only 11 psi when the key is on and 25 psi under load—well below the expected range. When I unplug the vacuum line to the fuel pressure regulator, pressure remains at ~25 psi, and after turning off the engine, the rail holds pressure for several minutes. This suggests a potential failure in the fuel pump or faulty fuel pressure regulator (FPR). No visible fuel leakage is present in the vacuum line. I’ve now ordered a new Delco fuel pump to test performance. After installation, the truck runs significantly better with no codes thrown so far. I’m sharing this experience for fellow owners of 1999-2000 Silverado 5.3L engines facing similar issues—especially those in non-emissions-heavy regions or used trucks with storage history.

Related fault codes
P0137P0157P0171P0174
Comments (15)
Anonymous 2015-09-20 12:35

P0171 and P0174 indicate a lean air-fuel mixture. Start by checking for air leaks downstream of the MAF sensor. Clean the MAF sensor carefully—avoid using oiled air filters. Verify fuel pressure with a gauge. Ensure you have access to a code reader or scanner. For parts, consider AC Delco components, which are known to be reliable in older GM trucks.

Anonymous 2015-09-20 12:35

P0171 and P0174 point to a lean condition. Check for air leaks after the MAF sensor. Clean the MAF sensor without using an oiled air filter. Test fuel pressure. Do you have access to a scanner or code reader? Consider AC Delco parts—ask local dealerships or shops for recommendations.

Anonymous 2015-09-20 13:05

Thanks! I recently replaced the MAF sensor. After reviewing your advice, I found that the EGR hose bracket on the intake manifold is warped and leaking severely. All connected hoses appear damaged. Since my intended use is only hauling and towing—not daily driving—I’m considering sealing the port with a delete plate. Would replacing all EGR hoses be better than a temporary fix? I don’t have a scanner, but several local shops offer free code reading.

Anonymous 2015-09-20 13:50

Emission regulations apply to registered vehicles. Removing or disabling the EGR system is illegal under federal law and could result in fines or vehicle registration denial. A simple fix like plugging a port is not allowed. Without EGR codes, focus on air leaks after MAF and fuel pressure testing. Do not confuse a code reader with a scanner—knowing a code is just the first step. I recommend rechecking for air leaks downstream of the MAF and verifying fuel pressure.

Anonymous 2015-09-20 15:14

The EGR tube connects just past the throttle body, which is located after the MAF sensor—so it falls under your earlier criteria. No other visible leaks are present. In South Dakota, vehicle emissions testing is not required for registration, and many owners run straight pipes without catalytic converters. However, if a vehicle was not originally equipped this way, it could still lead to fines during inspection. I’ve straightened the EGR tube and sealed the leak with silicone. The hose has two mounting holes while the intake manifold only has one—this may already be a modification that risks compliance. I’ll install a rail pressure tester next weekend after the silicone cures. I’m also ordering a scanner to monitor codes more closely. Thanks for the input—I’m not an expert, but this is very helpful.

Anonymous 2015-09-20 16:03

I'm providing factual information: it's a federal violation to remove or disable any emission control device. This is not opinion—it’s a legal requirement. Avoid spending on modifications until you verify the issue. Fuel pressure gauges are available as loaners at auto parts stores like AutoZone or Sears. If needed, search for 'fuel pressure gauge' and 'how to test fuel rail pressure'. Also, note: are you referring to the PCV valve? It connects from the top of the intake manifold to the rear valve cover. See this reference image: http://ww2.justanswer.com/uploads/ebroc/...123705.png

Anonymous 2015-09-20 19:01

The arrow in the photo points directly to where the leak was. The EGR hose has two bolt holes, but my intake manifold only has one—this suggests a mismatch and potential rigging. This may already be an illegal modification.

Anonymous 2015-09-26 12:32

I just received a rail pressure tester. With the key on, I read 11 psi; under load, it reaches 25 psi—only about half of the expected range. This is concerning and likely points to a failing fuel pump or regulator issue.

Anonymous 2015-09-26 14:02

When I unplug the vacuum line from the fuel pressure regulator, there's no noticeable change in pressure—it remains at ~25 psi. After turning off the engine, the rail holds that pressure for several minutes. This suggests either a faulty fuel pressure regulator or a failing fuel pump. At this low reading, it’s unlikely to be a regulator issue—fuel pump failure is more probable. The EGR leak has also been sealed.

Anonymous 2015-09-27 15:10

I hope the EGR fix wasn’t too expensive—many people avoid spending on what they see as 'unnecessary' parts. Honestly, a vehicle with such low fuel pressure would not run properly under load. This is where you should focus your efforts. I suspect the fuel pump has failed. Regarding the fuel regulator (FPR), did you observe any fuel leakage in the vacuum line? However, at this low reading, FPR testing isn’t reliable—fuel pressure is too low to be a valid test.

Anonymous 2015-09-27 15:21

No fuel is present in the vacuum line when unplugged—whether the engine is running or off. I was surprised by how low the rail pressure was, but it now makes sense: this explains why the truck stutters and cuts out at quarter throttle. When idle drops to 300 RPM, pressure stays around 11 psi and doesn’t rise to normal levels. I’ve ordered a new Delco fuel pump and will update once installed.

Anonymous 2015-10-04 15:55

Installed the new fuel pump today—the truck now runs smoothly with no diagnostic codes. Performance has improved dramatically, especially under acceleration and load conditions.

Anonymous 2015-10-05 08:28

Great to hear! Enjoy your ride—perfect timing for hunting season!

Anonymous 2015-10-05 17:24

Note: A user reported a P0174 code on a Toyota runner with a MAP sensor issue. This may not apply directly, but it highlights the importance of checking MAF or MAP sensors in lean conditions.

Anonymous 2015-11-06 22:37

Consider replacing the downstream O2 sensor before the catalytic converter and adding sea foam to fuel for Bank 2 (passenger side). This may help with combustion efficiency and reduce lean readings.