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2000 GMC Sierra PO171 PO174 PO300 - No Spark on Bank 1 Cylinders 1, 3, and 5

Model: 2000 gmc sierra Fault Code: P0171 Posted: 2014-04-09 21:20

I've replaced the distributor, cam position sensor cap and rotor, ignition wires, spark plugs, coil, fuel pump, fuel filter, fuel spider with regulator, and upper intake manifold gasket. I've also checked for vacuum leaks both externally and internally. The issue is no spark on Bank 1 cylinders #1, #3, and #5. Fuel trim readings show a long-term value of +10% and short-term -30% for Bank 1, while Bank 2 shows +25% long-term and -0.8% to +4.7% short-term. The truck starts fine but exhibits misfires, especially at idle. I've confirmed that spark is present and strong on all cylinders in Bank 2 (cylinders 2, 4, and 6), indicating the ignition system is functional overall. I'm concerned about whether the issue lies with the distributor cap, rotor, or secondary wiring for Bank 1. The engine is a 4.3L Vortec. I've also checked the spark plug condition—cylinders 1, 3, and 5 show no visible spark when tested at the plugs (AC Delco). I suspect weak or intermittent spark on Bank 1, possibly due to ignition component failure or misalignment in the intake manifold gasket installation.

Related fault codes
P0171P0174P0300
Comments (11)
Anonymous 2014-04-10 06:37

How did you verify the absence of spark? Is it complete no spark or only weak/intermittent? What is the engine size—4.3L Vortec?

Anonymous 2014-04-10 06:55

In a multi-cylinder ignition system like this, if there's no spark on cylinders 1, 3, and 5 of Bank 1, it suggests an issue with the ignition module or components specific to that bank. A misfire is likely present.

Anonymous 2014-04-10 10:16

The 4.3L Vortec engine—I'm referring to weak spark, not complete absence. The spark appears inconsistent and skips between cycles.

Anonymous 2014-04-10 11:50

Check the coil for consistent spark output. If the coil shows strong and steady spark, suspect issues with the distributor cap, rotor, or secondary ignition wires. If the spark at the coil is weak or intermittent, further investigation into these components is needed.

Anonymous 2014-04-10 11:56

Spark is present and solid on all Bank 2 cylinders (2, 4, 6). The truck starts easily—this indicates that the ignition system works for Bank 2 but not for Bank 1.

Anonymous 2014-04-10 12:35

The truck runs fine overall, but you report no spark on Bank 1 cylinders. Does it run smoothly or does it misfire? The same coil supplies spark to all cylinders—so the issue likely lies in the distributor cap, rotor, or secondary wiring for Bank 1. Without additional codes like P0301 or P0305, a CKP (crankshaft position) or ICM (ignition control module) failure is less likely. Also, ensure your code reader accesses all manufacturer-specific codes such as P0999 and above.

Anonymous 2014-04-12 05:27

The catalytic converter on Bank 1 may be clogged or restricted. Try removing the front O2 sensor to see if misfire symptoms improve.

Anonymous 2014-04-12 09:00

I removed the catalytic converters a year ago. The truck runs fine sometimes but frequently misfires—especially at idle conditions.

Anonymous 2014-04-13 07:53

Double-check the installation of the intake manifold gaskets, particularly for Bank 1, as improper sealing could cause misfire or fuel delivery issues.

Anonymous 2014-04-13 09:05

Clarify—was there a weak or absent spark on Bank 1 cylinders? You mentioned the truck runs fine. Are there any other diagnostic codes such as P0301 or P0305? Check the spark plugs for cylinders 1, 3, and 5: are they wet or dry, black? They are AC Delco plugs.

Anonymous 2014-04-14 18:30

Bank 1 is running rich—typically this would trigger a rich fuel trim code around 25%. Clear all codes and monitor which return. What are the long-term and short-term fuel trims for both banks at idle, 1500 RPM, and 2500 RPM? Misfires can stem from imbalance between fuel delivery across banks. Does your scan tool show current or historical missfire counts?