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A 360° Look Into the GM 60° 3.1L Engine

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Over the years, GM has saved a bundle on manufacturing the 3.1L engine by using the production line tooling it originally developed for the 2.8L V6. By simply changing the bore diameter, the displacement of the same engine block could now be increased for more power and torque.

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The General Motors 3.1L V6 engine enjoyed a long production run from 1988 through 2005.

More than 10 million of these engines were built during this period. The engine itself went through continual evolution and improvement during its production life, ­including Gen II and Gen III versions, plus an “Enhanced 3100” version from 1999 to 2001.

The engine itself was based on the earlier 2.8L V6 that was first produced back in 1980. The 3.1L was eventually replaced with various versions of the 3.4L V6. Today, the 3.1L lives on in China where it is being made in various displacements (2.5L, 3.1L and 3.4L) for GM’s Chinese-built Buicks. The larger 3.4L version has been imported into the U.S. since 2005 to power the Chevy Equinox.

Over the years, GM has saved a bundle on manufacturing the 3.1L engine by using the production line tooling it originally developed for the 2.8L V6. By simply changing the bore diameter, the displacement of the same engine block could now be increased for more power and torque.

The narrow 60° angle of the V6 cylinder banks was chosen so the engine would more easily fit into front-wheel drive cars and minivans (though it has also been used in rear-wheel drive applications, too).
Most of these vehicles have aged to the point where they don’t have much resale or trade-in value. A real cream puff low-mileage mint condition car might fetch a couple thousand dollars on a used car lot.

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But, many of these vehicles are so old that they are probably worth less than $1,000 — which makes it tough to justify spending a lot of money on repairs if major engine work is needed. Even so, many people are hanging onto their old cars longer than ever these days and are still putting money into repairs to keep them running. You might have a tough time selling a customer a rebuilt long block, but they might consider swapping in a used V6 as a less expensive alternative.

Except for the notorious leaky intake manifold gasket problem that has plagued many of these engines, the 3.1L V6 has had a reputation for being a long-lived reliable engine. Consequently, there are still a lot of these engines on the road and people are still spending money keeping them running. We’ll touch on some of the more likely repairs shortly.

Engine Notes
With one notable exception, all of the 60° V6 engines in GM’s 2.7/3.1/3.4L family have been conventional pushrod designs with two vales per cylinder. The one exception was the dual overhead cam (DOHC) “LQ1” version of the 3.4L engine produced from 1991 to 1997.

The 3.1L V6 utilizes a 3.50” bore with a 3.312” stroke crankshaft. The block has gone though half a dozen variants since its inception, with different mountings, sensor fittings and reinforcements for both FWD and RWD applications. Some of the engines (notably 1990-’95 FWD minivans) had cast iron heads, while most of the later engines came with aluminum heads.

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The Gen III version of the engine (L82 built from 1993 to 1999, and the later LG8 VIN code J engines) added a composite roller cam and used a number of slightly different cylinder heads. Roller rockers were also used on most 1995-’99 3.1L engines.

If you’re swapping in a used engine, interchangeability will depend on the make and model year. The major differences to watch out for would be the A/C compressor and starter mounting bolt holes, and sensor mountings.

The 1988-’92 engines did not use a cam position sensor, some of the 1993-’94 engines had cam sensors and some did not, while all of the 1995 and later engines had cam sensors. Early versions of the RWD engine and FWD minivans used a distributor ignition system while all of the FWD car applications had waste-spark distributorless ignition systems.

The only “problem” block in the 3.1L V6 engine family to watch out for was the one used in some 1988-’90 FWD cars and minivans, casting #10065459. This particular casting tended to develop cracks near the center cylinders.

Common Problems of the 3.1L
• Leaky Intake Manifold Gaskets. This is the most common problem on these engines. Some have blamed the problem on GM’s Dex-Cool antifreeze, but the real problem has been the intake manifold gaskets. The original equipment gaskets have a plastic carrier and soft sealing beads around the coolant and intake ports.

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Over time, the plastic carrier and seals soften and deform, causing the gasket to lose its seal. Coolant then starts to leak down into the lifter galley and crankcase. Eventually, the loss of coolant causes the engine to overheat, which may cause additional damage such as a cracked cylinder head or crushed head gasket. The leakage problem can occur in as little as 60,000 miles on some engines. The higher the mileage, the more likely the intake manifold gaskets are leaking coolant.

Coolant leakage can be diagnosed by checking the oil dipstick (if the oil looks milky or foamy it probably has coolant in it) or by pressure-testing the cooling system. If an internal coolant leak is indicated, the fix is to pull the intake manifold and replace both intake manifold gaskets. Several aftermarket gaskets offer design and material improvements over the OEM gasket to provide a longer lasting trouble-free seal.

Replacing the old intake manifold bolts with new ones is also recommended.

• MAF Sensor Problems. The fuel injection system on the 3.1L engines used a mass airflow (MAF) sensor to measure airflow. The PCM also looks at inputs from the throttle position sensor (TPS), engine speed and temperature to calculate airflow and how much fuel is needed for the correct fuel mixture.
The little heat-sensing wires in the MAF sensor can become coated with dirt, carbon or fuel vapor varnish over time, causing the sensor to misread airflow. A dirty MAF sensor typically under-reports airflow, creating a lean condition in the cylinders. The O2 sensors in the exhaust will pick up the lean mixture, causing the PCM to command a richer mixture to compensate — which may make the fuel mixture too rich.

Symptoms of a dirty MAF sensor may include rich or lean codes, fuel trim codes, poor fuel economy, rough idle or even black smoke (carbon) in the exhaust. If there’s a serious fault in the MAF sensor circuit itself, you may find a P0101, P0102 or P0103 code.

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Cleaning the sensor with aerosol electronics cleaner (nothing else!) will often fix the problem and restore normal operation. If the cleaning doesn’t solve the problem, the MAF sensor may be bad. A simple check here is to hook up a DVOM to the MAF sensor’s output signal wire and look for a change in the frequency signal as the engine is revved from idle. No output at all, no change in the signal or an erratic change would all tell you there’s a problem with the sensor. Check the MAF sensor’s input voltage and ground wires before replacing the sensor because the fault might be in the wiring, not the sensor.

• EGR Problems. The 3.1L engines use a variety of different electronic EGR valves. The common problem here is a buildup of carbon under the EGR valve that prevents the valve from fully closing when EGR isn’t needed. A leaky EGR valve will act just like a vacuum leak, causing a lean fuel mixture, rough idle and misfiring. You may find misfire codes or various EGR related codes when you do your diagnosis.
A dirty EGR valve can be cleaned with carbon remover. The EGR port in the manifold should also be cleaned to make sure there are no obstructions. A blocked EGR port can cause spark knock and detonation when the engine is under load. Install a new gasket under the EGR valve when it goes back on the engine.

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Another problem was a camshaft rear main oil seal leak. For more information on that issue, click here.

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