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Servicing GM's 3800 V6 Engines

April 1, 2008

The Buick 231 cu. in. 3.8L V6 engine has had a production run lasting more than 30 years. Like the small block Chevy V8, this engine has undergone many changes over the years to keep it abreast of changing consumer expectations and emissions regulations.

  The first Buick 3.8L was offered in the 1975 model year Skyhawk, Apollo, Century and Regal. The engine was based on an earlier 198 cu. in. V6 that Buick introduced back in 1962. The 3.8L engine shared the same 3.8” bore size as the Buick 350 V8. It also had an “odd-fire” crankshaft, which produced some idle shake and vibration.

Over the years various improvements were made to upgrade engine performance. Here are some of those changes:

1977 — Buick changed to an “even-fire” offset-pin crankshaft to smooth out the V6 engine.

1978 — Turbocharged version of the 3.8L V6 offered in the Buick Regal and LeSabre.

1979 — The engine gained some horsepower with improved cylinder heads (larger valves and ports).

1980 — Larger 4.1L version of 3.8L engine offered with bigger 3.965” pistons.

1981 — Stronger connecting rods and a revised harmonic balancer and flywheel were added.

1982 — 180 hp version of the turbocharged 3.8L V6 offered in Regal T-Types and Grand National. Also, a smaller displacement 3.0L version of the 3.8L V6 with a shorter stroke crankshaft was built for GM FWD cars.

1984 — Direct fire distributorless ignition and electronic multiport fuel injection were added. Also a new camshaft with a larger base circle and 0.015” shorter pushrods were added. This was also the first year for a front-wheel drive (FWD) version of the 3.8L V6.

1985 — The engine was refitted with a single serpentine belt to drive its accessories. The number of bolts on the oil pan was also increased from 14 to 20 to reduce oil leaks. The head bolts also changed to non-reusable torque-to-yield bolts.

1986 — The flat tappet lifters were upgraded to roller lifters to reduce internal engine friction, and sequential fuel injection was also added for improved performance, fuel economy and emissions. The deck height of the block was also reduced 0.035” to accommodate thicker composition-style head gaskets. Some FWD versions of the 3.8L V6 (VIN 3) were offered with roller lifters. FWD versions also got new cylinder heads with pedestal-style rocker arms, and a needle bearing thrust washer for the camshaft.

1988 — Buick now dubbed the engine the 3800. The block casting was revised and a balance shaft added to dampen vibrations. The cast iron camshaft was replaced with a steel camshaft, thinner, low-tension piston rings were added to reduce friction even more, and the mechanical EGR valve was replaced with an electronic digital EGR valve to reduce NOx emissions.

1989 — Smaller 3300 (3.3L) spin-off of the 3800 introduced.

1990 — The intake system was upgraded to Tuned Port Injection for more horsepower and torque. Also, a one-piece rear crankshaft oil seal was offered in some 3800 engines to reduce oil leaks.

1991 — L67 supercharged version of the 3800 appears. An Eaton blower boosts horsepower to 205.

1993 — The 3800 V6 got roller rocker arms, a higher compression ratio, and another reduction in piston ring tension to improve fuel economy and performance.

1994 — Supercharged engine gets larger blower pulley and larger throttle to make more horsepower (225 hp).

1995 — Series II 3800 introduced with revised, lighter block, cross-bolt main bearing caps, lighter pistons, a higher compression ratio (9.4:1)and shorter steel rods. It also had improved cylinder heads with bigger valves, a composite plastic intake manifold, revised accessory mountings on the engine, dual knock sensors, improved oil seals and a plastic engine cover to muffle noise.

1996 — Supercharged Series II 3800 gets a bigger supercharger for more boost and power (240 hp).

2004 — Series III L26 3800 V6 introduced, with electronic throttle control, returnless fuel injection, stronger powder metal connecting rods, and an aluminum upper intake manifold to replace the troublesome plastic intake manifold. Applications include the 2004-’08 Pontiac Grand Prix, 2005-’08 Buick LaCrosse and 2006-’08 Buick Lucerne. An L32 Supercharged Series III 3800 also is introduced, rated at 260 hp in the Pontiac Grand Prix GT and GTP.

2008 — End of the road for the 3800. Production will cease this year, with the 3800 being retired to the big boneyard in the sky. The engine will be replaced with the naturally aspirated LZ4 3500 OHV V6, or the LY7 3600 DOHC V6 in vehicles that used the supercharged 3800.

Service Issues
One of the reasons why the 3800 has had such a long production run is that it has been a very reliable, trouble-free engine for the most part. Many of these engines have racked up well over 200,000 miles with normal maintenance.

One of the few trouble spots has been coolant leaks on the Series II 3800 engines with the plastic intake manifold. The OEM intake manifold gasket tends to deteriorate after 60,000 or so miles in the area that seals the cylinder head coolant passage to the manifold. The seepage of coolant past the leaky gasket leads to overheating, and may cause bearing damage if coolant leaks down into the lifter valley and gets into the crankcase. The fix is to replace the OEM gasket with an improved aftermarket gasket, or the revised OEM gasket (P/N 89017554) per GM bulletin 04-06-01-017 issued in May, 2004.

The coolant leakage problem has been blamed on a number of factors, including coolant neglect and a less-than-robust OEM intake manifold gasket design. Though Dex-Cool is supposed to last up to five years or 150,000 miles, some say changing the coolant every two years can avert many of the problems that occur with aging coolant. Also, if the coolant level gets low, oxygen mixes with the coolant, which tends to cause problems with Dex-Cool.

On these engines, it’s not a bad idea to add a bottle of cooling system sealer to the cooling system for preventive maintenance, whether the coolant needs changing or not. The sealer will circulate with the coolant and hopefully stop any small seepage leaks in the intake manifold gasket from getting any worse, at least for a while. This may save your customer the expense of having to replace the intake manifold gasket. If the gasket is already leaking, sealer may plug it up temporarily. But, eventually, the gasket will have to be changed.

Another coolant leak problem prompted GM to issue a recall on certain 2000-’03 model year Chevys, Buicks and Pontiacs with the 3800 engine. The coolant leak on these engines was at the gasket between the intake manifold and throttle body or, in some cases, between the upper and lower intake manifold. The recall involved replacing the three throttle body fasteners, applying sealer to the threads, and dumping some sealer pellets into the cooling system reservoir. Recall 03034 was issued in July, 2003, but was only good until July, 2004. If a vehicle was repaired under this recall, there should be a GM recall decal affixed to the engine or under the hood.

Ignition System
The distributorless ignition system has also been fairly reliable, with some occasional crankshaft position sensor or coil failures. The 3800 engine has a “waste spark” distributorless ignition system with three ignition coils, (see photo above, right) an ignition control module, a dual Hall-effect crankshaft position sensor and an engine crankshaft balancer with interrupter rings attached to the rear. The PCM controls spark timing.

Each coil fires two cylinders with cylinders 1/4, 2/5 and 3/6 each sharing a coil. Since the polarity of the ignition coil primary and secondary windings is fixed, one spark plug always fires with normal polarity while its companion plug fires with reverse polarity. Because the ignition coil requires approximately 30% more voltage to fire a spark plug with reverse polarity, the ignition coil

requires more saturation time (loner dwell) and a higher primary current. This allows the coils to produce up to 40Kv if needed.

If you have a 3800 that cranks but won’t start because there is no spark, check to make sure the coils have voltage when the key is on. If there is no trigger signal from the crankshaft position sensor, the PCM won’t fire the coils and there will be no spark.

The coil pack on these engines runs hot, so it’s important to make sure there is heat sink grease under the coil to transfer heat. If the coil module gets too hot, it will fail.

If an engine is hard to start or has a misfire at higher speeds, the problem may be a weak coil, a bad plug wire, or a fouled or worn spark plug. On 1996 and newer vehicles, you should get a cylinder misfire code. A code for one cylinder would likely indicate a fouled plug, bad plug wire, or possibly a clogged or dead fuel injector, or a compression leak (burned exhaust valve). Misfire codes for two cylinders that share a coil would likely point to a bad coil.

Another way to figure out if a misfire is a bad coil is to swap two of the coils on the coil pack. If the misfire moves to the new cylinders, the problem is the coil. If the misfire remains in the same cylinders, the coil is OK and the problem is the wires, plugs, injectors or compression.

If you test a coil with an ohmmeter, the test specs are 0.5 to 0.9 ohms for the primary terminals under the coil, and secondary resistance of 5,000 to 8,000 ohms at the high-voltage terminal.

Fuel System
Fuel problems on these engines are no different than those on any other engine. The injectors can get gummed up from burning gasoline that contains low levels of detergents. GM recommends using “top tier” gasoline that contains higher levels of detergent to keep the injectors clean. This is especially important for engines that are used for short-trip driving and frequent stop/starts, or prolonged idling.

 If you have a no-start condition because there’s no fuel, the first check would be fuel pressure. On a Series II 3800 engine, fuel pressure should be 48 to 55 psi with the key on and engine off. GM does not provide a fuel volume test spec but, as a rule, a good pump should deliver about a quart of fuel in 30 seconds.

On a Series III 3800 engine in a Buick Lucerne, the returnless EFI system has the fuel pressure regulator mounted in the fuel tank with the pump instead of on the fuel rail. There is no fuel return line from the engine back to the tank. The fuel pressure on these engines should be 56 to 62 psi with the key on and engine off.

If you have a cylinder misfire, but have a good spark and compression, the fuel injector is probably clogged or dead. The 3800 engine uses high-impedance 12 ohm injectors, and the test spec is 11.80 to 12.60 ohms, so check the resistance across the injector terminals if you suspect a bad injector. If an injector reads outside this range, even a few tenths of an ohm, it may be enough of a difference to cause a problem.

If an injector reads good, use a noid light to check for an injector pulse from the PCM injector driver circuit. No pulse? The problem could be a bad injector driver circuit in the PCM, or no input from the camshaft position sensor (CMP), which the PCM uses to fire the injectors. The CMP sensor is mounted on the front timing cover.

On the supercharged 3800 engines, one item that is often overlooked is the oil reservoir for the supercharger. The oil reservoir provides oil for the rotor gears and bearings. If the oil runs low, the supercharger may seize. The oil level can be checked by removing the small drain plug located near the supercharger input shaft.

Caution: Do not open the drain plug when the engine is hot. Let it cool at least two hours so hot oil does not spray out of the reservoir. The oil level should be at the bottom of the inspection threads in the drain plug hole. If the reservoir is low, top it off with GM Supercharger oil P/N 12345982 (a special 5W-30 synthetic oil).

Supercharger boost is controlled by the PCM via a boost solenoid, and a vacuum-operated bypass valve, which regulates the amount of boost pressure according to intake vacuum (engine load). At idle and low engine loads, the bypass valve is open allowing air to bypass the supercharger. When the driver steps on it and intake vacuum drops, the bypass valve closes allowing the supercharger to deliver boost pressure. The PCM usually commands the boost solenoid at 100% duty cycle (on all the time), unless the vehicle is shifted into reverse, in which case it kills the boost pressure. If there is a problem with the boost solenoid, the engine may not receive normal boost when accelerating, causing a noticeable loss of power.

 

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