GM W body cars, 3100 3400 SFI, 3800 engines

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    GM 3100-3400-3800 and W body car pattern failures
    GM cars of W body type have been around for YEARS! and are EXTREMELY common in the US and in Canada, Buick Century, Buick Regal, Buick Lacrosse, Chevy impala, Chevy Malibu, Chevy montie carlo, Pontiac grand am, Pontiac Grand Prix, Oldsmobile Alero, Oldsmobile Cutlass are just a few too name that used this “structural” body style and shared similar drive lines many of them used 3100SFI 3400SFI and 3800 series I series II and Series III V6 engines, as well as 4T60E and 4T65E and as for cars equipped with supercharged 3800s or the 5.3L LS-4 the 4T65EHD transmission though some cars of later vintage beyond years of 2004 now use the 3.5L 3.6L DOHC, and 3.9L V-6 engines too. many of them share the same pattern failures or problems, and most of them start too appear as early as 80,000 miles or as late as 220,000 miles… the life expectancy of these cars can sometimes exceed 500,000 miles or more depending on how much the owner loves there car enough too take care of it, but neglect of car washing and lack of maintenance will end the life of any car… even the bulletproof 3800 bolted too a robust W body!

    pattern failures like eric said can be sneaky little things, my suggestion too you is before you make a assumption and replace parts that you do a good diagnosis, dont bust your butt and spend $200 on parts and gaskets only too find the issue was deeper in and then find out you are spending an additional $300 and have to do the work again!

    [color=#ff4400]it is also important too note that there may be more tips in the comments section below this thread as many of the viewers have contributed too this post.
    3100-3400 SFI pattern failures

    lower intake manifold gasket failure (leaks coolant on ground from engine, coolant in oil.)
    probably one of the most noted failure of the 60 degree V6 of earlier years is the lower intake manifold gaskets, they are know mostly for leaking externally, usually you will see a puddle of coolant and the coolant level will drop, the coolant should be leaking from what looks like where the lower intake manifold is joined too the inside bank of the heads… stop leak is not a permanent fix, it is advised too replace the junky factory lower intake manifold gaskets with the replacement Felpro metal framed gaskets with rubber seals. sometimes the coolant can leak into the oil, this is bad because this washes out the rod and main bearings and pits them, if the driver continues too drive under these conditions the engine crank case will over fill with a sludgy mixture of coolant and oil that at first looks like diarrhea, sometimes like a white baby poop color as commonly described.

    leaky camshaft seal (burning oil smell sometimes noted.)[/b][/color]
    earlier 60 degree V6 engines used to have a distributor ignition rather than the well know 3 coil system, the old area where the distributor shaft used to run through is plugged off with a plate, sometimes the gasket leaks.

    Piston slap (a ticking noise is heard that goes away as the engine warms up.)
    a ticking or almost knocking noise is heard as the engine is cold, but as the engine warms up and oil begins too flow more the ticking noise quiets, do not be alarmed this is a common issue with 3100s called piston slap and 3400 SFI engines typically with miles exceeding 140,000 or so, this is caused buy odd wear on the pistons and they develop excessive clearences slapping in the cylinder bores on typically the ignition stroke as the piston is forced down buy combustion… higher mileage engines exceeding 200,000 miles may begin too burn oil slightly but as long as you are easy on the engine while it is cold the engine usually continues too run despite the tick tick tick tick tick.

    here is what it may sound like


    Blown head gaskets (exibits blown head gasket symptoms)
    typically only if the engine has been over heated, the heads are aluminum and the blocks are cast iron, if the engine is ever over heated the expansion rate of the heads are different than the block and the heads can warp, the gaskets will no longer seal correctly and they will blow sometimes leaking coolant causing all the common symptoms of head gasket failure, you will have to do the head gaskets and probably get the heads machined.

    heater core bypass pipe failure (leaking coolant)
    hoses leading from the water pump too the heater core sometimes rust and start too leak, they rust badly at times and when they spring a leak they can sometimes sprey everywhere, bad news is this is a dealership part if it needs replaced!

    rockers come loose off heads (clattering noise while engine runs.)
    i have noticed that sometimes the rockers will come stripped from the heads on the 3400s, its a rare instance but it happens, it will commonly make a sort of a racket under the rockers.

    what it may sound like, and skip too about 5:30 this guy talks alot.


    3800 Series III Series II and some 3800 Series I

    Upper plenum coolant leak (burning coolant, hydrolocked engine, coolant in oil)
    N/A Versions of certian series I and series II have plastic upper plenums, series IIIs have a aluminum upper plenum, and the supercharged engines like the L-67 and L-32 SC 3800 engines obviously have aluminom supercharger housings, but upper gasket may still fail on supercharged models possibly on series III N/A L-26 engines as the gasket is still plastic, the passage for the EGR goes right through the Upper plenum as well as the coolant passages, as the coolant gets hot and cold it makes the upper plenum brittle, as time goes on the EGR passage melts and cracks, the coolant passages then crack themselves and start to leak into the intake, sometimes into the oil possibly through PCV, if they leak into the intake, the engine can suck in coolant and hydro lock the engine, if the coolant leaks into the oil it washes out the bearings pitting or even scoring them, and over fills the crank case with a sludgy mixture of coolant and oil, the fix too this is a new gasket and a metal insert you put into the new plenum and a new plenum itself, and while you have the upper plenum off you might as well do the coolant elbows and lower plenum too as you are only a few bolts away.

    lower intake manifold gasket failure (coolant leaking on ground from engine or coolant leaking in oil.)
    like the 60 degree V6 the gaskets are known for failure, they are made of plastic and the seals crack after many heat cycles and leak coolant up in the vallys between the lower and upper plenum through the bolts holding down the lower intake manifold. or they can leak coolant into the oil and wash out the rod and main bearings pit and score them. i have personally seen the effects of this, i have seen crank cases more than twice over filled with coolant and oil mixture which looks like a diareah color or a milky color. in many cases the engine will run roughly but it will still run. the fix is too replace the lower intake manifold gaskets with the felpro metal framed ones, the plastic ones cannot be trusted, this is why they failed initially!

    Coolant elbow failure (coolant leaks only at high revs full throttle.)
    a suspicions coolant leak is found from the front end of the engine, it only shows up when doing a full throttle freeway pass and all of a sudden your belt is squeaking and the low coolant light comes on, otherwise its near impossible too replicate the coolant leak buy just letting the engine run or even reving the engine with the car in park because the Rev limiter limits rev to 4,000RPM with the car in park… there are a set of coolant elbows one of them im particular joins the belt tensioner/coolant heater hoses bypass too the lower intake manifold. one of them is a 90 degree bend and is made of plastic… thats right plastic, these get hot and cold and eventually crack usually inside of the belt tensioner or mostly inside of the intake manifold and spray coolant at WOT. this leak can be found with a cooling system pressure test. the fix too the issue is too replace the crappy plastic coolant elbows with the aluminum units you can get at your auto parts store. NOTE, some belt tensioner assemblies only require one single coolant elbow as some of the belt tensioner assemblies come with the lower elbow that connects essentially to the timing cover cast solid into the assembly.

    rocker cover gasket failure (burning oil smell, some smoke, engine wet with oil, my car just caught on fire.)
    the plastic rocker covers on the 3800 are know for leaking oil after high miles, so badly that they have been known too cause under hood fires! too remedy the issue just get new gaskets… symptoms are a burning oil smell, under engine smoke, and the engine appears too be wet down the sides from leaky rocker cover gaskets… replace before a fire spreads.

    fuel pressure regulator leak (car runs rough and rich, my upper plenum just exploded)
    the fuel pressure regulators have been known for leaking on these engines, the diaphram will break and leak gas… the gas vapors will go into the plastic upper plenum. at this point your car may be running rough and may smell faintly of gas, remove the hose from the fuel regulator and have a sniff, if it smells badly of gas replace the fuel regulator, they have been known for causing upper plenums too explode on the 3800 series II from the trapped rich fuel vapors in the upper plenum and when a back fire accures it causes the plenum too burst.


    False low coolant light
    sometimes the coolant level sensor will act up in these cars, they will get gummed up inside and cause a fake low coolant light too come on even when the coolant level is full, replacing this unit should fix the issue

    supercharger coupler (supercharger knock and clatter L-67/L-32 engines only)
    people say the whole supercharger is going bad, not nessisarily, in fact there is a coupler in the supercharger that often wears out, this is the most common cause of the clattering noise heard, and should fix the issue.

    this is the sound of a clattering supercharger coupler


    Throttle body failure (3800 series III L-26 and L-32 only)
    engine randomly shuts off and display sometimes says “starting disabled due too electronic throttle control.” sometimes car may seem too accelerate out of control, replacing throttle usually fixes issue

    PCM failure (3800 Series III and later W bod cars only)
    engine may randomly shut off telling you the same thing as a electronic throttle control failure, the newer PCMs which are faster and much smaller than the bigger Aluminom PCM boxes are known for being a little more prone too failure TSBs are out for the PCMS.) keep in mind the old PCM is not reprogrammable which means you will have to get a new one and have it programmed for your car, it may be a $700 day!

    Crankshaft position sensor failure (engine randomly shuts off going down the road and car wont start unless it sits for a while.)
    a crank shaft position sensor is a common failure for the 3800, it is located behind the harmonic balancer, once you have the balancer off it is easy too replace, removing the balancer is the “fun part.”

    4T60E-4T65E transmission issues

    P-1811 Max adapt long shift (car upshifts hard)
    a very common code for these transmissions, what happens is as the transmission wears out its clutch plates and it begins too slip the transmission begins compensating buy shifting with max pressure on the clutch plates, so a warn out transmission or a bad pressure control solenoid sometimes only showing when the transmission is warmed up

    shift solonoid issues (erratic shifts)
    sometimes in these transmissions the shift solenoids are known for having issues which can cause erratic shifting sometimes only showing up when the transmission is warmed up

    pressure control solenoid issues (car upshifts hard, P1811 code sometimes just shifting erratically seeming too go into neutral in some gears at times causing engine too rev when it should shift down or up)
    sometimes the pressure control solenoid can fail or wear out causing a P-1811 code max adapt long shift, or even cause erratic shifting behavior such as the feeling of false neutrals or other weird things sometimes only showing when the transmission is warmed up

    Torque coverter clutch issues (car seems too shift up and down a gear sort of shutters)
    sometimes the torque converter clutch can act up, when cruising at highway speeds sometimes it feels like the car is going up and down from a higher too a lower gear or feels like its sort of shuttering, this is the torque converter clutch acting up, it engages and disengages on and off at times with earlier transmissions it would actually get stuck on and stall the engine at stop lights

    Overdrive spline strip (overdrive wont work)
    sometimes it feels like the car will not shift into over drive, earlier transmissions of the 4T60E and 4T65E had issues with the transmission overdrive spline stripping, when the transmission goes too shift into overdrive, the overdrive gear set simply slips on the overdrive spline because it is stripped and you loose over drive.

    good video here on this


    VSS vehicle speed sensor (shifts weird or wont shift stuck in 2nd gear limp in mode, no speedometer or speedo acts funny)
    located on the transaxle passenger side next too the Differential held on i believe buy a single 10MM nut, these commonly get metal shavings on the magnet, or they just go out, more commonly the wires too them corrode and fall off breaking connection, before you replace the sensor CHECK THE WIRING! common symptoms, weird shifting, and the speedometer will not work or will be all over the place.

    power steering

    power steering pump wearing out (whining noise changes with RPM steering feels hard when car is not moving.)
    as the power steering pumps wear out in these cars they make a very destinct whine sound that many mechanics know by heart because its a very common failure, the steering may feel hard with the engine at idle and the car is parked, but once you bring the revs up a little bit or the car is moving the steering feels fine… the common solution is too replace the power steering pump.

    power steering leaks (leaking power steering fluid.)
    a common place for the 3800 engine W body cars too leak power steering fluid somewhere from the lines leading from the power steering pump too the rack, look at the lines top too bottom and inspect for leaks.

    W body common issues

    where the A frame meets the body is where it typically rusts and structurally fails, where the trailing arms bolt too the frame is another pattern spot for failure, as well as rust where the lateral links/lower control arms for the rear also are bolted up too the car is often know for rusting out and falling apart. constant washing during the winter months should slow these rustings, and weather proofing should insure the life of the car… these failures are common in vehicles with high miles and abuse that hardly see a car wash

    Bent trailing arms
    sometimes you hit a pot hole or a rock, or someone tries jacking up the car, and the stamped steel trailing arms get bent… not too fear you can replace them really easy, and ZZP makes chrome Molly steel tubular replacements that are much more robust.

    Rusty rocker panels
    very common with cars like the Buick Century Custom and Buick Century Limited where there rocker pannels are not hidden buy fancy plastic trim, road salt and water and crap gather on the rocker pannels and in the rocker pannels they begin too rust from the inside out, and then sadly the only fix is body work.

    Bent lateral links/rear control arms (just hit a big pothole and my steering wheel is angled at 30 degrees too the left, but i am going straght.)
    the small thin lateral links in the rear that act as control arms are known for bending in accidents or if you hit deep rough pot holes, these can be a pain too replace, you may also discover the structural unit they bolt too the body may be badly rusted and falling apart.

    Broken sway bars (a clunking noise is heard when coming into a corner or out of a corner.)
    where the sway bar meets the sway bar links they are known for rusting and breaking, replacement units are solid metal and not hollow, some are thicker, this will not only fix the breakage issue in the future, but means a stiffer sway bar which means better cornering.

    engine light for evaprative missions leak/check gas cap
    there are several common fixes too this one, first is too replace the gas cap, sometimes the gas cap is no good because it simply will not seal because it wont tighten down enough or the seal that goes around the gas filler neck is cracked and rotted and leaks. sometimes the filler neck rusts out and developes small pinholes and causes slight leaks, and later W body cars seem too have a issue with the canister vent solenoid that bolts too the frame, sometimes they go bad and need replaced and they can really turn that engine light on.

    Electrical and other

    gas gauge does not read fuel level, seems too wave up and down very innacurate
    this is very commonly caused buy the fuel sending units “fuel level indicatior.” i guess you could call it, they tend too have issues after a while and they become very inaccurate and the fuel gauge will tend too wave everywhere at times from full too half full too near empty too everywhere… replacing the fuel sending unit may fix this issue and usually this is a indicator that the fuel pump will fail soon, so replacing is a good idea before you end up stranded somewhere because you ran out of gas or because the fuel pump called it quits next.

    here is another video too give sort of a demo


    fuel pump failure (car will turn over but wont fire under its own power, car misses and stumbles.)
    car wont start, it will turn over rapidly just wont fire, you have no fuel pressure, the result is typically the legondary GM fuel pump failure, and its not just with W body cars its with the H body cars as well, replacing the fuel pump usually fixes the issue and fuel pressure will be restored, sometimes giving a sharp tap on the gas tank a few times may get it too work again just too get you home but don’t count on it as a permanent fix.

    Battery terminal issues, old and new (car seems too cut out when driving, i loose power when i hit a bump or wiggle the battery cables, car wont start no crank no start condition, my battery terminals broke on my 2004 or newer GM Vehcile.)
    the batter terminals on the older GM Vehicles, mostly in the years between mid 90s too mid late 2000s where the side post type that bolted onto the the side of the battery rather than clamp on, these terminals had a tendency too wear out over time and even after tightened too the maximum had issues with wearing out and causing connection issues, even with them tightened down tight wiggling them would cause a connection problem, the solution is too clean connections first, then if that does not work replace the terminal components, for the newer vehicles most of the ones beyond 2004 they went back too a top post set up but rather than use a lead battery connector they used a cheep stamped steel one, and eventually get brittle and corrode VERY badly, there cheep and very bad design causes them too break and not tighten down too the battery properly causing connection issues, replace these with the good old fashioned lead connectors, so cheep and easy i did one in a parking lot on a black Friday.

    window regulator issue (window wont go up or down.)
    your windows not going up or down, GM window regulators are natorious for failure, too prevent this try avoiding the window regulators as much as possible during the winter after you just got done scraping the windows off, this is what commonly kills the regulators, when they are killed replace them usually the motor burns out or gears get stripped, and replacing them should fix the issue…

    PRNDL mielage indicator burnt out
    very common thing on 1997-2005 Buick Centurys and 1997-2004 Regals, right below the speedo tells what your gear you have slected and your mileage, these commonly burn out, some people replace some resistors and stuff and make it work again, others buy a instrument cluster.

    VATS system failure (car wont start, SECURITY light on)
    sometimes the security system acts up, either the chip in the kea goes wonky or more commonly the entire system needs replaced and its a expensive day. VATS security system disables the fuel pump and starter and all that too prevent theft, after the car gets quite old these are common failures and then turns on the car owner.

    Moisture in headlights (water in my headlights and water droplets, foggy from the inside.)
    too me this seems to be a pattern failure, and seems too be more common with pontiacs, in fact i seem too be experiencing this issue myself. sometimes the assembly for the headlights don’t seal properly and after a humid day or after washing your car moisture accumulates inside and its not good for your light bulbs… picture included this time!

Viewing 4 replies - 46 through 49 (of 49 total)
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  • #892506
    Ashley T Miller
    Ashley T Miller

    One thing I don’t see mentioned is the problematic placement of a few parts of the wiring harness, 3100 and 3400 I had would begin to slowly degrade, harden and melt parts of the harness making you think all kinds of crazy things are bad, the one I saw on both engines was the feed off the transmission where a lot of the harness is pinned down, the wires for speed sensor and side crank sensor are not placed well and melt due to exhaust manifold heat, also the o2 sensor 2 after the converter harness that runs up to the firewall gets cooked. Poor design similar to the manifold gasket. A foot longer or so and the wires could be kept along the firewall and further from the exhaust pipe respectively

    Timothy Mummert
    Timothy Mummert

    I know it’s been many years since you posted… However ? Anyone with this code could give this a try.

    On my 2003 Monte Carlo that had that code ( Long Shift Adapt ) I ordered a kit from TransGO shift kit and installed it, it was just a temp solution, but the code stopped.

    Timothy Mummert
    Timothy Mummert

    On my 2003 Monte Carlo the battery would go dead after sitting a while from a parasitic drain from the battery.

    I took the whole wire harness out of the engine bay, and ? attempted to take the whole wire harness out from the dash, thought twice about that.

    Only to fish for the short or break in the wire harness.

    Come to find out ?

    It was the Body Control Moduel.

    The Body Control Moduel had grimlins in it.

    It caused a parasitic draw when it decided to work or come online, and when power was applied ? It intermittently didn’t want to come online when the power was applied.

    I didn’t have the money to buy a new one and have the dealership reprogram one.

    So ? I made a separate switch and fuse for the BCM and instrument cluster and when ever I had problems it not coming alive, or coming online when you applied power to the BCM ?

    I would just toggle the switch until the BCM decided to come online.

    Timothy Mummert
    Timothy Mummert

    Fixing these older W – Body cars with no rust, low miles is cheaper than buying a new car taking a 2’nd mortage out.

    Once you get the ( GM created bugs a grimlins ) bugs worked out of these cars they are great dependible cars …

    I had 5 W Body GMs in the last 20 years.

    Should have never sold my 93 Lesabre and 2001 AND 2003 Monte Carlos.

Viewing 4 replies - 46 through 49 (of 49 total)

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