Worst Engines of All Time: Chrysler 318/360/400/440 V8 Electronic Lean Burn

well hey this is adam here again on rare classic cars welcome to another porch chat because the weather is cold again hopefully this week as the weekdays go on it will warm up but the weekend is not great so in any case we're going to talk about a topic that mopar fans and mopar haters are going to really enjoy and that is a topic that put fear and shivering and quivering into the boots of every mechanic in the mid 70s and early 80s that is can you guess the lean burn system so or electronic lean burn as chrysler used to call it so introduced in 1976 really is a way to get uh to achieve emissions without catalytic converters on the 400 cubic inch v8 in 1977 lean burn proliferated across the lineup in conjunction with catalytic converters and uh you know first i'll start by saying why is this on the worst list so chrysler made a number of really really excellent engines and transmissions in the 60s and 70s whether you think about the 318s 340s 383s 440s 426 hemis the slant 6 just really really excellent powertrains as the 80s went on yeah the v8s in general stayed stayed pretty good but um you know the mitsubishi 2.6 and it's makuni carburetor the 2.2 2.5 with their head gasket appetite the voracious appetite for head gaskets on those you know weren't quite so good but the lean burn system is something that got slapped on top of a number of good chrysler engines that gave a lot of mechanics and people trouble and let's just start with the name first the electronic lean burn what does lean burn mean well most cars the optimal ratio the optimal air fuel ratio for vehicles is 14.7 parts of air for one part of fuel so think about it if you had gallon jugs in general you'd have one gallon of gasoline think of your milk jug and you'd have almost 15 jugs full of air that would mix through with that one jug of gasoline to create the optimal air fuel ratio well on these lean burn cars and carburetors they tended to run at about 16 to 18 to one so more air relative to the amount of fuel that was used and that was purely for emissions reasons and also for fuel economy too i mean if you're running lean uh you know hopefully under certain conditions it delivered better fuel economy sometimes you really had to tip into the throttle because nothing happened and then you ended up burning more fuel if you were driving somewhat aggressively than if you were driving a car that didn't have lean burn but this was their solution that they came up with and introduced as i said in 1976 and continued on in some form for many years even the fifth avenues diplomats grand furies of the 80s up until the late 80s still used a variation of this system so in general what's different about it from other cars that just had the carburetor well this has a computer it has the spark control computer that you see on the air cleaner and that has a number of other sensors the system has a number of other sensors including a coolant temperature sensor a ambient air sensor which is actually in that box that's attached to the air cleaner it's trying to sense the temperature of the air in the air cleaner hence why they put it on that air cleaner which is one couldn't debate whether or not that was the right thing to do because it's sitting in a place where it's going to thermally cycle a lot and shake there's also a throttle now would be called a throttle position sensor they they called it it was more primitive version a throttle transducer a vacuum transducer and all of these things really combined to give that spark control computer under certain parameters the ability to vary the spark advance so most distributors the old-school distributors will have a set of centrifugal weights that change the timing relative to the engine rpm so the weights kind of spread or close and vary according to the engine rpm but then you also see the typical vacuum advance canister that varies the timing along with the engine vacuum so when you have wide open throttle wide open throttle there's no vacuum there is no difference between the air below the throttle plates and above the throttle plates because the throttle plate is wide open there can't be any difference so there's no difference in the vacuum when you have a wide open throttle plate but at par throttle conditions particularly you know under load part mid throttle ranges you have quite a bit of vacuum and so the typically that's contr the distributor vacuum advance can will control that amount of vacuum advance and then the uh the centrifugal weights will control it proportional to the engine rpm so if you go wide open throttle on any car whether it is a lean burn car or it is a typical car with a vacuum advanced distributor you're running off of the centrifugal weights and the advance is basically based on those when you have wide open throttle but the lean burn system was really different under a number of conditions and the first was that the when the car had reached 150 degrees fahrenheit the engine coolant temperature sensor once it reached 150 degrees fahrenheit the computer started doing some really interesting and funky things and that is it would take the base advance of about 10 degrees more or less and then so long as it detected there was more than 16 inches of vacuum so you were on the throttle and there was not closed throttle the computer would add for every minute that it sensed that you were on the throttle and that the vacuum condition was such that it was above 16 degrees of vacuum it would basically add five degrees advance for each uh for each minute that that condition were true up to i think about seven minutes so if the base timing were 10 and you keep your foot on the gas pedal for one minute then the timing is going to advance in the computer to 15 degrees then the if you keep your foot on the accelerator for continuously for another minute they go to 20 degrees etc etc and that timing would keep building and building so long as you were driving having your foot on the accelerator not at a stop light with your foot on the brake pedal so then when you take your foot off the gas on these lean burn cars for every half of a minute that you have your foot off of the gas the computer basically whatever the amount of total ignition advance is that the second that you put you take your foot off the gas it then stores that amount of advance in the memory and every 30 seconds that ticks by where you're not back on the gas it decreases the amount of ignition timing advanced by five degrees up until three and a half minutes are gone at which point you're back to the base timing so why was that done well more timing hotter combustion temperatures more emissions so running around town versus the freeway if you were on the freeway for a long time you got the advantage of the advanced timing and good fuel economy good power on the freeway and if you're around town you get the benefit of good emissions now i should say also if you will wide open throttle the computer would override whatever the ignition timing was that was in the memory or it had counted to that point and it would just go and go off the centrifugal weights in the distributor what does all this mean if i boil it down what does that mean well it means that these cars tend to feel peppier if you drive them on the freeway and then you get off the freeway and start accelerating than if you're just driving them around town normally because the computer has added that timing for all those minutes associated with you having your foot on the accelerator and it they feel kind of boggy around uh around town because they never have that chance to add all of the ignition advance in the spark control computers and they also feel boggy because the the mixture jetting is very very lean what does this mean a lot of mechanics back in the day would tune engines by advancing the timing until the point in which when you accelerated you'd hear spark knock or detonation or pinging you can't do that really with a lean burn system unless you go drive it on the freeway and see if you hear any pinging after seven minutes on the freeway because then the computer has fully advanced the timing so it takes a lot longer amount of time to figure out well what's the optimum point for timing on these cars because you can't just set it drive it around town and think you're good because you take it on the freeway the timing advances and like i said it's going to stay advanced until in 30 second increments the computer starts decrementing or decreasing the amount of timing there so this lean burn philosophy and componentry like i said was used in the 70s and all the way through on the 80s vehicles i have it on my 83 grand fury and i'll say a couple things what did i do to try to oh let's say help it out well i first of all i made it less lean burn so on the carter bbd carburetors you there's an access plate on the top with a number of screws you can just take that off and then if you flip the accelerator you can see that there are metering rods that move up and down they move they pull out to allow more gas to flow through the jets when you have your foot more on the accelerator so when you take the access cover off you'll see that you can actually change the reference point of those metering rods to make it so they pull out sooner rather than later so what i do i put it on the full rich setting basically so they pull out really quickly and the other thing i've done is i've advanced the ignition timing significantly i'm probably running about four or five degrees above base which i still don't get any spark knock in uh you know from the 318 v8 under hood even after being on the freeway aft past that point i start getting some spark knock but these the stock timing on these cars is just really really uh relatively speaking and the advance curves are really slow for emissions so you can run a decent amount more than the stock timing and honestly i tend to fill the car up with mid-grade or premium just to prevent the detonation well this was at least back when gas was reasonably priced you know now maybe i'll the timing a little bit but that's something else that you know that i would say that you can do and i hope that at least gives you a sense of how these things operate and why it caused mechanics so much trouble because imagine your coolant temperature sensor doesn't work well then if the coolant temperature sensor always senses that the engine temperature is below 150 degrees or so your thermostat's stuck open and it's winter time if the coolant never gets above 150 degrees or the sensor never gets above 150 degrees the computer never puts any incremental advance beyond the base timing into the timing curve so the car feels very very boggy it's only after that coolant temperature sensor has reached 150 degrees fahrenheit as the computers start advancing timing beyond the 10 degrees base setting that most of these cars have and you can imagine that there were issues with the throttle position transducer the vacuum transducer the spark control computer that was under hood i mean in general having primitive electronics under hood in areas where they're exposed to thermal cycling not good so a lot of these systems got thrown out thrown in the junk drawer or thrown out in the trash and a typical old-school style uh distributor and they have a points distributors and a standard carburetor would put on them because people were just fed up and i can understand why i mean it's hard to get something that's designed to run at a very lean ratio to run correctly and they also consequently have very high idles you know so they don't stall because the mixtures are lean when i change that setting of my grand fury that i i was able to richen the mixture i could then lower the fast idle speed so it didn't slam into gear uh and and have the motor racing when it was cold but that's also why a lot of these 80s era cars and late 70s era cars have very fast very fast fast idle cams because they have lean mixtures and they're trying to get the rpms up so the car doesn't stall and that's that's true of a lean burn or a quadrijet or the fords of the era the fords always seem to start and stall and then you have to restart them that was if it were anything below 40 degrees outside that was just the starting procedure for a ford but in any case the lean burn system is not a great system and if you get one on a car or you're thinking about a classic vehicle i would encourage you to try to stay away from it like if you want that chrysler with the waterfall grill you know you might as well get a 74. try to stay away from the 77 today it's not that they're bad not that i would pass one up i can deal with lead burn but i just told you there's a lot of different things about this you can also get around the system and change it as i mentioned but something for you to be aware of that if you have your choice and you really want that waterfall grill chrysler get the 74 the 75 uh or get the 70 yeah the 76 with a 440 don't get the 400 because by 77 it's everywhere so 77 and 8 it's everywhere but other than that you know that the engines that this lean burn is attached to are really reliable i mean 318s slant sixes is an example i mean 440s anybody knows these things run for a long long time well i thought that i hope at least that provided some color on one of the i'll call it worst engines of all time worst components of engines of all time certainly caused a lot of trouble for buyers dealers mechanics alike and help you learn something so feel free to put some comments below if you're new to rare classic cars welcome we just talk about cool things associated with old vehicles and the nitty-gritty associated with them too sometimes out here on the porch thanks again for watching and take care thanks again for watching this video on chrysler's electronic lead burn system if you like the video please be sure to 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Channel: Rare Classic Cars & Automotive History

Views: 93,402

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Id: JBmFF4WrqvA

Length: 15min 57sec (957 seconds)

Published: Wed Mar 23 2022