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So I have been trying to trace the source of the bucking that happens when I'm driving either when coasting and coming to a slow speed or during light throttle. My gut says that it has something to do with light aluminum flywheel. I bought the flywheel used years ago from a guy here on the forum. I tried to contact him to get specific info on the parts to no avail. I was told that it was an 8lb flywheel with the matching counterweight for my SE. I am starting to question if the counterweight is for a 2nd gen 13B, which according to RB, is a different part number compared to my 84SE 13B. I don't know how "out of balance" the engine would be if it had the 2nd gen counterweight instead of the correct one???? I think that the counterweight not being the correct one is probably unlikely as the cause, but I couldn't help to entertain the thought. Anyway, if any of you have a lightweight flywheel (11-12 lbs total weight with counterweight), I would like to know if you experience the same bucking on light throttle or when coasting and slowing down. Perhaps this is normal behavior for a light flywheel?
Thanks!
Mike
In my opinion, 8lbs is too light for a street driven car and can cause the bucking you describe. I have a 13lb steel flywheel in my car and still suffer a little bit of surging.
This is the consequence of an aluminum lightweight flywheel. The problem is that you've removed the heavy mass along with the rotational inertia of the mass being located at the OUTSIDE edge of the stock flywheel, which serves as a shock absorber of sorts. Without that mass spinning, your engine is better able to overcome the inertia to spin up, but the downside is that your buffer is gone, preventing a nice smooth idle and smooth deceleration. While its great for improving throttle response and acceleration, when youre not at WOT you're going to feel a bit more bucking as you described.
As to the counterweight question, a mismatched front and rear counterweight would be felt increasingly harshly with higher RPM. It would also likely lead to rapid bearing failure due to the imbalance, so if you can spin the engine up to 6-7k RPM without the engine feeling like it's going to leap out of the engine bay, you're probably fine.
Some SE specific things to try; check for any small vacuum leaks around the RE-EGI chamber as these can affect the VSV solenoids on decel, along with your gaskets between the upper and lower intake manifold and engine interface. Remove your fuel injectors and have them cleaned. Change your spark plugs and perform a tune-up (*distributor cap and rotor, plug wires, etc.), and check your '6'-port operation to be sure those gaskets aren't leaking. Also, have you ever changed your rear fuel filter? Cleaned the screen going into the Fuel Pump inlet?
In my opinion, 8lbs is too light for a street driven car and can cause the bucking you describe. I have a 13lb steel flywheel in my car and still suffer a little bit of surging.
Thanks for the reply. So is your total weight 13lbs----flywheel and counterweight or just the flywheel?
This is the consequence of an aluminum lightweight flywheel. The problem is that you've removed the heavy mass along with the rotational inertia of the mass being located at the OUTSIDE edge of the stock flywheel, which serves as a shock absorber of sorts. Without that mass spinning, your engine is better able to overcome the inertia to spin up, but the downside is that your buffer is gone, preventing a nice smooth idle and smooth deceleration. While its great for improving throttle response and acceleration, when youre not at WOT you're going to feel a bit more bucking as you described.
As to the counterweight question, a mismatched front and rear counterweight would be felt increasingly harshly with higher RPM. It would also likely lead to rapid bearing failure due to the imbalance, so if you can spin the engine up to 6-7k RPM without the engine feeling like it's going to leap out of the engine bay, you're probably fine.
Some SE specific things to try; check for any small vacuum leaks around the RE-EGI chamber as these can affect the VSV solenoids on decel, along with your gaskets between the upper and lower intake manifold and engine interface. Remove your fuel injectors and have them cleaned. Change your spark plugs and perform a tune-up (*distributor cap and rotor, plug wires, etc.), and check your '6'-port operation to be sure those gaskets aren't leaking. Also, have you ever changed your rear fuel filter? Cleaned the screen going into the Fuel Pump inlet?
Thanks Longduck. I think I'm going to consider putting the stock flywheel back on once winter is over. I'd rather have the smooth deceleration than the benefits of the quicker RPM's with the light flywheel. I'm 55 years old and comfort and ease of driving is more important to me than quickness, lol! And yeah, I checked for vacuum leaks way too many times when I had an issue with the LIM sealing. The intake gaskets are pretty tight. I don't have any emissions whatsoever, as I am running the car with the Haltech. Fuel filter is pretty new, and the fuel sender and screen probably have less than 5K on them. I appreciate the advice though.
I would consider the steel flywheel from RB. But that 17lbs I believe. The stock SE flywheel is 23lbs? So not much difference there. I may as well just put the stock flywheel back on and have the car drive smooth again. Anyone else experiencing issues like mine? Would love to hear from you.
It's not so much the weight of the flywheel mass, but where its located, that matters. The stock flywheel has a TON of mass on the outside edge that carries a lot of rotational inertia. Whereas, the light flywheel are just an aluminum disc and rely on the automatic transmission counterweight for balance which is only about 8" across - it's only there for balance of the rotating assembly. Your stock SE flywheel will definitely help with a smoother idle and deceleration, though.
Something else to consider is that a Haltech could likely be tuned to lean the mixture on deceleration to help with the burbles. What happens is that on decel, you've completely closed the throttle and no air is getting into the engine, so the car will be running rich. As that fuel is burned off by ignition, it tends to pop and cause erratic combustion pulses. The stock solution was the EGR and Air Bypass valve working with the Air Pump to push air into the intake and exhaust, but your Haltech tune may not,account for those systems.
Hey, I'm 52, myself! I'm no whippersnapper...
Edit to Add; when was the last time you tested, adjusted and set your Throttle Position Sensor? This can commonly cause light / no throttle hunting...
It's not so much the weight of the flywheel mass, but where its located, that matters. The stock flywheel has a TON of mass on the outside edge that carries a lot of rotational inertia. Whereas, the light flywheel are just an aluminum disc and rely on the automatic transmission counterweight for balance which is only about 8" across - it's only there for balance of the rotating assembly. Your stock SE flywheel will definitely help with a smoother idle and deceleration, though.
Something else to consider is that a Haltech could likely be tuned to lean the mixture on deceleration to help with the burbles. What happens is that on decel, you've completely closed the throttle and no air is getting into the engine, so the car will be running rich. As that fuel is burned off by ignition, it tends to pop and cause erratic combustion pulses. The stock solution was the EGR and Air Bypass valve working with the Air Pump to push air into the intake and exhaust, but your Haltech tune may not,account for those systems.
Hey, I'm 52, myself! I'm no whippersnapper...
Edit to Add; when was the last time you tested, adjusted and set your Throttle Position Sensor? This can commonly cause light / no throttle hunting...
Good stuff here Longduck, especially the tutorial on the flywheels as far as where the mass/inertia is located with stock flywheel vs. aftermarket. I never would have considered that as a factor. With that said, why doesn't RB/Mazdatrix just make them like stock? A lighter flywheel with the mass on the outer edge like stock would give the best of both worlds. Must be a cost issue or maybe they're not set up to do such a thing.
As far as the TPS is concerned, I had it set by the guy who tuned it for me, but I think it might be slightly out. Could definitely be contributing to the issue. But for the life of me, I still can't figure out how to set it. I go to TPS in the software, but I don't see anything about setting the parameters. Keep in mind that I have the Sprint RE ECU, so it's a bit primitive compared to what's available today.
52? You are definitely not a young whippersnapper anymore! Lol! Gosh, I haven't heard that word used in so long. It brought back good memories of when I was a kid.
I have written MANY tutorials on how to build the 2-light Test Rig, along with how to set the TPS, so have a look in forum search history. Additionally, the TPS is one of those mechanical items that is best set and adjusted by the guy sitting behind the wheel who drives it, not by the tech who tunes it and sends it out. In other words, once I get the TPS set where it should be perfect ELECTRICALLY, then I take it for a few drives with a flat-blade screwdriver, and make 1/8 turn adjustments until it drives perfectly. Usually all it takes is a warm engine, a sunny day, and a few 1/8 turn adjustments of the TPS screw and it's a dream to drive.
Yes, I'm familiar with how to adjust the TPS. I used to have my own set of wires with bulbs back in the 80's that a guy who worked at the Mazda dealer help me make. I have since chose to set the TPS with my ohm meter for better accuracy. What I do not know how to do is to set the TPS in the Haltech software. There's a way that you can set it at full rest and at wide open throttle. I don't see it anywhere in the software. This is probably a question for someone on the Haltech forum, lol.
01-08-24, 09:06 PM
