I was just wondering what happens when the speed limiter kicks in. I have heard various things such as the car will shut off, it will like downshift and then shut off, or it just wont go higher than the limited speed. What exactly DOES happen when the speed limiter kicks in???

 

you will have 0 power till the car slows down below the limit, just like the keys been shut off but the engine still runs.

 

It cuts fuel and feels like the car is hesitating.
Note the fuel cutoff speed and fuel resume speed.
EDIT: fuel cutoff is 255 (can't see it since this pic was used for showing the fans, fuel cutoff is above the fuel resume slider)

 

Your TBI, however, likely has the fuel cutoff programming set at 118 MPH.

 

Yea it does. 118MPH. I mean i know why the speed limiter is in place (because of the tires), i just wanted to know what exactly happens when you hit that speed.

 

The injectors cut off. The engine doesn't go lean - It just flames out.

 

When you get above the fuel cutoff limit the engine abruptly cuts out and below the fuel resume limit it abruptly comes back on and repeats endlessly till you take your foot off the gas.

 

I never understood the whole idea of fuel cutoff. yeah it seems to be more emissions friendly but I also have seen a few motors blow due to fuel cutoff. granted mainly rx7's but blow they still do.

 

its for safety and limitations of the vehicle. Like the pickup trucks will have the limiter set to 98 mph and its even lower for larger vehicles. Mainly its to try to stop people from killing themselves.

 

The motor basically just "shuts off." Party over. You hear the wind and tire noise but no more engine.

Just about the time you complete the thought "what the heck just happened??" you've slowed down enough it turns back on again. Then it back up to the shut-off speed again, over and over. If it's a low-powered engine this can take some time between cycles. If you've got a strong motor it's like it's doing Kamikaze assaults against the shut-off.

 

With my setup the engine will just blow up! lol or thats what it feels like when it gets that high. Without a computer I dont think there is anything thats going to stop the RPMs but me.

 

but why fuel cutoff?

a spark cut would be a much safer method in my opinion.

 

LOL! When moving from cali to kansas, I was driving the moving truck, I ended up going too fast down hill without knowing it (110mph w/camaro on trailer behind me) and the truck started to buck! I didnt know wtf lol, then I realized what happened hehehehehe.

 

I think Fuel Cut is easier to implement in the ECM, so they chose that.

 

I would think if the ECM can controll timing it can controll the spark being there or not.

but think it comes to emissions also
fuel cut should mean no emissions while spark cut means lots of unburnt fuel.

it just still seems like a stupid idea as what happens when your injectors leak a little bit, or some other stupid thing.


the rx7 has setup that cuts fuel to the rear rotor when too much boost is going on. cut the fuel but still manages to get into the combustion you are running ultra lean... BOOM!.
byebye apex seal.

I'm sure the same thing can happen with a piston motor as well.

 

Not one that's 5+ liters and only making ~200 hp or less.

 

With a CC HEI dist. you cant cut the spark. The only things you can do is cut the fuel or retard the spark.

 

detonation can still cause problems as can running lean with piston tops even with low horsepower numbers and higher displacement

 

shouldn't be that hard for GM to do I assume.
if they can retard the signal through the ECM why can't they retard it to infinity so to speak.

 

I know from experience that most of the motors on this board (mine included) don't have enough compression, or specific output to be damamged by a lean mixture.

Detonation is a different issue that we were not talking about in this thread. I agree detonation can cause severe damage. A lean A/F ratio CAN lead to detonation, but it's not the only cause. Lean A/F ratio -> high combustion temps won't hurt a thing on a 200 hp, 8:1 5.0 liter motor. Or even a 250 hp, same thing.

 

Even a spark limiter isnt easy on an engine. Bouncing off of a spark rev limiter can cause the engine to chuck a rod or some other bad thing. What GM has in there is good enough for what they needed at the time, which is a way to stop people from speeding excessivly.

GM could have put in a soft limit by retarding out the spark and then cutting fuel, which would be easier on a motor, but the ecms of that vintage where pretty primitive and only had limited processing power, so its unlikely they would displace some of the needed emmissions stuff for a more sophisticated limiter. That and as mentioned above these engines where weak. You could probably hit that speed limiter all day long and not one bad thing would happen. Hell, even trying to destroy these motors probably wouldnt be enough to break them

 

My car acts like that at 50mph! Sometimes.Could my ECM be the culprit?