speed limiter?.....

[CDW6212R]

FYI, the speedometer in the trucks is not accurate, especially at top speed. My 99 SOHC registered about 107mph when I first tested it, but the Scangauge I use to monitor the PCM saved the high speed as 99mph. Check your tire ratings, "S" or "T" etc, which is what you should stay below.

 

[axiom]

The speedometer looked like 110 or so when I maxed it out, by my GPS registered 107 which is what I went off of. Either way I haven't really gone to those speeds since then for very long at all, I'll cruise at 80 or so usually because I feel comfortable there.

 

[rwenzing]

Weird. My governer kicks in around 115 for my '01 sport.

Don't you have an Xcal2? The limiter speed has probably been raised in the tune.

Anyone care to explain exactly what happens while the governer is in action? Always wondered myself

The speed limiter on earlier fuel-injected Fords simply cut the fuel to all of the injectors simultaneously at the speed limiter's set speed. The speed then dropped by some calibrated hysteresis value, 3 MPH for example, and then the PCM cut them all back in again. The speed sensor operation was rather violent because it went from full off to full on - in fact, if you weren't expecting it, it would scare the hell out of you. It also sent giant slugs of air alternating with giant slugs of enriched fuel laden exhaust into the exhaust system. This created tremendous heat in the catalytic converters and could melt them if the driver could stand to let the violent bucking continue for very long.

In recent years, Ford has used a much more sophisticated speed limiter. Properly calibrated, it feels to the driver like the acceleration just levels off smoothly.

To achieve this, power is reduced in 3 stages. First, the spark is retarded, lowering power. At the same time, fuel is cut at one of the fuel injectors and the rest of the cylinders' mixtures are leaned out slightly to lower power and cool the cats. The cylinder without fuel is shifted from one location to another to prevent the engine from developing cold or hot spots. This is called "Round Robin" cylinder disablement. If cutting one cylinder will not stop the acceleration, a second cylinder is disabled at a slightly higher speed and then a third at a slightly higher speed than that, if necessary. (This is on a six cylinder engine, four cylinder trucks only cut out two). Again, this is done in a Round Robin fashion to equalize the heat in the cylinders, heads and exhaust manifolds.

Obviously, when you are actually driving near the speed limiter's set point, your foot is well into the throttle, primarily to overcome aerodynamic drag. Cut out two or three cylinders and the engine cannot push the vehicle faster than the computer will allow.

 

[reserved50]

Any "Tooner" willing to dissable your top speed limiter without asking questions is an idiot and just after your money. Im sure I can hit at least 150mph plus with my X or Y whatever speed rated tires and re-done drive-shafts, but did I "toon" it out, no. Put it this way, it hits the speed limiter easily before the end of the 1/4 mile. Driving a SUV at those speeds is flat out silly and who knows at what speeds the drive-shaft will vibrate and take out the extension housing or transfercase. Keep the speed limiter where it is, thats what I think personally. Stock vehicles usually have the speedo set to error on the higher side.

 

[rwenzing]

Driving a SUV at those speeds is flat out silly and who knows at what speeds the drive-shaft will vibrate and take out the extension housing or transfercase. Keep the speed limiter where it is, thats what I think personally.

Exactly. in most cases, the factory limiter speed is determined by the "weakest link" in the vehicle's components. For some vehicles, that would be the tire speed rating. In the case of rear wheel drive vehicles like the Ranger/Explorer/F-series/Econoline, the limiting factor is the driveshaft.

Every driveshaft has a critical RPM limit where it begins to whip, even if the balance is perfect. That RPM is determined by many factors including diameter, length, wall thickness, material, etc. In the case of a truck rear driveshaft, the killer is usually the length. It is possible to change the critical RPM by changing one or more of the other variables (diameter, wall, or material for example) but there are cost and/or weight penalties. Another approach is to make a 2-piece driveshaft with a center carrier bearing but that is even more expensive. It makes no sense for a manufacturer to invest in a more capable driveshaft if 99.9% of the buyers never invoke the limiter. Besides, a pickup or SUV manufacturer doesn't need any more liability exposure than it already has at speeds below 100 MPH.

 

[rwenzing]

Don't like your speed limiter at 92, 99, 110, whatever?

Be glad that our government hasn't passed a law (yet) to arbitrarily set a new vehicle's limiter to a speed that they consider prudent - let's say 75 MPH or 65 MPH or even 50 MPH. Virtually all modern cars already have a limiter strategy built into the EFI calibration software. All it would take is a stroke of the pen by the Congress and a few keystrokes by the calibration engineers to reset the limiter lower in the name of public safety and/or fuel economy. The 55 mph national speed limit imposed in the 1970's was basically unenforceable. That's no longer true for newer cars.

So, your present car/truck would be exempt, right? Think again. Just carry it a step further and the government could require a mandatory recall of all OBDII-compliant vehicles (95/96 or newer). A car dealer or government contractor would do a simple 10 minute reflash of the PCM for the lower limit and send you on your way. Refuse to participate in the recall? Registration and license tabs would be withheld to force compliance. Sure, you could still use an "off-road" recalibration to raise or remove or the limiter but I'm sure most drivers wouldn't invest the money for an Xcal2 or equivalent.

Scary? You bet. I wouldn't even type this on the public Internet if I wasn't 100% sure that it has been already been proposed, considered and shelved by the powers-that-be. However, as fuel prices and medical care continue to become so much more expensive, you can expect this kind of idea to go from radical to mainstream....

 

[Patton]

A lot of tax payers would leave this country if they tried to pull something like that. But I see where you're coming from.
And no, I don't have an XCal2. Now, if you loaned me $400, I could EASILY fix that problem

 

[MustangP51]

That would just be Un-American.

 

[springer]

If the engineers decided it shouldn't ever go that fast then why a speed limiter, why not take some gear out of transmission? Or something else to truly stop it from going that fast.

Several of you are incorrectly assuming that the engineers determined the top speed. Maybe in a classroom. I guarantee you the lawyers at Ford set the limit!

 

[Burns]

Either way it does not need to be going that fast on any public road.

 

[reserved50]

On one of my cars it was actually sent back to the dealer because of the factory 3:55 gears causing the drive-shaft to spin at a higher speed that seemed unsafe to Ford. Of course I thought that sounded silly, thats why I have 4:10s in the same vehicle. It can be set by engineering etc. The early 94? 5.0 Moostangs(Im sure it was this model of Ford) had top speed set by what tire size you bought, 16" (5 spoke rims)had a lower limit I believe than the 17" (tri-bars), so it can be set by either party.

 

[CDW6212R]

My 91 Mark VII has an AOD, that is by itself a speed limiter. My first with stock 3.27's would reach near 130mph, this one I stuck 3.73's in first thing. It tops out at not much over 100mph now in 3rd gear. High speeds should be only for racing or extremely short periods of time, with no one around to get hurt except yourself. Take care,

 

[rwenzing]

Several of you are incorrectly assuming that the engineers determined the top speed. Maybe in a classroom. I guarantee you the lawyers at Ford set the limit!

When the limit is set to protect powertrain components, it is determined by engineering. That is not an assumption. Every limiter on every Ford truck I worked on was set based on the maximum safe RPM of the driveshaft as determined through testing.