Are very low RPMs damaging to engines? Esp. w/load

[IndyIan]

I was driving the Focus this weekend and started paying attention to the upshift light.
With light enough throttle 10-20%, it will prompt upshifts that put the motor at 1400rpm. A bit more throttle and it will wait so you come into the next gear at a bit higher rpm.
Also on the scangauge, it has a Load gauge, which basically gives you the percentage of maximum power you are using, that is available at the current rpm.
So for low rpms it goes to 100% at 30-40-50% throttle opening, so I'd assume the ECU is mapped to protect the motor as well.

 

[rationull]

Originally Posted By: IndyIan
Also on the scangauge, it has a Load gauge, which basically gives you the percentage of maximum power you are using, that is available at the current rpm.
So for low rpms it goes to 100% at 30-40-50% throttle opening, so I'd assume the ECU is mapped to protect the motor as well.


Can you actually see this by looking at LOD vs TPS? I was always under the impression that LOD was pretty much just TPS shown as a percentage.

 

[Shannow]

at 50% throttle opening, 70.7 percent of the available orifice area is exposed.

Unless at high airflow (high RPM), you can easily get 100% power due to no real throttling taking place after about half way.

 

[Vikas]

Anybody knows how the PCM computes the load? I have tried to find the algorithm from all the available literature but so far have come empty.

 

[IndyIan]

Originally Posted By: rationull
Originally Posted By: IndyIan
Also on the scangauge, it has a Load gauge, which basically gives you the percentage of maximum power you are using, that is available at the current rpm.
So for low rpms it goes to 100% at 30-40-50% throttle opening, so I'd assume the ECU is mapped to protect the motor as well.


Can you actually see this by looking at LOD vs TPS? I was always under the impression that LOD was pretty much just TPS shown as a percentage.

Nope, LOD is definetely independent of TPS. I suppose at peak HP rpm they are almost the same, but at low rpms its easy to max LOD with very little throttle with a manual trans atleast. With a hypershifting many many speed automatic, you might have a hard time seeing that though.

 

[IndyIan]

Originally Posted By: Vikas
Anybody knows how the PCM computes the load? I have tried to find the algorithm from all the available literature but so far have come empty.

It might be just read off a table stored in the ECU? I assume its used more for ATX cars for shifting decisions, and the shift up light if equipped?

 

[Vikas]

Originally Posted By: IndyIan
Originally Posted By: Vikas
Anybody knows how the PCM computes the load? I have tried to find the algorithm from all the available literature but so far have come empty.

It might be just read off a table stored in the ECU? I assume its used more for ATX cars for shifting decisions, and the shift up light if equipped?
The thing is the load is "computed" from the other sensors and if the load is then used in the computation to control say timing or fuel injection, why not just use the sensors themselves? Load is never really measured as a value. If a sensor reading is off, then your load computation would be off too.

 

[CBR.worm]

Load is typically inverse of manifold vacuum.

 

[ueberooo]

Originally Posted By: demarpaint
Originally Posted By: zaibatsu

While we're at it, do you guys think that turning engine off and back on while warm (i.e. at lights) accelerates wear on anything (apart from starter motor)? To any significant degree?


Why to save a few pennies on gas? The more times the starter has to start the engine the more wear on the starter, period. Not to mention if God Forbid you had to move somewhere fast to avoid an accident. Unless your car has start stop technology by design don't do it.


Yes, probably not good unless it's a very long cycle light (~2 minutes or more). One might also put some extra "wear" or at least stress on the timing belt, since startup from 0 rpm to 1000 rpm happens pretty quickly, and it's the angular acceleration in the engine (i.e. time rate of change in rpm) that puts a load on the belt. The starter is not a big deal, it's cheap, and easy to replace, and I plan to keep my car for long enough to need two starters anyways.

You're wasting about 2 cents of gas every idling minute, for a normal FI engine with about 2 litre engine displacement (1/3 gph, at $3.60/gal gas); this is one big reason car makers are getting more efficient with DI engines popular nowadays.

Back to the original question. I kind of tend to think if it were doing something harmful to the engine you could hear and feel that; if there's real lugging, you'll feel that; it's like forgetting to pull the car out of gear (MT) while coming to a stop.

Second, if you put full load at very low rpm, the engine is operating in a very inefficient regime. For a typical modern FI engine to be able to operate near top efficiency it should typically be in the range of 1600 to 3300 rpm (and the manifold pressure must be near half to near full power 0.5 atm to near WOT). Direct injection engines are able to operate more efficiently at less than half power.

I put light load even down to idle rpm (800). By light load I mean 0.4 atmospheres in the manifold (idle is about 1/3 atm). (You still see a surprising little bit of power, just by adding a tiny bit of gas to an idling engine) even at very low rpm's like 1000-1300.