I've recently picked up a 2000 F150 4x4 with the 4.6L. As I've been checking it out I've logged some data while driving around, mostly out of curiosity. Now I'm wondering how is the Engine Load usually calculated and how it affects the lifetime of my engine. Below is a snip of some of what lead to my question.





The figure shows an inverse relationship between rpm and engine load with a trailing increase in coolant temperature.

The increase of engine (coolant) temperature appears to be due to the engine load instead of the engine speed. This seems counterintuitive to me. I was under the impression that running the engine at higher RPM would cause higher engine temperatures and more wear and tear on the engine leading to a shorter engine life. This data suggests otherwise.

From this consideration, it looks like running the engine at a slightly higher (obviously not too high?) engine speed is ideal for maximizing the lifetime of the engine, assuming that engine temperature and lifetime are directly related.

Next time I go out, I plan to collect some more data on a warm engine. From a stop in neutral, I'll ramp the engine from idle to full throttle over a minute or so. This might tell me how the engine speed and temperature are related sans engine load. But it's also convoluted because the water pump is powered by the drive belt and the coolant flow would perhaps introduce another variable into the analysis.

Any thoughts on this are appreciated. There are dozens of sensors to collect data from and I'm sure many of them could show some interesting things to this question, but I'm really just beginning to learn about these engines.

 

My thoughts - FWIW.


You seem to have an inquisitive mind like me. I've been 'hacking' the OBDII system on my 2004 5.4L Triton for a couple of years now (using Torque Pro). Mind blowing!


My sense is you are missing a number of variables that are very difficult (if not impossible) to accurately sort out - but I agree, fascinating. These vehicles have so much software logic in them it is virtually impossible to know What the programmer was thinking.


What I see in your data is something COMPLETELY different from what you asked. The PCM adjusts the actual throttle plate, EGR, Spark timing, and probably other things to reduce the engine POWER momentarily (thus load) at the instant of transmission shifts to give you a smooth shift - and minimize band slip/wear. Although you are correct, the % "load" is heaver at the lower RPMs right after that shift. I do sorta' believe your momentary step up in ECT has to do with two things - slower coolant movement due to lower RPMs & a spike in Cylinder Head Temp due to your increase in load %. BUT, heat removel does not necessarily relate to bearing ware or loss in engine longevity. Mine is clearly designed to operate at lower RPMs most of the time at a very high load factor.


HOWEVER: I think you misinterpret load. 100% load is not ALL the HP the engine is capable of delivering to the wheels. (Chart those two, Load, Calculated HP, or Torque at the Wheels) Load% is a sorta' a sliding, variable scale calculated (SOMEHOW) on a number of variables pertaining to the %Load under current conditions. My 5.4l Triton has variable valve timing instead of EGR. It plays with Spark Advance / Valve timing retard / Absolute throttle position in an obvious effort to keep engine RPMs low and load WAY HIGHER than one would think (80% - 90%) the majority of the time, no matter speed, gear, or throttle after it levels out to cruise.
How is Load calculated?


PID # 04 formula is A/255 (OR) A/2.55. Custom PIDs vary between manufacturers and even within models. Mine has calculated load located at PID# 115A , Calculated Engine Load, formula = ((A*256)+B)*(128/32767)


If you get that thing figured out --- let me know!! LOL


I just learned, mine runs a constant diagnostic "RATIONALITY CHECK" comparing fuel flow (based on sum of injector pulse widths), Fuel tank level sensor decline from that amount of consumption, AND fuel tank pressure decline from evacuation of fuel through that consumption!!! Failure in that rationality check will set a DTC. !!! Like I said, mind blowing.

 

The 2000 PCM does not adjust the throttle plate - it's a cable throttle. Electronic throttle didn't start till 2004.

 

Throttle cable / Choke cable whatever - the PCM adjusted something - or else he let his foot of the accelerator just at the instant the engine transmission shift (or whatever caused his RPM to nosedive from 3700 to about 2400).

 

I believe it momentarily cuts off fuel and/or spark during the shift. It can't adjust the throttle.

Of course it's going to nosedive - it shifts to a higher gear........

 

Yes, my transmission is manual, the MR2 4 gears + 1 overdrive. What you see in the RPM is a preparatory increase in engine speed before the shift, a total release off the throttle during the shift, then a gradual increase in throttle after the shift is complete. (These transmissions from what I've read like to shift really slow, very inadvisable to maintain throttle throughout the shift, unlike the automatics obviously). The sharp engine load increase occurred when letting off the clutch.

I've come across that equation for engine load at some point of google searching. Some of the other equations I saw brought in measurements from air intake temperature sensor, MAF sensor, predetermined constants like wide open throttle etc.

You brought up a good point of coolant temperature being a measure of engine cooling efficiency rather than a measure of engine stress. So, now I'm wondering what are the most significant sources of engine temperature increase. I wish my obd-II reader let me pull oil temperature. RPM certainly should scale with temperature due to both friction and combusted liters of fuel per minute. Other sources of temperature increase could possibly be torsion stress in the cam and crank shafts.

So in my attempt to maximize engine lifetime based on real data, maybe the so called 'engine load' isn't really a measure of engine stress as I thought, but more of a calculated regulation checkpoint for combustion conditions. Then maybe the increase in ECT isn't as interesting as i thought either, maybe simply due to a decreased coolant flow from the RPM drop.

 

Here's a list of the supported data that I can pull off my obd-II reader with time dependence (maybe I need to look at a better reader)

Fuel System Status
Calculated Engine Load Value
Short Term Fuel Trim Bank 1 and 2
Long Term Fuel Trim Bank 1 and 2
Engine RPM vehicle speed
Timing advance for #1 cylinder
Intake Air Temp
Mass Air Flow rate
Absolute throttle position
Bank 1/2 Sensor 1/2 Oxygen and short term fuel trim

 

Whoa! My bad. "ASSUME" fits me perfectly here. I totally '***-umed' (based on the chart) that we were dealing with an automatic transmission. (common pitfall in communicating via writing - LOL)


My understanding (subject to all the flaws that accompanies THAT) of so called "engine Load" is that it's a measure of power production ability - RIGHT NOW UNDER ALL RELEVANT PRESENT CONDITIONS? Fuel flow is MAXED OUT (in open loop) within upper limits of emissions for current mass air flow rate (considering air temperature / density and minimum vacuum), EGR (or cam retard) is limited to max, and spark is advanced to maximum for present RPM (limited by Knock) .... While that sounds like you're working the engine to death - not necessarily. The condition occurs quiet easily in high gear / overdrive at 25 MPH. It becomes a very good measure of when to downshift, either automatic or manual. While definitely a 'factor' in what your scenario, I do not think it equate directly to 100% of the amount of "ENERGY" the engine could produce - under ANY conditions (ie: increased air mass).

Your consideration of temperature is sound - considering its direct relationship to energy conversion - like you say "due to both friction and combusted liters of fuel per minute". But it seems that gets very involved in heat transfer efficiency (such as RPM effecting coolant flow and radiator heat exchange to varying outside air temp).

I have monitored my Cylinder Head Temperature sensor -A LOT- trying to perfect a formula that matches the PCM's presentation of normalized CHT in ºF. My '04 uses CHT to 'extrapolate' coolant temp and does not even have a coolant temp sensor (I THINK yours might also). And I can attest based on experience - CHT spikes real good (from around 201-202 degrees decel/coast to 215-222 floor-boarded - high engine load, exacerbated by higher RPMs.) I can also SEE cam retard (and probably EGR on yours) dramatically COOL combustion temperatures - (interesting!).


If you can input / monitor specific OBDII sensors and customize formulas with your data scanner, I think you would find CHT and CHT Volts very interesting.


CHT - #1624, Deg F (normalized), formula= ((A*256)+B)*1.999
CHTV - #1685, Volts, formula to convert to Deg. F = (65535-((A*256)+B))/93.3

 

@orad7676


I'm not a Torque Pro salesman (although I scream its praises often) and I readily admit my ignorance as to any other scanner/reader, but a video I thought you might find interesting is -> https://www.youtube.com/watch?v=3CO1...ature=youtu.be


This plug-in allows Torque Pro users to view live data on Torque Pro - while recording graphs (on ANY PID output by your PCM) in the background for later viewing.


There are somewhere around 500 PIDS available from the PCM on my 2004 5.4. I'm using this APP/Plug-in to see the relationship between different sensors to 'identify' WHAT they are - and WHY. I have some 400 in an spreadsheet that I have identified and grafted. Manufacturers keep the PID information so close to their chest hoping to nickel and dime us to death for diagnostics by their technicians.


FWIW