.

 

I keep reading from some on how the EGR system allows the motor to "reburn" fuel to improve mileage.

That is simply an uninformed statement. No malice meant, it is just wrong!

The only function of the EGR system is to reduce the peak combustion temperature in the combustion chamber, which in turn generates less NOX emissions (because of those lower peak combustion temperatures.)

There is nothing in the exhaust that will burn, once the combustion process has occurred. EGR gasses simply inhibit the peak temperature of the explosion in the cylinder.

The laws governing thermodynamics state that peak efficiency of the internal combustion engine is limited by the difference in the temperature of the intake charge and the temperature of the exhaust charge.

If you can increase the combustion temperature by burning your fuel more efficiently, both exhaust gas temperature and mileage will increase, provided you can keep the intake charge temperature the same.

You will never increase efficiency by reducing peak combustion temperatures, assuming that the intake charge remains at constant temperature.

Your EGR system does just the opposite. EGR reduces peak combustion temperatures and thus must reduce efficiency (fuel mileage), all other factors being held constant.

This is true for all internal combustion engines, be the fuel gasoline, diesel or even CNG (Compressed Natural Gas). It cannot be any different.

Probably not what one would care to hear, but a little research on the internet will bear this out.

 

Please note that the OP of this thread (clear back in 2012) was referring to a 1987 Ford F150, which would have been, at best, a MAP (Manifold Absolute Pressure) engine, not a MAF (Mass Air Flow) engine. (assuming the 1987 F150 4.9 six even had EFI.)

(I know my 1986 F150 with the 6 cylinder engine was still carbureted.)

A 1987 F149 with the 4.8 six would not have had the ability to adjust the AFR based on EGR, much less air flow.

MAP systems are not capable of adjusting AFR based on air flow. That takes MAF system.

MAP can only measures manifold pressure and then (using engine rpm and air temperature) calculate a "speed density" value, and then compare that value to a predetermined value in the computer to determine the width of the injector pulse.

Since MAP engines can't measure airflow, MAP engines cannot respond to high performance cams and head porting, (with out ECU modifications) as it can't "see" the cam (and its increased airflow) and thus can't adjust the injection pulse to match the increased airflow.

Many have discovered this when they try to modify their early 5.0, 5.8 and 7.5 engines with hot cams and head porting. With no further modifications, these engines invariably "run like crap". The porting actually decreases the manifold pressure (vacuum) and you do not need an engineering degree to predict the result.

One literally has to create a new speed-density table. This is why it is hard to "hop up" early Ford EFI engines as one needs a new or reprogrammed ECU.

I think that much of the discussion I have read is very interesting, but even though an SAE engineer would probably understand the theories being expressed better than I do, The initial inquiry has been degraded to such an extent, as to reinforce the point Earnest Hemingway was trying to make when he penned the play "Much Ado about Nothing".

No disrespect intended, but when posters get in a "pissing match" most people will tune out.

I used to tell my students to "Lighten up Francis" when the discussion degraded to this point.

Lets all remain friends in our shared interest in FOMOCO.

 

'87 was the first year of the "brick nose" truck and along with the new model came EFI.

While your statement relating to MAP vs. MAF is true in many ways, let's not forget that once in closed-loop operation the O2 sensor "takes over" fueling and adjusts fuel pulse-width dynamically. As such, when EGR is operating and effectively making the engine "smaller", fueling is adjusted accordingly on-the-fly.

Admittedly, the above statement may only be academically correct and often doesn't translate to practical, operational reality. As discussed here, there are other factors in play. But I find it's always best to understand the theory of operations before one begins shooting holes in it.

 

Good read here

Ive put about 5000 Miles thus far daily driving the 87 listed in my sig below over the last 4 months or so. Every tank hand figured has been around 15.5-16 mpg. This is a mix of two lane stop and go and mostly interstate highway with the occasional red light.
Piddling with the truck checking for vacuum leaks with my vacuum pump this weekend i discovered the egr was stuck shut. Previous owner had unplugged the vacuum line, which i connected not long after i purchased the truck. With 25 lbs of vacuum applied and engine running a few good raps with a hammer to the valve has it opening and closing with vacuum. I did notice the increased throttle required to maintain cruising speed with my first long drive this morning.
I anticipate my mpg to increase based on a previous experience.
I daily drove this exact truck, but a white one from 2006-2012. Initially it was getting around 17 mpg in stop & go/highway mix.
I deleted the egr with a fooler that i purchased from fordfuelinjection?(no longer in business?) and the rest of the time i drove the truck it always averaged in the 14-16 mpg range. Never could squeeze any more out of it.

I'm interested too see what changes here.

Let the flaming begin

 

Also i should add that i keep a book to record mpg on every fill up as i did on the previous 89 i speak of above. Engine is tuned up and runs great with about 21 lbs of vacuum at warm idle. EGR is now opening and closing, verified with vacuum gauge to manifold vacuum as well as vacuum pump attached directly to egr valve.
12* base timing with motorcraft plugs and the usual tune up items. Truck was cat-less with free flow exhaust when i bought it, smog pump missing as well. vacuum lines have been gone thru, cannister replaced(leaked)

 

Look forward to your results. I also record fuel mileage on all my vehicles, if only to give me an idea if something is headed south. My truck sees such mixed use, it's hard to tell anything meaningful from tank to tank.

 

Thank you, i do as well
I keep a service/mpg book on all my vehicles, have since i started driving. I like to be able to look back months or years on mpg, you can definitely see an issue developing even if it hasnt reared its ugly head yet. This truck has two jobs, take my *** to and from work, and runs to the store on the weekends. So the mpg is pretty consistent. Towing is out of the question

 

Theoretically EGR should slightly increase fuel economy by reducing pumping losses - but at the same time it slightly hurts combustion efficiency by dropping combustion temperatures. Will be interesting to see your results.

 

first tank 16.49. better than my average, but im not going to call it an improvement yet.
Verified egr is still not stuck last night with vacuum pump.
Truck is running great.
will fill up again this evening and see what it says, been doing some light hauling and around the house stuff.

 

 

Thanks for posting. Look forward to the ongoing updates.

 

 

 

In a properly working system, EGR does reduce pumping losses. It doesn't work when the engine is making power so it doesn't affect power output. Injecting exhaust (low O2 content) is like a little fire extinguisher. Kinda the opposite of nitrous (high O2 content). It's effective in reducing poison output.

It's a system, injection system. It's a simple system that doesn't cope well with changes. Side effects and such come into play quickly.

Many trucks of this age are being nursed along until hitting the junkyard. Do what you gotta do with those. If you are acting like the caretaker for the next owners, keep the EGR. Clean out the EGR tube if you get access for another reason.