Maximum MPG out of a diesel

Well, i've deleted the EGR on both my diesels and it seemed to boost MPG a bit. Now a get a solid 6L/100 km with both.
 
Totally anecdotal, but from what I've seen, that really only applies with gasoline engines. With diesels, deleting the EGR actually seems to improve mileage.
I should say I learned this on electronic diesels where unplugging the thing did you no good as the ECU expected it to be there. Mechanical is a whole different story and lapsed on that thought.

So ya you are right in that aspect.
 
I should say I learned this on electronic diesels where unplugging the thing did you no good as the ECU expected it to be there. Mechanical is a whole different story and lapsed on that thought.

So ya you are right in that aspect.
One of my observed cases was a 6.0L PDS (VT365). My buddy picked up a solid 2MPG deleting the EGR. Apparently, on the Ford's, you could just unplug the EGR and despite the EGR position sensor obviously not reporting the valve functioning, it didn't throw a code. The ECM just acknowledged the EGR wasn't working and continued on, at least that's my understanding of it (it wasn't my vehicle). Thought it was interesting.

Correct me if I'm wrong, but my understanding of EGR on a gasoline engine is that under low load, exhaust gas, which is inert, is allowed to blend with the air charge, which facilitates both the reduction in NOX and allows for a leaner mixture with more timing (improving efficiency).

Given how much broader the enrichment range is for a diesel, and the fact that you don't have to worry about spark knock, I don't believe the same benefits, at least nowhere near of the same magnitude, are attained. It's mostly for reduced emissions with the side effect of introducing much dirtier exhaust, due to all the soot, into the system, which shrinks intake ports and causes build-up. Diesel EGR also needs to be cooled, resulting in the fitment of EGR coolers, another problem/failure prone item.
 
One of my observed cases was a 6.0L PDS (VT365). My buddy picked up a solid 2MPG deleting the EGR. Apparently, on the Ford's, you could just unplug the EGR and despite the EGR position sensor obviously not reporting the valve functioning, it didn't throw a code. The ECM just acknowledged the EGR wasn't working and continued on, at least that's my understanding of it (it wasn't my vehicle). Thought it was interesting.

Correct me if I'm wrong, but my understanding of EGR on a gasoline engine is that under low load, exhaust gas, which is inert, is allowed to blend with the air charge, which facilitates both the reduction in NOX and allows for a leaner mixture with more timing (improving efficiency).

Given how much broader the enrichment range is for a diesel, and the fact that you don't have to worry about spark knock, I don't believe the same benefits, at least nowhere near of the same magnitude, are attained. It's mostly for reduced emissions with the side effect of introducing much dirtier exhaust, due to all the soot, into the system, which shrinks intake ports and causes build-up. Diesel EGR also needs to be cooled, resulting in the fitment of EGR coolers, another problem/failure prone item.
On VW's it would throw a code almost immediately especially on a cold start. It expected a certain volume and checked that against the MAF's reading on incoming air. I cannot say whether I lost or gained because at that time the car was so restricted via LSD/PCV clogging up the intake I just got 38-40 consistently and at the time I was happy with that. I also removed the EGR cooler and bypassed it once I cleaned my intake manifold and only ever put a non-cooled EGR back on before I sold it. I did gain some in the fuel economy dept. but I attributed that to a clean intake more than anything else.

Speaking with people more intelligent on the subject than I explained to me that at part throttle, it would run slightly higher boost and blend in EGR for better fuel efficiency on the highway. I will admit to believing all of that being the naive 21 yr old I was at the time and knowing nothing about TDI's. They also mentioned the car in turn could use more fuel when it didn't have too and your MPG would suffer especially during warm-up in cold weather but your fuel efficiency is crap anyway so who knows if that is true or not.

I would definitely agree to EGR being a crap shoot back in the early 2000's but today considering the way pollution goes limiting what we breathe in a daily basis may not be such a bad thing.
 
EGR gives you better fuel economy at part throttle so that wouldn't be wise. It would delay warm up when cold especially.
Not on these diesels. It adds soot to the intake and reduces combustion temperatures.

The only issue is if the electronic diesel controls on the IP will disallow boost if there isn’t sufficient egr flow noted.
 
Most of the time yes. Boost and RPMs will affect EGTs but generally speaking higher EGTs are from more fuel being burned.
So when I drop from 6th gear to 5th and the egts go from 950-800 that means it's burning less fuel in 5th even though it's spinning more rpms?
 
So when I drop from 6th gear to 5th and the egts go from 950-800 that means it's burning less fuel in 5th even though it's spinning more rpms?
Not necessarily better or worse fuel economy with more rpm, but a lower EGT suggests a leaner a/f ratio. With more rpm, you're putting more air through the engine and pumping more oil for piston cooling for a given load.
 
Both my diesel cars also seem to smoke less without the EGR. Unrelated observation but once again, i managed to get the best mileage with 15W40.
 
Does higher egts mean more fuel being burned? Towing a trailer I can have about 150 degree difference between 5th and 6th gear. 6th gear has a higher egt temp.
yeah, it is counterintuitive but you can get better fuel economy running the engine faster in a lower gear when under a load than using the slower engine speed you receive in higher gear.. and its all about load and the torque curve of the engine.. in my case I have a 3500 series truck w/410 gears,6.7 litre engine and I used to make this 200 mile trip with a 12000 lbs trailer on a routine basis.. and I have ran it all the way in either direction in 5th in one direction and 6th the othe and compared the fuel economy gauge and average fuel economy derived from truck computer pretty much the same in either gear. so yeah, the answer is it depends.
 
I have ran it all the way in either direction in 5th in one direction and 6th the othe and compared the fuel economy gauge and average fuel economy derived from truck computer pretty much the same in either gear. so yeah, the answer is it depends.
Wind direction might have played its part to offset the gain in fuel economy. Just a thought.
 
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