Disconneting Fuel Enrichement Line for MPGs

[Eli]

Same as the 90's Ecodiesel VWs. Disconnecting/Plugging the fuel enrichment line would lead to a turbo diesel with no fuel enrichment under boost.

Thus using less fuel, and getting better mileage.

If this is a viable way to use less fuel. I was thinking of installing a switch to actuate a valve that would block off the line from inside the cabin. So that you could easily disconnect it when on the go for highway use ect.

I am wondering if any of you are tried this and what your results were. I've heard very good things about VW Ecodiesels.

Thanks!

[Slobodan]

Sounds like an idea! I might be inclined to give it a go.

[piper109]

It may not make much difference on the highway. With diesels, fuel usage is very closely linked to HP usage. If you are going along at a certain relatively constant speed, the HP usage will be the same. You are moving the same weight at the same speed so energy used would be the same. Fuel mileage might be very close. It could actually be worse as turbo diesels are touted to be more efficient than n/a.

[Jason]

All that will do is keep you from getting enrichment under boost. You need a certain amount of fuel to keep your car going a given speed. If you are making say 5lbs of boost on the highway, the AFC is giving the engine enough fuel to go with it. If you disconnect that, you will just end up having to give it more throttle to make up for the loss of the automatic fueling the AFC is taking care of. I cant see how you will get any better mileage at a constant speed. Maybe around town you would see a gain, but you would be down on power as you would have no fuel to go with boost, and probably not be able to build much boost, as fuel=heat & engery which makes drive pressure. Thats what spins the turbo.

Jason

[Eli]

I disagree, I believe this will yield better mileage. Or at least it is worth trying.

This was the concept Volkswagen used when they created the '91 Jetta EcoDiesel.

A little info on that:
About the ECODiesel-
Around 1990, Volkswagen in Germany set out to create an environmentally-friendly diesel engine. In order to save time and money, they decided to modify an existing diesel engine instead of creating a totally new one. So they took the standard VW turbo diesel engine, which had been used in millions of Volkswagens and Audis since 1982, and made some modifications to it in order to clean up its emissions.
With any engine, gas or diesel, one major step in reducing emissions is to add an oxidation catalyst (often called a catalytic convertor). So the major difference between the ECOdiesel and a regular VW turbo diesel engine is that the ECOdiesel has a catalyst. But they didn't stop with just adding a "cat." The VW turbo diesel engine has a thing called a "boost enrichment device" attached to the injection pump. Its purpose is to supply extra fuel to the engine when the turbocharger is making a large amount of boost (i.e. full-throttle acceleration, or going up a steep hill). But often the engine can't burn all of this extra fuel, and some of it ends up going out the exhaust pipe.

If this unburnt fuel in the exhaust was allowed to enter the catalyst, it would damage or even destroy the catalyst -- causing VW's efforts at reducing emissions to (quite literally) go up in smoke. So the second modification VW made was to simply remove the boost enrichment device. Of course, this reduces horsepower a little bit, but the turbocharger is still there so the ECOdiesel is still more powerful than the non-turbocharged VW diesel engine. And the Umwelt diesel's turbocharger has the same maximum boost pressure (9.6 psi above atmospheric pressure) as the regular turbo diesel, so the turbocharger can do the same amount of work; but without the boost enrichment device, there is less fuel reaching the ECOdiesel engine at full throttle. This helps with fuel milage.

These are the two main features that distingiush the ECOdiesel engine. Otherwise it is pretty much mechanically identical to the regular VW turbo diesel engine. In the real world, these modifications do seem to work very well; in most driving conditions, the ECOdiesel emits no visible smoke from the exhaust pipe, at least when the engine is warmed up. In fact, it is clean enough that VW was able to sell the ECOdiesel in California, a state whose tough emissions regulations prevented VW from selling regular ECO-diesels there since the mid 1980s. This also makes the ECOdiesel ideal for GREASE systems, as it reduces emissions from less refined fuels.


Source:
http://massachusetts.estia.com/cars/60206.html

It may not make much difference on the highway. With diesels, fuel usage is very closely linked to HP usage. If you are going along at a certain relatively constant speed, the HP usage will be the same. You are moving the same weight at the same speed so energy used would be the same. Fuel mileage might be very close. It could actually be worse as turbo diesels are touted to be more efficient than n/a.

While power is closely tied to fuel, diesels naturally run lean, and this would just be leaning it out a little more. While there should be a loss in power, VW was able to get more power (at a lower RPM) by adding a turbo and not adding fuel enrichment to an N/A diesel (While also adding a CAT!). Look at the HP numbers:

1.6 D-------------1983–1992 I4 Diesel----- 1588 cc 40 kW (54 PS; 54 hp) @ 4800 rpm 100 N·m (74 ft·lbf) @ 2300–2900 rpm -----(N/A)
1.6 ECOdiesel-----1989–1992 I4 Turbodiesel 1588 cc 44 kW (60 PS; 59 hp) @ 4500 rpm 110 N·m (81 ft·lbf) @ 2400–2600 rpm-----(ECOdiesel)
1.6 TD------------1983–1991 I4 Turbodiesel 1588 cc 51 kW (69 PS; 68 hp) @ 4500 rpm 133 N·m (98 ft·lbf) @ 2500–2900 rpm-----(Turbodiesel /w fuel enrichment)
1.6 TD------------1989–1991 I4 Turbodiesel 1588 cc 59 kW (80 PS; 79 hp) @ 4500 rpm 155 N·m (114 ft·lbf) @ 2500–3000 rpm-----(Turbodiesel /w fuel enrichment)


Source: http://en.wikipedia.org/wiki/Volkswagen_Jetta


All that will do is keep you from getting enrichment under boost. You need a certain amount of fuel to keep your car going a given speed. If you are making say 5lbs of boost on the highway, the AFC is giving the engine enough fuel to go with it. If you disconnect that, you will just end up having to give it more throttle to make up for the loss of the automatic fueling the AFC is taking care of. I cant see how you will get any better mileage at a constant speed. Maybe around town you would see a gain, but you would be down on power as you would have no fuel to go with boost, and probably not be able to build much boost, as fuel=heat & engery which makes drive pressure. Thats what spins the turbo.

Jason

And as for needing to depress the throttle more on the highway because of loss of fuel = loss of power:

I believe this is a good point, one that may be the final cause of my idea not working. Although if Ecodiesels could spool the turbo, I don't believe that our straight 6 varieties will have any problem.


One thing to note is that more fuel in the cylinder can actually lower temperatures. Thus leaning out an engine too much can cause the engine to overheat, or melt things. I'm sure all of you know this, it is not a foreign concept to car guys. I don't believe any damage will be done by simply disconnecting the fuel enrichment hose, but it is something to keep an eye on.

If you are planning to mod your D24/T at all, you should have an EGT (exhaust gas temperature) gauge installed. I have my probe in my exhaust manifold, but my gauge is not installed/wired yet.


I know I have spouted off here a good bit, whilst still not proving anything. I will try this soon to see if my idea has any basis in reality. I can jabber on about this forever, but nothing will speak like actually results.

Thanks guys!

[Jason]

Diesels don't follow the same rules as a gas car for lean = high egts and melting cylinders. Too much fuel is what causes melt down. The air intake is totally open, engine output and rpm is solely dependant on fueling. At idle, the air/fuel ratio is something above 100:1.

I'm not saying you wont be able to spin the turbo, but the idea behind the AFC housing is to be a smoke limiter. The injection pump at a given full load screw setting will be able to pump out X amount of fuel. With the AFC housing connected, when off boost you will get less than that amount even at full throttle. Full fueling potential wont happen untill boost is there. The idea is to give more fuel to go with the extra boost. Does some go out the exhaust, yes, but if you have the AFC housing set properly it wont. The eco diesel was a marketing thing with VW. I have never heard of one getting significantly more mileage than a regular 1.6TD.

As I said combined mileage may get better because when accelerating you will never get the extra fuel the afc housing provides, but at constant speed, the fuel needed to push the car at 70mph is a given amount. Whether or not the afc housing is connected wont make a difference. If the spring was set too soft and it was actually injecting more fuel than it should at say 3 or 4lbs of boost, that just means to maintain your same speed you will just back off the throttle a bit.

Jason

[Eli]

This all makes a lot of sense. Perhaps I am completely wrong about this whole concept. If you bear with me, I just have a few more questions on the subject.


I don't know why it didn't click before, but you are right:
The amount of fuel (or energy) it takes to push the car through the air at any given speed is not going to change. This makes sense to me, I just have a few questions.


Can you enplane how VW got more power from the ECOdiesel then with the N/A diesel? I would assume the only way they could do that was to have the fuel pump set-up to inject more fuel then the N/A version. Except that when it was not under boost it would be running rich, which I don't believe VW would do because the main purpose of this car was low emissions.


Perhaps this is going over the basics a little too much, but play along with me here.

I am wondering about the difference in power/fuel usage between Turbo Vs. N/A diesels.

The N/A diesel can cruse the same at 55mph that the Turbo can. The Turbo can make more power then the N/A at a lower RPM, but assuming that the Turbo and the N/A are geared the same so they are running at the same RPM at 55mph. To achieve the greatest efficiency is it better to have an N/A diesel or a Turbo? Or is it safe to assume that the Turbo and the N/A are using the same amount of fuel (or energy) at the same RPM to move along at 55mph?

Now I don't think they use the same amount of fuel, because if they did they would have the same MPG rating.

The '85 Jetta diesel is EPA rated for 41 MPG Highway. While;
The '85 Jetta turbodiesel is EPA rated for 38 MPG Highway.

I wish I could post the page where these two cars are compared next to each other, but that is not how the website is setup. Though the information can be found here: http://www.fueleconomy.gov/Feg/findacar.htm

Assuming they are using the same amount of fuel (or energy) at cursing speed, is the Turbo getting worse mileage then the N/A because of the exhaust gas restrictions caused by the turbo itself? Or perhaps the Turbo was a higher trim lever and had luxury options and such causing more weight?


I am really not trying to be a jerk rambling on about this, you guys are obviously well versed on diesels and I just want to further my understanding.

These things seem like discrepancies in the thought process to me.

Thanks!

Eli

P.S.

Thanks for pointing out that I was wrong about the lean mixture meaning overheating. I read that somewhere, someone mentioning it in reference to diesels. I do not want to be one of those people spreading false information.

[piper109]

My wife gets 47 mpg highway in her tdi diesel. I get 43 mpg highway in her tdi diesel.

Same car, same highway, different foot :-)

Unless you have really controlled conditions I'm not sure you can be that accurate.

Winter fuel usually gives you fewer mpg than summer fuel. On a hot day the tires may be inflated to a higher pressure. There are so many little factors that could enter in.

Do you think the EPA do a better job of controilling all of that?

Just drive what gives you the most satisfaction :-)

Steve

[Jason]

VW was able to get more power with the eco diesel because of the turbo. At a given rpm, the engine can only suck so much air, and the injection pump was set to supply only enough fuel to go with it. With the addition of the turbo, the injection pump could be set at a higher injection quantity compaired to the NA car, because the turbo was pushing in extra air to burn all the fuel. The injection quantity is dependant on the fuel screw setting and your foot. If you pushed the car to the floor at low rpm, it would be rich untill the turbo spools up to clean up the smoke and burn the fuel. That would only last for a time it takes the turbo to spool though. When cruising around even with no boost, you wont be running rich becuase the pump wont be injecting more fuel than the engine needs, unless your foot tells it to do so. The Turbo diesel did get less mileage for a couple reasons. You are right about the luxury options, many of the regular diesels did not have power steering, or a/c. Most all the turbo diesels had those options, along with cruise, some had sunroofs, and I believe the turbo diesel had a different final drive ratio, or 5th gear I cant remember. I had a '85 Jetta TD that I restored, and have had a number of NA jettas, but the NA cars don't have a tach. I'm just going by my ear at 70mph the TD was spinning a little higher rpm.

Also, look at the power difference of the NA and eco diesel. A whopping 5 hp. Pretty much all the turbo was doing was cleaning up the little bit of unburnt fuel you would have if the car was a NA diesel. In order for a NA diesel to operate with no smoke at all, it would barely accelerate. Some fuel has to go out the exhaust in order for it to have any power at all... That may improve fuel economy slightly but I cant imagine it was that much. I've never owned an eco diesel to be able to tell you what kind of mileage it got. My 85TD however, averaged 42mpg cruising 70mph, which is better than the EPA rating, though I did have a low restriction exhaust system, and was running the timing advanced a little beyond vw's spec.

Hope this all makes sense.
Jason

[cuaz64]

Eli, I remember that Matt form TB, in his diesel+t, use the N/A injection pump without troubles, and later installer the LDA to get better power.