w124 E320 fuel system..does the return line really run through the AC cooler?
 

Okay I dont see much on MPG performance modifications for the CIS engines..Although the system is capable of higher mileage, Im pretty sure..Ive seemed to get over 30 MPG and other times less than 20..And Im looking at the fuel system to consider preheating the fuel line as it supplies the fuel rail as many have done on other cars..And OMG..I see the return fuel line seem to go into a little chamber attached to the cold side of the AC unit and then on to the fuel tank..

Im wondering if the design purpose of this is to reduce the possibility of vapor lock in the fuel system..And no matter how warm the car is, one can feel the fuel rail is much colder than other parts in the engine compartment..And Id like to set up a preheat system from the engine coolant to raise the fuel temp too increase the vaporisation and encourage higher MPG..

Amazing the design features one discovers on these things!

Thanks..

CIS (K-Jetronic) systems do not have a fuel rail. Fuel is delivered to the nozzles thru individual lines from the fuel distributor.
The fuel temperature is raised above tank temperature by virtue of having work performed on it when the pressure is raised during pumping. The cooler then reduces the temperature of the previously warmed fuel.

How are measuring MPG?

calculate mileage on every fill, divide the miles run by the gas used.. Is there another method?

The OP has the HFM sequential multiport fuel injection and not CIS unless he is talking about a vehicle not in his profile.
I always found my 95 E320 to be quite good on fuel although I do need to use premium or mileage drops and I get an increase in carbon buildup.

That is indeed a fuel cooler. The CIS cars have them too.

-J

Thanks Compu 85..yes HFM Injection..gas m104..I will google but hope to learn the purpose of this feature..

Regarding the comment that there is no fuel rrrail, this must be assuming its an M103? Its the HFM injection....I didnt indicate the year, 95..maybe that was confusing..I thought these were all continuous injection..This is sequential? Thanks..

yes, gotcha..I feel like my buddy who told me his pickup had a V four engine..:( He was our class valedictorian and an attorney now.. This is from Merz-bulgaria, they have awesome tech info but one cant post their link here..


1.1 HFM Sequential Multiport Fuel Injection/Ignition System (HFM-SFI) Contents
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1.1 Engine 104
Diagnosis Page
Diagnostic Trouble Code (DTC) Memory . . . . . . . . . . . . . . . . 11/1
Complaint Related Diagnostic Chart . . . . . . . . . . . . . . . . . . . 12/1
Electrical Test Program
Component Locations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21/1
Preparation for Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22/1
Sequential Multiport Fuel Injection System Test . . . . . . . . . . . 23/1
Ignition System Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24/1
Hydraulic Test Program
Fuel System Pressure and Internal Leakage Test
Preparation for Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31/1
Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32/1
Fuel Pump Test Page
Preparation for Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33/1
Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34/1
Injector Test
Preparation for Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35/1
Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36/1
–––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– ––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– ––––
bDiagnostic Manual • Engines • 09/00 1.1 HFM-SFI C/1

The wild swings from over 30 to under 20 makes me wonder about the accuracy. Also, some use the instant MPG meter on some cars to claim high numbers while neglecting time of low MPG so I had to ask.

When using the fill method, are you using the same pump and location of the car gets constant fills? Using the gas gauge can be inaccurate however MB seems to have them calibrated pretty well.

Thanks 97SL..

Nothing fancy, and no, just routine fill tracking and on trips Ive confirmed 30 plus MPG..probably with the AC off and other times I idle a lot and do lots of local stop and go and it will come in at 18..Sure, lots of errors likely but its also pretty wildly different.

Also been chasing repairs as well, fuel pump failure and the cylinder head rebuild didnt seem to affect mileage much, but I also fixed the AC so its now working and the engine runs cooler with the aux fans working so this would reduce mileage..And its winter. Summer gas blend gives better MPG..

Id simply love to get more like 30 than 20! and the gas gage doesnt work..I use the trip meter and fill up when the warning light comes on around 200/250 miiles..

Small wheels, 15 inch, same as my older 94 E320 but it got substantially better MPG than the wagon which is the 95..Larger rims would be nice..

You will gain way more for little cost by not idling and managing acceleration / deceleration where you put just enough energy into moving the car so hard braking isn't needed.

I don't see preheating fuel helping much. In fact, if heated fuel is returned to the tank, it raises internal pressure and might vent vapors.

Some summer gas has added oxygen content, your car might be running too rich if you get better mileage in winter with summer gas. It is normal for MPG to drop in winter, the engine runs rich when cold, engine takes longer to warm up, oils ( engine , trans , rear axle ) are thicker and produce more drag, idling to warm the car eats fuel, driving on snow causes more rolling resistance.

For the most part, wheel diameter does not affect MPG, overall tire diameter can. ( just be sure to correct for odometer errors. )

Thanks for the thoughts 97 SL320.. Im not thinking of disabling the fuel cooler that returns the fuel to the tank..Very interesting the car has this feature.

One method used to increase MPG is heating the intake fuel supply, this is commonly done by Hi Mileage tinkerers..So you are saying its not productive although its commonly done? Interesting..YOu go against the tide here??

So how would I get summer gas in winter?? I just know that any vehicle Ive had gets substantially better MPG in the summer and I nkow the stations change the blend to a different mix of hydrocarbons..summer/winter due to temperatures encountered..specific to any region. So I also take this into consideration..

It would be unwise to expect summer performance in winter and this could partly be due to higher fuel temp. The higher the engine operating temp, the greater the thermal efficiency of the internal engine..Just in general..Not to overheat the engine, of course. An old pickup, any car gets about 2mpg better in summer than it does in winter. Perhaps more..In my expereince..


i dont mind using gas, I just want my car at its most efficient possible..Idling or at highway speed...And Ive seen it vary widely and I believe it can do better! By the way it comes out beautifully on the emissions at DEQ..And the plugs are white-clean as if it has a very lean mixture..

Heating fuel and having it still remain liquid just reduces it's density. If the engine was running too rich and fuel is heated, it might improve fuel mileage due to a leaner mixture however if the too rich problem was fixed, it would get better fuel mileage.

And, if the intake air is heated, it's density is also reduced. This makes mixtures comparatively richer, offers no cylinder cooling and reduces effective compression ratio.

The next question, does a hydrogen system on a gasoline engine increase / decrease / make no change to fuel mileage?

Thanks 97SL..Yes, I agree with this science and its right on..

The only counterpoint is that if you can get fuel to vaporize prior to intake then it burns cleaner and more efficiently..The injector atomizes but does not vaporize the fuel..And many do claim the temp increase adds to MPG..We dont heat intake air, only fuel..although you could..but as you say it would decrease performance and set you up for preignition..

Hmm Hydrogen systems such as water-for -gas from HO gas generators run by alternators? Again I have claims from very reputable guys, one runs a service dept at a dealership..The service writer..That yes, they can do very well. Now from the pure physical science aspect you use the energy you take out of the HO gas, burning it, when you split the water into HO with the alternator so its just taking out and putting back..No net gain. But I suspect there is a water mist injected which actually causes a water injection effect which has been consistenlty used to boost IC engine output, both mileage and power significantly..Water injection has been used in aircraft and autos..going back to to wwII..And this may actually be what produces the so called water for gas hydrogen benefit..

Looking forward to your comments

Yep, I'm aware of the atomization / vaporization difference. In the early 80's Smokey Yunick built a road going car or two ( one was a Dodge Omni I think ) using gasoline vapor. It supposedly ran very strong and got great fuel mileage but it did have a turbo,. . . supposedly because the expanding fuel vapor would not be sucked into the cylinder . . .and Smokey is a well known NASCAR rules bender so who knows the truth.

Another thing to think of, atomized fuel takes up less space than vaporized fuel. There will be a loss of volumetric efficiency with vaporized fuel because there needs to be a corresponding reduction of air entering the intake port. This could be official why Smokey used a turbo, ( and for the rule bend, added more boost than needed to get more power. )

I think the largest issue with vaporized fuel is having enough ready in storage to get past varying throttle requirements of a road going car. Will it help fuel mileage overall? I'm not sure, combustion science is pretty complicated.

Is it worth the effort? Probably not at this point but it would make for some interesting experiments.



Yep, in the world as we know it, energy can't be created or destroyed, it can only change form.

The mayor of my little town was building a hydrogen system to run a small engine. He said that he got it running for a few seconds.

I asked: Where did you get the Hydrogen from?

Him: I made is using electricity.

Me: Where did you get the electricity?

Him: From the car batteries over there.

Me: How did you charge them?

Him: I hook it up to my car.

He didn't get it that his car was using more fuel to charge the batteries.

Water injection was used more for cooling cylinders in turbo / supercharged engines to prevent knock / pre ignition / detonation ( or whatever term you want to use though there is probably a fine distinction between them. )

The whole water turning into hydrogen thing takes energy that is mostly recovered when it is burnt. There goes that pesky energy can't be created or destroyed, it can only change form thing again.