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Mylestone
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Discussion Starter #1
I have a 1997 dodge ram2500 3.9 liter v-6 ,auto trans,with tbi,and the best Milage I can get is 10MPG!!!!! I have a K+N Air filter,Mobile one oil and filter,new plugs,wires,rotor and cap,dome oil cover breather and thats about it!Can ANYONE think of some dodge part I forgot? I haven't checked the timing and I realize a 3/4 ton truck doesn't get 30MPG with a V-6(what idiot bought that combination should be steerilized so he or she can't breed)But has Anyone have a solution to my problem? I could and HAVE got better milage on my hemi cuda in 1971 when I turned wrenches!
Thanks ALL
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Seating for 12
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How many lug nut are one each wheel of the van? 5-lugs = 1/2 or 3/4 while 8-lugs = 1-ton for these vans.

See your other thread for additional postings.
 

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Mylestone
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Discussion Starter #4
yes

I did buy it 2nd hand in a trade in at my dealership for $2000 as the owner of the dealership is a best friend.It was worth $5000 back then but I had no way of knowing what milage it got as everything I have ever owned got 12MPG+ even my 1968 hemi cuda got better MPG when I kept my foot out of it.
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A '68 Hemi vs. a '97 six-cyl. van is an interesting comparison. The Cuda would have a huge engine (but with a lot less emissions control crap on it) and a carb, but way better aerodynamics and (maybe?) a more efficient manual tranny. But the van weighs more, has an auto trans and pushes a lot more air....hmmm.
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If your van's engine actually is an older TBI, non-Magnum, I wonder which PCM was used? One switched from an older van or the '97? If things weren't setup properly, it could result in bad MPG. Then you may look into rumors about the oil on K&N filters fouling MAF sensors...if it's true, that also could affect mileage.

Have you ever quizzed up any local folks who drive a similar van what they got for MPG?
 

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Gone but not forgotten
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Do you have the TBI or MPI engine? Yours should be the MPI (Multi Port Injection) engine. A way to tell is if your has the black fuel rail on the outside of the manifold with a cross over in the back and the fuel line entering the rail on the drivers side. There are two electrical connections to the throttle body, 1 is the MAP Sensor, and the other is the Throttle Position Sensor.

Also what trans do you have? My combination is the 5.2 with the 36RH with 3.25:1 axle and I get about 10.5 city and 13.5 to 14.5 on the highway while the overall combination mileage is about 12.2.
 

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4 Wheel Power Disc Brakes
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There is no MAF sensor on a TBI or magnum engine so don't bother looking for one.
A bad coolant sensor will cause rich running and bad mileage. From what I have heard eventully the thermister inside fails to make contact with the body of the sensor and gives a false reading to the PCM. A bad 02 sensor will also drop mileage as will low tire pressure.
 

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Mylestone
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Discussion Starter #8
Hello my friend

This has been a 1/2hour e-mail! I got bumped out and had to reset password to get back to you,anyway I will replace the tenp sending unit,its $12 at autozone and a cheap insurance poicy! I do have oxygen sensors 2 of them.One before the catalynic converter and one after So thats up in the air for now being $80 apeace!! I do have 4 new 235-75-15 goodyear tires I keep at 40psi but they will handle it! I have decieded to get 8.5mm new wires as my old are 3 years old.Plus a cap with brass terminals as I was told aluminum contacts won't last a year.Great advice!!! And I figure good platnum plugs won't hurt!Do you have a better suggestion for the best plug to use? And do you think a high performance coil might help?MSD mutifire coils are to much$$$$$$$$$$$$$$$$$$ so a $60 coil will do.That along with k+n air filter,Mobile one oil and filter what else might help me in MPG that I have forgot.I looked for an overdrive switch but have none.I put synthetic in the rearend $$$$$$$$ If you think of anything else ,e-mail me D-300 and thanks!
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There is no MAF sensor on a TBI or magnum engine so don't bother looking for one.
He's right, it's a MAP sensor in Dodges but it has a similar function, sensing the density of incoming air. It's a possibility oil from filters may foul either one and cause inaccurate inputs to the PCM.
 

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fuel filter? aftermarket exhaust? did you get the cone type k&n or the stock replacement? You can modify your air box to make sure you are getting cold air and not from beside or on top of the radiator. some simple dryer hose makes for a cheap "ram air"

Also I went to a training class put on by michelen tires and the concensus was the recommended air pressure gives the best milage. unless you are looking for more traction you don't need to run them low.
 

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As others have said, it sounds like you have a pre-magnum engine in a magnum era Van, but you have not confirmed this. Does it indeed have just 2 injectors in the throttle body?

If this swap was done by the previous owner, they would have had to replace the ECM/PCM/SMec or whatever the computer is called.

I don't see how a multiport fuel injection computer will correctly run a TBI engine, if at all. And since a TBI engine AFAIK only has one O2 sensor, what is that second one doing? Plugging a hole in the exhaust?

A MAF sensor heats a wire and determines air flow by how much the air flow cools the wire. Oil on this wire will obviously throw off this number.

A Map sensor has a diaphram and is measuring how much vacuum the engine is creating at the throttle body. I don't see how air filter oil, if it could make it through the vaccuum hose to the diaphram, would distort the reading. I guess the oil could rot the rubber diaphram.

City driving is certainly very variable depending on the City. If you Idle at a light for 3 minutes, accelerate for 100 yards to do it over again, then 10 MPG is pretty good for a heavy Van. I alway seem to have to hit the brakes for a light right after acccellerating up a hill, where 50 cars will have to stop to let one out.

Infuriating to say the least.

If indeed your engine is running correctly, then plugs, wires, cap and rotor really are not going to give you significantly more MPG. The CTS and O2 sensors if giving wrong readings will certainly affect the economy significantly.

So can a vacuum leak.

If your Van originally came with a v8 then it might have a taller axle gear ratio, and your v6 is struggling in that city environment.

Have you checked for Codes via the key dance? or a code reader?

And if the Computers and engines have been swapped out, could the Speedo/odometer simply be wrong, since it takes it's distance readings from the VSS or some other method and is getting reading for a different ratio or some such?

Go drive exactly 60 mph on a highway, and see if it takes you exactly 1 minute to go 1 mile according to the mileage markers, or find one of those radar speed displays, or a friendly cop with a radar gun.
 

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Mylestone
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Discussion Starter #12
hello

I can look at the TBI and I see no fuel rails on either side of the intake manafold .I didn't see a Mass air flow sensor feeding the TBI just a straight run to the air box(round)with no sensors inbetween.This v-6 has got me beat I will just live with 10MPG.With 80,000 on it I might go for the two o2 sensors.One before the catalynic converter and one after!But at $80 apeace its a big investment for a maybe on MPG.Have you thought of how to get more MPG besides a complete tuneup which I have just finished except for checking the timing as I have no timing gun!
Have a geat day
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4 Wheel Power Disc Brakes
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Two 02 sensors is correct for a '97 however TBI isn't. Something, most likely the engine and possibly the transmission have been swapped.
A magnum engine will also have a crank sensor that a TBI engine doesn't have were the engine and transmission bolt together.
 

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If it is a replaced engine/ tranny combo, and it has TBI, then there is no need for replacing the second after cat O2 sensor because as far as I know, TBI systems only have 1.

Isn't '97 OBD2, would not the codes be po1962xx or something? Would an OBD1 computer display codes on an OBD2 dash?

I think it is logical to determine which engine is in the vehicle, pull the codes, if any, from the computer, and then proceed.

After determining the engine is running correctly, the only thing I've ever heard of really impacting MPG, and only slightly, is removing the belt driven fan and replacing it with an Electric.

I have a friend who runs a performance shop who keeps asking me If I have installed a TB spacer yet, as he says the HP and Mileage gains are significant on a TBI set up like my '89 LA 318 TBI, or a carb'd engine. He has a Dyno, and more or less indicates I'm a fool for not having done so, yet.:ugh
 

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quick note

landyacht; i looked into the spacers pretty heavilly. but all the research pointed to the spacers not makin enough difference, to be worth the effort. although they help with hp & torque, for racing purposes, for daily driving, not so much. since i wrenched for many years, & have seen many different things tried. i pretty much stick with proven things for regular use.
for those of you who follow this stuff, i justed posted my mileage figures last week. i also concur with landyacht, without knowing exactly what your dealing with there are too many different paths to choose from to allow us to help you in your mileage quest. without the basic info, its just a crapshoot. if you arnt sure what you have, the best advice right now is to find a shop that knows the product, figure out what you have, post it then we will help from there.
but any way you look at it, the engine is too small for the load, & nothing will help enough to offset that, short of having a la, or magnum v8 reinstalled in the van. if that doesnt interest you, then good luck in your quest for better mileage.:rck:
 

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I have a couple of lists in terms of work to my VAN:

The NEED TO DO list.
The SHOULD DO list.
The WANT TO DO list
The At SOME POINT list
The IF I WIN the LOTTERY list.

There is a little room for overlap on some of the lists, but

A TB spacer is currently not on any of them.
 

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Seating for 12
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A Magnum 3.9L engine would look like this ...

 

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The link does not work.
 

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Mylestone, could you post a pic of your engine taken from the dog house side? This will help us to determine which engine you have in your van.
 

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