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2nd gen ram mileage/mpg improvements

Mopar_Fanatic

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Hey everyone, I'm looking to improve my mileage I'm my 01 ram. It's a rcsb 2wd with a 318, 3.55 gears, and a 2/4 drop kit (the front at least, it's been too damn cold to do the rear). Currently, the truck has a 3x14 air cleaner, a set of shorty headers, stock y-pipe to a 2.5 in/3 out flowmaster with a 3 inch side dump. Anyways, the truck has been getting 11 mpg with mainly highway driving. I've been chalking this up to mainly letting the truck warm up for so long (hell has frozen over in Iowa recently). If anyone has some ideas, I'd greatly appreciate it

Thanks
 
Pardon my ignorance, I'm a General Automotive and Light-Truck mechanic, now retired; but what is rcsb?
Is that truck a stock 5.2 Magnum/Sequential injected/overdrive?
or a transplanted low-perf LA318 carbureted?
How fast are you driving and how high is the engine reving?
I'd start with a compression test before I did anything;
and then if the pressure is up and even, see below.
a 3x14 air cleaner, usually indicates a carburetor; so what carb is on what engine? and how good a tune is in it?
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General info:
If your vehicle requires 50 hp to cruize@65, that translates to 15.6mpg, about the best yur gonna get. But,
if your carb is 10%fat, and the engine sees lazy timing, which loses another 10%, now yur down to 12.5
If you clean up the airflow under and around the vehicle, and lighten it up, all so that now it only takes 45hp, that will translate to 17.3mpg. If you then lean it out and add a bunch of timing and get the pressure up to 190psi, well you could see another 20%, so now up to 21mpg .
The stock 318/5.2 cam makes peak torque around 2400rpm, but it will pull pretty clean down to 2000, on a good combo, down to 1800. If you have an A518 and 29" tires, yur gonna be down around 75=1850, like I was. But whereas I was pushing 3650 pounds with a sleek 68 Barracuda, that cuts thru the wind pretty good; not so with your pick-up. To get the big EFI numbers, you are gonna have to slow down. But if you drive too slow, and the rpm gets into dirty fuel delivery, then the economy goes down again.
Ignition timing, weight, and speed. are the big players when it comes to sipping fuel.
My 68 Barracuda, in one iteration, was able to get over 30 mpgUS, with a modified 600Holley, at 3650 pounds, geared for 75=1850rpm, and cruise timing of more than 40*
The other things that affect your economy, are warm-up routine and driving style. Even in my 2014 Orlando 2.5liter, DOHC/DI/6speed auto, CUV; winter driving can cut my overall average in half.
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The following is for a carbureted model;
>>Here is a test I developed for my carbureted vehicle.
You have to know your cruize rpm.
Then in Neutral, I just reved the engine up to that cruise rpm, and started feeding it timing until the rpm peaked, then cranked the rpm back down with the speed screw. Then I just leaned out the AFR, until it wouldn't maintain that rpm. Then I added more timing to see what would happen. In my case, it liked a bit more.
So, now I had a baseline to shoot for.
With a load on, it liked a little less timing and a little more fuel.
Now, when I got my overdrive, this changed the Cruise rpm, so I had to redo this baseline.
Bear in mind that my various iterations have run various pressures from 185 to 195 psi CCP (Cranking Cylinder Pressure. (with alloy heads).
Of course, anytime the baseline timing is changed, you have to always check and limit the Power-Timing for the fuel you are using.
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But if you have an EFI engine;
I'd put a scanner on it and see if the sensors are all up to snuff,
and I'd clean the injectors.
With a factory ECM, you're kindof fubarred, in that, you get what the ECM was programmed to give.
In this case, if your engine still has a distributor, I would check the sync on it, to make sure that when the ECM is calling for 40 degrees, that the engine is actually getting the full 40 degrees......... cuz the ECM makes all it's decisions on the baseline timing. If the baseline is wrong, it's ALL wrong, and it depends on somebody having set the baseline, cuz it doesn't actually know what the baseline is.
And, if you have a knock sensor, that is pulling timing or has recently pulled timing, and is still in recovery mode, some of those ECMs require several driving cycles to give it all back. That is gonna suck and that is why you need a graphing Scanner to catch it. Then you have to figure out what caused it and how to prevent it from happening again.
BTW
Like I said, I'm a General Automotive and Light-Truck mechanic, now retired. So, IDK chit about your truck, lol.
 
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AJ,
I apologize, I should've given more information.

The truck is a reg cab short bed (rcsb). the truck has a magnum multipoint efi motor in it, I built a bracket for the filter because I wasn't going to spend 500 bucks on a cold air intake. It has overdrive with 255/55r20 tires (31 inches) and cruises at 1600rpm at 60mph. Being that the torque band is up at 2400rpm, would it be smarter to cruise at 70ish? I'm planning on doing 4.56 gears in it, not for mileage, but for some more go.

Let me know if you need any more info about the truck.

Thanks,
 
Being that the torque band is up at 2400rpm, would it be smarter to cruise at 70ish? I'm planning on doing 4.56 gears in it, not for mileage, but for some more go.
The faster you drive, the more power it takes to overcome the air resistance, which is guaranteed to cost you more gas. But as we found out many years ago, if the engine becomes more efficient at the higher rpm, then you can break even or even win. What I'm talking about is early 60s Big-inch carbureted cruisers that got better mileage sometimes at 85mph, than lugging along at 60.
Or like the 340 Mopars, where the cam was all wrong for a cruiser.
Additionally with a higher cruise rpm, comes more internal engine friction., also costing power.
With 31" tires, your 3.55s are comparing to 3.09s with 27s which are the typical tires that most street-rodders run, so, 4.56s would be a 28% improvement all round. and Cruise rpm would be up to 65=2200, which obviously is a more efficient rpm to be at. Whether or not you'll get better steady-state fuel-mileage remains to be seen. But yes your take off will be much improved. and so, it might cost less fuel to get up to speed.
Plus your engine will be working quite a bit less hard at the new Cruise rpm, therefore pulling a higher vacuum, Which your ECM should properly interpret and crank up the timing and down on the fuel. If it does that without annoying the knock sensor, that is guaranteed to decrease fuel usage.
I hope your ECM knows that you are running 3.55s. Cuz if it doesn't then she won't know you vehicle speed. which it uses for some of it's calculations. and if the calculations are wrong, then the economy takes a dive.

I would still do a compression test to get an idea of the health of the engine, I mean it is 25 years old right..... and again, if the pressure is up and even, then I would put a scanner on it, and check the sensor outputs; and I would compare the engine timing at say 2400rpm on the balancer, with what the ECU is commanding, to be sure they are synced up.
And, you gotta be sure your O2 sensors are working ......... you do have O2 sensors right?
Without working O2 sensors, your check engine light comes on, which you might thing not much about, cuz the truck is running just fine; but If the light is on because of the failed O2 sensors, then the ECU has been forced to go into limp-in mode, and the programming has fallen back to the pre-programmed warm-up program, which is often killer-rich and lacking timing, and away goes your fuel economy. So, if you don't have a scanner, and your CEL is on, I'm not feeling sorry for your 11mpg, lol. However, IMO, if your combo is is only getting 11mpg in steady-state cruising, my guess, is that the ECM has been deceived. Check your tailpipes; if they are black and sooty, that's part of your problem.
I highly recommend to buy a good quality scanner and learn how to read it. If everything is working the way it's supposed to, then you will have a hard time improving fuel-economy.
FYI's
The rule of thumb is that a reduction in rpm, by percentage, will improve fuel economy by half of the reduction, in percent. So like, if you drop the rpm by 10% you should get a 5% increase in fuel-economy. That 10% reduction could be just slowing down, too.
But in your case, the 31" tires have skewed this rule up a bit.
If you want to see what 4.56s will do to your fuel economy, Just run the rpm up to ~2400 in Direct/LU, which should be about 58mph, and see what happens.
Warm-ups in winter will decimate fuel-economy. It'll be cheaper to run the block heater for ~4 hrs on a timer, to shut off when you get in the truck. Run a multigrade like 5W20 in winter, cuz your Magnum has roller lifters. Give it two minutes and drive!

Some other things that suck gas are;
soft tires, dragging brakes, tight U-joints, a bad alignment, and an overfilled crankcase. Also, tight wheel-bearings; which if you have those cartridge type deals you can't do much about. Tailgates IDK about.

IMO,
A 5.2 injected Magnum, in a full-size Ram pushing close to 5000pounds (I'm guessing) thru the wind cruising at 65=1600, is gonna have a pretty big throttle opening, with a correspondingly low engine vacuum, and I have a feeling the ECM is not gonna fuel that correctly. I suppose you could put a vacuum gauge on it and see, but the scanner will read that too, and more accurately.
If the vacuum goes below about 13 inches, a carb would be tickling the "main circuit".
By about 10 inches, the mains are flowing.
By 7>/8 inches the power system would be engaged.
The EFI System doesn't have 3 separate systems like that, but on the fuel map, you can still see the injection time rapidly increasing as the vacuum goes down. The problem with a low vacuum, is that the ECM doesn't know exactly why the vacuum is low. It may be thinking your climbing a hill, so it just injects what it's been programmed to do, and cuts timing to keep the engine out of detonation; which for cruising, kills the power, and is the wrong thing to do...
And since I'm not an EFI guy, I don't know any work-arounds for that kind of chit, lol.
For a carb'd engine with deep hi-way gears, the vacuum goes down too. But I am the ECM, so now it's up to me to figure out how to get the cruise-timing that the engine desperately needs, in that circumstance. And when I get it, I can lean the carb out.
 
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AJ,

The truck doesn't have a CEL or any codes, but huffs a little blue oil smoke on startup. I'm going to say the motor is slightly wore out (no, I didn't check the mileage on the parts truck, that's a boo boo on my part) but, I have a 360 magnum with 60k on it to solve that problem eventually. Now, the tailpipe isn't really sooty, but you can definitely smell fuel when the truck is running.

When going down the road in od, I'm really not laying into the truck at all, but if I take my throttle position it takes to run 60mph in od, it'll run about 68-70mph in direct drive. So I don't know how hard I'm really lugging it. I'll definitely try the mileage with the od off and report back.

Thanks,
 
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If the truck does not have a CEL (check Engine Light), then how does it communicate to you that one or more of it's sensors are malfunctioning?
 
If the truck does not have a CEL (check Engine Light), then how does it communicate to you that one or more of it's sensors are malfunctioning?
Sorry for the confusion, I meant the truck doesn't have one on, as in it currently isn't throwing any codes
 
Well, assuming the O2s are working as per their design, and with no cell, me the carburetor guy, hasn't got a clue how you can coax anything more out of the engine, with the factory ECM, other than ;
making sure the cylinder pressure is up and even, and
the fuel pressure is on spec, and
The engine is getting up to spec-temperature, and
the injectors are spraying nice patterns, and
all the sensors are working on spec.

After that, if the convertor locks up at cruise,
and the chassis ain't dragging, the only thing I got left is soft tires.


BTW
I'm not an EFI tech, and it's been about 35/40 years since I went to an EFI seminar, so don't quote me on this.
From what I remember, your truck has a speed-density system.
This system bases it's "speed " calculations on rpm; and it bases it's "density" decisions on Two or three sensors that your ECM is monitoring. All it's fuel calculations are based on those, with trimmers from the others.
But Density is a whole can of worms.
Air-Density is not measured directly unless you have a flapper valve in your intake, which hasn't been used in a few decades. So, it is inferred from the temperature of the incoming air, and the baro-sensor, and the throttle position sensor, and and and, so on, but the engine temperature sensor is the main controller.
So then, as soon as the key is turned to or past, "on", the ECM checks the engine coolant sensor and the barometric pressure sensor and the Throttle position, and the rpm sensor. From the CTS and Baro, it shuffles thru it's pages and page and pages, to find a match, selects that table for it's main page, and begins the " injector on-time process". as to rpm and tps. From those, it modifies the "on-time". then it looks to it's other sensors, like inlet air temp and manifold air pressure, and modifies the "injector on time some more. All of this happens on the first revolution during cranking while the ECM is looking for TDC compression #1 from the crank and/or cam sensors.
As soon as it has found the intake stroke, KABAM! it injects, and fires. and quickly checks the rpm sensor to see if it's running yet. As soon as it finds the engine running, it starts leaning it out, and closing the AIS throttle controller. then it keeps doing that while waiting for the CTS to change, so it can move to the next page. Finally the ECM recognizes that the engine is warm, and switches the O2s on
Here are a few very important things;
1) the entire system depends on somebody having set the fuel pressure to a factory spec and
2) If the coolant temp never comes to the temp-spec that turns the O2s on, then the engine will stay on the warm-up map forever; which is always rich, and with retarded timing.
3) the ECM usually only checks the baro-sensor at start up. If you are climbing up a mountain, the engine will eventually go lean and give you driving problems. The cure is to pull over, shut the engine off, then to "on" which will reset the ECM to that new higher elevation, and she will select a new injection-map. Start it up and go.

Now, the ECM also checks the IAT, which is usually between the air-filter and the throttle body. It uses this sensor to modify it's injection event. If yours is missing or has been bypassed, well, you get what you get. Some early EFI-systems had a system which mixed hot-air coming off the exhaust manifold with air coming from in front of the rad, to always have a constant Inlet Air Temp. IDK your system, except you told me you had a 3x14 air cleaner on it, and I'm guessing it's an "open type" sucking underhood air...... the temp of which can vary from ambient to 200 or more degrees. The ECM is not programmed to guess. So if you bypassed yours, with a resistor, it will be/or could be, right, at exactly one temperature. The rest of the time, the injection event will be dead wrong.

Ok so, that's all I know, and not all of it might be right, lol.
But if you had a scanner, you could prove me wrong just by watching the sensors.
 
AJ,

I really appreciate all the help, everything has been super informative. I will say, for you not being an efi guy, you sure know your crap. I dunno if any exhaust leaks before the 02 sensors would mess with their readings or not (still chasing them from the headers).

Now, say this is a truck with a carb you can't mess with. What tricks would you have to pick up some mpg? I'm going to pull some weight by dropping the factory spare and drop in bed liner, along with switching to a sport bumper (not entirely sure if it's lighter or not). I also plan on switching to an electric cooling fan to free up some HP, along with 4.56 gears and a posi for some more fun.

I dunno if someone with some experience doing these mods on the 2nd gens can chime in and give their 2 cents, but I'd like to get back to the mileage I had with the 6 banger of around 15mpg (I figured the V8 would get better mileage, that v6 was working it's tail off moving this truck)

Again, thanks a million for the help. I really appreciate it
 
I if any exhaust leaks before the 02 sensors would mess with their readings or not (still chasing them from the headers).
ANSWER
Yes, if the headers are sucking air at the head, then the O2 will read lean, and the the ECM will compensate with added fuel Of course with headers, ALL cylinders will now go rich. You will need to pull all the plugs and look.
Now, say this is a truck with a carb you can't mess with. What tricks would you have to pick up some mpg?
Oh boy, with a carb I can't touch? That's a toughie.
Lemmee think
Well, on a carb, firstly, I'm gonna install a spread-bore, metering-rod type carb, like a Thermoquad.. Next,
I can't do much with the low-speed circuit anyway, so I'm gonna play with the fuel level, and
and I'm gonna map the timing, and see where I can improve it.
and for sure I'm gonna check the cam-timing, and look for worn lobes.
and I would NOT have installed headers. Sorry man, especially not shorties. but for sure it would get dual exhaust. New plugs and a base timing reset is next on the list.
Then I'm moving on to the chassis. You already have an overdrive, and a LU so that would be my first go-to.
Next I would install my G-tech ProSS, and I'm gonna see which items on the chassis are costing me money. I'm gonna do a bunch of coast-down tests in Neutral, and see what's slowing me down the fastest, find out if that's acceptable or not and if not, I'm gonna fix it. The G-tech is just an accelerometer with graphing capabilities. It is normally used to diagnose power problems during acceleration. But it works in both directions. You can measure how much power is being consumed by the chassis, by coasting down in neutral. The tool measures speed and rate of deceleration, and after you have entered the details it asks for, it can graph a reverse power line. Then you go make a change and repeat the test. This you can see what 45 psi tire pressure can accomplish over 40, over 35. Or how much power dragging-brakes are costing you. Or the 300 pounds of dead weight in the box, or even how much power the closed TGate is costing you. And so on; no more guessing and hoping. Just the facts man, lol.
The 5.2 Magnum cam is a reasonable piece, but 65=1600, is a bit of a low stretch for it. I think that can make it work with a carb that I can adjust and I can get an easy 20 mpgs out of it with a screwdriver and a timing light, in my Barracuda @3650lbs, car and driver. But my Barracuda takes forever to coast down from 65 mph...... meaning that the chassis is costing almost nothing more than it it's weight. With that gear ratio, in a manual trans, I have taken a 360 with a 2.5 sizes bigger cam, to over 30mpg, but that is working all the angles.
IDK how much MPG can be had out of a 2001 full-sized Ram.
BTW, when I talk MPH it's always point to point, like a day trip on the freeway, with no stops between filling stations One more BTW, if your speed-o is not calibrated for those 3.55s, then you cannot use the odometer to measure miles travelled. But I'm sure you would know that. Not only that, but the ECM is counting revolutions of the driveshaft to compute how fast the vehicle is going and it uses that information in some of it's calculations. So, the ECM needs to know what gears are in the back, and what size tires are are on the axles. If your truck originally came with 29s and 3.91s, that's gonna measure 2946 rpm. Whereas with 31s and 3.55s, it measures 2502, a difference of 15% which is a lot!
In terms of gas mileage, since the rpm has gone down 15%, you might expect the mileage tom have gone up, a like amount, over 11, makes it 12.65 by the math alone..
also plan on switching to an electric cooling fan to free up some HP,
Comment
IMO if you have a Thermostatic Fan clutch, this is a waste of time and money.
 
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My truck came factory with the 3.55s and I calibrated it for the 31s, so the speedo is accurate. For the G-tech deal, if my phone has a gyroscope (basically reads where the phone is and the angles it's at) is there something I can do with that to find my deccel G's? With the exhaust leaks, turns out the header bolts loosened up a lot, so that's an easy fix. Also, usually my tires are at 35-38 psi, so I'll try bumping them up to like 42 (max 44) and see what that does.
 
I have heard that you can download an app for your phone, but I'm not a techno-geek, so you're on yur own with that. lol

The problem with running high tire pressures is two-fold; IIRC you are running 20s?
1) the ride with low-profile tires is harsh enough; and it only gets more harsh, with higher pressures.
2) the tires tend to burn the centers off faster than the sides. With expensive tires, the cost of the tires can quickly offset the savings in fuel.

On the other stuff, yur doing good. Best of luck to you.
 
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