Hi, I have a 1999 Ram 1500 5.2L and I am getting 10.8 MPG average with a mix of highway and city driving. I have changed the plugs, wires, cap and rotor. I just changed the IAC (after checking the fuel economy) and I have the hughes plenum kit installed. I also replaced the ignition coil proactively. (Accel coil, cap and rotor) I haven' rerouted my ignition wire yet. (7.5mm wires) I resolved all of my known vacuum leaks but I can sometimes hear a noise that sounds like a vacuum leak while accelerating. I have no idea if my cat is clogged. The truck has more power than it did when I bought it and it idles pretty well at 600RPM. (a little smoother since the IAC was installed) I replaced the precat O2 sensor due to a CEL.

My question is: what should I do next to try and improve the fuel economy? Throttle position sensor? MAP sensor? Camshaft position sensor?

Also would a new timing chain set make a big difference in performance/fuel economy? (or even smoother idle)

 

Trade it in on something else......

 

The only other thing I can think of is cold air intake WITH a function hood that will force the air in other then that (as mentioned above) trade it in. I'm getting 15.2 MPG with a mostly City driving.

 

Umm, 15.2 in city driving? Stop and go? I don't believe that. These engines can see 15 on the hwy but not city. Also, 11 is a tad low unless you push it hard. I coast a lot and use the torque to gather speed shifting quickly to 3rd and 4th. I see between 12-13 and I've done everything to maximize mpg. Best tank ever was 17.9 non-stop hwy at 60mph. Worst tank was 9 towing in winter.

OP: I would replace the cat with magniflow, throw on a KN filter (dropin) and run some seafoam through it. Then run a tank of Chevron (best gas) and a couple bottles of Techron. Go real easy on the throttle keeping the rpms below 3k. You should see 13mpg. Also use stock heat range Champion plugs and air up the tires to their max.

 

Thanks Ramman. The cat might be clogged. I may order a magnaflow universal cat. (or should I get a vehicle specific?)

It downshifts sometimes and other times it won't and sounds like a vacuum leak. (whistling noise almost) It will only do that under load, not at a stop. It did have a bad plenum before I replaced it with the Hughes kit. I was thinking of adjusting the kickdown cable and it wouldn't have to work so hard as it would just shift on time.

Truth be told, I don't daily drive it, it is a project for my son. We work on it and test drive it mostly. We drove it an hour away to get a used rust free (Texas) fender recently and I filled it during that trip. (1/2 highway I would imagine) I'm not easy on the throttle when we test drive it after a project. (though I don't beat on it either)

I used to have a 1996 5.9L and I got about 14 most of the time but that was years ago. I would get close to 16 on the highway. It didn't matter if I pulled a large boat or not, I got about the same mileage. Maybe it is my driving habits. Lots of small trips and too much idling could be part of it. Who knows how long the kid has it idling for. (he doesn't have his license yet) Also, it idles better after changing the IAC. I want it to idle perfectly and it is almost there.

When I bought it, I had to replace the fuel sending unit. It had a bad fuel pressure regulator. Now it is starting to lose fuel pressure when it sits again. (though not anywhere near as bad) I did the injector o-rings and they went on really really hard. Maybe one got pinched and is leaking pressure, who knows.

I posted some videos of our 'project' on youtube. I am painting a rust free fender and installing it soon. https://www.youtube.com/channel/UCGR...BPhwaQh_MS2rPw I have a lot of video to add but I don't edit video so my kid is going to do that part.

It is a good looking truck and we have done a lot to it. I hope it isn't something like a leaking head gasket causing that noise though.

 

You don't have to believe that but filling up a 25 gallon tank and then dividing by the miles driven on that tank of gas and that's the number I got 3 times in a row. If I told you what the truck had you definitely wouldn't believe it.

OP: I have 4.56 gears, cold air intake with the SSK hood, engine modified a tad (have about $650 into it), TB spacer (supposedly useless but it's purple chrome so I left it, headers with true 3in dual exhaust, MSD coil and wires, Iridium TT Plugs, only run 93 gas, and a few others I'm probably forgetting

 

Thanks Mopar Fanatic. I don't know which gears I have. I haven't tried higher octane gas. I run the 87 octane that is the cheapest in Minnesota. (10% ethanol) I do not have the death flash so I think it would benefit from higher octane gas. I can try that for a tank or two and see what happens.

I also put in the FFDynamics electric fan conversion and I have the Spectre cold air intake. (not connected to the hood though) I put up 3 videos so far and talk about several things we did to the truck so far. I like being able to stand in the engine bay and work on the truck. It almost feels like cheating as it is so easy to get to most things.

If anyone has any other ideas, please let me know. Knowing it had the bad plenum, are there any other parts I should look into? How about the hall effect sensor in the distributor? Should I change that or the MAP sensor? I'm not afraid to put a few more dollars into it. How about the timing chain? Has anyone done this and what was the effect?

Our truck has 143,000 miles on it.

Thanks,

 

There are three major things wrong with these trucks that affect gas mileage: No aerodynamics, heavy truck with little HP motor, and no Mass Air Flow Sensor. Changing the sensor I don't think will help much IMO. The basics to gas mileage is less friction, less throttle to move the vehicle (this is where higher HP comes in), and more air and freer flowing exhaust. Depending on your budget I would do headers and new exhaust and maybe truck to either reduce weight or bring up hp. You can change your driving habits and drive like an old man, just enough throttle to move the vehicle and don't punch it up hills (you will lose speed greatly). These trucks are good towing rigs and yes the engine bay are huge. You could also try a 180° thermostat idk if that will help and that you will see. I am eventually going to swap a 600HP hell into my truck. Honestly though the gas mileage varies by person (and by truck it seems) one person gets 20mpg ones gets 5mpg

 

I did my t-chain at 200k. Only thing I noticed was less 'rattle' when turning it off. No other changes or improvements. If you're not sure how much time it has idled, or only take it out after you've done something to it, then you need a good couple weeks of daily driving to see what its mpg really is. Your test model is bad.

The whistle could be coming from the intake. You have an aftermarket unit? Check the connection. My stocker whistled after the plenum job cause the shop forgot to seat the ring properly. My 14x3 had lots of noise also. I went back to stock a couple years ago and its much quieter.

 

I would replace the timing chain. I did it on ours at around 150,000. It had a lot of slop in it. I would add shorty headers, do something with the cat, and a nice exhaust. Some guys have installed 1.7 Harland Sharpe rocker arms. With the age of our trucks, I'm considering replacing all of my sensors. Mopar are best, and NTK O2 sensors. Check your gasket on top of the throttle body for the vacuum leak sound. I think you said you have E fans already. I changed the axles, power steering, and transmission (when it was rebuilt) to synthetic oil. If I ever rebuild the engine it will get Amsoil also. MPG is hard to judge. One guy has 60 stop lights on a 5 mile hour long commute, the next guy drives 15 miles in 15 minutes. Do you live in mountains or on flat ground? Sea level or 5000 ft? And of coarse how it's driven. Seems like you're headed in the right direction.