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Discussion Starter #1
I am new to the site. Have a 99 Dakota, reg cab, 4x4, 5-spd, 3.9, 3.55 gears with 216,000 miles that we use for small lawn business. It tows a trailer with 3000 lbs on it about 50% of the time. Gets 18-19 mpg highway, 14-16 most driving, 12 or less towing.

I am looking for ‘real world’ info/opinions or pros and cons on tune-ups and any mods that are worth it.

Tune-up thoughts
1. Which Sparkplugs, Autolite 5223 (cooler plug) or 5224? AP5223 if have upgraded ignition? Any others?
a. What GAP?
b. Is it worth upgrading coil (Acell maybe?)
2. NAPA Belden Premium wires, new cap and rotor with brass connections?
3. Replace both O2 sensors? Has 216,000 miles
4. Replace Timing Chain?
5. 180 thermostat? What does the lower therm do?

Mods
1. K&N drop-in filter? Modify box? Real CAI, $200 does not seem worth it.
2. Rubber flap removal? May let in rain, snow, etc
3. IAT sensor relocation? Cheep just not sure if worth it
4. 5.2 Throttle Body swap? Sounds like a good mod, just don’t want to lose any low end. I will try to get from same year.
5. Injector Sync?
6. TPS adj? not sure worth messing with sensor
7. Crankcase position sensor mod? not sure worth messing with sensor

Looking for any thoughts that will give us more power without losing MPG. Or MPG without losing power. And without doing any damage to an older motor(216,000 and counting).

Thanks in advance for any help
 

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i put a 4.1 gear in my 2001. 3.9, auto trans. in town only my MPG went from 9 MPG to 13 MPG. but thats ONLY cause i drive in town ONLY. my hint. the dist cap has a vent in the top, plug it with JB-weld. it will keep the moisture out. took me 5 years to figure that out.
 

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To answer directly:

1. You don't want a colder plug. I use the 5224 plugs in my truck, they seem to work well.
a. Stock gap
b. No, don't bother.
2. I like brass terminal caps. I have the Airtex 3D1088A cap and rotor on mine I picked up at Rock Auto. I use the Standard Motor 7649 wires (very nice). The 27649 wires are on wholesaler clearance at RA right now, dirt cheap, but don't know if they're as nice.
3. I wouldn't bother unless you start getting codes or your mileage tanks. If you do replace them replace the front(s) only and buy NTK branded stuff. The rear is only there to report whether the converter is working or not. Looks like you're doing good with fuel mileage right now.
4. IIRC, 98+ has a factory tensioner installed. I would only do that if you're feeling really ambitious, or hearing excessive noise, getting codes, etc.
5. I would just stick with a stock thermostat. These trucks don't get heat in the winter with anything lower.

Mods
1. Stay with paper, K&N is more nonsense than it's worth. They plug up and require frequent cleaning.
2. I wouldn't...
3. I can only see this worsening mileage.
4. Pointless, bores in intake need to be opened up to see any benefits to this.
5. No experience here...
6. Unless it is idling funny it's probably fine
7. Not too sure either

A cheap mod to help improve flow at the throttle body would be to bend up a 1/4" rod to take the place of the factory stud arrangement. You probably won't notice anything from this though.

Other things I can recommend are headers, a crank under drive pulley, numerically higher gears, and an electric fan. Headers really woke mine up, but be advised that the factory bolts are known to snap off in the heads... The crank pulley I have did cause my stock 90 amp alternator not to charge at idle. If you have the 136 amp it shouldn't be a problem. It did help mileage, and I noticed a slight increase in power. My truck really liked the 3.92 rear I put in it, but it is an auto, and I don't know what the 5 speed gearing is like. I just put an electric fan on my truck, and this made the truck feel a lot smoother and freer revving.

Ford 4 hole injectors are another popular mod. I just put some on and didn't feel any power gains. Still waiting to see what fuel mileage does. Some guys have modded kegger intakes on their trucks and have reported power gains. I did one, but still need to install it. 1.7 rockers are another one of the popular mods I haven't tried.

the dist cap has a vent in the top, plug it with JB-weld. it will keep the moisture out. took me 5 years to figure that out.
Caps are vented to allow moisture to escape to prevent cross-firing. If you were getting water, it's likely your hood seal has issues.

Hope it helps!
 
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