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21:27:08 - 11/03/2025
General Dakota Board
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sdd
Dodge Dakota
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3/01/2013
17:55:46
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 Subject: 3.9 tune-p and mods
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Message:
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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RalphP
Dodge Dakota
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3/03/2013
10:48:13
| RE: 3.9 tune-p and mods
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Message:
I can't say for sure on the first set, but for #5
- without resetting the SBEC to match the lower
thermostat, you run a strong risk of dropping MPG
as the motor never quite warms up to where the
SBEC decides "It's hot, no more idle enrichment
needed!"
For the rest - A good quality drop-in filter (Wix,
Purolator, etc.) is better for a daily-driven work
horse. The K&N requires oiling, and it's actually
the oil that captures the dust. I'm not fond of
that extra step of maintenance. Oh, and for a
"Cold Air Intake" - hey, look for where the intake
comes in NOW. Then consider most "CAI"s suck in
the underhood air ... Yes, they test better on
dynos, where they're sucking in cooler air, not
hot air trapped under the hood. Under the hood,
most so-called CAIs are HAIs, and will hurt power
and MPG both.
I presume the rubber flap is the one at the end of
the intake? If so, removing it may improve the
tone and sound - it won't make much difference on
the actual performance, though.
What's the advantage supposed to be for the IAT
relocation if you stick with the stock airbox?
What's your current injector duty cycle? Don't
know? It'd be REALLY helpful to know that to know
if you need to sync them any better.
As far as the others - before I fiddled with
either sensor, I'd get the books, a good XCAL3 or
whatever the hot deal is for a Mopar SBEC, and
learn how to tune the SBEC to do the fiddling you
want, instead of fiddling with the sensors (it's
usually better to alter the programmatic response
rather than alter the input signal on a control
system.)
RwP
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SDD
Dodge Dakota
JOIN HERE
3/03/2013
12:25:54
| RE: 3.9 tune-p and mods
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Message:
Thanks RalphP
I have a 99, sounds like SBEC are for 95 and older. My understanding is the PCM will adjust over time with the 180 therm and other sensor mods to improve HP and MPG.
I agree the location of the CAI has an affect on the performance. I will prob at this time just modify the stock box to improve air flow and temp.
From what I understand the IAT relocation from the intake manifold (hotter) to the CAI or stock box (cooler)( after the filter before the TB) will improve performance since it is measuring the air temp from a cooler source.
I do not know my duty cycle for the injector sync. My question was more about if the adjustment was worth it or not. I will check it and adjust all at the same time, if it is worth the effort.
I am a little fearful of messing with the stock TPS and Crankcase sensor. Unless the mods show improvement in MPG or HP.
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