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DakotaDog
Dodge Dakota
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6/10/2008
08:25:56
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 Subject: Exhaust Temperature
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Anybody know what the typical exhaust gas temperature range is for an unmodified 2000 model year 3.9L Dakota is?
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well
Dodge Dakota
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6/10/2008
19:38:29
| RE: Exhaust Temperature
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hold your hand on it for awhile and take your best guess
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DakotaDog
Dodge Dakota
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6/11/2008
12:42:36
| RE: Exhaust Temperature
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I was hoping I might get a better answer than that. Here's what I found looking around on the web (if anyone knows different, say something).
Something like 700F at idle.
At wide open throttle:
<= 1470F rich
1550-1650F roughly ideal
=> 1700F too lean, possible engine damage
>1800F dangerously lean
Of course this depends on where you're doing the measurement. Typically it is measured where the pipes intersect from the exhaust manifold.
I read somewhere else that 1600F is the max you want to operate at.
I'm actually going to measure it on my truck, but I wanted to get an idea of what range the thermocouple should operate in/where I should install it, so on so forth.
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dakota49
Dodge Dakota
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6/11/2008
20:24:00
| RE: Exhaust Temperature
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DakotaDog, the problem is, you will get different readings under different operating conditions. For example, if you are cruising along at 60 MPH on flat ground at light throttle, it will be a lower temp than going up a hill under full throttle (a higher temp) and as you stated it can change by where you put the probe usually the closer to the manifold the hotter it will be, also, while going down hill with your foot off the throttle the temp could drop very low. (Nothing to worry about, its normal) I have had a lot of experience with an EGT (exh.gas temp. ) but it has been with big trucks only, i.e. diesel engines. It sounds like an interesting idea to have one in your truck, mostly people only add them to diesel powered pick ups.
Good Luck
Dakota49
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DakotaDog
Dodge Dakota
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6/11/2008
22:49:43
| RE: Exhaust Temperature
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I've read up a lot on "closed loop" operation and it has become clear to me that there is pretty much nothing you can do to increase mpg in these beasts by putting in fancy plugs, wires, caps/rotors etc. I've done all of the above with zero or negative results. I see in the forums where others have had the same experience. The PCM computer is too good at adjusting for any changes you make - so your net mpg stays the same.
Even throwing it into neutral at stop lights and costing down hill in neutral has only netted about +1 mpg on average (this is referred to as "hypermiling"). Reducing friction and drag would also help so I've been thinking about how to do that also.
But I've been watching instantaneous mpg on the trip computer and noting that everything goes to sh*t when I'm in heavy traffic (I do a lot of that). So I was thinking I might try leaning out the mix by offsetting the upstream O2 sensor voltage and using HHO injection. HHO is supposed to reduce NOx while running lean, so your catalytic converter continues to work. Theoretically, you could lean it out until the O2 level starts to rise downstream of your cat. I know this is probably all snake oil, but I'm committed, so I'm going through with it to see what happens (worst case is I end up with an HHO generator I can make a cutting torch out of).
Running lean increases your exhaust gas temperature which can damage your engine, so I want to monitor that.
If gas prices keep going up like they have (regular is $4.01/gal here today), there's going to be a lot of interest in this sort of stuff.
==============================
2000 3.9L V6 2WD Quad Cab SLT Automatic
91K miles.
Solid Tonneau cover.
Tires: Yokohama AVID S/T P275/60R15 107T
K&N Stock Replacement Air Filter
Taylor 8.2mm Spiro ProWires
Napa M026/MO28 Cap/Rotor
NGK V-Power FR5-1
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Todd Bouton
Dodge Dakota
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6/12/2008
14:21:14
|  RE: Exhaust Temperature
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Just wait daddio will chime in with the correct answer. He knows everything, so he thinks. At least he says he does in his email to me.
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DAKOTA49
Dodge Dakota
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6/12/2008
19:07:38
| RE: Exhaust Temperature
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DakotaDog, I have had good luck with using Halo plugs, but mine is an 88, so that may make a little difference. You can use synthic oil in your trans, (if manual) or syn. auto trans fluid, as well as using syn. in the drive axle. All of these will work. I understand how you feel about making changes and nothing seems to help. I have had a lot of good luck with different things, like the plugs, I first used Bosch Plus2, they did great for about 1000 miles then they started missing, so I switched to the halo's and it made a big difference, easier starting, smoother running and better fuel mileage. Another thing that can really help with fuel mileage is the up stream o2 sensors. If you have to replace them, try to use only the NGK's they are the factory install, and they made a big difference in my fuel mileage. With a Bosch I was getting 15-17 MPG after replacing it with a NGK my fuel mileage went to 18-19, the Halo plugs boosted it to 19-20, I have gotten up to 22, but those were the unusual, not the norm.
Mine uses the throttle body injection, not the port fuel inj.
Good Luck
Dakota49
1988 3.9 4x4 5SPEED
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DakotaDog
Dodge Dakota
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6/12/2008
21:49:53
| RE: Exhaust Temperature
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Tried Halos. Sent 'em back on the 30 day "no risk" guarantee (but they haven't refunded my money yet so I'm wondering about the "no risk" part). The old plugs definitely needed changing, but the Halos seemed to slightly degrade my mpg, even though it ran better. Runs as well with the $2.00 NGK FR5-1.
The new upstream O2 sensor seemed to work for a while, but then back to normal mpg again.
One thing that really killed my mileage was taking the crappy old stock wires and corroded cap/rotor out and putting in the shiny new Taylor SpiroPro wires and the M026/M028 brass cap/rotor. Immediately lost about 1.5 mpg. I double checked everything and it's all hooked up/connected right, seated right on the connections, engine runs smoothly. Only thing I can figure is that the lower wire resistance is causing high EMI (ElectroMagnetic Interference). The coil wire runs right in parallel and touching the Fuel injector harness (crappy design) so I moved it tonight to see if it makes a difference.
I will also try the synthetics (already using sythetic engine oil), fluids are due for change anyhow.
I'm going to keep working on it 'till I get results.
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J and J Auto
GenII
6/18/2008
02:27:18
| RE: Exhaust Temperature
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Message:
very interesting
my stock dakota 95 4x4 got 17 18 mpg
now I get 20mpg winter 24 25mpg summer
If the halo plugs decreased your mileage and
power that tells me you have a big problem with
your air/fuel ratio
This is the key my friends the air/fuel ratio
must be right and readjust for any increase in
flow
The 3.9 has no knock sensor so if you move the
crank sensor the comp thinks its at 10 but really
its at 14 does it knoe the diff hell no
You can add a Nordask anolog A/F meter for around
$250 the guage is around $120 now you must weld
in another o2 bung run it not more that 6" from
exsisting upstream o2 and run it on its own o2
sensor
Now while crusing this ratio should be right at
14.5 to 15.0 there is your gas mileage leaner no
power richer sucks gas
To check this just take just a LP gas torch and
stick a hose and a tee in the PCV line temp turn
on the torch and watch the ratio change and
readjust itself if it does not you have some
serious A/F ratio problems going on that need
to be takin care of
This is a very easy and inexpensive way to test
the system operation
under excelleration droping to a ratio of 13.5
12.5 is a very good power ratio coasting down
the road no throttle upto 16.5 is normal with
no load
the nordask will read from 12 to 18 A/F ratio
I bet you any amount of money saying better
plugs hurt mileage and power that you have a
very serious air/fuel problem that most shops
would never even have a clue how to check or
haow to fix
Just over a .2k ohm los in the signal in the o2
signal wire will create havoc with the ratio
You need to take a closer look at what is going
on there is another factor here as well some
of the computers even new do not work like they
are suposed to these are the trucks that never
get good gas mileage and do not respond to any
mods even make it run worse
As Hughes Engines put it most would be better
getting a new computer that works right than
doing any mods
This is about 1 in 8000 trucks have this problem
but it does exsist and is hardly ever found or
fixed and the poor guy goes on forever trying
to make it run beter use less gas and never gets
ahead
It takes a very savy tech to find and fix one
of these problems and they are virtualy none
exsiting in 99.9% of the shops, dealers and
garages very hard to find a guy who truly
understands what is going on
Larry
J&J Auto
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DakotaDog
Dodge Dakota
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6/19/2008
13:48:29
| RE: Exhaust Temperature
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Message:
250+120=$370 doesn't seem so inexpensive to me. :-) I'll try to check it somehow. I have an old oscilloscope someone gave me, I can monitor the voltage on the O2 sensor and see if the computer is adjusting the A/F ratio up and down with time. Maybe try to estimate off the voltages and O2 sensor curves. I will also check the wire resistance between the sensors and the computer.
The problem (for me) is that gas mileage depends on so many different things that change from tank fill to tank fill that it's hard to get an idea if anything worked. So if next fill you sit in a bit more/less traffic, pump is different, gas is different, weather is different, the mpg goes down or up. You tend to see what you want to see. I can get something of an idea by judging the overhead instant (not average) mpg meter. Did not see a significant difference on the Halos - for an extra 7 bucks a plug, I'd expect to see a big difference. So I sent 'em back. They did make good on their guarantee and refunded my money by the way.
I will tell you this, I changed over to synthetic fluids over the weekend and I could really feel the difference in how she coasts in neutral. I would recommend that mod to anyone. The average mpg is higher also, but hard to say because the traffic is less since school is out for the summer & all the moms are staying home (must be nice).
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J and J Auto
GenII
6/23/2008
00:19:07
| RE: Exhaust Temperature
IP: Logged
Message:
You got that a little wrong
The bung guage and o2 sensor all togather
around $250
The anolog nordask
guage $120
nordask quick reacting o2
sensor $89
bung $5
getting someone to weld in $25
and some wires
The sensor and guage come with a wire diagram to
make it easy to install
I have 1 permanent in my 2 daks
I have 1 setup in a box all I do is drill a hole
weld a bung in plug it into the cig liter in cab
run the o2 wires in tru window and we go down the
road watching the ratio
when done I just unplg and put a plug in the o2
bung I weld in
Its just a cheap setup I made most air fuel
readers also record and graph but they are also
all around $1000
Its just something I made to use on the problem
trucks after a customer spends all kinds of money
replacing all kinds of sensors and parts I wish
they could have come to me first to see what is
going on before spending all the money and never
getting it to run right
Most of the problem trucks have either of 2
complaints
crap gas mileage
or
no power
first I run a scan and make sure all sensors are
working properly not just sitting there idleing
but letting the customer drive while I watch
all the sensor operations on the fly
I know most just hook it up take a look and say
all is well that is not true another thing to
check during operation is fuel pressure again
not just sitting idling but during operation
But this is only done on the problem trucks
as I said there are very few of them but they do
exsit and are harder to trouble shoot
Larry
J&J Auto
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