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mhall02
Dodge Dakota
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3/09/2005
22:34:57
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 Subject: stock V-6 gas milage
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Ok, I have a '91 Dakota, 8-bed, 5-speed with the TBI 3.9 V-6. I've had the truck about 2 years now and the best gas milage I have ever got was 21 MPG (once). Typical highway milage is 19 mpg at 70-75 mpg yet I've read this truck is supposed to get 22 mpg highway, but I have never seen it. It runs good, has about 139,000 miles with good plugs, plug wires, cap and rotor. I'm considering changing the O2 sensor to see if I can get it to the 22 (get a code 51 O2 sensor in lean position) mpg mark but am doubtful I'll see any difference. Anyone with this Gen 1 engine ever consistently see 21-22 mpg highway on a stock setup, or am I expecting too much?
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Dan M
Dodge Dakota
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3/10/2005
05:58:37
| RE: stock V-6 gas milage
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I have a 95 SLT CC 4x4 3.9 auto that is almost all stock. I recently upgraded the air intake (edelbrock open element with a K&N filter). I have a tonneau cover as well. I have gotten as much as 25mpg (driving 55-60). I usually get 17 combined city/highway. My last all highway trip I got 22mpg (prior to air intake upgrade and at speeds of 70-75 and occasionally hitting 80).
the O2 sensors are supposed to be checked every 30k miles. I finally replaced mine after 140k. And I did it because i wanted to, not because i got an error code. If you got the code, i'd say go ahead and change it. The part for mine was like $45 and was simple to change. In Nov I was getting at best 15mpg, but 95% of the time i was getting 12-13. What fixed my issue was doing a tune up (it was time, i replaced the plugs and wires , been using autolight plugs for years but decided to go with autolight wires too) and getting the engine flushed (made the most difference). I had ALOT of crud in the oil. I was taking the slow route and changed my oil and put in 1 qt of transmission fluid, rest oil. This was working but taking too long so I paid the $80 and got the engine flush service done at pepboys. The engine flush is something that you might not need since you are getting "decent" milage.
After the tuneup and engine flush, i was getting 16mpg, then i started getting 17 when i switched to synthetic oil. The better air intake system gives me better throttle response and I can "get on it" with out the gas milage suffering like it used to. You may want to check our your air intake system? I usually get the air induction service done once a year. Now I also use seafoam.
Honestly, I don't ever expect to get the sticker milage.
this is just my experience, you may not get the same.
- Dan M
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olscout
Dodge Dakota
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3/10/2005
09:57:40
| RE: stock V-6 gas milage
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Man, I sure wish my Dak was doing as good as you guys are! I'd kill to get 17 overall. Mine is a 92, 3.9 automatic, all stock. New Mopar timing chain install per Larry's parts list (but not degreed), and redone heads due to bent valves and pushrods as a result of the first 'replacement' timing chain going South; also had a cracked head. New mag core wires, new Autolite double platinum plugs, new cap and rotor. Compression is good, but we had injector issues (ie, WAY RICH) on start up since the truck had sat for well over a year due to the timing chain self destructing. Everything is up to snuff now injector wise, and the truck seems to run and idle great. BUT, I'm getting maybe 14 mpg, combined, and a lot of that is not technically 'highway' but it's rural, 55 mph in OD, so it should be better. The truck has about 121K on it- worth it to throw another $50 at it and replace the O2 sensor? Exhaust pipe is black, which tells me it's running a little rich-and from what I have read, that can be caused by a faulty O2 sensor. I'd be happy to put the money into it to get the mileage up a couple MPG to where it makes more sense to run a midsize- I've gotten better mileage out of a full size
Dodge Ram with a 3.9 magnum with a five speed.
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CaptDon
Dodge Dakota
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3/10/2005
10:11:59
| RE: stock V-6 gas milage
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I've got a 98 Sport with 95K, 3.9 w/standard transmission and a fiberglass bed cover. Setting the cruise from 65-70 MPH on the freeway with no significant head wind gets me 21-22 MPH.
Don
Olathe Ks.
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Dan M
Dodge Dakota
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3/10/2005
11:36:35
| RE: stock V-6 gas milage
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if the O2 sensor is bad, you will get below normal gas milage. The thing to keep in mind with them is that they are based of a voltage. The senor could still be good according to the computer (no code) but not be operating optimally. In a perfect world, the O2 sensor keeps switching from lean to rich. In this case, the average would be the middle, neither lean nor rich.
Olscout, you said the truck sit for a year? That's along time for fluids to be sitting idle. I'm assuming you changed the oil?
- Dan M
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Purplemonster
Gen III
3/10/2005
11:53:11
| RE: stock V-6 gas milage
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I got a 98 v6 4x4 and I would kill to get 15MPG!!! I am going to give it a tune up and change the o2 sensor to see if that makes any change. Seriously, from what I've heard, there is no difference in gas mileage between v6 daks and v8s. I got about 14 when I bought it, and with my 3" jba exhaust (too big) and body lift, it gets about 12.
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spt
Dodge Dakota
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3/10/2005
11:55:22
| RE: stock V-6 gas milage
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1988 4x4 3.9, 5 speed and I have a topper on. I get 20 mpg city/highway. If I am just doing highway driving I have gotten 24 mpg(no strong wind). I do not drive fast and stay about 65 mph on highway. I have just had my exhaust system re-done, so I am interested to see if that is going to make a difference.
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daddio
Dodge Dakota
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3/10/2005
11:59:04
| RE: stock V-6 gas milage
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within the last couple of months i've changed my driving habits and have gone from 19-20 hwy to a best of 23.5 hwy. don't rev past 2k when possible, shift before that stupid shift light comes on and 60-65mph tops highway. this is in a heavy '00 QC Sport w/ 3.9-6, 5 spd manual, 3.55 gears and 235/75/15 tires. i'm lovin' it, especially when i filled up this morning @ $1.999 a gallon! OUCH
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00Dak
Dodge Dakota
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3/10/2005
13:21:26
| RE: stock V-6 gas milage
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to get 20-21 mpg ya have to drive 55-60 mph. these trucks are about as aerodynamic as a barn... and the drag goes up by the cube (^3) of the speed difference. That is the force to push air at 100 mph is 8 TIMES that needed to go 50 mph (2^3).
all ya have to do is slow down (but who wants to do that?!)
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JFH
GenII
3/10/2005
13:41:16
| RE: stock V-6 gas milage
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I get 20-22 city, but I have lots of mods. I can pull 23-25 on the highway
http://www.cardomain.com/memberpage/546400
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mhall02
Dodge Dakota
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3/10/2005
16:24:28
| RE: stock V-6 gas milage
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My 21 mpg trip was all highway driving about 60 or so, but here in ole Missouri the speed limit is 70 on the interstate so thats what I'll go. Maybe I'll try shifting before the light comes on, I thought that was a little too soon, but as also mentioned above, $1.99 per gallon makes one think.
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p2gee
Dodge Dakota
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3/10/2005
19:31:17
|  RE: stock V-6 gas milage
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One thing you might want to check is your MAP sensor. Chrysler products have a pretty good history of these things getting out of calibration and causing drivability/ MPG issues. If you have a DVOM and a hand held vacumm pump can do a calibration check of most Mopar MAPS like this:
1. Connect vacumm pump to MAP vacumm port. Some MAPS may have to be remove from TB to do this.
2. Back probe the MAP signal wire with your DVOM. Signal wire is usually the center wire on 3 wire sensors.
3.With key on engine off apply 5 inches vacumm to sensor and note volt reading. Write the reading down.
4. KOEO apply 10 inches vacumm to sensor and note volt reading. Write the reading down.
5. Subtract the second reading from the first. Good sensors should show a difference of between 2.33 to 2.85 volts.
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Dex
Dodge Dakota
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3/10/2005
20:40:12
| RE: stock V-6 gas milage
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Research the threads on this topic a lot of info.
Key points
- these are trucks
- they get the same mileage as similar trucks
I get about 21mpg on the highway @ 65-70mph
City driving about 17mpg
I have a Sunfire I drive to & from work that gets about 24mpg city driving.
So about a 7mpg difference city driving or about $6.32 more per 100 miles driven - assume $2/gal gas.
Or $63.20 more to drive the dakota every 1,000miles
Or $632.00 more to drive the dakota every 10,000 miles.
If you drive 10K/year you are paying $620 more a year to drive the dakota than a sunfire.
Is that worth it to you?
Do you know a truck that gets 24mpg in city driving?
2000 Quad Cab 4X4-Sport V-6 Automatic Sports Plus Package
31X10.5 tires, Limited Slip, 3.55 Gears, Trailer Tow Group, HD Package, Skid Plates, LineX Spray in bed liner; Added:Airaid air filter & heat shield, Flowmaster 3 chamber muffler, Steel Horse Torneau cover, front hitch, Autolite Double Platinum 3923 Plugs, Removed air horns from Throttle Boddy, added new TB bolts, Cool Tape around air filter and A/C tubes, Amsoil in: crank case, differential and tranfercase.
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olscout
Dodge Dakota
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3/10/2005
20:40:48
| RE: stock V-6 gas milage
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Dan, all the fluids have been changed- oil twice, due to metal bits from the first replacement timing chain that fragged. Mine seems to run fine warmed up, but I was doing some reading over at the Allpar site, and one guy mentioned that a bad O2 sensor can cause cold start or cold driveability problems. Can't say I have major driveability issues, but it does run rough till it warms up- noticeably rough. Next step is to put a scan tool on it and see what the O2 sensor and MAP is doing, and go from there. I've had people say 13 may be all I can get with the Magnum engine and the hotter cam than the old 3.9, but obviously some guys are doing better than that....and I don't expect five speed mileage with the slushbox, but it should be 16-17 anyway in my opinion, with a tight engine and new tuneup.
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Dan M
Dodge Dakota
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3/11/2005
06:24:30
| RE: stock V-6 gas milage
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The O2 sensor is not used when the vehicle is cold - it doesn't start sending signals until it is warm. At least, it is not supposed to. If you have alot of miles on the truck, there is no harm in changing the O2 sensor. The bad gas milage could be coming from a faulty O2 sensor, but it's no guarantee.
- Dan M
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Pete
Dodge Dakota
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3/11/2005
09:26:10
| RE: stock V-6 gas milage
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I have a 97 3.9 CC with 80K miles and I get 15-16 around town and my best on the highway with the wind in my favor was 19.5, and on the highway with a strong headwind I only got 16.5. I have a tonneau (sp) cover, champion truck plugs, and a rattling timing chain, but I started to notice my tailpipe was starting to get black. Maybe time for an 02 sensor.
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olscout
Dodge Dakota
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3/11/2005
09:32:25
| RE: stock V-6 gas milage
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It's got about 121K on it. It was pretty well maintained, up til it got the first replacement timing chain :( The guy that did it apparently didn't bother to see, or didn't realize, that the old flopping chain had destroyed the 'oil slinger' thing behind the chain. The new chain ate itself and the gears up for lack of lube in short order. We cleaned out all the metal powder we could find, and have run two oil changes through it so far and it's coming out clean. BUT, when the timing gears went, the guy kept trying to start it, and bent some valves. That turned out to be fortunate because it had a cracked head....just a PITA to get it right, since the replacement, 'just redone' heads also had two bent valves (grrr!!!) AND one of them was also cracked. And, on start up there were the injector problems I referred to, it was loading up badly. All in all, I'm thinking if the O2 sensor isn't fouled out by all the gas dumped into it, or the antifreeze it was likely burning due to the cracked head, it's a miracle, so I'll probably swap it out. Can't hurt, it's fairly cheap, and it may help. Beyond that, we can hook up the scan tool or use the VOM to check the MAP sensor and see what I have there. I love the truck, but it has to do better on gas than that- I paid a buck ninety-nine yesterday afternoon, but an hour later it was $2.15.9! Can't handle 13mpg on those prices....
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Dan M
Dodge Dakota
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3/11/2005
10:18:12
| RE: stock V-6 gas milage
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Sounds like you have had quite a time. At 121K it is not a bad idea to change the O2 sensor, especially with all that has gone on and you said it had thrown a code once. However, it could be that the O2 sensor is good, just that the engine really was running rich. It might help, might not. You can't find out until you try - it's a 50/50 shot. Are you hearing any ticking sound from the engine? A sticking lifter could cause gas milage to suffer. Really anything that makes the engine work harder is going to cause bad gas milage.
The entire time I had sucky gas milage, I never had a code thrown. This made it hard to track down. Everything always checked out, i had the truck into 3 different shops, all telling me there was no issue, however they did note the sounds and the rough idle. The rought idle was fixed by replacing the grommet and hose on pcv and breather.
You might want to consider using 1 qt of transmission fluid and the rest oil next oil change. Run that for about 500 miles (or sooner if you notice oil pressure vary from the norm in anyway). It's a cheap way to help clean out the engine from any possible oil issue. Just a WILD guess on this one.
What is nice about the engine flush ($80/peopboys including proline oil change) is that they run a warm cleaning solution at 42PSI into the filter port and vaccuum it out the pan. This should flush any crap. Some say this is not good, cause stuff could eventually get knocked lose afterwards and clog the filter, etc. I am going to have this done every year. Also, I know run seafoam in the oil, gas and air intake, little cheap insurance and it seems to help and is highly recommend here.
Good luck on tracking this one down.
- Dan M
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dang...
Dodge Dakota
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3/11/2005
10:57:57
| RE: stock V-6 gas milage
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so i have a 97 3.9 4x4 club cab with 82k on it. yesterday i filled up and got 11.2 mpg. a week earlier i got 15.3 mpg. usually i get 14 in town and 15 on the highway. is something wrong? any help would be great!
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olscout
Dodge Dakota
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3/11/2005
10:59:28
| RE: stock V-6 gas milage
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Went out and did the self test I found on the Allpar site. The only code it showed was 'battery recently disconnected...' which it had been, so nothing there. I kinda didn't expect to see any results from that anyway, the older computers aren't that good at showing codes unless it's a total failure it seems like. I think my buddy's Snap On scanner shows 'real time' data- if not, I know where I can borrow one that does, and I should be able to check the O2 sensor and MAP that way. PITA, but still better than my other friend's 01 Ram 1500 4wd- he's ready to sell it, and it is showing a tranny code at 21K miles. Pretty hard to sell with the 'check engine' light on....
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jake
Dodge Dakota
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3/14/2005
22:01:25
|  RE: stock V-6 gas milage
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i get 12mpg if i'm lucky with my mostly stock 97 3.9 4x4 cc, it sucks (gas). I do half highway and half city...I've tried to help the mpg with a freer flowing muffler and air filter. I also did a complete tune up and everything to find no improvement. BTW, Gas here in FL was $2.20 for 87 octane tonight. I have like 3.90-ish gears too. I've learned to live with it. Moral of the story= want better gas mileage? get a moped...
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