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Killboy
Dodge Dakota
JOIN HERE
3/10/2007
21:37:55
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 Subject: engine revs funny at highway speeds
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hello i have a 2000 3.9L 2wd.
today when i was driving at 100km/h @ 1900rpm, i noticed the truck would rev high (2000rpm-2100) for a second or so and then back down to normal cruising revs.
I know that it could be a few things.
Either the timing is off, a problem with the engine elec (plugs, wires etc.) or my PCM needs to be replaced.
All i want to know is if I is safe for me to drive the truck for another week before i can fix the problem.
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J and J Auto
GenII
 
3/10/2007
22:11:41
| RE: engine revs funny at highway speeds
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Message:
It sounds like the transmission is going in and
out of lockup
Causes
throttle position sensor
speed sensor on trans
bad connection on trans
sticky change valve trans
bad or dirty lockup sol
bad pressuer sensor and sol 96 and up obd2
check the easy things first
the only way the motor can rve up like that is
the torque converter unlocking
not plugs wires or timing LOL
the computers are very resiliant and hardly ever
fail
It should hot harm anything but get it fixed as
soon as you can
Larry
J&J Auto
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GB2000
GenIII
3/10/2007
23:06:36
| RE: engine revs funny at highway speeds
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Message:
Mine does it...changed the TPS sensor, didn't fix it. Dunno what's causing it. But mine does a bunch of weird stuff. I just need to pull out my credit card and take it in...
I'll definitely make a post with the cause of my problems when I decide to do it...until then, hopefully you figure it out fairly easily. It's been a royal PIA for me.
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ryan
Dodge Dakota
JOIN HERE
3/11/2007
11:58:11
| RE: engine revs funny at highway speeds
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Message:
mine does that when on cruise control. it'll rev for a split second like it came out of gear but the speed stays the same. it only happens on cruise though.
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TuckerLdlow
Dodge Dakota
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3/11/2007
14:26:41
| RE: engine revs funny at highway speeds
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Message:
I would think if it was coming out of lockup it would rev higher than 100rpm. Mine did that a year or so ago, but it was only going up about 50rpm, and only did it with cruise on. Had no idea what was causing it, but then a few days later I had a split hose that tripped a code. Once that was fixed, the reving problem went away.
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GB2000
GenIII
3/11/2007
19:49:27
| RE: engine revs funny at highway speeds
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Message:
I notice mine most when my cruise is set on the highway...but I *think* I recall it happening while maintaining highway speeds without cruise on as well.
Ryan - Mine does EXACTLY as you described. TuckerLdlow - do you know which hose this was that split so I could examine mine and find out if it's possibly causing my issues?
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ryan
Dodge Dakota
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3/11/2007
20:52:55
| RE: engine revs funny at highway speeds
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Message:
yes that would be very helpful.
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shatto
Dodge Dakota
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3/11/2007
21:23:58
| RE: engine revs funny at highway speeds
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Message:
Do I know about this?
I had three dealers and two transmission shops tell me I needed a new transmission.
The Amsoil oil analysis showed no wear at all.
I believed Amsoil and have now gone 557,000 miles, replacing only solenoids.
Your problem is probably the Throttle Position Sensor.
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Trevor
Dodge Dakota
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3/11/2007
22:36:41
| RE: engine revs funny at highway speeds
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Message:
Mine does the same thing...please keep all of us posted.
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TuckerLdlow
Dodge Dakota
JOIN HERE
3/12/2007
12:51:35
| RE: engine revs funny at highway speeds
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Message:
Ryan and GB2000 - Raise the hood, look on the driver's side - direct your attention to the Fuse and Relay box. Coming from that area, you have two vacuum hoses. One goes to the Throttle Body, and the other goes to the evap test port (Green plastic fitting on mine) and on to the back of the engine. Stock, that thing sits right above the manifold, and the heat is murder on it. Mine split at that fitting 3-4 times before I finally replaced the 1/4" tubing with 5/16" fuel line tubing, rerouted it along the top of the firewall, and around the top of the fender. The 5/16" tubing came from NAPA, and the hangers came from Lowes. No problems since - knock on wood.
I also had the one from the throttle body split where it connected right in front of the Fuse and Relay box, probably to the vacuum pump (I don't know what it is, really).
Unfortunately - I can't remember which fixed-split corrected the oscillating cruise control. Sorry!
Most cruise control systems use vacuum to determine what to do with the throttle position, so I'd check all the vacuum lines before I went and spent a lot of money on other stuff.
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Chris
Dodge Dakota
JOIN HERE
3/13/2007
10:31:24
| RE: engine revs funny at highway speeds
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Message:
My 93 3.9 Auto does the same thing. About a year ago I had the tranny rebuilt and it has done it since then. It's wierd in that it unlocks and revs slightly when I LIGHTEN UP on the throttle. When I push back down on the throttle, it locks back up again and the revs drop. I know they replaced the speed sensor when they re-installed the trans, because they broke the original one. But I'm not getting any fault codes which "should" indicate proper functioning of the TPS and speed sensor, right? It drives me crazy. The transmission shop that did the work just does the dumb act and says that is how it's supposed to operate. If that's the case, then I had a "malfunctioning" trans for about 13 years before they got a hold of it.
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GB2000
GenIII
3/13/2007
10:44:31
| RE: engine revs funny at highway speeds
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Message:
Mine seems to have a multitude of problems...mine has a BIG problem where on cold starts, I have to baby it when I'm accelerating because my transmission over rev's in between gears. It'll take off, goes to shift from 1st to 2nd and it'll rev about 400 rpm's and then shift. Doesn't jerk or anything, but you can just watch that tach needle shoot up. Then it'll randomly gear hunt...sometimes if I go to pass someone and floor it, it'll buck and surge trying to figure out whether it should downshift 2 gears or 1. Then I got the issue mentioned in this thread where it'll randomly rev while at highway speeds. I'm pretty much waiting til I got money so I can trade it in for a V8 4x4 Dak ext. cab. I either need to get it fixed already or trade it in...I got a shift kit I wanna install (and I'm not having it installed in a transmission that's f'ked up) and a Reflexxion cowl induction hood sitting primed in the shed waiting to be painted and installed. Haven't gotten it painted yet cuz I dunno if I'm keeping my red Dakota or getting a different one. lol
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Bob Lincoln
Dodge Dakota
JOIN HERE
3/14/2007
07:49:06
| RE: engine revs funny at highway speeds
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Message:
A TPS can be bad without codes, and also the harness can cause intermittent problems. A friend had a problem on and off for 2 years, and it turned out that unplugging the harness, cleaning the contacts and using new dielectric grease solved it. The harness had measured good with an ohmmeter. Sometimes you need a scope to catch these things.
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Super bee
GenI
3/14/2007
09:33:15
| RE: engine revs funny at highway speeds
IP: Logged
Message:
i had something similar on my 01 ram
they tried the TPS, but ended up changing the valve body and that fixed it
i dont know what it is but dodge cant seem to make a good valve body
1990 sport RC SB, 1995 318drivetrain, 3.92 gears (came with truck) Powertrax "traction system", 95 dash/steering wheel, hearthrob exhaust, headers, cutout after y-pipe, necessary electric fan add-a-leafs, 30x9.5 mud tires, cranked T-bars, AR 39 15x8 rims, grill guard, roll bars
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J and J Auto
GenII
3/17/2007
02:34:05
| RE: engine revs funny at highway speeds
IP: Logged
Message:
GB2000 it sounds like pressure sensor and sol
Heres a little tidbit of info
when you let off the gas and the comp reads idle
if you get back on the gas a little hard it will
be unlocked
Also taping the break enough to get the brake
lights to come on now hit the throttle instantly
and it will be unlocked
If this is over sensitive its usualy the TPS and
as Bob said reading this with a scanner or a
digital volt meter will not always show its bad
these sensors all have a pattern that can be read
with a ocilliscope and this sometimes is the only
way to find a bad sensor by watching the scope
pattern
Snap on and a few others now make a tester that
will detect small resistance or voltage loses
in wires, a bad connection can also cause this
unlocking but may not be seen with a ohm meter
On the obd2 RE transmission there is also another
plug inside the trans so you can replace either
the presure sensor and sol or the o/d lockup
sols seporatly that go funky
things like this you just need to start
eliminating things 1 at a time untill you hit
the real problem
I and the other 2 mechs go threw stuff like this
all the time and the way it ends up its usualy
the last thing you check LOL
I know its enough to make a grown man cry LOL
Just the way it is sometimes it takes weeks,
months to find these little quirks the computer
controled cars and trucks have today
One big thing most overlook is unlike the older
vehicles that switched the pos + side these new
vehicles turn grounds on and off a$$ backwards
of what one would think and it can trow the best
for a loop
Time and patiants is what the modern mechanic
needs more than anything and learning to look
far behond what the scanners and digital meters
will tell you
as one said here so many problems so little time
LOL
So don't feel bad if you cant find the problem
to be something simple and easy those days are
over
Larry
J&J Auto
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J and J Auto
GenII
3/17/2007
02:38:00
| RE: engine revs funny at highway speeds
IP: Logged
Message:
I just wanted to add this to the head ach
a small undectectible voltage loss or resistance
can cause big problems and is very hard to find
Larry
J&J Auto
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GB2000
GenIII
3/17/2007
05:35:40
| RE: engine revs funny at highway speeds
IP: Logged
Message:
Thanks for that info...
You wouldn't happen to know the part # for the governor pressure sensor/solenoid, would you? I haven't been able to find it anywhere online (I prefer to order online...usually MUCH cheaper). Are there any other sensors I might as well replace while I'm at it?
If all else fails, I just got another credit card that I used to buy a laptop...I intend to pay it off within the next month, so once it's paid off, I may use it and take my truck in and just have my dad's mechanic fix it as well as heli-coil my stripped tranny pan bolt-hole...and my exhaust leak...and while I'm feeling generous with my money, maybe I'll have him install my trans-go shift kit too. lol
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shatto
Dodge Dakota
JOIN HERE
3/17/2007
13:02:29
| RE: engine revs funny at highway speeds
IP: Logged
Message:
Larry,
Thank you. I'm glad to see I'm not the only blurry-eyed miss-speller at 2 in the morning!
You make a point for not throwing on parts until the problem goes away, unless you have bucks to burn.
Everything is interconnected with the computer in modern vehicles and it often is cheaper to pay the big bucks to the guy with the proper tool, to talk with the computer,(not a code reader)and zero in on the actual problem. Which is exactly what you said!
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