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2006 cruise control problem

16K views 10 replies 4 participants last post by  Speedy57 
#1 ·
Hi all. Having an issue with my 2006 Dakota. I recently installed a throttle body spacer and intake onto my truck and now the cruise control wont maintain a speed. Example: driving 65 on the freeway set the cruise and then it slowly coasts down to about 50-55 and really doesn’t get back up to speed. I'm pretty sure the cable needs to be adjusted but when I inspected the cable housing there is no adjustment nut like I'm used to with other vehicles. Same goes for my throttle cable but I don’t seem to have a problem with the skinny peddle. If anyone has any suggestions or a solution I would greatly appreciate it.
 
#3 · (Edited)
Hi all. Having an issue with my 2006 Dakota. I recently installed a throttle body spacer and intake onto my truck and now the cruise control wont maintain a speed. . I'm pretty sure the cable needs to be adjusted but when I inspected the cable housing there is no adjustment nut like I'm used to with other vehicles. Same goes for my throttle cable but I don’t seem to have a problem with the skinny peddle. If anyone has any suggestions or a solution I would greatly appreciate it.
The dakota speed/cruise control is operated by that cable from the vacumn servo diaphram. The PCM is also involved with speed control.

The speed control servo cable is connected between the speed control
vacumn servo diaphram and the throttle body control linkage.
This is a critical area and the linkage setup has to be correct
for it to function the way it should.

This cable causes the throttle control linkage to open or close
the throttle valves inside the throttle body in response to the
vacumn servo diaphram , run by engine vacumn at various rpms.

The PCM operation is more involved, but here is a partial description
of how it affects the speed control servo.

The servo unit consists of a solenoid valve body,
and a vacuum chamber. The solenoid valve body contains three solenoids:​
1.​
Vacuum

2.​
Vent

3.​
Dump
The vacuum chamber contains a diaphragm with a cable attached to control the throttle linkage.


The PCM duty cycles the vacuum and vent solenoids
to maintain the set speed, or to accelerate and
decelerate the vehicle. To increase throttle opening,
the PCM grounds the vacuum and vent solenoids. To
decrease throttle opening, the PCM removes the
grounds from the vacuum and vent solenoids. When
the brake is released, if vehicle speed exceeds 30
mph to resume, 35 mph to set, and the RES/ACCEL
switch has been depressed, ground for the vent and​
vacuum circuits is restored.


The position of the throttle valves is monitored by the TPS sensor and fed back to the PCM.

So by adding spacers and other mods to your truck, the factory set
cruise control parameters in the PCM may be off.

Besides that, there could be a change in intake manifold vacumn that
governs the speed control servo..there is a vacumn reservoir that is
there to allow "buffered" engine vacumn to operate the vacumn servos
on the speed control and heating/A/C duct doors...
...or the speed control cable is now (perhaps) too tight or too loose,
in regards to factory settings PCM speed control maps in it's
speed controlled pgrm memory. The PCM remembers the speed
you set the speed control at the cruise switches.

Assuming you have no vacumn leaks or VACUMN CHANGES with your modifications to the throttle body, more than likely, the speed control cable tension has been affected somehow by raising the throttle body.

This would be the area I would investigate..and you say there is no
adjustment?
 
#4 ·
yes that is correct on most cars i have worked on before have a threaded end which has an adjustment nut to adjust the tension of the cable but on this truck it is just a sheath that the cable passes threw with a rubber seal at the end. i did pull the rubber cover off and underneath is just the opening of the sheath. does that vacuum pod have and adjustment internally? i don't want to go in blind if at all possible but if no one knows i guess someone has to do it right?
 
#7 · (Edited)
yes that is correct on most cars i have worked on before have a threaded end which has an adjustment nut to adjust the tension of the cable but on this truck it is just a sheath that the cable passes threw with a rubber seal at the end. i did pull the rubber cover off and underneath is just the opening of the sheath. does that vacuum pod have and adjustment internally?
No, it doesn't appear to have any adjustment, as the vacumn servo bolts up tight to the servo bracket (3 bolts) and there is a clip to keep the cable from
pulling through, from what I can see in the diagram.

I don't have Cruise on my truck, so I'm only going by pictures of the vacumn servo in my 2001 Dodge Ram shop manual..but the Dakota should be pretty much the same.
As far as I can see the only way to adjust this cable is by adding washers
(to the 3 bolts that bolt the servo to the servo bracket) to move it
back to take up any slack. if the cable is too loose
or move the servo forward on it's bracket somehow to relieve any tension
on the cable. Trust Dodge to make it more difficult.

i don't want to go in blind if at all possible but if no one knows i guess someone has to do it right?
No you shouldn't go in without some knowledge of how to remove and
re-install the servo on the servo bracket. In my reply to your
"vacumn post", I included some steps on how to do that, by directly pasting
from the RAM shop manual, so you being a knowlegeable mechanic, should be able to figure it out from the instructions. :D

Here's the thing..you modified the standard setup by adding a riser to
the throttle body and whatever else you did to it.

Doesn't the riser change the engine vacumn on the throttle body?..similar
to the "venturi effect" on carbed versions. I've seen race cars with
velocity stacks attached to the carb throats, so doing any kind of change
in the intake manifold could affect air and vacumn parameters..otherwise
why did you make the changes?

The cruise control relies in the VACUMN and VENT solenoids controlled by the PCM, according to input it receives from other sensors on the vehicle.

Now here's something else I'll throw into the works..

the MAP..Mass Air Sensor.(attached to the throttle body at the front)..this sensor measures ABSOLUTE BAROMETRIC PRESSURE, INTAKE MANIFOLD PRESSURE and AMBIENT BAROMETRIC PRESSURE.
The PCM uses the data from it to adjust engine parameters such as the
fuel injection mixture.

Maybe by changing intake manifold air dynamics it has caused the MAP to
provide erroneous data to the PCM which then affects the cruise control.
(ie: cruise operating parameters have changed as a result of the mod)
 
#6 ·
well here's the scoop from the 2001 Dodge Ram Shop manual..in regards
to SPEED CONTROL (CRUISE CONTROL)

Gas Powered Engines​
On gasoline powered engines: actual engine vacuum,
a vacuum reservoir, a one-way check valve and
vacuum lines are used to supply vacuum to the speed
control servo.
(1) Disconnect vacuum hose at speed control servo
and install a vacuum gauge into the disconnected hose.
(2) Start engine and observe gauge at idle. Vacuum
gauge should read at least ten inches of mercury.
(3) If vacuum is less than ten inches of mercury,
determine source of leak. Check vacuum line to
engine for leaks. Also check actual engine intake
manifold vacuum. If manifold vacuum does not meet
this requirement, check for poor engine performance
and repair as necessary.

(4) If vacuum line to engine is not leaking, check
for leak at vacuum reservoir. To locate and gain
access to reservoir, refer to Vacuum Reservoir Removal/
Installation in this group. Disconnect vacuum line
at reservoir and connect a hand-operated vacuum
pump to reservoir fitting. Apply vacuum. Reservoir
vacuum should not bleed off. If vacuum is being lost,
replace reservoir.

(5) Verify operation of one-way check valve and
check it for leaks.

(a) Locate one-way check valve. The valve is
located in vacuum line between vacuum reservoir
and engine vacuum source. Disconnect vacuum
hoses (lines) at each end of valve.
(b) Connect a hand-operated vacuum pump to
reservoir end of check valve. Apply vacuum. Vacuum
should not bleed off. If vacuum is being lost,
replace one-way check valve.
(c) Connect a hand-operated vacuum pump to
vacuum source end of check valve. Apply vacuum.
Vacuum should flow through valve. If vacuum is
not flowing, replace one-way check valve. Seal the
fitting at opposite end of valve with a finger and​
apply vacuum. If vacuum will not hold, diaphragm
within check valve has ruptured. Replace valve.

Remove servo from the servo mounting bracket.

(13) Pull speed control cable sleeve and servo away
from servo mounting bracket to expose cable retaining
clip and remove clip.

Note: The servo mounting bracket is a typical
bracket and may/may not be applicable to this model
vehicle.
(14) Remove servo from mounting bracket. While​
removing, note orientation of servo to bracket.

(Reinstall SERVO)
INSTALLATION​
V-6/V-8 ENGINES​
(1) Position servo to mounting bracket.
(2) Align hole in cable connector with hole in servo
pin. Install cable-to-servo retaining clip.
(3) Insert servo studs through holes in servo
mounting bracket.
(4) Insert servo studs through holes in servo cable
sleeve.
(5) Install servo mounting nuts and tighten to 8.5
N·m (75 in. lbs.) torque.
(6) Connect vacuum line to servo.
(7) Connect electrical connector to servo terminals.
(8) Install three bolts retaining servo/servo mounting
bracket to battery tray.
(9) Connect servo cable to throttle body. Refer to
Servo Cable Removal/Installation in this group.
(10) Connect negative battery cable to battery.
(11) Before starting engine, operate accelerator
pedal to check for any binding.
Fig. 16 Servo Cable at Throttle Lever​
1 - PINCH (2) TABS
2 - CABLE MOUNTING BRACKET
3 - PINCH TABS (2)
4 - OFF
5 - THROTTLE CABLE
6 - THROTTLE LEVER
7 - THROTTLE LEVER PIN
8 - OFF
9 - CONNECTOR
10 - SPEED CONTROL CABLE​
Fig. 17 Servo Location—Removal/Installation​
1 - BATTERY TRAY
2 - SERVO ELECTRICAL CONNECTOR​
3 - SERVO BRACKET SCREWS (3)

 
#8 ·
awesome thx for all the info. i was talking to manufacturer of the intake spacer because in the instructions it references a cable adjustment if the throttle body doesn't fully move with pedal depressed. the tech told me the provided spacers that they may be too long and to remove the spacers and trim them until the cable is the desired tension. so before i go tearing everything apart and chasing my tail on vacuum leaks which dodge is pretty common for im going to try that. and if it doesn't work all the information provided will be an extreme help. i will keep you posted.
 
#9 ·
update: i did what the tech said to do but i made new spacers and all that did was raise the idle and no effect on the cruise control. i then proceeded to check the vacuum line that goes to the cruise control unit all the way to the vacuum pod on the fire wall. the line has no cuts scrapes or brakes in it. i checked the one way valve and it is operating properly. and any adjustment to the placement of the cruise control vacuum pod pulls the cable which in turn raises the idle. i guess with the added airflow from the intake and turbulence from the spacer changed the dynamics so much that the vacuum pressure no longer is enough for the cruise control to work properly. unless i get a programmer that changes the ecm parameters for vacuum controlled components the only other option is to remove the spacer and see if the cruise control operates with the intake kit only. its too dark for me to continue experimenting so im going to call it a night besides, i hear dinner calling me and a nice cold mug of so home made brown ale calling my name.
 
#10 · (Edited)
update: i did what the tech said to do but i made new spacers and all that did was raise the idle and no effect on the cruise control. i then proceeded to check the vacuum line that goes to the cruise control unit all the way to the vacuum pod on the fire wall. the line has no cuts scrapes or brakes in it. i checked the one way valve and it is operating properly. and any adjustment to the placement of the cruise control vacuum pod pulls the cable which in turn raises the idle.
Ok, so all you have done so far is verify that the cable isn't binding
and the vacumn line has no leaks..but did you measure the actual
vacumn available for the two vacum valves at the rpm where the
cruise control is malfunctioning? Probably not. The Dodge shop
manual mentions a test for vacumn at idle and you need to pull at
least 10 inches of mercury in the first place..if you have less, you
may not have enough vacumn at road speeds to operate the thing
properly.

i guess with the added airflow from the intake and turbulence from the spacer changed the dynamics so much that the vacuum pressure no longer is enough for the cruise control to work properly.
You should buy an aftermarket vacumn guage and run it to a vacumn line
tap and run the line inside the cab somehow so you can observe the
vacumn at dynamic highway speeds. Right now, it's like trying to troubleshoot this symptom working blind.

Who knows what is happening to the vacumn levels inside with the manifold modification at road speeds when the cruise is engaged.

Question: what was the reason for adding the spacer under the throttle
body in the first place? Added performance or more HP at certain rpm?

unless i get a programmer that changes the ecm parameters for vacuum controlled components the only other option is to remove the spacer and see if the cruise control operates with the intake kit only.
well sometimes when there is a lot of confusion with modifications, it
is best to go back to square one to verify what is STILL working.

If you remove the spacer and go back to as much of an original intake manifold configuration as possible now, you should be able to prove
whether there is or isn't a problem with the vacumn servo.

Perhaps it's an "anomaly" that the spacer, or the other parts of the intake manifold mod kit are contributing to the type of symptom you are seeing with the cruise control.

Don't get frustrated, Do it one step at a time and use your trouble shooting skills.
ie:
1. Did the cruise on my truck work properly BEFORE I modified the
intake manifold? What was the vacumn (inches of mercury) BEFORE
I modified the throttle body?

2. When in calendar date/time did it stop working, if it worked properly
before the mod?

3. How would adding a spacer or moving the throttle body affect
air flow INSIDE THE MANIFOLD? What was the vacumn reading
AFTER the mods were done?

4. Where is the vacumn port (takeoff) on the stock intake manifold,
would that be affected by the throttle body mounted up higher?

5. How would the increased turbulence caused by the throttle body
spacer affect engine vacumn..obviously here a vacumn guage will be
necessary to prove that. ,

So far, from your description, all you have proven is that there is
no mechanical or vacumn hose connection issues. It's a good start,
but you need to dig a bit deeper.

its too dark for me to continue experimenting so im going to call it a night besides, i hear dinner calling me and a nice cold mug of so home made brown ale calling my name.
Ah! I love brown ale..and reds too. My favorite beers. have one on me
and maybe we can talk this thing through...I wouldn't go thinking about
reprogramming PCM algorithms..that's too expensive (and much too
"hit and miss", and makes it far too complicated for what may be
the TRUE CAUSE.

As a troubleshooter for many years on large computer systems..I have learned..

THERE CAN BE MANY SOLUTIONS TO A GIVEN PROBLEM...BUT ONLY ONE of
those..WILL BE THE BEST SOLUTION!
 
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