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larry1987
Dodge Dakota
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8/20/2010
20:09:16
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 Subject: 5.2 dakota loosing power on interstate
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To start off I just put some shorty headers on and took the cat out. This is fine other than the engine light being on because of the o2 sensor.
Now for the problem im having that is driving me crazy. On the interstate crusing with or without the cruise on i start loosing power but if i floor it it will pick back up and go back to the same thing. it felt like a fuel problem to me so i replaced the fuel pump and still the same thing.
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larry1987
Dodge Dakota
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8/20/2010
20:39:09
| RE: 5.2 dakota loosing power on interstate
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Sorry forgot to say its a 1997
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The Joe.C
Dodge Dakota
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8/21/2010
15:04:50
|  RE: 5.2 dakota loosing power on interstate
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Well, this could be a leak in the recirculation hose or if not this would be a fuel related problem.
Worse case scenario could be something going bad in the transmission such as pressure loss or the torque converter.
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JasonB
Dodge Dakota
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8/21/2010
15:04:51
| RE: 5.2 dakota loosing power on interstate
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Which O2 sensor did you remove? The one closest to the exhaust manifold is required. The one after the cat can be simulated.
When you "floor it" (WOT), the engine computer goes to open loop mode and uses stored fuel maps for fuel delivery to the engine. When no longer at WOT, the engine computer reverts to closed loop mode and uses feedback from the O2 sensor(s) for the fuel management.
So you see there is a need for the O2 sensor.
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larry1987
Dodge Dakota
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8/21/2010
17:41:49
| RE: 5.2 dakota loosing power on interstate
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All the o2 sensors are still there the only thing i removed was the cat. Today while on the interstate when it started loosing power i couldnt give it any throttle. When i tried the truck would start bucking and wouldnt go over 50.
Thanks for the suggestions
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JasonB
Dodge Dakota
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8/21/2010
19:15:50
| RE: 5.2 dakota loosing power on interstate
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Well, one of the functions of the O2 sensor after the cat is to measure the efficiency of the cat. If both O2 sensors are giving the same reading, the PCM thinks the cat is bad and throws a code.
If you don't have a code reader, Ignition switch ON-OFF-ON-OFF-ON (without starting the engine). Read codes in the odometer readout and post here.
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larry1987
Dodge Dakota
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8/21/2010
21:13:14
| RE: 5.2 dakota loosing power on interstate
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I have a scanner at work but no codes for the problem im having only the one for the rear 02 sensor because the cat is not there.
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well
Dodge Dakota
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8/22/2010
10:12:19
| RE: 5.2 dakota loosing power on interstate
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Without a cat you've loss back pressure with it goes
alot of low end trq.
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Gregg
Dodge Dakota
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8/22/2010
10:52:09
| RE: 5.2 dakota loosing power on interstate
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Backpressure: The myth and why it's wrong.
I. Introduction
One of the most misunderstood concepts in exhaust theory is backpressure. People love to talk about backpressure on message boards with no real understanding of what it is and what it's consequences are. I'm sure many of you have heard or read the phrase "Engines need backpressure" when discussing exhaust upgrades. That phrase is in fact completely inaccurate and a wholly misguided notion.
II. Some basic exhaust theory
Your exhaust system is designed to evacuate gases from the combustion chamber quickly and efficently. Exhaust gases are not produced in a smooth stream; exhaust gases originate in pulses. A 4 cylinder motor will have 4 distinct pulses per complete engine cycle, a 6 cylinder has 6 pules and so on. The more pulses that are produced, the more continuous the exhaust flow. Backpressure can be loosely defined as the resistance to positive flow - in this case, the resistance to positive flow of the exhaust stream.
III. Backpressure and velocity
Some people operate under the misguided notion that wider pipes are more effective at clearing the combustion chamber than narrower pipes. It's not hard to see how this misconception is appealing - wider pipes have the capability to flow more than narrower pipes. So if they have the ability to flow more, why isn't "wider is better" a good rule of thumb for exhaust upgrading? In a word - VELOCITY. I'm sure that all of you have at one time used a garden hose w/o a spray nozzle on it. If you let the water just run unrestricted out of the house it flows at a rather slow rate. However, if you take your finger and cover part of the opening, the water will flow out at a much much faster rate.
The astute exhaust designer knows that you must balance flow capacity with velocity. You want the exhaust gases to exit the chamber and speed along at the highest velocity possible - you want a FAST exhaust stream. If you have two exhaust pulses of equal volume, one in a 2" pipe and one in a 3" pipe, the pulse in the 2" pipe will be traveling considerably FASTER than the pulse in the 3" pipe. While it is true that the narrower the pipe, the higher the velocity of the exiting gases, you want make sure the pipe is wide enough so that there is as little backpressure as possible while maintaining suitable exhaust gas velocity. Backpressure in it's most extreme form can lead to reversion of the exhaust stream - that is to say the exhaust flows backwards, which is not good. The trick is to have a pipe that that is as narrow as possible while having as close to zero backpressure as possible at the RPM range you want your power band to be located at. Exhaust pipe diameters are best suited to a particular RPM range. A smaller pipe diameter will produce higher exhaust velocities at a lower RPM but create unacceptably high amounts of backpressure at high rpm. Thus if your powerband is located 2-3000 RPM you'd want a narrower pipe than if your powerband is located at 8-9000RPM.
Many engineers try to work around the RPM specific nature of pipe diameters by using setups that are capable of creating a similar effect as a change in pipe diameter on the fly. The most advanced is Ferrari's which consists of two exhaust paths after the header - at low RPM only one path is open to maintain exhaust velocity, but as RPM climbs and exhaust volume increases, the second path is opened to curb backpressure - since there is greater exhaust volume there is no loss in flow velocity. BMW and Nissan use a simpler and less effective method - there is a single exhaust path to the muffler; the muffler has two paths; one path is closed at low RPM but both are open at high RPM.
IV. So how did this myth come to be?
I often wonder how the myth "Engines need backpressure" came to be. Mostly I believe it is a misunderstanding of what is going on with the exhaust stream as pipe diameters change. For instance, someone with a civic decides he's going to uprade his exhaust with a 3" diameter piping. Once it's installed the owner notices that he seems to have lost a good bit of power throughout the powerband. He makes the connections in the following manner: "My wider exhaust eliminated all backpressure but I lost power, therefore the motor must need some backpressure in order to make power." What he did not realize is that he killed off all his flow velocity by using such a ridiculously wide pipe. It would have been possible for him to achieve close to zero backpressure with a much narrower pipe - in that way he would not have lost all his flow velocity.
V. So why is exhaust velocity so important?
The faster an exhaust pulse moves, the better it can scavenge out all of the spent gasses during valve overlap. The guiding principles of exhaust pulse scavenging are a bit beyond the scope of this doc but the general idea is a fast moving pulse creates a low pressure area behind it. This low pressure area acts as a vacuum and draws along the air behind it. A similar example would be a vehicle traveling at a high rate of speed on a dusty road. There is a low pressure area immediately behind the moving vehicle - dust particles get sucked into this low pressure area causing it to collect on the back of the vehicle. This effect is most noticeable on vans and hatchbacks which tend to create large trailing low pressure areas - giving rise to the numerous "wash me please" messages written in the thickly collected dust on the rear door(s).
Also read this
http://www.nsxprime.com/FAQ/Miscellaneous/exhausttheory.htm
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Barney
Dodge Dakota
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8/22/2010
19:11:27
| RE: 5.2 dakota loosing power on interstate
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Gregg, Exelent explanation!!
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me
Dodge Dakota
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8/22/2010
19:28:15
| RE: 5.2 dakota loosing power on interstate
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Gregg is completely full of shyt!
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larry1987
Dodge Dakota
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8/22/2010
21:06:44
| RE: 5.2 dakota loosing power on interstate
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So today i checked the tps and map sensor
and both checked ok through voltage checks. I
also hooked up a fuel pressure gauge to c if I
was losing pressure due to voltage drops in
the fuel pump circuit but I was ok as well. So if
anyone has anymore suggestions they would b
appreciated.
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JasonB
Dodge Dakota
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8/22/2010
23:32:29
| RE: 5.2 dakota loosing power on interstate
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Still waiting for those codes.
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larry1987
Dodge Dakota
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8/23/2010
10:07:26
| RE: 5.2 dakota loosing power on interstate
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The only code is for o2 sensor
voltage too high.
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Dammit
Dodge Dakota
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8/23/2010
20:04:04
| RE: 5.2 dakota loosing power on interstate
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He wants the numbers, Larry. This guy is trying to help you. He's been around a while and is one of a dozen or so real helpers on this board. Post the dam numbers. Geez. Why the big secret.
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JasonB
Dodge Dakota
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8/23/2010
20:05:06
| RE: 5.2 dakota loosing power on interstate
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Just like at the dealership, if there is a MIL, the code numbers are much more important and informative than the description of the code. To the technician, it is absolutely essential that we know all failure code numbers, to help eliminate guesswork. You have at least 2 O2 sensors. The code number tells us which one. There are also several failure code possibilities for each O2 sensor.
Good luck.
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JasonB
Dodge Dakota
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8/23/2010
22:47:35
| RE: 5.2 dakota loosing power on interstate
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Hehe. Thanks, Dammit.
Just trying to help.
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larry1987
Dodge Dakota
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8/24/2010
10:22:06
| RE: 5.2 dakota loosing power on interstate
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The o2 sensor code number is 21. its not giving me a p code.
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Jim
Dodge Dakota
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6/05/2011
15:51:55
| RE: 5.2 dakota loosing power on interstate
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Message:
Hi - My 97 5.2 Sport 5-speed (150k miles)has a
similar problem. It loses power at steady 60 mph
or higher. It will slow and then with light
increase in throttle buck and backfire. It also
sometimes bucks at low speed under light throttle.
Feels like a fuel delivery problem. Always starts
instantly and runs pretty strong when it wants
too. Mechanis said engine computer and code was
for electrical interuption to that computer. I
changed the computer and no improvement. Ideas?
Thanks!
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daddio
Dodge Dakota
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6/05/2011
16:02:21
| RE: 5.2 dakota loosing power on interstate
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Message:
Check for codes again and post here. what was the first code the mechanic found?
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Jim
Dodge Dakota
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6/11/2011
13:07:26
| RE: 5.2 dakota loosing power on interstate
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Message:
12 My Dak gives me the code on the electronic
odometer, not the blinking light. It was the same
before and after the computer swap. The mechanic
cleaned up the leads off the battery,...new copper
ends, new wingnut, etc. He was trying to solve a
possible power interruption. I am thinking about
cleaning up ground on the harness....
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