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Patriot QC
Dodge Dakota
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8/29/2005
09:13:48
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 Subject: MAP sensor Q?
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I am having driveability problems with my 03 Dak (4.7l) and am wondering how to test the MAP sensor? The truck is sluggish, idles rough and is down on power. Yesterday I disconnected the MAP sensor and the truck died. I restarted the truck with the sensor disconnected and the truck seemed to idle smoother with the sensor disconnected. I didn't drive it this way, so not sure what effect it had on performance.
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bykerdude59
Dodge Dakota
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8/29/2005
11:40:32
| RE: MAP sensor Q?
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Here you go:
http://autorepair.about.com/library/faqs/bl917d.htm
The voltage should be at 4.5 to 5 with the key on engine off. Then with the truck idling it should be low (1.5 to 2.1 volts) then give it some gas and the voltage should rise until 4.5 to 5 at wide open throttle.
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Patriot QC
Dodge Dakota
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8/29/2005
11:47:53
| RE: MAP sensor Q?
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I've got an Actron scanner that shows the In-Hg for the MAP sensor. Do you know what the factory manuals say the sensor should read at idle and under load?
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bykerdude59
Dodge Dakota
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8/29/2005
12:40:00
| RE: MAP sensor Q?
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Correct me if I am wrong, but the map sensor just reads the vacuum in the motor and transmits the information in voltage format back to the pcm. So I don't think having a meter that measures vacuum would help much in testing the MAP. If the MAP is not functioning properly, then it wouldn't be sending the appropriate voltage signal. The vacuum meter may help you determine whether or not you have a vacuum leak or not. In short...I am not sure
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Patriot QC
Dodge Dakota
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8/29/2005
13:27:36
| RE: MAP sensor Q?
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I think you are correct to a point. If I knew what the factory specs were in terms of In-Hg at idle and at cruise and/or WOT, then I could see whether the sensor signal is being converted at the PCM to the correct value.
I don't know if that makes sense or not.
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bykerdude59
Dodge Dakota
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8/29/2005
13:43:58
| RE: MAP sensor Q?
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In regards to if that makes sense or not, you are just trying to determine the amount of vacuum that goes to the sensor (in/hg) at idle to WOT? correct? I am not sure as to where one would find this information. Seems to me it may be easier to inspect your vacuum lines for cracks and or disconnected lines. Then simply check the voltage read out. If you don't have a voltmeter, I think Autozone just requires a deposit, and you get your money back. You can check it in the parking lot.
On a second note, what kind of problems are you having. Your original post didn't mention much. Where are you located?
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Patriot QC
Dodge Dakota
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8/29/2005
13:55:28
| RE: MAP sensor Q?
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I'm in Lewisville, Tx. I've got the 4.7l, so the cracked vacuum line is out as the sensor is bolted directly to the intake manifold.
Yeah, I think that we were looking at it from two different angles regarding the manifold vacuum vs the sensor value. I think that you're saying that I need to verify the actual vacuum being produced by the motor. I am trying to determine if my MAP sensor is lying to my PCM and causing a mixture problem. So, you are probably correct in what you're saying. I probably do need to get a vacuum gauge to see of the actual vacuum compares to the converted sensor reading.
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Duner
Dodge Dakota
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8/29/2005
14:03:10
| RE: MAP sensor Q?
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Your original symptoms sound more like old and worn sparkplugs or dirty stock injectors. Both issues will effect idle and performance in general. I'd leave the MAP alone and check those first.
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Patriot QC
Dodge Dakota
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8/29/2005
16:00:01
| RE: MAP sensor Q?
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I wish it were that simple! I've changed the plugs twice in this dang thing. Counting the originals, thats three different sets. The second set was Autolite. In my travels trying to get the problem fixed, the dealership tried to blame the issue on the wrong brand of plug, so I switched them back to Champions.
The truck only has 30,000 miles. Do you think that the injectors could really be dirty enough to cause this kind of issue.
Another thing that I didn't mention before, sometimes when I floor-board it, the engine will bog down around 3,000 RPM.
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bykerdude59
Dodge Dakota
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8/30/2005
13:16:26
| RE: MAP sensor Q?
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Originally I thought you were trying to test the MAP sesnor, so I gave you a link on the voltages that should be put out roughly. But you mentioned the in/hg so that is where I got confused with what you were tyring to do. Anyhow good luck with that. I have a 99 5.2 so I don't have clue as to the 4.7. My truck also bogs down at 2500-3000 rpm, only sometimes though, it will nearly stall whether or not I am giving it full throttle. Good luck, sorry for my confusion
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Patriot QC
Dodge Dakota
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8/30/2005
13:47:46
| RE: MAP sensor Q?
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No reason to apologize! I appreciate your taking the time to try and help me out.
Yesterday, when I got home, I hooked up my OBDII scanner to see what the sensor was reading. The MAP was reading 10 In-Hg at idle. That seems awfully low. Can someone tell me if that sounds like a normal vacuum level.
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ticats
Dodge Dakota
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8/31/2005
07:52:58
| RE: MAP sensor Q?
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Don't know about the 4.7L but that would be way low for the 3.9/5.2/5.9 family (pcm would be able to handle vacuum that low). If same for the 4.7, then there's a vacuum leak somewhere.
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Patriot QC
Dodge Dakota
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8/31/2005
09:37:45
| RE: MAP sensor Q?
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Would a clogged cat cause the same thing?
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ticats
Dodge Dakota
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8/31/2005
10:24:44
| RE: MAP sensor Q?
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It's possible depending on the amount of contamination and break up of the substrate in the cat. You can tap the in and out pipes at the cat with a rubber mallet and see if you hear anything rattling around inside.
That MAP vacuum reading is awfully low though. With the magnums, anything in the low 12s usually translates into driveability problems. Google search and see if you get any hits about it for your 4.7L.
Good luck.
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Patriot QC
Dodge Dakota
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9/01/2005
09:25:51
| RE: MAP sensor Q?
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I tried a search with Google and didn't get anything 4.7 specific. My truck has been running like crap since around 15,000 miles. Various dealerships have changed the cam position sensor, the crank position sensor and the O2's. I think that I'm gonna take the truck back and tell them about the low vacuum level from the MAP sensor. I bought the OBDII scanner after all of this work had been performed, so I don't know if the vacuum has always been this low. It's just frustrating when you drive the truck every day and you know that there has been a degradation in the way that the truck performs, but the dealership refuses to take an interest in resolving the problem and continuously tells you that the vehicle is operating as designed!
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ticats
Dodge Dakota
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9/01/2005
15:57:45
| RE: MAP sensor Q?
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An all too common occurrence :-(
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dickc
Dodge Dakota
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9/01/2005
20:21:08
| RE: MAP sensor Q?
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I have the Powertrain Diagnostic Manual for my '01 4.7. The PCM monitors the signal voltage from the MAP Sensor. Voltage below 0.1 volt will set a P0107 code. Voltage above 4.88 will set a P0108 code. I have been unable to find a chart that translates the voltage readings to vacuum. Just because a code hasn't been set doesn't rule out the sensor as the source of your problem. I had an S-10 that would suddenly shut down for no obvious reason, mostly in the middle of intersections. The MAP Sensor was shorting internally and never set a code.
Good luck
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Patriot QC
Dodge Dakota
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9/01/2005
21:14:53
| RE: MAP sensor Q?
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I disconnected the MAP sensor and drove the truck around the block. The idle seemed smoother, but the power still seemed off. A couple of times, with the gas pedal to the floor, the truck bucked. Is this characteristic of having the MAP sensor unplugged and driving it?
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Patriot QC
Dodge Dakota
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9/03/2005
11:15:33
| RE: MAP sensor Q?
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Alright, I did a couple of tests this morning to see whether the MAP is working correctly and if the CAT is clogged. I unscrewed the O2 sensor before the CAT and started up the truck with the scanner plugged in. The MAP sensor still reads 10 In-Hg. So that pretty much rules out the clogged CAT. I then disconnected the vapor canister port from the throttlebody and hooked up a vacuum gauge in its place. The vacuum gauge was reading 19 In-Hg vs the scanner reading of 10. Is it pretty safe to assume that the MAP is indeed gone south?
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Patriot QC
Dodge Dakota
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9/04/2005
13:05:52
| RE: MAP sensor Q?
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bump
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Patriot QC
Dodge Dakota
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9/10/2005
10:55:26
| RE: MAP sensor Q?
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Replaced the MAP sensor and all is well! Got my power back and fuel mileage is going back up.
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