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pete
Dodge Dakota
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2/16/2008
13:24:55
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 Subject: TYPICAL VACUUM READING
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Hey anyone can tell me a typical vacuum reading at IDLE at MAP Sensor with engine operating Iam getting 10-11 inches this normal ? when I connect to vacuum port on right side I get 17-18 inches. I thought MAP Sensor should have full vacuum at idle and decrease as engine load changes? Engine 3.9L
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dakota49
Dodge Dakota
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2/16/2008
14:49:09
| RE: TYPICAL VACUUM READING
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pete, you are correct, you should have engine/manifold vacuum at the port, you can block off the port and hook up to a manifold port and it should work fine.
Good Luck
Dakota49
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pete
Dodge Dakota
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2/16/2008
16:26:47
| RE: TYPICAL VACUUM READING
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dakota49,Is this telling me Map Sensor bad? or port where it connects blocked? engine runs fine. On my scanner is showing like the engine is reading that 10-11 inches at idle makes me think the engine is underload at idle drawing me to think its using more gas Thanks for input before I make a decesion what to do or replace sensor.Also thinking with Map sensor is screwed on the throttle body might be difficult to run a hose from underneath it might kink up on the manifold or melt from temperatures from intake manifold because of Mag. motor with that bulky aluminum manifold, or can relocate Map sensor like the older dakotas like on the firewall fenderwall?
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dakota49
Dodge Dakota
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2/16/2008
22:15:09
| RE: TYPICAL VACUUM READING
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I think you can relocate the Map sensor, but yes I think the port may be pluged up, you could remove the sensor and clean out the port and that should do the trick. Thing is, it could be clogged in the throttle body its self and may require removing the throttle body to clean correctly. If you remove the throttle body to clean I would suggest you remove all sensors and do a through cleaning. Just be very careful with the sensors because they can get hurt easily if mishandled. You are right if its only getting between 10-11 inches of vac. then the computer will think the engine is under load and could be using more gas than it needs to.
Good Luck
Dakota49
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pete
Dodge Dakota
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2/17/2008
09:28:58
| RE: TYPICAL VACUUM READING
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I was thinking the throttle body could use a though cleaning has never been done, I have cleaned out IAC twice as maintenance with tuneups,overlook this but after reading many posts here and other places suggest to do this to keep your mileage steady and running properly.The only thing Iam suffering in mileage about 13.7 average and was thinking was just the colder weather and winter grade of gas.I know my 02's are ok change them bout 65,000 miles and switching good and concerned that the Map sensor could foul them out or plug the cat up which isn't the case yet.
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daddio
Dodge Dakota
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2/17/2008
10:08:42
| RE: TYPICAL VACUUM READING
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did you check the little rubber hose that connects the MAP to the TB? if its cracked it will not see full vacuum. either that or the map is bad.
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pete
Dodge Dakota
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2/17/2008
15:15:26
| RE: TYPICAL VACUUM READING
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yes did swap with new one no change in vacuum reading thinking so more sensor might be on its outs but either diaphragms in there are cracked causing it to lose vacuum or the spring broke and just in the right spot to still work maybe iam going to much detail there but thoughts why iam getting low vacuum to sensor before i clean the throttle body going to try moving vacuum to another source and compare reading then to determined if sensor is bad not a cheap sensor by means
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OBIO3
Dodge Dakota
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2/17/2008
16:42:06
| RE: TYPICAL VACUUM READING
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Don't forget you drop a number for each 1000 ft elevation apx.
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pete
Dodge Dakota
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2/18/2008
10:30:54
| RE: TYPICAL VACUUM READING
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OBIO3, currently at 580ft. above sea level in the state of MI the area I live in which no correction factor needed here. Also when I go though the routine check starting with key on no start I get a reading of 28 inches of vacuum NOT RUNNING? when running like I stated before 10 inches? debate whether to clean throttle body or sway sensor which is bout $100 and some change. Also have no faults stored or MIL on.
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pete
Dodge Dakota
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2/18/2008
16:03:32
| RE: TYPICAL VACUUM READING
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Well,I swapped vacuum line to another full vacuum source and compared readings still the same,then hooked up vacuum gauge to see if port was plugged which wasn't the case getting same reading every where i connect to full vacuum source and sprayed some carb/throttle spray into the port where Map Sensor goes rechecked vacuum reading same.Restored everything back to its original location and leading me to believe sensor is bad,if this matters when hook up my scanner it reads Map sensor in KPA and when i convert the math which 33-34KPA = 10-11inches right? so this tell me i have a bad MAP Sensor but bothered why it hasn't tripped my MIL or is it borderline of failing to come or is my PCM not ? whatever the case, hate to babble on just would like to see this 13.7 mpg go back up have gone through everything else this is where cant go any further till iam sure this sensor is doing its job dont want drop a 100 bill and not cure this problem i stumbled on
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OBIO3
Dodge Dakota
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2/18/2008
16:28:28
| RE: TYPICAL VACUUM READING
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Without going back here to read again take it to a parts store that can read codes. the key trick does not always work
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daddio
Dodge Dakota
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2/18/2008
16:55:20
| RE: TYPICAL VACUUM READING
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pete, your math is correct 34kpa= 10.0402"Hg have you checked the voltage to the sensor maybe it is low causing the false readings. i'm sure you could check it using a vacuum pump and a DVOM while the truck is not running. backprobe the connector and apply vacuum to see if the readings change.
what year is your truck? '00 & up the key on/off trick works for displaying codes.
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pete
Dodge Dakota
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2/18/2008
17:19:42
| RE: TYPICAL VACUUM READING
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Truck is 02/3.9L MagMotor and Iam using my ACTRON CP9180 Plus tester and was going to invest in hand vacuum pump when i was at the store but didn't,wouldn't i get a fault stored in my tester if i wasn't getting 5 volt reference to the sensor or any fault showing in this sensor?
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daddio
Dodge Dakota
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2/18/2008
17:44:12
| RE: TYPICAL VACUUM READING
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"wouldn't i get a fault stored in my tester if i wasn't getting 5 volt reference to the sensor or any fault showing in this sensor?"
probably true, unless possibly it was low but within allowable tolerances. i am not sure what the specs are on those sensors.
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pete
Dodge Dakota
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2/18/2008
23:36:46
| RE: TYPICAL VACUUM READING
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what i meant wouldn't i have trouble code fault stored in PCM or if my scan tool pickup a fault in the MAP sensor, far as 5 volt reference voltage just was throwing one of the codes it would detect if it faulted i know most MAP codes fall under from P0105-P0109 and my scan tool showing NO faults and assuming this sensor is doing its job but when doing the recording data feature i get that low vacuum reading and not storing a code something isn't right?? look at all possibilties like vacuum leaks,intake leaking injectors leaking-o'rings throttle body leaking just a few ruled out and anything hinder the MAP Sensor readings but running out of ideas, and most of all truck is running good just rotten mileage the typical common complaint among most? of us dakota drivers?
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daddio
Dodge Dakota
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2/19/2008
08:42:37
| RE: TYPICAL VACUUM READING
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trust your mechanical gage reading. if there was a leak it would have indicated such. technology is great, until it breaks!
the pcm won't store or indicate codes for a lazy O2 sensor either, but it will sure make your mileage take a dive.
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pete
Dodge Dakota
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2/19/2008
09:44:56
| RE: TYPICAL VACUUM READING
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daddio,agree Iam old school mechanic from the 80's to early 90's as day in age of fuel injection was just coming into the picture and that when i left the field around 2000-01 or so do know much about fuel injection and training that i have and vacuum gauge is the mechanics best freind if they understand how to read it and same goes for these scan tools which is an aided device for technician to make an easier diagnoisis.And thats what iam i going do dive in and gamble with my knowledge
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daddio
Dodge Dakota
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2/19/2008
09:57:48
| RE: TYPICAL VACUUM READING
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pete, i am old enough to remember rebuilding and adjusting carbs with my trusty vacuum gage, which i still have. i love technology and yes those handheld scanners are invaluable tools to the modern mechanic.
it is a shame that these manufacturers use cheap sensors to monitor engine functions and they are probably no more accurate than aboout + or - 10% if you're lucky. if they tightened up those tolerances these new vehicles would be way more efficient.
sounds like you know hat you need to do. good luck and keep us posted.
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pete
Dodge Dakota
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2/19/2008
10:14:59
| RE: TYPICAL VACUUM READING
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same here carbs were fun and when they went to mixture controlled solenoids sealed mixture screws one wire 02 sensors and could go on
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pete
Dodge Dakota
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2/19/2008
10:26:12
| RE: TYPICAL VACUUM READING
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will keep you posted weather turned cold up here and dont have a garage tinker with it wait till gets a little warmer again, any more input from anyone pass on thanks again
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pete
Dodge Dakota
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2/20/2008
21:59:15
| RE: TYPICAL VACUUM READING
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Back again for some thinking and waiting for it to warm up some I was reading in ALLPAR page fixing common problems thread and stumbled across something with some 2.2&2.5L 4cylinders not related to the 3.9L's the MAP Sensor on those collect condensation inside and causing the armature to rust up and fall apart and cause all the symptoms you would expect,my thoughts were thinking maybe this is my case got moisture in there collected and might cause the armature in there to rust up and possibly hanging up were it collaspe just enough to keep it in tact were its telling the PCM that throttle is over 1/2 to 3/4 or somewhere in there (even though truck is idling) and scanner showing that the MAP sensor is only getting 10 inches of vacuum.Once its gets warmer I going to take a drive over my folks house my dad has same truck but 03'/3.9L going swap out his MAP sensor with mind and compare readings that will save my wallet until I know this sensor is bad or good. Also heard some Fords exhibit similar issues with MAP sensors not that anyone cares since were all DODGE here and will keep on driving a DODGE long as I can!
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