over drive wont hold?
Champion
Joined: Jan 2013
Posts: 4,737
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From: Northwest Louisiana
Since my 1988 is TBI, not MPFI/SEFI, I have to look at drawings.
My drawings say the MAP sensor is on the back.
If it's sucking vacuum, it's broken; you need to replace it.
And yes, it's used to help determine how much vacuum you have at any given moment, which is used in conjuction with the TPS to decide how much throttle you have and what the engine load is; the O2 is also used as feed back. The ECU can figure out close'nuff sometimes with one of the three out - but if your MAP is sucking vacuum, the internal is broken, and that may explain why the overdrive is dropping out (not enough vacuum according to the ECU; also not enough vacuum in real life.)
(The IAC is on the other side, but the drawings in the 2001 FSM show the IAC towards the #1 cylinder. If I'm reading it wrong, then your IAC is sucking open air; and THAT'S wrong also. It should be bleeding air from the throttle body upper side to the lower side to bypass the plates on idle.)
RwP
My drawings say the MAP sensor is on the back.
If it's sucking vacuum, it's broken; you need to replace it.
And yes, it's used to help determine how much vacuum you have at any given moment, which is used in conjuction with the TPS to decide how much throttle you have and what the engine load is; the O2 is also used as feed back. The ECU can figure out close'nuff sometimes with one of the three out - but if your MAP is sucking vacuum, the internal is broken, and that may explain why the overdrive is dropping out (not enough vacuum according to the ECU; also not enough vacuum in real life.)
(The IAC is on the other side, but the drawings in the 2001 FSM show the IAC towards the #1 cylinder. If I'm reading it wrong, then your IAC is sucking open air; and THAT'S wrong also. It should be bleeding air from the throttle body upper side to the lower side to bypass the plates on idle.)
RwP
Champion
Joined: Sep 2013
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If there is no rubber elbow from the bottom outlet of the MAP sensor to the TB then that may be all that is missing. When you purchase a new one it asks that you reuse the rubber elbow which on mine was stuck dangerously tight to the sensor and the TB I almost tore it apart. Here is a link to a pic of one for my truck http://www.rockauto.com/en/moreinfo....249&cc=1087578 Seems to be the same as the one for the 93 5.2L
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Veteran
Joined: Jul 2017
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From: Rich Square NC
I Cant take a picture right now its pouring down rain, BUT I replaced the IAC and it runs smoother BUT it STILL takes half a tank to go to and from work, and it STILL goes in an out of od, does anybody have any other ideas before I saw screw it and send this thing to a junk yard and but a scooter? Compliments of the hurricane in Texas and the lie about gas shortages gas here is up to 265 a gallon and rising and I cant afford to put gas in the dodge. map sensor is in the front on mine and working no broken line, I work 40 miles away in Robersonville and half a tank there and back is totally unacceptable since my wife's F150 makes it there and back on 1/8 tank with a V8
Champion
Joined: Sep 2013
Posts: 2,728
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OK then this description has me back at my original take. I have the 94 3.9 with the 22gallon tank it ran out at 150 miles on the trip odo on my first fill up. That's 6.8 mpg. The thing I landed on doing after going through the advice on many sites and joining here which fixed that is the plenum kit and all the sensors on the intake and TB as well as the Cam sensor and crank sensor. The crank sensor I did a few months later and it made a big change in how it responded. The first tank after the plenum etcetera I got 17.5 mpg or 385 miles. I intentionally ran that one out to see what I would get. I had a can of gas with me. Changing out the injectors and fixing broken exhaust studs and new exhaust further improved it. It is a dodge but now at least it is reliably the same each time I get in. MPGs have settled on 14-15 as I drive mostly in town.
Good Luck whatever you choose to do. I also changed injectors for a rebuilt set. I did not notice any changes from that. http://www.fuelinjector.citymaker.co...25/4735745.htm
Good Luck whatever you choose to do. I also changed injectors for a rebuilt set. I did not notice any changes from that. http://www.fuelinjector.citymaker.co...25/4735745.htm
Thread Starter
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Veteran
Joined: Jul 2017
Posts: 264
Likes: 15
From: Rich Square NC
OK then this description has me back at my original take. I have the 94 3.9 with the 22gallon tank it ran out at 150 miles on the trip odo on my first fill up. That's 6.8 mpg. The thing I landed on doing after going through the advice on many sites and joining here which fixed that is the plenum kit and all the sensors on the intake and TB as well as the Cam sensor and crank sensor. The crank sensor I did a few months later and it made a big change in how it responded. The first tank after the plenum etcetera I got 17.5 mpg or 385 miles. I intentionally ran that one out to see what I would get. I had a can of gas with me. Changing out the injectors and fixing broken exhaust studs and new exhaust further improved it. It is a dodge but now at least it is reliably the same each time I get in. MPGs have settled on 14-15 as I drive mostly in town.
Good Luck whatever you choose to do. I also changed injectors for a rebuilt set. I did not notice any changes from that. http://www.fuelinjector.citymaker.co...25/4735745.htm
Good Luck whatever you choose to do. I also changed injectors for a rebuilt set. I did not notice any changes from that. http://www.fuelinjector.citymaker.co...25/4735745.htm
Champion
Joined: Jan 2013
Posts: 4,737
Likes: 374
From: Northwest Louisiana
I wondr if teh PCM even does anything, I have YET to see teh engine light on start and it never comes on, if it was a checy that light would have 4 million codes by now
After change ing the valve now it runs too good for a plenum gasket being bad unless they can go bad and pull good vacuum
After change ing the valve now it runs too good for a plenum gasket being bad unless they can go bad and pull good vacuum
2) Didn't you say 14 inch of vacuum earlier? That's not good vacuum, that's either "Vacuum leak" or "Motor's shot" vacuum.
RwP
Record Breaker
Joined: Apr 2010
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I Cant take a picture right now its pouring down rain, BUT I replaced the IAC and it runs smoother BUT it STILL takes half a tank to go to and from work, and it STILL goes in an out of od, does anybody have any other ideas before I saw screw it and send this thing to a junk yard and but a scooter? Compliments of the hurricane in Texas and the lie about gas shortages gas here is up to 265 a gallon and rising and I cant afford to put gas in the dodge. map sensor is in the front on mine and working no broken line, I work 40 miles away in Robersonville and half a tank there and back is totally unacceptable since my wife's F150 makes it there and back on 1/8 tank with a V8
In the time you have been here asking about what to do you could have been 1/2 done with the job.... just sayin.
Champion
Joined: Sep 2013
Posts: 2,728
Likes: 153
Make sure the exhaust manifold studs are not broken and the CAT is not plugged. That will affect the data the computer acts on and that may affect rpm's and by that how the OD behaves. I had a loose tappet sound when I was going up a hill, that was fixed when I fixed the broken studs on the exhaust manifold. It made a difference in how it drove and the early kick in drop out of OD. It made me nuts when I was on an on ramp and it would go into OD at 40 while I was trying to accelerate because of how much power that drops out from the peddle. It rarely goes into OD unexpectedly now.
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Veteran
Joined: Jul 2017
Posts: 264
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From: Rich Square NC
Then on the days when it does run correctly explain the shift at 15 27 35 and 45, if I keep my foot in it?
Yes I looked the rust is all external, nothing inside (yet)
I'm STILL preying to the dodge gods that I don't have a plenum problem, but I might just do it anyway, gonna pull a vac test today since I did the iac, the trans still does the in and out thing starting to think its the $38 sidelong set in the trans I did find a video on it BUT the gas mileage thing may very well be the O2 sensor, I'm in the dark here since the check engine light never comes on.
one of tease days I gotta rip the dash out and see if there's a missing bulb, unless I just don't give a rats behind and do it all the old fashioned way
the thing is that if the plenum gasket is bad it WILL give you a vacuum leak!!! it will suck air from within the crank case.
I would do the intake as a matter of maintenance just due to the age of the truck... gaskets are around $26, valve cover gaskets are around $20 and a gallon of anti freeze (if you buy concentrate and add your own water) plus a bypass hose ($6 that's the 1" hose at front of intake that leads to top of water pump, almost a must unless it has been replaced recently, if not, it is a water leak waiting to happen. is your engine leaking oil? ANY oil at back of intake? That means intake has to come off anyway for new gaskets. and at that point it's a few more minutes to flip the intake over to change the plenum gasket. the oil leaking out the front or back of the intake is no indicator of plenum condition, sure... take the lid off the air cleaner, and WITH ENGINE OFF, open the throttle fully and look inside with a flashlight. If it is coated with oil within the plenum gasket NEEDS TO BE CHANGED! do not be afraid of this job it isn't as bad as it may appear to be, I just did my 92 this past weekend.... I had to replace the water pump, and "as long as" I had the AC comp and alternator off along with their mount bracket and had the cooling syst. drained (which also coincidentally have to also come off to pull the intake) I might as well.
It appeared to have never been apart since being assembled at the factory but saying that, I found that the rear most 3 intake bolts especially on the driver side were barely snug, definitely nowhere near the 12 ft/lb they are supposed to be.
I had been putting up with that oil leak since I bought the truck 15 months and 30K miles ago....
I would do the intake as a matter of maintenance just due to the age of the truck... gaskets are around $26, valve cover gaskets are around $20 and a gallon of anti freeze (if you buy concentrate and add your own water) plus a bypass hose ($6 that's the 1" hose at front of intake that leads to top of water pump, almost a must unless it has been replaced recently, if not, it is a water leak waiting to happen. is your engine leaking oil? ANY oil at back of intake? That means intake has to come off anyway for new gaskets. and at that point it's a few more minutes to flip the intake over to change the plenum gasket. the oil leaking out the front or back of the intake is no indicator of plenum condition, sure... take the lid off the air cleaner, and WITH ENGINE OFF, open the throttle fully and look inside with a flashlight. If it is coated with oil within the plenum gasket NEEDS TO BE CHANGED! do not be afraid of this job it isn't as bad as it may appear to be, I just did my 92 this past weekend.... I had to replace the water pump, and "as long as" I had the AC comp and alternator off along with their mount bracket and had the cooling syst. drained (which also coincidentally have to also come off to pull the intake) I might as well.
It appeared to have never been apart since being assembled at the factory but saying that, I found that the rear most 3 intake bolts especially on the driver side were barely snug, definitely nowhere near the 12 ft/lb they are supposed to be.
I had been putting up with that oil leak since I bought the truck 15 months and 30K miles ago....
Make sure the exhaust manifold studs are not broken and the CAT is not plugged. That will affect the data the computer acts on and that may affect rpm's and by that how the OD behaves. I had a loose tappet sound when I was going up a hill, that was fixed when I fixed the broken studs on the exhaust manifold. It made a difference in how it drove and the early kick in drop out of OD. It made me nuts when I was on an on ramp and it would go into OD at 40 while I was trying to accelerate because of how much power that drops out from the peddle. It rarely goes into OD unexpectedly now.
one of tease days I gotta rip the dash out and see if there's a missing bulb, unless I just don't give a rats behind and do it all the old fashioned way