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Every time I hook the vacuum line up to the map sensor the truck just dies but with the map sensor unhooked it will idle but not perform under load????

I have put in a new timing chain a new distributor, all new ignition system, new computer, new fuel pump, new fuel regulator, and fuel filter, basically everything but the head gaskets is new.

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  • Cars & Trucks Master
  • 14,585 Answers

It's normal for this to happen. It should start back up though. When trying to restart, open the throttle all the way. If it still doesn't start, you may have to reset the codes.

Posted on Apr 19, 2015

Testimonial: "Randy was extremely helpful. A Pleasure to deal with thanks for you patience Randy."

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  • Debbie Knepprath Apr 19, 2015

    It will restart if I unplug the vacuum hose????

  • Randy Ohler Apr 19, 2015

    Leave the hose on and start it. With it unplugged and plugging it in, it is like going from Florida(sea level) to Colorado( 1 mile higher) in a split second. Try starting it and rev it up some, then put the hose on. Give the PCM a little time to adjust.

  • Debbie Knepprath Apr 19, 2015

    I am actually asking for my son, as soon as he tries this I will let you know. Thank you for your help

  • Debbie Knepprath Apr 19, 2015

    He tried this and if he plugs vac hose in and map sensor unhooked it will run when he applies vac hose from vac pump to map sensor motor dies?

  • Randy Ohler Apr 19, 2015

    The map sensor vacuum line goes the intake. not the pump. This could be the problem. What year is it? There can be a pump on older models, but the pump is for Exhaust. It pushes air, not a vacuum. Again, year make and model please. Also engine size. diesel or gas?

  • Debbie Knepprath Apr 19, 2015

    1994 Chevy Suburban 2500 with a 7.5 litre engine and gas. He says it doesn' t have a pump. He can get it to run by creating a leak by putting the vacuum to the map sensor and it will run (not good but stays running). All Electrical is new

  • Randy Ohler Apr 19, 2015

    having to have a vacuum leak to keep in running means there is air restriction from the throttle body to air air filter. Remove the air filter and clean the throttle body inside. Behind the plate and where the plate seats around the throttle. Also look at clean the idle air control motor or replacing it.

  • Debbie Knepprath Apr 19, 2015

    He wants you to know how much he appreciates your help, he has talked to a lot of people about this and you are giving him different options than anyone else has so is encouraged you are probably on the right track. He said to let you know the throttle body and plate and idle air motor are all clean. Pretty sure idle aire control motor is good but not positive.

  • Randy Ohler Apr 19, 2015

    Tell him, I applaud him for doing the work himself. Not many young ones (even older ones) do this now days. Mostly want Dad( or Mom) to fix it or pay to have it fixed. Just tell him to keep in mind the idle air control motor. Older ones that go bad,usually the spring in them will push them closed and shut off air. These are the equivalent of the older choke systems.

  • Debbie Knepprath Apr 19, 2015

    When he hooks up the vac line to map sensor the idle air valve closes and tries to shut the motor down. He will go ahead and replace the idle air control motor.

  • Randy Ohler Apr 19, 2015

    I don't really think I would do that. If the IAC( idle air control ) Is open and then shuts off. I would suspect other things. He should be able to hear the IAC on and off. Open it will make a louder sucking air noise. Closed wouldn't make the noise or just get quieter. This means the IAC is working. This would have to be read by a scanner. But is probably his best bet at this point. Does he know how to use a volt /ohm meter? Let me know before he puts the new motor in. I'll tell him/you how to check the old against the new. Once the new one is in, you can't get your money back.

  • Debbie Knepprath Apr 19, 2015

    Ok yes he does know how to use the Dvom and according to your instructions above it is working right. What would you suggest from here. He says he has good compression every cylinder has 130 PSI.

  • Randy Ohler Apr 19, 2015

    This is just a guess. But I would say the MAP sensor is bad. Get a new one have have him check the resistance of the old and new. Check all the leads against each other, then check the old one and compare values. They should be close if both are good. If the old one checks way off, it is bad. After that would come checking wires for continuity ( No more than 5 ohms resistance) After that would be the computer.

  • Debbie Knepprath Apr 19, 2015

    He had replaced the MAP sensor with a new one but went ahead and checked it like you suggested and it tested bad. Praying this is the cause. Thank you so much for all your help. I will let you know how it turns out.

  • Debbie Knepprath Apr 19, 2015

    Ok the Map sensor was ok but he checked the wires for continuity and they are reading above 5 ohms and not consistent. What can he do about that?

  • Randy Ohler Apr 21, 2015

    Replace the wires. Any thing above 5 is to much. I run new wires from the part(MAP?) to the PCM. Give your self enough wire at the plugs to reconnect. I always solder computer wires and shrink wrap them.

  • Randy Ohler Apr 21, 2015

    PS. recheck the wire when you cut the. From the plug end to the cut. Make sure the resistance is good. Should be 0 or really close.

  • Debbie Knepprath Apr 22, 2015

    Wow he is ready to get rid of this vehicle, He did the wires ohms were good so changed the computer and still same problem. He says there isn't anything left thats not new.

  • Randy Ohler Apr 23, 2015

    This is way out there, but did he replace the PCV valve. It is a fairly big vacuum line. I hae seen effect engines , that never would have thought it could do.

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  • Cars & Trucks Master
  • 3,206 Answers

Just wondering if you plug the vacuum line to the MAP when it is disconnected?
If you don't then as well as having a disconnected MAP you also have an air leak and maybe it is that which keeps it idling if the idle air valve is stuck or malfunctioning.

It could be the vehicle basic settings need installing with diagnostic equipment.

Posted on Apr 19, 2015

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1 Answer

What does code PO108 mean on a 2001 Grand Cherokee


wow , you actually tried to look it up, a 1st time here.

the MAP is a baro sensor used to calculate fuel injection RATES.

if you have gross air leaks to the system the engine IDLE screams.

is it?

108 means the voltage is too high.

usually its unplugged, or bad sensor.

otential causes of a P0108 code: Bad MAP sensor Leak in vacuum supply line to MAP sensor Engine vacuum leak Short on signal wire to PCM Short on reference voltage wire from PCM Open in ground circuit to MAP Worn engine causing low vacuum



Bad MAP sensor Leak in vacuum supply line to MAP sensor Engine vacuum leak Short on signal wire to PCM Short on reference voltage wire from PCM Open in ground circuit to MAP Worn engine causing low vacuum



http://www.obd-codes.com/p0108



and last. but before ECU.

low engine compression, is 1 more, causes , many



what i do is reseat the MAP sensor

i then make sure he vacuum port is not clogged. (both sides)

i then measure the output , keyon, and idle and gunning throttle.

any Voltmeter works here,

key on is 5v or near.

idle 1.8v

gun engine as the RPMs fall like a rock the volts tries to hit 0.5vdc.



http://www.fixkick.com/look/odds-ends/jeep/MAP-sensor-output-real.jpg



very very easy to find with a voltmeter

if the meter agrees with vacuum gage, then the MAP is ok

and you have air leaks or low vacuum for (VAST reasons)

ask.

Aug 19, 2014 | 2001 Jeep Grand Cherokee

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Have you checked the compression in the cylinders? Low compression can cause stalling.

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code p 0106 refers to manifold absolute pressure (MAP)sensor or barometric pressure (BARO ) sensor---range /performance problem====causes ---intake / exhaust leak---wiring --- MAP pr BARO sensor problems
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I have a 1988 GMC 1500 with a 305 the problem is that it wont idle I found that if I pull the vacum line off the MAP sensor it is fine for 30 seconds then dies I got a new map sensor and nothing chan


Change the PCP valve and run the heater. This should take care of it. You only have to run the heater one time as this is controlled by the vacuum system. This will cause your motor to run proper.

Apr 09, 2012 | Cars & Trucks

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89 jeep dies when u hook up map sensor


If you connect it while engine is running, engine will die, start engine and check that you have vacuum going to MAP sensort, if you do, could be a bad MAP sensor, if no vacuum add in-take vacuum, if engine light is on, do a computer diag. where you can see MAP senor data.

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Check the map sensor on the firewall and make sure the vacuum line is not broken.

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Car starts good but has rough idle and dies in a few seconds.


sound like intake leak. get a scanner to see if egr valve not staying open . check map sensor + make sure the vacuum line didnt come off it . check coolant sensor. oxygen sensor .check fuel pressure regulator. check vacuum line that goes to fuel pressur e regulator . make sure there is no gas in it. make sure its getting vacuum. check pvc valve.shake it make sure it rattle .

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