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coulsonan 07-07-2013 08:00 PM

Jeep Stalling
My 99 Jeep Grand Cherokee is stalling out. If I'm standing still it just dies, but if I'm moving I can pump the gas and sometimes it will come back alive. Most times I have to slide off the road and continue to try to start the engine. This will take anywhere from 2-5 minutes, often longer. This started about a year ago happening 10 times in 10 months, and has escalated to every time I run the jeep for the last two weeks. What could be wrong?

Frango100 07-07-2013 08:26 PM

Re: Jeep Stalling
Which engine? Is the preventive maintenance done in time (ignitor plugs, air filter etc)? Did you check for eventual fault codes set, using the key dance? (ignition switch off/on three times and leave in on at the third time. The odometer will show "DONE" when all ok, or any fault code.)
Does it run ok at higher rpm's? Could be a problem with the Idle Air Control stepper motor or a dirty/clogged idle air passage. Remove the IAC stepper motor and clean the plunjer (don't twist it, otherwise you could damage the anti rotation tabs) and the air canal.

coulsonan 07-07-2013 09:51 PM

Re: Jeep Stalling
4.7v8, and yes maintenance is done, key dance reads P 1296 and then done, yes, it seems to run better on higher rpms, will check the IAC in the morning

Frango100 07-07-2013 10:49 PM

Re: Jeep Stalling
P1296 = No 5 Volts to MAP Sensor, Loss of a 5 volt feed to the MAP Sensor has been detected.
Eventhough cleaning of the IAC is a good thing once in a while, it most probably will not help in this case. There could be something wrong with the MAP sensor (intake Manifold Air Pressure sensor), or one of the wires is shaved through and makes contact to ground once in a while. The sensor is mounted on the front side of the intake manifold with two bolts. Check the connector for dirt/grease and the wires as far as possible for shaving or other damage.

coulsonan 07-08-2013 04:16 PM

Re: Jeep Stalling
I replaced the sensor a year ago, I tested the sensor and it's getting 5v, but it's not putting out 5v, and when I was trying read the output it wasn't consistent, it was fluxuating.

Frango100 07-08-2013 05:43 PM

Re: Jeep Stalling
The input voltage is regulated by the PCM at 5 V, so that seems to be ok.
The output voltage depends on the barometric pressure (and because of this, on the altitude the jeep is at). At sea level the voltage should be around 4.6 V and this value goes down to 0.3 V at high altitude. A fluctuating value is not normal. Did you measure it with the engine running or off (and ignition in run)? When the input voltage is steady, then or the MAP sensor is faulty, or there is a problem with the wiring.
There is a splice in the wiring close to the #7 ignition coil, splice S107.
You could measure the continuity of the wiring to rule out any problems there.
Measure from MAP sensor connector slot 2 to the PCM connector C1 slot 4. (this is the sensor ground). There should be continuity and a steady indication when you wiggle a bit with the wiring.
Do the same from MAP sensor connector slot 1 to PCM connector C1 slot 27. This should also give continuity and a steady indication. When these measurements are ok, then most probably the MAP sensor is faulty again.

coulsonan 07-09-2013 03:17 PM

Re: Jeep Stalling
I apologize, I tested the wrong sensor, don't know what was in my head, but I did replace the sensor a year ago, on the correct sensor this time when the key is on and I ground my tester and test wire 1 it reads 5v and the same with wire 3, and when I put pos on wire 1 and neg on wire 3 I get nothing, what does that mean?

Frango100 07-09-2013 06:26 PM

Re: Jeep Stalling
Slot 3 is the supply reference signal from the PCM, which should be 5 V= OK
Slot 1 is the output signal from the MAP sensor and should be slightly lower then the supply power at sealevel or a lot lower at higher altitude.
If you get exact the same voltage at point 1 as at point 3, then there is ofcourse no differential between those points and you will measure 0 V.
That the supply voltage is the same as the output signal, that is strange. Did you already measure in ohms range between slot 2 from the MAP sensor and slot 4 from PCM connector C1 (both connectors disconnected)? There should be no or a very low resistance.
The fact that input voltage and output voltage are the same, does me make believe that there is a problem with the sensor ground. This sensor ground doesn't necessarely have to be connected directly to chassis ground, it goes into the PCM. As told before, there is a splice in this ground wire close to ignitor coil #7 (left aft cylinder as seen from drivers position). So when you check the continuity of the sensor ground wire, wiggle a bit with the wire bundle, especially close to the ignitor #7, and see if it is steady or fluctuating or maybe even open.

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