motor help

all right this one has me stumped. I swapped over a 5.2 and hooked everything up and the motor fires up for a couple of seconds and shuts down. I got it to run for about 5 seconds once and was able to rev it a couple of times before it shuts down again. Those couple of seconds it did run it sounded strong, no hesitation or missing. Now I'm starting to wonder if it may be a fuel issue? I have a new fuel filter on and the pump seems to be pumping a good amount of fuel but the motor still dies like it has ran out of fuel or someone has shut the key off. Also as soon as it dies I can start it right back up again if that makes any difference.

I think the problem is wih the crankshaft position sensor. This is what happens during startup mode

The following actions occur when the starter motor is engaged.
The PCM receives inputs from:
-Battery voltage
-Engine coolant temperature sensor
-CPS
-Intake manifold air temperature sensor
-MAP sensor
-TPS sensor
-Starter motor relay
-CMS position sensor
The PCM monitors the CPS. If the PCM does not receive a CPS signal within three seconds of cranking the engine, it will shut down the fuel injection system.
The fuel pump is activated by the PCM through the fuel pump relay
Voltage is applied to the fuel injectors with the ASD relay via the PCM. The PCM will then control the injection sequence and injector pulse width by turning the ground circuit to each individual injector on and off.
The PCM determines the proper ignition timing according to input received from the CPS.

If it was the crankshaft position sensor it would not fire at all. I think it the thief alarm was there one on the grand it came out of. Gill had this problem with his white Cherokee when the battery disconnects itself. We had to reset the alarm to get it to continue to run.

test it by locking the doors then unlock the rear first. That was the damnedest thing when it happened to me

one of my old grands did that once and more recently my wife's 5.2 durango, both times it was the battery gone bad. how good is your battery?? it might need replacing. also check all your grounds.. a bad or loose ground can be issue.

okay I'm 99% sure its in the computer now. Because I can make it run if I keep dumping fuel down the throttel body. So that means for some reason the injectors quit working after the jeep starts. so i'm guessing its some sort of sensor or like paul was saying in the alarm system. The only prob is i'm not sure how it works because the PCM came out of a jeep that had alarm, and went into a jeep that did not. so the door trick wont work becaue this jeep doesn't have the SAM installed. Also Bill what is a ASD relay? Someone posted up on another board about swapping out the BCM, but i'm not quite sure what it is, and they haven't responded back.

You swapped in a 5.2 from what?

If it were a smaller engine it may be that your fuel pump can not keep up.

The reason it may work when you first start it is the fuel pump will prime the system when you first turn the key to "on". Once that buffer is used your fuel pump has to take over the demand.

It is just a thought.

The anti theft is a good suggestion too. This may work by only cutting your fuel.

5.2 from another zj. As for the fuel pump thats what I thought also so I went ahead and swapped fuel pumps. I checked the fuel pressure right after it shut down and it still had plenty to the injectors. I guess nect stepis i'm going to have to pull the bcm apart and ground out the alarm system.

automatic shut down relay
couple links for you to try: http://autorepair.about.com/library/a/1h/bl651h.htm

ASD is in the box of relays under the hood:
http://autorepair.about.com/library/illustrations/bl508a-lib.htm

Found an answer for the security system bypass but you need to find a wire that came from the door. "Well, if you take your door panel off and find the wires going to the sensor in the door, there will be one that is purple with a yellow stripe. Cut it and ground the wire"

ASD (automatic shutdown) relay- The circuit to this relay is controlled by the computer to give power to the fuel system, specifically the injectors, o2 sensors, coil, CPS and others. This relay is located in the PDC but can be wired individually if you do not have the PDC.

BCM (Body Control Module)- Grand Cherokees have a body control module that operates many other features of that model. The absence of this module will not affect the engine unless the PCM is equipped with a security device. The PCM looks to the BCM for signs that the security system is de-activated. There is no way to deactivate the security system without the BCM because only the BCM has the required inputs to sense deactivation.

Link for the above information:
http://jeep.off-road.com/jeep/article/articleDetail.jsp?id=277042

One option is to remove the ASD relay and install a jumper wire in its place to provide constant ignition power for ignition and fuel system.

Here is a good link to the ASD relay that will help with the bypass. I think.

http://autorepair.about.com/library/faqs/bl561g.htm

Here is a link to the trouble codes if you have that working.
http://www.go.jeep-xj.info/HowtoECUcodes.htm

thanks bill lots of good info thank you very much. Looks like I have to figure out how to trick the computer with the security thing. I'm not sure if the door lock thing will work because the zj never had a theft system installed, so it doesn't have the SAM module to trick by grounding the door. I may be wrong on this though but i think I have to do something in the actual PCM to trick the computer.

okay it looks like i'm screwed. the problem turns out to be the pcm I have is from a zj with a security system so it wont work in a zj with out a securuty system. So I have to find a PCM from a non security system OBDI 5.2 ZJ which will let my zj fire right up. So if anyone knows were to pick one up let me know.

okay heres what I got, the 95 PCU is shutting the motor down due to the fact that the 93 did not come stock with a factory alarm. So the PCU is not reciving a signal from the SAM unit which was replaced in the 96 models and after by the BCM. So the problem now is that I have to get a signal to the PCU from the SAM unit. but the problem is that none of the wiring is built into the jeep (as far as I know) on the 93 to make it work. Ie the switches for the doors and key fab. So in doing reasearch I came across the following



DISARMING
Passive disarming occurs upon normal vehicle entry
(unlocking either front door or liftgate, with the
key). This disarming also will halt the alarm, once it
has been activated.
Active disarming occurs when the remote keyless
entry transmitter is used to unlock the vehicle doors.
This disarming also will halt the alarm, once it has
been activated.
POWER-UP MODE
When the battery is disconnected and then reconnected,
or when the battery has been drained and
the vehicle is being jump started, the VTA system enters
its power-up alarm mode which:


flashes the headlamps

flashes the park and tail lamps

prevents the engine from running.


The alarm system must be actively or passively

disarmed to exit the power-up mode after
any battery reconnection.


VEHICLE THEFT ALARM MODULE
The Vehicle Theft Alarm (VTA) module controls the
operation of the VTA system. Power for the module is
supplied from several sources. A constant battery
feed is supplied on circuit X3. This circuit is HOT at
all times, and protected by a 15 amp fuse located in
cavity 6 of the fuse block. Power for the fuse is supplied
by circuit A7 from the Power Distribution Center
(PDC) fuse 14.
Power is also supplied by circuits F86 and F87. The
F86 circuit is HOT in the ACCESSORY and RUN positions.
This circuit is protected by a 10 amp circuit
breaker located in cavity 27 of the fuse block. Power
for the circuit breaker is supplied by circuit A31 from
the ignition switch. Circuit F87 supplies power to the
module in the START or RUN positions and is protected
by a 15 amp fuse located in cavity 21 of the
fuse block.
The VTA module uses the CCD bus to communicate
with the Powertrain Control Module (PCM). Circuit
D1 is the CCD (+) and circuit D2 is the CCD(-).
Ground for the VTA module is supplied on the Z1
circuit from two cavities of the module.

DOOR AJAR SWITCH OPERATION
The VTA system uses the door/liftgate ajar
switches to provide an input to the VTA module.
These switches are normally OPEN with the doors/
liftgate closed. When a door or the liftgate is opened
the switch CLOSES completing a path to ground.
Circuit M2 is used to monitor the doors. This circuit
is also used as the ground circuit for the interior
lamps.
The G85 circuit is used for the liftgate ajar switch
input to the VTA module.
ARMING INPUT
The keyless entry module is used to supply the
VTA module with the arming input. This is accomplished
on circuit G49.
DISARM SWITCH OPERATION
There are three switches used to ARM and DISARM
the system. Two are located in the left front
and right front doors, and the third is located in the
liftgate. These switches are normally OPEN. When
the switch is CLOSED a path to ground is completed.
All of the switches are wired together and a single

input is provided to the module on circuit G71.

After reading this I came to the conclusion in order to trick the SAM unit and CPU into thinking that they circuits are functioning is to power up the unit but not grounding the switches that the SAM unit uses to arm the system, which would be the M2, G85, G70 and G71 circuit. But then I relized that with the power up mode you still would need some way to ground out the circuit temporarly so the SAM unit would think I used a key to disarm the system.

To make things even more fun I found out that the 93 and 95 Sam units are different. The plugs are differnt that come in from the jeep harness. So now I have to splice the 95 harness into the 93 wiring. So I'm guessing I will need to splice the following wires together in order to make it work.
*CCD Bus+ and CCD BUS- so the SAM unit can talk to the PCU
* coststant power feed
* the 2 ign feeds
* the 2 grounds
* and a ground switch to g71 which is the door and hatch controls

well, after searching for about an hour i came up with this
http://autorepair.about.com/library/faqs/bl152i.htm

ENABLING

Vehicle Theft Security System:
The VTSS engine no-run feature is disabled when it is shipped from the factory. This is done by programming within the Powertrain Control Module (PCM) . The logic in the PCM prevents the VTSS engine no-run feature from arming until the engine start counter within the PCM sees twenty engine starts. The VTSS no-run feature must be enabled when the vehicle is received from the assembly plant.

The preferred method for enabling the VTSS engine no-run feature is to electronically advance the PCM engine start counter using a DRB scan tool. Refer to the Vehicle Theft Security System menu item on the DRB scan tool for the procedures. Once this condition has been met, the PCM will allow the engine no-run feature to arm.

Once the VTSS engine no-run feature has been enabled, it cannot be disabled unless the PCM is replaced with a new unit. The same VTSS engine no-run feature enable logic will apply anytime the PCM is replaced with a new unit.[b]

Sorry for the bad news.
from the looks of it, not even the factory or a pcm flash will do the trick

on a good note, it seems you can get a reprogrammed one off of ebay
http://cgi.ebay.com/ebaymotors/94-06-Jeep-Grand-Cherokee-ENGINE-COMPUTER-ECM-PCM-ECU_W0QQcmdZViewItemQQcategoryZ33596QQihZ002QQitemZ120241749501QQrdZ1QQsspagenameZWDVW
u may want to email them or something

actually the PCU and VTSS are from the same vehical and were programmed from the factory to work together. I just need to figure how to make them talk and operate so they still think they are in the original jeep. So I guess I'll give this a try and see if it works then go ahead and order a new PCU. I didn't even think about looking on ebay for them, so I appreciate the heads up.

ah, I didnt read your whole post before, sorry.
Now that I did, it sound like you have a game plan. I wish you the best of luck.

well after a valiant try it looks like i'm going to have to admit defeat. I'm going to have to order one of the those PCUs off of ebay.

nothing at a local junk yard?

problem is 99% of the zjs came with the alarm stock. its actauly rare to find one that does not have it from what ive been told.

there is no way to install the wiring for the door to deactivate the alarm?

no because the wireing for the SAM doesn't even exist to splice it in. so I tried to tap into the wires going into the pcm in the enigine compartment and after an hour of messing around i gave up. I already have over a day tied up with it and figure my time would be better spent other places. I called The pcu people from the internet and he said that he didn't even think that any of them even came with out the security and that all his were programmed for it. So it would take him a few days to program one without the security. To make a long story short the new pcu should be here next week.