Question about 1999 Jeep Grand Cherokee

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I have a 1999 Jeep Grand Cherokee Limited with the 4.7 engine. I had to replace the cylinder head but the car sat up a year before I could find the time to fix it. After, replacing the heads I ran i

I think the PCM is bad but I'm not sure

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Posted on Jan 02, 2017

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SOURCE: 1996 jeep Grand Cherokee has a scan code P0351.It says

Wiggle the connectors on the PCM during those four or five minutes...
I'm going to try the hose clamp fix myself. I have been struggling with stalling for about a month now. As a matter of fact, my PCM looks just like the one with the hose clamp. Connector C1 (black) missing the locking tab. I have tried the screw repair and zip ties. Zip ties worked for about a week and then I had a hiccup followed two days later by a full blown stall. Now it's stalling about 4 to 6 times in a one way trip to work (11 miles).
I was able to procure a clamp tonight and got it installed. When I go home we'll see. I was throwing a P0351 code with a code 43. This is an aggravating fault to be sure. I am an aircraft electrician by trade so and thanks to the volumes of people who have had this problem I have been able to do some really good fault isolation.
It exists either in the C1 connector for me or the PCM. Initially I changed the TPS and then found found C1 ready to fall off the PCM (Thus the zip ties).
Later I found that even though zip tied wiggling the harness could duplicate the fault. So another zip tie around the harness to pull tension on the connector. The fault returned. I also took a rubber mallet to the computer while the engine is running and duplicated the fault as well.
At this point I'll try the hose clamp and see how that works out. Either I don't have a good connection on C1 or the male pin 7 in the computer is a problem. Since I have an obvious defect in the locking tab on the C1 connector I'm swaying towards that. I want to talk a little system knowledge here courtesy of a guy who posted on CNet.
1. P0351 is a coil code. However:
a. The coil receives a signal from the PCM connector C1 Pin 7 to "fire".
b. There are only two wires at the coil, signal wire from the PCM pin 7 and a ground wire.
c. In order for the PCM to throw code P0351 the PCM had to fail to send the proper fire signal. Of course this assumes that you have a known good coil, clean ground and no breaks in your wiring.

2. A multimeter checks continuity not integrity. The average 18 gauge wire has 22 individual copper conductors(wires) inside the insulation. You can have 21 broken strands and still read full continuity through that single strand of wire. But that single strand of wire will not be able to handle the signal being sent to the coil (load). A load light will always check integrity AND continuity. A weak light means not enough current going through the wire and a strong light means good wire integrity.
3. So with this said, In order for P0351 to set, the computer has to give an erroneous signal to fire. Pin 7 is an OUTPUT. Now is this caused by a bad computer? Possible. A bad connection? More likely.

Let's face it computers will fail, but in my 22 years of electrical experience bad/loose/dirty connection points are the weakest link. A cold solder joint on the PC board in the computer? Yes, however this will generally show up shortly after the vehicle rolls off the assmbly line. Not 13 years later!
As for the "screw" fix. I read a post from an engineer who scraped all the resin out of the PCM to see what was on the board. The long screws go to a NYLON nut on the board. But does not come near the current path of the PC board.

Posted on Jan 23, 2011

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SOURCE: Jeep Hesitates. P0303 code

Check the cylinders Commpression. over 115 psi is good, 120 psi is normal.

Posted on Sep 17, 2008

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SOURCE: 1993 jeep grand cherokee limited no running lights/tail lights.

Id look at the headlight switch and do some voltage tests to see whats coming out of there. Pay close attention to any wires which look like someone was in there already.People can mess stuff up faster and better than the vehicle can by itself!

Posted on Jan 05, 2009

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SOURCE: 1999 Grand Jeep Cherokee (limited) shuts off while driving

Starter...if the starter is old, it is getting heat soaked. Replace the solenoid.

Posted on Mar 17, 2009

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SOURCE: 2000 jeep grand cherokee 4.0 liter engine timing belt replacement

If you have the same pulley arrangement that most 4.0 engines have that pulley is an idler not a tensioner. Your power steering pump has a pivot bolt, and a slide under the pump. You adjust belt tension using the pump.

Posted on Apr 05, 2009

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1999 Jeep Grand cherokee Limited, 5.9 liter torque setting for head bolts

posted the fsm
5.9L, 1999 WJ?
check it covers this engine,
buy my WJ, fsm skips the 5.9L, not sure why.
ah only the limited has that. engine.
my online links show no 5.9L. so see why you are asking here.
why not go to real jeep forum and ask.

here are the (what else) questions
are they TTY?
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those are always a question. and the FSM answers them all.
for your car.

if the expensive WJ (limited) FSM is too pricey, (it is)
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one search, you can too, or better ask them.

the intake is TTY bolts.
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im not sure what book covers the 5.9L, it might be a supplement.
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