WEIRD JEEP PROBLEM....HELP WITH IDEAS PLEASE!!!!

ok so this is the deal...i have a 2001 Jeep Cherokee Sport about 4 months ago i went wheeling and a few days later spun a berring in the motor......but ok so i decided to replace the motor with a jasper re manufactured motor...i have a mechanic put it in and it seems like its been all down himm from there...now heres what happened...after i put like 1000 miles on it

Now i cant say nething is wrong with the motor..Thats working fine...but having major misfire issues...now the sensors like that crank, cam, temp are new....the mecanic that put the motor in stop trying...so i took it to another mecanic and hes been looking it over LIKE CRAZY!!!..he did extensive electrical testing and came up with nothing...he says that everytime he clears the code that comes up.(usually something that has to deal with the ignition) he addresses it and another code comes up...it seems like hes running in circles.... always a new code and...he thinking it could be the computer like there's a short in it...cause he addressed everything els and and alwayse something different...but with the same issue being the misfire or running really rough....BTW it seems to run weird at idle it smooths out as the RPM raise and the dash board acts all funny like it can b revving at 750 RPM and the TACK would jump to like 2000 but the engine would still be missing at 750....something is seriously wrong...if u guys have any insight i dont want to jumk a jeep that has a brand new motor.. it makes not sense...please help!!!

If the Jeep was running correctly before the replacement, what I'd look for first is an error in wiring installation. A damaged harness, perhaps, or a missing ground. It seems trivial, but make sure, for example, that the ground strap from the rear of the cylinder head to the firewall got put back.

the mecanic looked through all the wiring....im gonna look it over again when its not raining...i gotta look at the schematics for the wiring to get a...but do u think it could be a computer issue? especially with the TAC jumping and all?

I'm sure it could be a computer issue, but the computer is not usually that glitchy, so I'd first look for problems with the wiring to and from it, and with grounds that might not have been put back with the new engine.

You should have a ground strap running somewhere between the engine block or head and the body. If you do not see the braided strap at the back of the engine, that goes up to the firewall, then you are missing one.

Check all the engine wires for damaged wires or chafed/melted insulation and the wire plugs for loose connections. Check all the grounds. A short circuit is most likely in the wire harness and not the ECU.

Google SCAN TOOLS, O-SCOPES AND TOOTHPICKS and find a toothpick or paper clip.

Note from DJ
Cherokee 2001 you have a new nicely painted engine this is good but paint is a very poor conductor.

I think your problems are being caused by poor grounds caused by the nice paint job.

That the ground strap from the rear of the cylinder head to the firewall remove it completely, remove all the paint from the point of connection at the firewall down to bare metal, next attack the point of connection at the head and remove all that nice new paint from this connection point especially.

Now reattach the ground strap [after cleaning its connection] points] at both points very securely.

Now follow your negative battery cable from the battery down to its point of connection beside the oil dipstick, remove the nut from the stud, and remove the battery cable and the small ring connectors from the stud.

Now remove all of that nice new paint from the stud and the block at this point of connection, now clean the battery cable end and the ring connector till they are nice and shiny then reassemble and tighten the nut nice and secure.

Examples of the connection points cane be seen hear in drawings 2 and 3

Engine bay Bad Ground Points of Connection
http://www.lunghd.com/Tech_Articles/Electrical/Ground_straps.htm

Hope these tips solve your problem; please keep us posted as to your progress.

What are the exact codes?

These photos may be helpful in locating your engine bay grounds. The photos are of a 1999 XJ but I'm sure they're the same for a 2001.

G101 has two locations, one by the oil dipstick and one under the coil (not sure if it's the same on a 2001).





The firewall and head stud locations do not have a designator in the '99 wiring diagrams.

By the way, it's pretty common for that rear strap to turn to powder over time, so I would recommend replacing it if there's any sign of corrosion.

WOW!!!...i wasnt expecting to see all this when i cam home from work today....u guys r really helpful....its raining both today and tomorrow so either friday or saturday ill look over the grounds clean them and make sure they have good contact......i also stopped by jeep today and spoke to one of there service guys..he suspects computer malfunction saying that usually at the end of a CPU's life it would trigger random codes and make for weird things to happen....before i jump on a new 550$ computer tho im gonna check out what u guys are suggesting.. cheapest things first!!!...and next time ill post the codes its throwing....i need to borrow an OBDII scanner..i hope to get those codes by tomorrow....Thanks!!!...illl keep updating...

BTW "Sidewinder CC"...thanks for thos pics. thats gonna be a real help this weekend!!!

Note from DJ

The G-101 location by the oil dipstick in Sidewinder CC first photo he posted is where your PCM gets it ground from. If this ground is inferior the PCM and every sensor it services is transmitting improper voltage.

Ground ohms test
From Ecomike: http://www.naxja.org/forum/showthread.php?t=939154&page=2
With the key off place Red lead on what you want to test, Black lead to Battery ground post[NOTE connect to the center of post not the cable connector], place meter on lowest ohms setting available if it is reading is over 1.0 ohms it is a problem.

Hope these tips solve your problem; please keep us posted as to your progress.

In addition to what dj said about G101 being the primary PCM ground, it should be noted that G106, near the PCM, (see pic) is important in that it is the ground for, amongst a bunch of exterior lights, the Transmission Range Sensor, Radiator Fan, Engine Starter Motor Relay, and the Vehicle Speed Control Servo.

ok so i wasnt able to borrow the code reader...but i did look through the wiring....everything looked pretty good...grounds are all in place where they should b..not really sure what direction to go next....it def seems electrical.....if my driver side window regulator didn't work could that cause a short..and cause another electrical system to act weird?....idono just throwen that out there....

Note from DJ
Your quote from post #14 “BUT I DID LOOK THROUGH THE WIRING....EVERYTHING LOOKED PRETTY GOOD” looking at the ground points doesn’t do any good; they must be removed and cleaned down to shiny metal. Then reassembled and do the ohms test as I previously described. Cleaning and performing this test is the only way to rule out bad ground connections causing all the weird codes that you are getting. Bad grounds will cause faulty and out of range information being returned to the PCM which = codes.

Seconding digray's post above, you're going to have to get in there and really test. Remember that this vehicle just had an engine transplant, and there's a lot that can happen to wires and harnesses during that kind of operation. Even if the main grounds test all right you may have to test a number of wiring paths to make sure nothing was torn apart internally during the job.

It seems tedious but it's way cheaper than getting another PCM and finding it's not the answer.

yea u guys make really good points.. when the mechanic had the jeep he looked over all the electrical to find a short somewhere...and he didnt fine nething....he told me he went as far as he could (and i know hes good with checking electrical casue that part of what he does as a mechanic) that was y he was pointing twords the PCM....i pulled all the grounds today and cleaned them down to shiny metal and polished the grounds to b sure of good contact....i also was able to borrow an OBDII scanner today these were the codes:

P0205 (injector 5 control circuit)
P0320 (Ignition/Distributor engine speed input circuit)
P1391 (Intermittent Loss of CMP or CKP)

thats what was up at the time...after the codes were cleared the first time then the P0205 didnt come up again..but the other 2 did..when the jeep was revved to about 2 to 3 thousand RPM it smoothed out with still a slight miss but when it was let back to idle it wanted to bogg out and missing....the tack at idle was jumping like twiching up and down like to 1200 to 750 RPMs...but the rpm would stay around the same like between 700 and 800 RPMs

http://motorage.search-autoparts.com...30/article.pdf

READ THIS ARTICLE... Search the forum on the toothpick method for aligning the Camshaft position sensor... you may also have mechanical slop in the oil pump shaft that the sensor mounts to.

"McQue"...Link didnt work...but i looked at the toothpick method...ill try that sometime this week. when i have some sunlight after work...i totally wish i had a garage!!!

x2 something is a miss with the cam sensor and injector #5 could be something else. Start with indexing the cam sensor correctly.