External voltage regulator or not - JeepForum.com
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post #1 of 22 Old 01-10-2016, 09:42 AM Thread Starter
Sloepoke
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External voltage regulator or not

2005 Liberty 3.7 . With field wires plugged into alternator I get a code for # 4 injector & engine won't rev above 2200 rpm's .
Unplug field wires , clear codes & engine runs fine . Have tried two alternators & batteries & new PCM .
I read to test the alternator to see if it's charging to unplug the field wires & jumper the field terminals on the alternator , one to battery terminal on alternator & other wire to alternator case . When I tried this the injector code & no rev problem came back .
Seems like I have an overcharge problem instead of an undercharge problem or it's something else entirely . I am considering adding an external regulator kit . Any ideas on these problems ?

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post #2 of 22 Old 01-11-2016, 01:39 AM
Billwill
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Quote:
Originally Posted by Sloepoke View Post
2005 Liberty 3.7 . With field wires plugged into alternator I get a code for # 4 injector & engine won't rev above 2200 rpm's .
Unplug field wires , clear codes & engine runs fine . Have tried two alternators & batteries & new PCM .
I read to test the alternator to see if it's charging to unplug the field wires & jumper the field terminals on the alternator , one to battery terminal on alternator & other wire to alternator case . When I tried this the injector code & no rev problem came back .
Seems like I have an overcharge problem instead of an undercharge problem or it's something else entirely . I am considering adding an external regulator kit . Any ideas on these problems ?

The field wires plugging onto the alternator should be Pin1 Brown/Dark Green from the PCM and Pin 2 Black which goes direct to ground.

The plug on injector #4 should have Pink/Gray and Brown/Tan wires.

I do not have a 3.7 gasser so do not know if these two plugs are interchangeable or not..maybe they are swapped over?

It is possible these two seperate harnesses are shorting to each other or shorting to ground somewhere...you need to physically trace these wires!

You should be able to fit an external regulator or use an alternator that has an internal regulator.

You can download the 2005 Jeep KJ Service Manual here...includes theory of operations and circuit diagrams:

http://www.colorado4wheel.com/manuals/Jeep/KJ

2002 2.5 Export CRD Manual 5 speed.
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post #3 of 22 Old 01-11-2016, 08:44 AM Thread Starter
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The plugs are far apart & it wouldn't be physically possible to mistakenly interchange them . I think it's very possible that it could be a wiring harness problem though . I just hate the thought of having to separate & inspect all the wires in the harness . I can leave the field wires to the alternator plugged in & remove the serpentine belt so the alternator isn't spinning & the engine runs fine . There is battery voltage on the heavy wire that goes from the alternator to the battery . It seems like with all wires connected & the alternator adding voltage to charge the battery is when the problems start .
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post #4 of 22 Old 01-11-2016, 11:36 PM
Billwill
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Originally Posted by Sloepoke View Post
The plugs are far apart & it wouldn't be physically possible to mistakenly interchange them . I think it's very possible that it could be a wiring harness problem though . I just hate the thought of having to separate & inspect all the wires in the harness . I can leave the field wires to the alternator plugged in & remove the serpentine belt so the alternator isn't spinning & the engine runs fine . There is battery voltage on the heavy wire that goes from the alternator to the battery . It seems like with all wires connected & the alternator adding voltage to charge the battery is when the problems start .
What is the charge voltage across the battery when reving the motor?

If it goes above about 15 volts then it would seem that the PCM is not sampling the voltage properly and adjusting the charge rate accordingly.

Very difficult to seperate the injection wires in the harness as the positive side of the injectors all get spliced together in a large harness above the front of the transmission.

Try putting a voltmeter on the leads going to #4 injector....on DC setting you expect the Pink/Gray wire to show a steady +12 volts with respect to chassis while the Brown/Tan wire...pulsed ground from the PCM....you should see a slightly pulsing DC voltage with respect to chassis....really need an Oscilloscope to measure that. Compare your readings to the other injectors and see if there is something strange going on there

2002 2.5 Export CRD Manual 5 speed.
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post #5 of 22 Old 01-12-2016, 10:12 AM Thread Starter
Sloepoke
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I haven't yet checked charge voltage above idle . I'll do that soon , it's turned cold & wintry here & this vehicle isn't a daily driver . I agree I need to compare injector voltages . Since it's always # 4 that's affected it stands to reason there might be a problem with # 4's wiring . I did check voltage to that injector & had battery voltage . When it throws the P0204 code & that injector stops firing there isn't a ground signal from the pcm to it . Something is causing the pcm to shut down that injector when all wires are connected & the alternator is spinning . Since it's always # 4 it must have something to do with the wiring for # 4 . I have changed # 4 injector & it didn't help .
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post #6 of 22 Old 01-12-2016, 08:42 PM
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Keep in mind, the PCM is what controls the alternator, and charging voltage. Need to see what the voltage is at idle, as well as when you rev it. May need to check at the PCM as well, via the wire going to the pcm from the alternator, and the power feeds to the PCM. I would also perform voltage drop tests of the PCM ground circuits as well. If all of that tests fine, I would unplug the pcm, and check for a short to ground on the control side of the injector, and also for short to ground on the power side. I would also check for voltage drop on the power side of the injector. With everything unplugged, and battery disconnected, you may check for a short from one of the wires of the injector to the connector to the alternator. I still suspect a bad ground issue and if you have not performed voltage drop tests on the grounds of the pcm, then you need to do so. Make sure you are familiar with how this is done, as many do not know how to do it right.
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post #7 of 22 Old 01-13-2016, 11:51 AM
streetglideok
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Make sure grounds g100 thru g112 are all good. Then also check for a voltage drop thru the asd relay
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post #8 of 22 Old 01-13-2016, 01:35 PM Thread Starter
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streetglideok , I was really hoping you'd take an interest & post on this thread . I have read numerous other threads you have posted in & you seem very knowledgeable . My next step was to disconnect , clean & reinstall every ground I can find . If that doesn't fix it I'll proceed to the other things you mentioned . Billwill & others that are making suggestions , I really appreciate the help so keep it coming , sooner or later we'll solve this problem .
It's supposed to warm up in the next day or two & I'll get back on it then & then post again .
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post #9 of 22 Old 01-13-2016, 07:15 PM
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There are known issues about the tps not working correctly, and generating "noise" and triggering injector faults. It takes a lab scope to see the noise, not something many have, not even techs. I'm not convinced it's even an issue in your case, as it seems related to the alternator.
eta: My PM box is full right now, I know in case anyone tries to message me. Will get around to upgrading my account later this month.
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post #10 of 22 Old 01-14-2016, 01:27 PM Thread Starter
Sloepoke
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I found what seems to me to be a problem . Since it's always a P0204 code which relates to # 4 injector & no codes for any other injector I concentrated on the wires for # 4 . With an ohm meter I got a constant reading to ground on the pcm ground signal wire with the injector unplugged . I checked a couple other injector ground signal wires & didn't get any reading to ground . I found that wire at the pcm & made a small bare spot in the insulation close to the pcm connector . Checked continuity from the bare spot to injector connector & continuity was good .
I unplugged the pcm connector that wire was in & reading from the bare spot I made to the connector terminals I found which pin in the pcm that wire goes to . That pin in the pcm reads to ground . I traced another injector ground signal wire to its pin in the pcm & got no reading . With all pcm connectors unplugged the pin for # 4 still reads to ground & pins for other injectors doesn't .
Backing up just a little , the ground signal wire for # 4 no longer read to ground after being unplugged from the pcm . All this leads me to believe that there is a pcm problem . What I find weird about all this is that the original pcm was doing the exact same thing . Just came in for a cup of java & am going back out & see if I can get any reading from # 4 injector ground signal wire to power or if it maybe has stray voltage on it . Will post again a little later .
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post #11 of 22 Old 01-16-2016, 01:40 AM
Billwill
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Quote:
Originally Posted by Sloepoke View Post
I found what seems to me to be a problem . Since it's always a P0204 code which relates to # 4 injector & no codes for any other injector I concentrated on the wires for # 4 . With an ohm meter I got a constant reading to ground on the pcm ground signal wire with the injector unplugged . I checked a couple other injector ground signal wires & didn't get any reading to ground . I found that wire at the pcm & made a small bare spot in the insulation close to the pcm connector . Checked continuity from the bare spot to injector connector & continuity was good .
I unplugged the pcm connector that wire was in & reading from the bare spot I made to the connector terminals I found which pin in the pcm that wire goes to . That pin in the pcm reads to ground . I traced another injector ground signal wire to its pin in the pcm & got no reading . With all pcm connectors unplugged the pin for # 4 still reads to ground & pins for other injectors doesn't .
Backing up just a little , the ground signal wire for # 4 no longer read to ground after being unplugged from the pcm . All this leads me to believe that there is a pcm problem . What I find weird about all this is that the original pcm was doing the exact same thing . Just came in for a cup of java & am going back out & see if I can get any reading from # 4 injector ground signal wire to power or if it maybe has stray voltage on it . Will post again a little later .
The problem with shorted or grounded wires is that they can blow that part of the PCM up. You replace the PCM with a new one and that same part of the new one gets blown up.

So you have to find the problem in the wiring to injector #4 first before once again fitting a new PCM and ending up with a pile of PCMs.

I personally would completely cut off both the leads going to injector #4 and leave them floating. Then fit a pair of new wires from the injector #4 connector back to the PCM pin for the ground signal and to the splice in the harness where all the injectors get their +12 volts from. Also check #4 injector again..maybe this also got blown up!

Then try a new...hopefully last....PCM with your new pair of wire attached.

2002 2.5 Export CRD Manual 5 speed.
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post #12 of 22 Old 01-16-2016, 09:22 AM Thread Starter
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I have been all over the internet trying to find if there's a way to read the pcm pins with a meter . For example , If 12 volts is applied to pin 23 then pins 17 , 34 & 9 should read 12 volts . That is just a made up example . So far I've found nothing . I guess it's time to start stripping & inspecting harness .
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post #13 of 22 Old 01-16-2016, 03:39 PM
streetglideok
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Quote:
Originally Posted by Sloepoke View Post
I have been all over the internet trying to find if there's a way to read the pcm pins with a meter . For example , If 12 volts is applied to pin 23 then pins 17 , 34 & 9 should read 12 volts . That is just a made up example . So far I've found nothing . I guess it's time to start stripping & inspecting harness .
Not sure I follow you. If you view the diagrams, the wires going to fuses will be battery power, or switched on battery power. If they go to ground, then its ground.
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post #14 of 22 Old 01-17-2016, 01:08 AM
Billwill
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Quote:
Originally Posted by Sloepoke View Post
I have been all over the internet trying to find if there's a way to read the pcm pins with a meter . For example , If 12 volts is applied to pin 23 then pins 17 , 34 & 9 should read 12 volts . That is just a made up example . So far I've found nothing . I guess it's time to start stripping & inspecting harness .
You cannot really "apply" voltage to a pin unless you know what you are doing and are very careful. Your example above makes no sense...you can look at the circuit diagram and there is a section that shows the pinouts of the various connectors. Look at the pinouts for the 4 connectors on the PCM and you will see that your example makes no sense....C1 pins 29 and 30 pick up +12 volts for example.

You need to have the ignition ON or sometimes have the engine running, all plugs connected, then strap sewing needles or pins onto your meter leads so as to be able to piece the insulation on the wire that you need to read.

Then following the circuit diagram 8W-30-18 with your meter set to Ohms and the ignition OFF, pull the connector off injector #4...make sure you are counting the injectors properly...should have a Brown/Tan wire on it.

Then piece the Brown/Tan wire at the PCM connector C2 Pin11 with one of the meter leads and have the other meter lead to ground. You should read next to nothing on the meter ie. a couple of M Ohms...not a low reading such as 5 Ohms....wriggle this wire around while doing this. Then disconnect C2 from the PCM and repeat the process....you should get an infinite Ohm reading because the lead should be totally floating in the air.

Now plug the injector back in place and connector C2 back on the PCM.
Pull out the ASD Relay from its socket in the box under the hood.
Jumper pins 30 to 87 with a short piece of wire inside the ASD Relay socket...this is to simulate the ASD relay being energized as it would be if the engine was running.
With ignition ON, your meter set to DC Volts, the Black meter lead onto chassis or negative battery post, measure the voltage on the Brown/Tan wire with the red lead of the meter..should show +12 volts. Measure this at the injector #4 plug pin 2...should show +12 volts as the +12 volts should go through the fuel injector coil. Likewise pin 1 on the injector #4 plug...Pink/Gray wire....should show + 12 volts.

Repeate these action on one of the other fuel injectors and compare results with #4 injector.

Then with the jumper removed from the ASD Relay socket and relay back in place, engine running and the meter set to DC volts, check what you are reading on the Brown/Tan with the other meter lead on chassis....you are expecting this Brown/Tan wire to be at +12 volts with respect to ground most of the time and then for a very brief moment as the injector fires this wire should go to ground. It is difficult to see this brief action with a meter...you can try set your meter to AC volts, take the reading and compare with the other injectors.

If the PCM has blown Pin 11 on Connector C2 then you will get different results compared to the other injectors of course....you need to first do all your measurements with ignition OFF to see if you can find a fault on the injector #4 lead while moving the lead around....if you do not find a fault this way then you will probably blow up the next PCM you put in.

Hopefully you will find a a fault in the Brown/Tan wire in which case repair the fault before putting in a new PCM.

If you do not find a fault, what I would do is cut the Brown/Tan wire off a few inches from pin 11 on C2 connector at the PCM, cut off the other end of the Brown/Tan wire a few inches from the Pin 2 at the #4 connector...leave that wire hanging in mid air with insulation tape on both ends!

Then replace that wire with a brand new wire taking the shortest route as a temporary measure and insulate both ends with insulation tape and see if things now work with a either the original PCM in or a new PCM.

Have fun!!!
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2002 2.5 Export CRD Manual 5 speed.
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post #15 of 22 Old 01-17-2016, 11:32 AM Thread Starter
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I'll freely admit I'm all wet as this is my first problem of this sort with a vehicle . A little back history how I got into this mess . I bought this jeep from a friend & the engine had already been condemned due to bad compression . I ran a compression check to satisfy myself it was actually bad & it was . I then bought a wrecked jeep , same year model , same engine & low mileage & the wrecked jeep still run & drove & the engine ran fine in the wrecked jeep which had been hit in the side behind the drivers door .
I pulled the engine out of the wrecked jeep & installed all new expansion plugs , new rear main oil seal , new motor mounts , new spark plugs & a new torque converter seal in the transmission . I then installed the engine & ran into these other problems . Since the engine ran good with no apparent problems in the wrecked jeep & I'm sure I didn't damage anything in the removal & installation process I'm assuming the sensors & all are OK .
This leads me to believe this jeep had more than low compression issues . I drove this jeep about 40 miles home when I bought it & the engine ran like crap which wasn't unexpected . I found a compression gauge adapter still threaded into # 4 cylinder with a spark plug threaded into it & the electrode on the plug was mashed flat . This is the engine I replaced . I realize all this doesn't have much to do with my current problems but it shows the alternator & sensors & such seemed fine on the engine I installed .
I now believe this jeep had wiring or pcm problems in addition to low compression . As far as replacing the pcm to injector signal wire for # 4 injector , I had already considered it might be open or shorted . I used a noid light & it wouldn't flash on that injector connector. The power wire to that injector has battery power . After further testing I found the continuity on that signal wire to be good with both ends of it disconnected & it won't read to any of the other wires in its harness .
With all 4 pcm plugs disconnected the pin for # 4 injector signal wire reads to the pcm case / ground . I traced the signal wires for a couple other injectors & they don't read to the pcm case / ground . It appears I now have a constant ground on that pin internal to the pcm . I assume if I tried a noid light again it would light up without flashing but I haven't tried it . With 2 pcm's exhibiting the same problems with # 4 injector & the alternator connected no rev problem I can't help but think something , somewhere in the wiring harness is the problem . I will remove # 4 signal wire from the harness & hope I find a problem with it . I will also inspect the power wire to # 4 to make sure it isn't intermittently shorting to ground . Since # 4 injector signal pin in the pcm is giving a constant reading to ground , I imagine this pcm is fried . Sorry for such a long , rambling post .
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