Who is telling the truth/voltage problem

Hello all. First wanted to say Thank you for all of the great information I have received from this site. I was a lurker here for long time, and have gotten by with just looking at the tech articles or searching but came across a couple questions that I did not find anything about.

1990
Cherokee Limited
4.0 Auto
NP242 (per FAQ)

First question is who is telling the truth about 4x4 being engaged, the dash or the shift lever on xfer case? Logic would tell me that the shift lever would engage/disengage the xfer case and the dash would just be what the vacuum for the front axle is doing. Correct? Also it only likes to engage/disengage while moving. Seems from a couple threads I have read that is somewhat common?

Second question is when I have headlights and fan on high, and I come to a stop, my volts drop down to the red. Never dies, but lights dim and blower motor definitely get lower. It never gets up to 12v while driving either. I have replaced alternator and battery, but no help there. The only thing else I can think of is replacing battery cables or if there is a short somewhere? Ideas?

While I am on it, the thing starts every time and cranks fine, but it takes forever to start. Just cranks and cranks and eventually fires. I am thinking this is tied to the charging problem, but am open to suggestions.

:worship:

Appreciate the help in advance.
Ian

imwoodhouse said:

First question is who is telling the truth about 4x4 being engaged, the dash or the shift lever on xfer case?

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The front axle, then the shift lever, then way, way down on the list, the dash light.

Here's the thing: the transfer case shifter linkages can get out of adjustment over time. You may get engagement in some ranges but not others if this is the case, or it pops out of certain ranges because it's not getting full engagement. It also means that what the light is telling you may not be anywhere near the truth.

Try this: put it in 4HI Part-Time. Try turning the steering wheel to lock while moving at low speeds. If you get progressively more resistance (and feel hopping from the front end), the axle is engaging. Now straighten the wheel and put it in 4HI Full-Time, repeating the turning-to-lock manoeuvre. You should feel pull from the front but no steering bind like in Part-Time. Finally, repeat all of this in 4LO; it should feel like it did in 4HI Part-Time.

Watch the dash light while doing this in each range and see what it does in relation to what you're feeling while driving. That should tell you if the light is accurate or not.

Also it only likes to engage/disengage while moving. Seems from a couple threads I have read that is somewhat common?

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Not abnormal. Some are more touchy in that regard than others.

I have replaced alternator and battery, but no help there. The only thing else I can think of is replacing battery cables or if there is a short somewhere?

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Battery cables, battery terminals, engine-to-firewall ground strap, and serpentine belt tension as basic checks.

While I am on it, the thing starts every time and cranks fine, but it takes forever to start. Just cranks and cranks and eventually fires. I am thinking this is tied to the charging problem, but am open to suggestions.

Click to expand...

It's possible, but check on the charging system stuff first and see what happens - there are other possibilities (CPS springs to mind), but rather than pointing fingers at what are ghosts for now, make the easy and obvious checks and fixes and go from there.

Sounds good! I appreciate your advice!

As casm noted, the shifter and the light don't really tell the full story. If it goes into gear and stays there, trust the shifter. Usually the light will lie to you and say it isn't engaged when it is instead of vice versa; it is triggered by the actual position of the shift cams inside the transfer case, so if the light is on, you are almost certainly in 4wd. If the light is off, you could be in 4wd and a vacuum line or wire is disconnected...

Definitely agree on the wiring too. The self-destructing engine to firewall ground strap is a common problem, depending on year there also may be a ground wire (approx. 10ga to 8ga or so) from the negative battery terminal to the fender wall. If there is not one, add one - it should improve things a bit. Also check the ground wire from the battery to the engine block, and make sure the connections are clean and tight and the crimp terminals are not corroded.

Do yourself a large favour and upgrade the battery/alternator/ground cables to 2 awg.
Just about everyone on this forum will tell you it will eliminate any number of current and future gremlins.

RoadHog_ZA said:

Do yourself a large favour and upgrade the battery/alternator/ground cables to 2 awg.
Just about everyone on this forum will tell you it will eliminate any number of current and future gremlins.

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Agree with this - even if just for good GP. PM 5-90 about his cables.

RoadHog_ZA said:

Do yourself a large favour and upgrade the battery/alternator/ground cables to 2 awg.
Just about everyone on this forum will tell you it will eliminate any number of current and future gremlins.

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You meaning just get some big 'ol cables and be done with it? :laugh3:

Pretty much - it's one less source of electrical problems.
Just be sure to provide strain relief where those "big 'ol cables" screw down onto the starter solenoid and alternator posts - any weight on those will rip them right out of the starter/alternator.
It also helps to squeeze in the largest capacity battery you can - the stock one is barely adequate and when you start adding accessories..... well it comes up short.

10-4. Just pm'd 5-90 for his, from what I have seen his are the 'cat's meow' if you will. Again, thanks for all your help guys!

imwoodhouse said:

the dash would just be what the vacuum for the front axle is doing. Correct?

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Actually (and I feel dumb for not mentioning this earlier): XJs with the NP242 transfer case didn't have the vacuum disconnect for the front axle, so you should be able to disregard this as a potential issue.

casm said:

Actually (and I feel dumb for not mentioning this earlier): XJs with the NP242 transfer case didn't have the vacuum disconnect for the front axle, so you should be able to disregard this as a potential issue.

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Electrical connection then?
"New Process NP231 Command Trac: 2-speed, chain drive, part-time 4WD. 2.72:1 low-range. 87-01 2.5l 4cyl and 4.0l I-6 models with manual or automatic transmission. 87-89 21-spline input, 90-01 23-spline input. The older models used a vacuum switch to activate the dash indicator lamp and engage the front axle disconnect. Newer (non-disconnect axle) versions used an electrical switch to activate the dash lamp. The shift indicator pattern is 2WD > 4WD high range part-time > Neutral > 4WD low range part-time. "

Are those pretty reliable? I haven't specifically looked for that yet....


EDIT: So the axle is always engaged and the electrical switch is just for the cute little light.....

All of the Select Trac (NP242) transfer cases, at least from 87+, used a straight electrical switch for the 4x4 indicator.

And yes, no D30 CAD vacuum axles in an XJ with OEM NP242.

As for the long cranking time--the blessing of the Renix system. The engine must "spin up" to 300+ RPMs BEFORE the crank sensor will generate a strong enough signal to the ECU for ignition spark to happen. What can you do to reduce the time it takes to hit 300+ RPMs? Big cables! Powerful battery! Starter-solenoid in tip-top condition! That is about all you can do.

Now, if the fuel is draining back into the tank due to a bad fuel pump check valve, you can either replace the pump (expensive) or put an inline check valve back by the fuel filter to stop the drain back. HOWEVER, this will make little difference (if any at all) in a Renix--see above re: 300+ RPMs cranking speed.

Now, new BIGGER cables will help the charging system. Read this article: http://www.olypen.com/craigh/charge.htm

Ok, here is my advice on ALL electrical issues: fully charge the battery and have it load tested. Without having done that you are just P/ing into the wind. After the battery has passed a load test OR been replaced, and you have good cables with clean ends, then put a multimeter between the battery posts--should read about 12.5 volts (varies based on ambient temps) for 100% charge. Next, start the engine and observe the voltage--should be 13.0 volts up to 15.3 volts--this indicates the alternator is charging.

Now, the in-dash voltmeter doesn't read voltage at the battery. It is reading voltage after all of the loads, so this tends to make them a bit inaccurate.

As for 5-90's cables--you have chosen wisely.

Also, if the IAC--idle air controller (a stepper motor, actually)--is dirty and or lazy it could be failing to maintain the proper 700-750 RPM idle speed. For your AW4 that is measured after 20 minutes of driving when the engine and transmission have been fully warmed up and you check the idle speed with the transmission in DRIVE--parking brake set and someone's foot on the service brake pedal.

imwoodhouse said:

Hello all. First wanted to say Thank you for all of the great information I have received from this site. I was a lurker here for long time, and have gotten by with just looking at the tech articles or searching but came across a couple questions that I did not find anything about.

1990
Cherokee Limited
4.0 Auto
NP242 (per FAQ)

First question is who is telling the truth about 4x4 being engaged, the dash or the shift lever on xfer case? Logic would tell me that the shift lever would engage/disengage the xfer case and the dash would just be what the vacuum for the front axle is doing. Correct? Also it only likes to engage/disengage while moving. Seems from a couple threads I have read that is somewhat common?

Second question is when I have headlights and fan on high, and I come to a stop, my volts drop down to the red. Never dies, but lights dim and blower motor definitely get lower. It never gets up to 12v while driving either. I have replaced alternator and battery, but no help there. The only thing else I can think of is replacing battery cables or if there is a short somewhere? Ideas?

While I am on it, the thing starts every time and cranks fine, but it takes forever to start. Just cranks and cranks and eventually fires. I am thinking this is tied to the charging problem, but am open to suggestions.

:worship:

Appreciate the help in advance.
Ian

Click to expand...

1) The lever. You don't have a vacuum front axle with the NP242, but the mode indicator switches are, I believe, still vacuum-controlled. The 'case is mechanically shifted - when in doubt, look at the shifter. And it's usually easier to shift in/out of 4WD when you're moving just a bit.

2) This is reasonably normal - at idle, your alternator might give you 40% of its rated output (should be either 80A or 100A for you - the 100A is fairly rare, and usually gets the "Power Everything + Tow Package" background. I think my 89 Limited had an 80A - no tow.) The more load you put on the alternator, the more voltage is going to drop as spindle speed drops. And, the blower fan is a huge draw (I think it's got a 30A fuse, so somewhere between 25A and 30A.)

3) The IP voltmeter is also a notorious liar on RENIX. Any suspect reading should be verified/refuted by direct measurement with a "known good" DMM or analogue meter. I've long since drawn a red grease pencil mark on my gage window (88) for that reason - it's more a "relative state of charge" indicator than an absolute value voltmeter. (I answered your PM...)

4) This is normal - RENIX is programmed to not fire ignition or fuel injection pulses until it sees 300rpm at the CKP and it looks for a valid SYNC signal from the sensor in the dizzy. It can start without the SYNC signal by "guessing" which cylinder is coming up (it will act like the timing it out until it starts, but smooth right out once it's running...) but it can not start or run without the CKP signal. Upsizing your mains can help with this - both by improving the ground reference for the ECU (the ECU is down by your right knee, and the chassis is only grounded through the braided strap at the firewall. Not really a good situation, but AMC - while not stingy with their wiring - could have designed their wiring better...) resulting in a cleaner CKP signal; and by allowing more current to flow to the starter motor faster (allowing it to get up to speed more quickly.)

. And it's usually easier to shift in/out of 4WD when you're moving just a bit.

X2
As per my factory owners manual. You can shift in to 4HI up to (((55))) mph. 4LO at 5 MPH.

IN a hurry, have to go out and plow some snow, so I may have missed something above, but....

Just to clarify, on the NP 231 system with axle disconnect, you should believe the light, assuming the light is working. The light is powered by a vacuum switch, and that vacuum switch is, in turn, actuated by the axle disconnect motor, which is in turn actuated by a vacuum switch in the TC. A failure in any of the vacuum components will leave your axle disengaged no matter how well your transfer case is working. When that light goes off, it means that your axle has popped out, and you have no 4WD.

for the other stuff, I think 5-90 and Joe have covered it.

upgrading the dash with some grounds from the cluster and blower motor will make the volt gauge more accurate. In order to rule out a real chargind problem make some long test leads, attach them to the battery terminals. Secure them to your test leads, wire tire DMM to the wiper arm and take a drive watching the voltage coming from the alternator. You should see 13V or upwards when engine RPMs are above 2K. 13.6-13.8 is nominal. Anything over 14 is a problem. Anything lower than 12 is a problem, except when cranking, when cranking voltage should not drop below 8, mine usually hits 9V when cranking.

Welcome to hillbilly Renix diagnosis.

Regarding Question 2:

I am hoping we can explore the low voltage, dim dash lights issue further. I have the same problem and I have already tried the solutions presented to no avail.

Big healthy battery...check. Big ol cables, grounds etc....check. New alternator...check.

Here is what I am thinking and could use some additional input on...

It seems that the system is making the juice, but there is a bottleneck somewhere getting it into the cab. I notice when the Jeep warms up, it is even worse. I suspect some heavy resistance somewhere in the factory wiring leading from the engine bay to where it meets the interior electrical.

If I am not mistaken, I believe we have "fusible links" that I suspect could be the bottleneck. Or perhaps just some small gauge wiring leading into the cab that is now 21 years old. Extra resistance is going to drop the voltage and cause the problem we are having. Even if the Renix voltage gauge is inaccurate, the interior lights dimming, blower motor slowing, is definitely due to a voltage drop.

Here is another tidbit. My blower motor would slow with the dimming lights...clearly power issue...my blower is now hard wired on its own circuit and aftermarket fuse panel connected to the battery. The interior lights dim, but the blower runs normal now. Again, this points to the problem being somewhere in the line(s) that carry the power into the cab.

If anyone has anything to point me in a direction, I will investigate and post back. I am fairly electrical savvy so just some input on what wires feed in, or where the fusible links are could be very helpful.

First on the xfer cases. over 75% of the new process/new venture cases did NOT use a vacuum switch to indicate 2wd/4wd, they used physical notched rods that were moved back and forth by the gearing inside the case. Inturn these rods depressed or released a mechanical switch that in turn illuminated the dash light. Your Vac operated axles were independent of this. As example the 76 quadratrac unit didnt have a switch unless it had the optional low range and then it only indicated 4wd LOW In the glove box was the vacuum switch labeled emergency drive which engaged the locking differential, there were different schemes for the vac switch over the years but the dash light was almost always mechanically actuated

Ob the voltage problem this is most likely a two point issue, first remove the wire bunch at the dipstick tube ground point clean all connections and remount.
Next pull the cable that goes from the battery to the solenoid on the starter and replace with one twice as thick (known issue on XJs) if you can, pull the whole starter and clean all connections on it as well since it is a point where corrosion builds quickly.
The thing to remember on any electrical issue is the rule of "Gozinta" (what goz inta it hazta come outta it) Its corney but it is a MAJOR rule of all circuits so both the hot lead and ground must be solid. You may have sufficient voltage at the alternator but if the amperage isnt making it all the way through the circuit, the components wont work right (in this case dim lights) One application of this checking fuses. a good fuse will read zero volts across it but if its burned out it will read full voltage (battery or alternator) across it on a meter. they make neat little led testers for this as well... if you have a voltage loss such as a bad connection the voltage across the part not working right (dim lights) will read low. Its obvious that voltage is low on the lights but on other things not so much. in an extremely bad situation in the case of a bad ground, with a GOOD meter you can read a voltage difference across the ground, but the typical home mechanic doesnt have a meter with high enough input impedance to read this. If it isnt Obvious by know, I'm an Electronics Engineer by profession, been spinning a wrench over 45 years, thanks to a father who was a product of the great depression and taught me that you wont always be able to pay for it when it needs to be fixed. Ive changed professions 3 times (not just "jobs") and still love mechanics, it takes me 'home' and reminds me of my late father, keeps me connected to my dad, even though I'm in my retirement.

You do realize you responded to a 5 year old thread. The info may be helpful to someone with a problem.