ZJ 4.0 Engine Ground Locations? And Mysterious Gauge Behavior - JeepForum.com
 
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post #1 of 8 Old 09-24-2017, 12:22 AM Thread Starter
Some_Anchovies
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ZJ 4.0 Engine Ground Locations? And Mysterious Gauge Behavior

Hello everyone!

I was wondering if anyone had a diagram for all of the ZJ's engine ground locations for the straight 6 (This one is a 95'). I can seem to find lots of info for the XJ but after looking at my ZJ They don't seem to share the exact same locations as I don't see a ground on the dipstick tube like on the XJ.

I'm going through and cleaning all of the external ground locations because I noticed some corrosion on the main ground that is just below where the ignition coil is located. There seem to be two grounds there.

I've also had some strange gauge behavior over the last year and I'd like to figure that out as well. Just running it by to see if anyone has run through this issue before. It seems that most of the gauges all read low, unless of course the engine is off and the key is on. Then it seems to read correctly.

For example, the coolant temp gauge always seems to read around the 1/4 mark when the engine is at operating temp. But as soon as I turn the engine off and immediately put the key to the RUN position it reads just below 210 like a Jeep normally should.

The gauges that seem to read fine are the fuel gauge and voltmeter. The Tach's reported RPM reads very low (at 55 mph it will read about 1250 RPM and about 1600 at 70mph) Oil pressure seems low (around 7psi idle warm) and of course temp is low. I suspect the speedo to be 5-7mph low just based off of that lady officer who pulled me over saying I was doing 70 something when my cruise control was set to 65.

Vehicle is completely stock basically, no big wheels or anything.

Since the temp seems to work perfectly fine key-on engine-off I'm suspecting some kind of excessive electrical resistance somewhere in the circuit, either in a ground wire or the gauge cluster itself that is causing excessive voltage drop when the load is higher. I think it's likely a corroded ground strap or something but it could very well be in the cluster. Either way, when the engine is on, and all of the gauges are live, they read low. Having a wiring diagram of the cluster circuit certainly would help here.

Anyway, thanks for any help with this issue. I'll start tracking some stuff down with a multi meter once I have some wiring schematics but for now I'll just drive it around.

SA

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post #2 of 8 Old 09-24-2017, 03:15 AM
Uniblurb
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Unfortunately there is not a lot of good info where the ground locations are on a ZJ. And even the FSM doesn't mention where these ground locations are and the schematics don't show locations either so it's clear as mud. Plus the 93-95 OBD1 ZJ's have different wiring than the 96-98 OBD2 (upgraded electrical system) years.

It's my understanding the PCM grounds on the inner fender next to the battery on the 93-95 and you may want to clean that stack of eyelets and where they attach if you haven't already. PCM ground is tan/black and normally a 2-wire eyelet with the same colors.

I looked through a bunch of schematics in the 95 FSM on the gauge cluster along with grounds. Not going to take screen shots of all of them and post them since like I said it doesn't show the ground locations anyhow. But will pass on what I found.

Fuse 12 (40a) in PDC supplies voltage to fuses 21 & 22 (both 15a) in the cabin fuse block which in turn supplies voltage to all the gauges. Since Fuse 12 is between battery and ignition switch that fuse should be ok. You may just want to make sure the contacts on fuses 21 & 21 are good and clean while checking voltage.

Ground Z2 is for all the dash warning lamps and it's a black wire which grounds at both G101 & G105. Ground Z1 is for all the gauges themselves and it's a black/light green wire which grounds at G106. Again, even in the "Ground Distribution" section (8W-15-1) they don't mention any ground locations.

Is your overhead console still working well? Only reason I ask is some people have problems with them and it's also grounded into G106, same as the gauges.

Believe I'd remove your whole gauge cluster and clean/spray down the connector contacts with electric contact cleaner.

Strange you don't have a ground on the oil dipstick bracket stud. Know many of the XJ's have it as you said and my 96 4.0 also has a ground on it. I always thought this was for the gauges on mine but there again your 95 4.0 OBD1 is different than my 96 4.0 OBD2.

Without needing to say make sure your battery terminals are clean and there isn't corrosion going up into your cables. Good luck.

PS. there is some real good info in the dirty dozen thread in my signature. There again it's mostly aimed at the 96-98 but does show some things such as alternator connections to clean.

96 4.0 ZJ Laredo, 2004 4.7L WJ Limited, 96 4.0 XJ (son's)


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post #3 of 8 Old 09-24-2017, 10:17 AM Thread Starter
Some_Anchovies
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Thanks for the response! Do you possibly have a link to the FSM for the 95? I have a Haynes manual but the wiring schematics are pretty... Well they're not great.

I have already cleaned the terminals that I can see but there is a connection near the fender eyelets that is a female terminal that looks to accept a male blade terminal. It is a black wire with either a tan or yellow stripe. I can only imagine this goes to some accessory that I don't have.

My overhead console works fine. I added it from another ZJ because mine didn't have it from factory. Temp doesn't show because I have no ambient temperature sensor installed.

I'm going to take pictures of what is on my ZJ. Does yours have a ground on the firewall to the valve cover? I don't see one of those either.
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post #4 of 8 Old 09-24-2017, 01:15 PM
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You're welcome and read the PM I sent you regarding the FSM.

Just went out and looked at my 96 4.0. I too have that open female blade connector on the passenger inner fender so it must not be needed.

Rather than the valve cover believe I have a ground on the far back driver's side of the head with flat ground strap from head bolt. This may go over to the firewall but can't see back there.

I don't think you can have enough grounds and made/ran a new ground from oil dipstick tube bracket to the firewall under the AC evap tubes. It may be connected to one of the HVAC box bolts which come thru the firewall.

I can't nose (pun) around my wiring too much since have cayenne pepper dumped on my coolant reservoir with some on the wiring. Trying to stop a cursed squirrel who's in love with my coolant reservoir cap who's stole it at least a dozen times! Would be funny except they chew on my wires, hoses, hood insulation, etc...

96 4.0 ZJ Laredo, 2004 4.7L WJ Limited, 96 4.0 XJ (son's)


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post #5 of 8 Old 09-24-2017, 03:33 PM
Marcos
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the single blade connector is probably for the hood ajar switch on security-equipped vehicles.

94 and 95 4.0 PCM is grounded on the left stud on the ignition coil bracket. 93 was grounded on the passenger side engine compartment ground, passing through a 1-wire round inlne connector and the large oval interconnect above the PCM.
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post #6 of 8 Old 09-24-2017, 04:10 PM
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That's pretty interesting Marcos about the 94-95 4.0 having the PCM ground on one of the coil bracket studs. Have you seen this before and I don't want to be passing along misinformation I've read before? Know that's the case on the 96-98 but didn't realize it's true for the 94-95 4.0 also.

If that's the case then ZeeJay has a real good photo/link of the PCM ground on a coil bracket stud in his grounds section in the dirty dozen thread in my signature.

96 4.0 ZJ Laredo, 2004 4.7L WJ Limited, 96 4.0 XJ (son's)


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post #7 of 8 Old 09-24-2017, 08:47 PM Thread Starter
Some_Anchovies
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The PCM Ground is actually what caused me to search out and clean other grounds, because it looked corroded. The ground locations I have cleaned and protected so far are the ones on the coil bracket, and the 3 on the passenger fender. I checked the fuses and such that you mentioned earlier and they're nice and clean. I'm starting to lean towards a cluster internal/wiring issue for the gauge anomaly. I will try and find the ground for the cluster inside.

Here's a picture of the dipstick tube stud. I only see the bracket that holds the wiring harness in place, no ground strap.

https://drive.google.com/open?id=1vN...uPG0dBzYVvgoYA

I didn't see a ground on the head bolt either, although I couldn't see back there very well so there could indeed be a ground strap there.
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post #8 of 8 Old 09-24-2017, 10:07 PM
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Good deal you cleaned that PCM ground on the coil bracket stud. Salt corroded/oily one on my 96 4.0 took out 2 PCM's and 2 crank sensors to boot.

Yeah, doesn't look like you have any type of ground on your oil dipstick tube bracket. Look below at the "#1. Grounds" section in the dirty dozen. Zee has good photo links of both of those grounding points but seems like yours is different on the dipstick tube bracket since there's none.

http://www.jeepforum.com/forum/f13/1...talls-1407423/

I really couldn't see clear back there on mine if there was a ground strap on that far back head bolt and may me thinking of my son's 96 4.0 ZJ.

You may want to try to push the plastic face of your gauge cluster on both sides to make sure it doesn't rock and is tight in the receptacle. Also there may be a ground up under the dash just to the left of the steering wheel on the top/metal part. Seem to remember one but not sure what it's for.

96 4.0 ZJ Laredo, 2004 4.7L WJ Limited, 96 4.0 XJ (son's)


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