bzauche

A little back story:

Monday (I think), I started having random stalling/engine bogging down, but it only happened occasionally when I was braking. My CEL popped up, and I had it checked at AutoZone...the code it was throwing was P0705, which as far as I know is for the NSS. I went home, took the NSS off, cleaned it, and re-greased it. That didn't fix the issue. After I started the XJ up, hitting the brake pedal would still cause the engine to bog down some. The CEL was still there as well.

Yesterday, I checked the vacuum on my brake booster, because it was suggested that possibly the brake booster was bad or had a leak. Based on the test I was told to perform, I needed a new brake booster, which would hopefully solve my issue. So after work, I went to AutoZone and picked up a new brake booster.

When I pulled up to my mailbox, I rolled my window down, and then when I went to roll it back up, it barely budged. The engine bogged down to the point that it stalled out. I finally got the window back up and rolled it into the garage. Based on the window bogging the engine down, I didn't bother installing the brake booster, but rather spent time cleaning battery terminals and battery cable contacts. No dice. Engine still bogged down when the brake pedal was pressed or I tried to roll any window down. Keep in mind that this whole time, the interior lights work just fine, as well as all my gauges and the radio. The XJ would also run if I unhooked the battery after starting, or even if I unhooked the alternator's ground wire.

This morning, I took my battery out and got a ride to AutoZone to have it tested. It's a 5 year old Interstate installed by the PO, and it turns out it had bad cells, but a 100% charge of the cells that were still good. That ruled out the possibility of the alternator being bad. So, I took this as an opportunity to get a new battery, hoping that it would solve my problems. 1 DieHard Platinum later, and still no progress.

I'm stumped, simply because it starts up and runs perfectly until I try to apply the brakes or roll a window down. I have noticed that my taillights have been a little funky, and the other day when I was driving home, my turn signal occasionally blinked double fast.

I plan on adding a second alternator ground wire later tonight just for the heck of it, but other than that, I have no idea. Any help would be greatly appreciated!

RTorrez1

I would start by cleaning all f the grounds. Not just the battery. Also you do not want to disconnect your batter while the engine is running. You have a chance of frying the computer doing that. It fine to check the alternator on older vehicle without the computer but you take a big risk doing it on any vehicle with all the computer electronic.

bzauche

I cleaned the body ground and the engine block grounds (are there more?) when I cleaned all the other contacts. I haven't touched any wires to or from the starter simply because I know the starter is working fine, unless I need to. Didn't think about frying the computer...I only had the ground off the battery for a second or two, and it's running fine still so I don't think it did any harm, but I definitely won't do it again.

RTorrez1

You have your battery of course, battery to fender, oil dipstick, rear of head to the firewall, on the coil (unless you are working on the 01 in you signature) and the starter mounting area between the starter and the engine block. Take a wire brush or some sand paper and make sure to scrub the clean until they are shinny.

bzauche

I'll go out and clean the oil dipstick and the head/firewall grounds real quick, and probably hit the starter contacts while I'm at it. I am working on my '01, so I don't have a coil.

bzauche

Went out and cleaned more grounds and contacts...still no luck. Checked the whole engine bay to make sure everything was plugged in where it should be, and cleaned some plugs and connections with cleaner. Checked every fuse in the PDC and the passenger kick panel; all were good to go. I just don't understand how it can start up and run perfectly until I open a door, try to roll a window down, press the brakes, or flip on my headlights.

Roler

Your ECU has two grounds as well...didnt read the whole thread because its late, but those are in the list too...can't miss them, next to the ECU, attached to the metal platework...

bzauche

No dice. One thing I just noticed is that, even with it in park, my taillights are partially lit up...I can see the bulbs a little bit. I'm about to take a video of the bogging down just in case it helps.

CCKen

What 'tailights', brake lights, running lights, back-up lights?

Waiting for bogging down vid.

bzauche

All of the above. I didn't get that in the video, but I can tell that the brake bulbs, turn signal bulbs, and reverse bulbs are dimly lit all the time...unless I've never noticed it before, I don't think that's normal.

I haven't been able to get the ground plug off of my alternator, so I will attempt that again tonight. I replaced the alternator > PDC cable last night though, but that didn't do anything.

You can see in the video that the front turn signals aren't lit like the back ones are. I paused after I opened the door because I thought it was going to bog down, but it turns out that it's only the driver side doors that do it. The CEL is on for the NSS code still as far as I know. The guy that scanned the codes at AutoZone didn't scroll to see if there were more codes. I might have to buy a ScanGauge and see if it's throwing more codes than just the one.

CCKen

I hate to be a pest, but it can't be overstated that the ground circuits in the XJ must be serviceable.

All the unrelated problems you are seeing may be related to the primary grounds in the engine bay.

There must be a clean ground path (less than 1 Ohm resistance) between the battery and the chassis and between the battery and the engine.

Some of the circuits you are seeing problems with are chassis grounded and some are engine grounded. The chassis and engine must have a clean ground loop.

Below are pics of the engine bay chassis and engine grounds.

Several points:

The PCM itself does not have a chassis ground, it is grounded to the engine, which in turn, makes its way to the chassis.

The ground strap that goes between the firewall and the engine block is primarily for radio noise suppression but it is also an alternate engine to chassis ground path.

The ground wires at the oil dipstick tube are for the Data Link Connector, and have nothing to do with your problems.

I suggest you revisit all the grounds shown in the pics below and disconnect them, clean them using Scotchbrite pads, then coat each wire ring terminal with either NOALOX or Ox-Gard (see pic below).

At ground G100 and at the firewall, replace the bolts, and at G106, replace the sheetmetal screws. G100 is a 1/4-14x5/8" bolt. The firewall is an M10-1.50 (As I recall). I can't recall what size sheetmetal screws are used at G106, but all you have to do is match them up at the hardware store.

At the firewall connection, at G106, and at G100, use sandpaper to remove all the rust.

NOALX and Ox-Gard can be found at Home Depot or Lowes.



Note the circuits that are grounded at these ground points. Your XJ won't have the ignition coil shown at G101 but the ground wires are there.









If, after addressing the engine bay grounds, you still have problems we can address them.

bzauche

Thank you so much for the extremely informative reply! I have addressed all the grounds you spoke of other than the G106 grounds I believe, but I will go back and scuff them all up more and put the anti-oxidation compound on them. Where are the G106 grounds located in the engine bay? Is that the firewall behind the stock air box location? Also, what is the plug on the back of the alternator for? Voltage regulation? I assumed that I needed to take it off and clean it, but it has proven difficult.

CCKen

G106 is on the left inner fender, near the PCM and the Air Filter box.

The electrical connector plug on the back of the alternator is the alternaor field control wires. The cable that has it's own stud is the B+ power cable to the battery bus on the end of the PDC. This is not a ground wire even though it is Black (with a White tracer).

bzauche

Ok, thanks for the further info. I will spend a couple hours cleaning the grounds some more tonight and update with the results!

CCKen

Here's a test you can perform when you finish all your grounds:

96 + XJ Body Ground Connection Test

This test checks the condition of the vehicle body ground connection (Braided cable on firewall to engine cylinder head bolt). This test should be performed with the battery positive cable removed from the battery.

Start: Disconnect both battery cables, the negative cable first, then the positive battery cable. Reconnect the battery negative cable and perform the test as follows:

(1) Connect one ohmmeter test lead to the vehicle fender. Connect the other test lead to the battery negative post.

(2) The resistance should be less than one (1.0) ohm.

(3) If the resistance is more than one ohm, check the braided ground strap connected to the engine cylinder head and the vehicle body for being loose, corroded, or damaged. Repair or replace the ground strap connection and replace bolt at firewall connection or nut at engine cylinder head bolt connection, if required.

Finish: Disconnect the negative battery cable. Reconnect positive battery cable, and then connect the negative battery cable.